Advanced RemovablePartial Dentures

James S. Brudvik, DDS, FACI'Professor Emeritus of Prosthodontics

University of\VashingtonSchool of DentistrySeattle, \ Vashington

Quintessence )lublishing Co, IncClJicago, Berl in. Loudon , Tokyo, Paris, Barcelona, Sao Pau lo,~ toSC()W, Prague, and \ Varsaw

I

l.ihntl)"of Con~n'~~ C;t lalogi ng-in-Puhlic:;tlion Data

Bru(hik. [ nmes s.Advanced removahlc part ial dentures I [anu-s S. Brudvik.

p. em.Includes index.IS BN O-1i67 15-.3.'31 -2 (hard cov r-r}L f'urnal dentuu-s, Homovable. I. Tltk-.Il ) XL.\l : I . Deutu n-, Partial. Hemovnhlr-. WU .515 USfiSa I!/!)!)]

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Editor: Lori Ball 'IIMI\Iksign/P rOOtiction: Mil-hat·1 Shanaha n

Prinn ...1in the US,\

Introduction

Contents

IX

Chapter 1 Pat ient Evaluation, Diagnosis, and Treatment Planning ]Initia l Examination · Decision Making for RPD Treat ment Planning >Preliminary Impressions · Preprosthet icTherapy

Chapter 2 He~novahle Partial Denture DesignElements of Design· Design Specifics: Class I-IV

7

Chapter 3 Mouth Preparation 37Surveying th e Diagnostic Cast · Diagnostic Mo uth Preparatio n >

Clinical Mouth Preparat ion

Chapter 4 Final Impressions and Maste r Casts 55Altered Cast lmpressions > Jaw Relatio n Records

Chapter 5 Laboratory C onstruction of the F ramework 63Design Transfer · Bla ckout and Duplication >W axing· Spruing,Invest ing, and Casting · Met al Finishing · A ddit ion of W ire Clasps·Addit ion of Alte red Cast Trays

Chapter 6 Estahlishing the Tooth-Frame Relationship 7.5Tooth Contact Surfaces > Static Fit • Functional Fit · Poo r Cast ing Fit

Chapter 7 Completion of the Partial D t::nture 79Jaw Relat ion Records · Placement of Dent ure Teeth·Flaski ng,Tinting, and Packing · lnsertion > Metal Occlusal Surfaces ·Long-Term Maintenance

•

Chapter 8 Repairs, Additions , and Relines 93Pick-up Impressio ns · Res in Repairs · Metal Repairs > Restorat ionsUnder Existing RPDs • Crowns Under EXisti ng RPDs • Relines andRebases

Chapter f) Special Prostheses lO.5Splint ing with the RPD • Hinged Major Connectors · RotationalPart ial Dentures

Chapter 10 Precision Attachments 11 ,5Common Clinical Procedu res · Precision Attachment Systems

Chapter 11 Implants and Removable Partial DenturesClass I and II Situ ations ' Class III and IV Sit uat ions

Index

I

1.5:3

160

T he removable partial den tu re In" a1­way~ 1)('('11 Ill)-' speci al challenge i ll

d en tistry. As a clinician , researcher; 1I('lIlallaboratory direct or, 'lect ure r, and IIIPHtor, Ihave s[X'llt almost 3-5 years Il")ing to cometo grips wi t II t lie co mplexit ies o r th is fo rm orprosthodoutt c treatment . r would estimatethat 2()1}t of parual W{'aTeTS are more th an

just a litt le dissatisfied " ; 11. the ir denture.Unlike \\il l. the fixed part ial denture. till'pa tient has the option of removing the p lUS­thesis at tile slightest hint of d iscomfo rt .physical or men tal. Civcu the act ual state ofpructice-c- thc dent ist docs only the occa­_..ional partial denture with almost tota! T('­

Hance 011 t Il t ~ dcu tallal»lmlnty for desi gn aswe ll as const rucuon-c-I .nnmost pessimi sticus to the e f1i.·d of this, or :I ll: ' oilie r text onthe subject .

\Vhile there are a number of excellen tbaste texts Oil the rr-movuble pa rtial den­ture . they arc all direc ted toward tht, un­de rgraduate dental studen t. I han ! notfou nd anyt hing that I ca n m e as an ad­vanced text for th e graduate student andstudy club participant who wishes to pur-

Preface

Sill ' this form of therapy at the highestlevel . After years of be ing asked if I hadever conside red putting Illy lectu re mater­ial in written form and protesting tha t I didnot have the time. my partial ret ire men tfrom the University of \Va.~hillgtuTl Schoolof Dentist ty has made my excuses nolonger valid .

T his work is not in ten ded to be a text­book ill th e classical sense. It is, rathe r. amonog raph on the rem ovable partial den­ture , writte n wi tl r the expec tat ion tha t thereader will already have covered the basicsof the part ial denture and is now ready totake a more sophi...t icatcd look at this tre at ­mcut modali ty It dops not have a btbl iogru­phy, and the Illustrations consist o f draw­ings that I have placed 011 countlessblackboa rds over the years i ll all attempt 10

make things clr-ar to m)' students. \ \ 1.:lt 1'01.lows an' my thoughts as they have evo lvedover these yea rs orpractice and teaclnug inth is f ascinating urea.

While I take complete rcsponstbtltty forthe content of thf.. work, r have l WC B aidedin tlll ~ writing hy Illy friend and coworke r,

vii

Advanced Removable Part ial Dentures

[uuiuc Nr-mcrevr-r Coal; \~ , who, as pro·gram coordi nator orthe (; radu alp Programin Prosthodontics, has long stood watch

ove-r Illy fau lty gram mar and sentencestruct ure. I han:' also had the ln-lp of DrAlex Shor, present ly in OIl f graduate pro­gram, who has rovh-wed the entire hook toprovide insight and guidalll'l' from the eyt'Sor the pote-ntial readership.

viii

This boo k is dt'dicakd to Illy grad llalesuu k-nts-c-past , pn-sent , and hopc-Inllv fll­tnfl"- --who provide. 0 11 a daily basis. the joyofsl"{'ing S( 1111{"O Il(' learn. It is also rk-dicatodto Illy longtime friend ami colleague, theeminent functional anat omist . ProfessorJ('an I~OI I 11' row~ki (If tilt) Unlversity of Part s.VII , who has h('('11 an inspiration in thismailer as i ll so mallYotln -r endeavors overthe H'aI~.

T he removable par tial denture bas lon g!JPCH considere d an in fer ior means of

replaci ng missing ' teet h and assoc iatedstructures when compared 10 the fixed par­tial de ntu re. Some have even spoken of itas a stepping stone to a complete denture .The old rhyme, "Litt le HPD , don't yon C'Y.You'll be a CD by and by" may be st expressour feelings toward th is tre atment modal­ity. Many Slll\'CYS published over IIH~ years

in our journals indicate that den tist ry docsa rathr-r pOOT job witlr th e HPJ) . These re­ports testify to the hid that most RPDs arccreated entirely bv the technician wtth a, ,mi nim um of Input from the clinicia n in thefo rm of mouth p reparat ion or de.sign.

Dental schools make it serious effort toteac h th e subject, and excellent texts forthe undergraduate are available. None­theless, the state of removable partial den­turc s scou in the commercial laboratoriesand in the cross-sectional studies availableto IL~ indicates that , in general, pa rtials arepoorly de signe d and cons tructed andpoorl y maintained.

Introduction

Therefore , it is no wonder th at patientsdislike t hei r partials to tile point of notwearing them and, if they can afford alte r­native treatment , request it routi nely It hasbeen my experience that the pattent whostates , "1 had a partial once and couldn'twear it!" most likely hall a substandardprosthe sis; when t reated ,vith a sta te- of­the -art partial dent ure, the patient wou ldlikely find it tolera ble and easily accept thelimitations of this fonu of tooth awl tissuereplacement .

Plainly stat ed. th ere ts a dramatic diffe r­ence bet ween the standard RPD and theone th at approaches the state of the art aswe know it today. It is in the attemplto cre ­ate that qu ality rem ovable part ial denturethat this book is written . It is intended toserve as a KI dde to both gnHlwlfe studentsin prosth odont ics and conce rne d generalpractitione rs-to challenge the m to thinkof the removable app liance as they wouldthe fixed partial denture, with all th e sameconsiderations of soft tissue man agem ent ,cades control , periodontal supp ort, ortho-

ix

Advanced Removable Partia l Dentures

don tlc therapy. ami implant involveun-nt.In almost eH'ry clinical situ ation . the pa­tieut who requires a removable part ial den­turc will have a need for so me fonn of fixedprosthodontics as well, from a si mpl ebonded rest to the most complex precisionattachments extending from fixed unit s.

Philosophy of Care

\\"hat makes a SlIt'('('SSflll RPD? At tilt, riskofoversimplifi cat ion . on e co uld say that thesuccessful rem ovable appliance Ill't 'tl beonlv Ion I' things:, . , .

I, Strong. in that it does not wear, break.distort , or COII\I' apart when worn.

2. He/entire, so that it rem ains in positionin the patient's mouth duri ng usc andg1VtoS tho patlcut confide nce that it willcontinue to do so (JVP I" the life of tile par­tial.

3. Est/wtie, to satisfy the patien ts cxpI'ela­tious without undue evidence of its pws­r-ncc.

,I. 1'(1; 11-/1'(.'(', lIw,lIling that it docs not ( .IlI\('

discomfort when in the mou th for theshort term ami that it causes no 101lg­term damage to eit he r hard or soft tissueOW l" the life of tho parti al.

If these four requirements can hl' met ,the partial stands a good chance of long­k r ill success. Unfort unately, the Sll l,(,(.'S.~ ofthe part ial in and of itself does 1I0t ~lIar.m­

h't' the long-tr-rm he-al th of the rr'mainingh 't,th ami soft tissues. Matntenancc . there­fore. becomes the primary factor ill thelong-term succe ss (If the treatment . Theprofession has usually subst ituted conce rnover the tn )e of clasp to be used for themore fundamental requirem en ts (If n'WI-

x

lady scheduled recall and app ropriatemamtcuancc. Preparing tile mouth to itsvery la-st state of hr-alth be fore startingprosthodontic procedures and then keep­ing the tissues in that state of hea lth overthe life of the pa rtial is f ar mon- importantthan .IIlY desigll considerat ions, It has he­come obvious to me that a part ial den turein a healthy mou th , assum ing that it meet sour four requirements. will he successfulregardless of its design. lk -st placementand clasp (I"sign, Intcrcst iug lLs Ilie}' may IK'to argile ove-r fro m a tlu -orotical point ofvtew, an' simply not germane to the realq llP SIiOIl vf what makes a success ful re-ruov­'lhlf· pa rtial denture. Suppositions de rivedfrom bench studies do not nece ssarilytransfe r hithe clinica l realities of long-te rncare.

l low loug should a properly d(~s ignpd,

cohstrucu-d . and maintained H.PD lu...t ?Good evidence exists that this state-of-the­art pali ial cou ld be l'xpt,tkd to last a ruini­mum of 10 years, assuunug tha t the patien twas se-en at reg ular inte rvals and that boththe mout h aut] the partial received the indi­cateduuuntr-nancc . Partial.s pn l\i lIing glKxlservice for 20 ~l-'ars art' not unheard of, al­tlltlllgllil lt' long-term maintenance re-quire­mcnts lncrcnsc dramatically afte r 10 years.

Th e constru ction of the removable par­tia l dent ure , more than allY other fonn ofdental the-rapy, is almost always delegatedto the dental labora tory since the equip­mcnt required to prod uct.' all acc eptableellst framework is not goillj!; to he found illthe dent al offlce. In lllauy cases, the clint­dan urav have never even met the techni­d ans cn-ating the prostlu-sc-s. Tl us fact re­qui res that the clinicians maintain co nt r olby inse rting themselves into the pmcess atthe cri tica l steps in construction . Thesesteps will he co vered in depth in thi s book.

Since the actual construction is d{'lq~ated,

the an'mge clinician is apt to have \'('r)" lit­tie confidence Of experience in th ese mat­tors and is likelv to take the techniciansview of the desig n am i construc tionprol'pss, a view thai will he more nu -chani ­cul than btologi cal . T he wtsc ch uiciau willmake a po int or l"t ' lllailling in close coutuct

with the techn ician and brin ging; th (~sc nux­ilfurtos into the clinical aSjx'd s of earewhen ever possible.

The modern rem ovable partial denturecom bines Iixcd and removable prostho d on ­tics and f(,,(pli n 's a thorough understandingof I10th aspects of care by the clinician and

Int roductio n

by the h·d lllid an . Unfortuuan-ly; the evolu­tion of the dent al lnboratorv ind ustrv has. .separated ted lllicians into often isolatedspecialties: comple te dentures. remova bleparti al dentu res. and fixed partial dentures .The technician who is knowledgeable in allareas is a \'a ni.shillg hn ·(·t1 . To direct till'con struction of the most sophist icatedrest orations. the clini cian must assume thercspouslblllty of coordi natin g the laboru­tory phase s. Th is text is intended to setstandards of care fo r tln- comprehensive­management of the partially edentulous pa­ttcnt w ho will req uifl' so me form of a rc­movable n-sto rattou .

x i

James S. Brudvik, DDS, l·j\CP, joined tile faculty of the Unive- rsity of\Vashingloll School of Denti st ry, Seattle, ill 1979 alter a 22·)'('<\1' can-e r inthe United Sta ll' s Army Denial Corps. I Ie se rved as Directo r of C raduat ePrustluxlonttcs from IHH9 to 19!JG and is curren tly Professor Emeritus andAssociate Direc tor of the graduate program. D r Brudvtk is a Fellow of theAcademy or Prosthodontics nnd the American Acad em y ( If MaxillofuciulProsthetics, and is a Charter "Fellow of both the American nnd ti leInternational O lllcl4c ( I f I' rosthodont tsts. The partial den tu re has IW{ ~ '1 hismajor urea of' researc h inte rest over h is40-year career i ll p rosthodontics.

Chapter 1

Chapter 2

Chapter 3

Chapter 4

Chapter 5

Chapter sChapter 7

Chapter 8

Chapter 9

Chapter 10

Chapter 11

CONTENTS

Patient Evaluation, I)iaguosis, andTreatment Planning

Removable Partial Denture D esign

Mouth Preparation

Final Impressions and ~Iaster Casts

Lahoratorv Construction of the Framework~

Establishing the Tooth-Frame Helationship

Co mpletion of th e Partial Denture

Hepai rs, Additions, and Relines

Special Prostheses

Preci sion Attachments,

Implants and Removable Partial Dentures

4IIPatient Evaluation, Diagnosis,

and Treatment Planning

T he 0 1)\;0115 firs t step in t reatment for

the partially eden tulous pati e nt in­elu des the gath('rin~ of diagnostic data andth ose di agnostic p rocedures commonlyg rouped tinde r the heading o f t reatmentplanning. Th ese procedures must also ad­d R '55 the prognos is, wtth and without trea t­mcn t. of individual tee th as well as themou th as a whole. An integral part of then -quiu-d d iagnostic data will I w ~ the lnfor­mutton ga thp fec! from a dia~llI)st ic W, lX- t1p

ami S('f - ll P that Includes a te ntative HPDdesign as well. It may wel l bo that the diag­nostic phase is second on ly to malutcnanccas an indicator of long-Ierm 5 1K' {'('SS.

Initial Examination

Th e foll{)\\i ng sPCjuene(' rcpn-scuts the!I.lsi<: Information that must he obtainedbe fo re t reatment planning ca n occu r.

1. Idcntif lcat iou or the- pat ien ts chid CO III ­

p laint

2 . l leud and neck exam ination

3. TMJ evaluation to include so unds andmout h ope ning

4. Int raoral examinat ion or bot h soli andliard tissues with emphasis on C<lII('( ' (

sc n't 'lling

a . Accurate and co mple te chart ing of:

• emi l'S• Existing restorations• Periodolll({! tissues , to include Jl(l('~"f'!

pmhillg. (/I/(! 1/whility, ([/I( ! gl'7wm lhOI //' II'pd s

• PilIp oitll!ily , especilllly of po!enti ([ l([!mllllt'tli {('('Iii

• Ulld illgm p/,ic jim!iugs (if /Il'Tillll ica!films (f ill! a pal/fograph (;11 C.HoW'S U) W/"(,

j mc dlv-n -pancles mlll l1w!ocd"s;ollSan'obdow" a Iotcrolhead film Id/ll Im d '.gmill ('t",fl!lIal iol/ o m be " 'lflll'sin l td/ll1,,1Iull !llll/ ic n"~~'II!tal io,,)

• (Jc.dllsal nmlads, cent ric mil! eccentric

Advanc ed Removable Parti al Dentures

6. Add itional procedures souu-times imji­

catcd:• D tct (Illah/si....• Caril's risk: assessment

7. Imp ressions for diagnostic casts

8. Int e rocclusal jaw relation reco rd (if imli­c ited )

9. Shark- an d mold selection

T he ne-ed for th is diagnostic data shouldbe obvious to al l)' cl inicia n. Uufo rtunutcly;the planning for the ave rage HPD seldomincludes all these issues and. as a result ,the treatment is compromised from thewry heginning. Tlu-re is 110 point evenconsidering the "l!t' sigll" port ion of thetreatment plan unti l this Informat ion isavailahlo und has n -cofved S( J lt l( ~ con sider­<I lion am i fPl1edioll.

Decision Making for RPDTreatment Planning

A series of que stions (ill no particu larorder) 1I1l1st be addressed i.LS pa rt of th(·eval uation (If ti l l' gathered dat a .

ls a n'lII o r iJhle partiol dentn rv ilUJicntcd/lu'ce'\'S(//~1 for f Ilh IN/liellf 01 I IIi.<> l ime?

Wrmlr/ the pfl[ielIt !w better s('I1:aLwith afixed or fil l illlplall/-retai1ln l prosthesis,and o w the illl 'rt ,fl.''il' it' ("( ~"I of can.' IwjllSlifil'clP

\\ 'hnl pnl<;11IOdolll idn>sfomti ri' needs arenpl"m 'll l ill the tlpl,w.iug arch, (lIIlJ hou:u:ill 11II'i r treatment a{fixf the 1"l'lIlOfjabierlflrl ;al denture? ..

Are the han! mlfJ ,wift tiss ues thnt wlllild rr­late 10 {f n ' lIIot'ah!e Ilpp!i({tu't' ncceptabic(i ll f/1l it!l'll! staft> ofhealth } ut Ihis t ime,

2

or Idll flll'y require pn'pm sthelic tho r­(fpy? Th is C01l1d illcllldl' en 'nj l h i llf!..fnml0I1hof!.lwthic slIrgen) 10 II IJOnr/f'{!IIIl'fa!rest. \Vill ti ll' abnun ent f l'dh p rockle allI III' reontred support , or leill m/dit;otw!SIIJIJ)()rl /X.' reqniredfrom ttse soJll isSfWSof IJU' edentulous areas (.'ilress rl'!kj)?

An' IIU' palierl/:" expectations achiet;abll'?Will tlie paficfll be able to procule the re­

lf ll in 'r/ !eet,1 I{ home care thai leill be/l('('(>,\'sfI'"'!I.{rw long-fenll success?

Should id('{/[ln '(/[lI ll'nt he 1I/odified /)('('(IllSl~

(lJa{!,I' , chronic snstemic disease, or psy~chological fadon';?

Most. ifnot all. of these questions shouldbe add ressed as a pa rt of the initial examt­nation . Some \\i ll requir e direct quest ion ­ing of the pat ien t. Othe rs may only nor-d tobe a pa rt of the clinician's thought p roc t'ssbut shou ld he considered while the patien tis still present. Some questions will n-sn lt inreferrals to other specialists and/or i.l< lcli ­

tional diagnos tic tests.TIl(' wise clinician wil l not give the pa­

ticnt allY definitive plan or fee at the timeor the initial examlua tion. It is ELr bet ter tote ll II\(' pa tie llt tha t 110 Intelhgcut respo llsecan be made until all of tln- d iagnostic da ta

havelx-en evaluated and allY required (.·'OIl~

sultat lons obtained .

Preliminary Impressions IThe (Iuality of the initial impn 'ssio ns andthe casts that result fmm tln-m , although di­agnost ic only, 11("("(1to be of far higher qual­ity than that normally see ll. Most e\'t' l)' spe~

cialist i l l re movable prosthodon tics lias,while attending a meeting or seminar, lx-enapproached for help in treatment planninga case. A plaste-r cast is pulled From a

Patient Evaluation, Diagno sis, and Treatment Planning

pocket , usually \\ ilI1OIlI a d ecent base . fullof blebs and voids and with no evidence ofvvvr 11:1\ing been Oil a dental Slllrvt.·) o r; " I

alx)logizt> for this cast, b UI can you ln-lp mewith a design?"'

Thc preliminary impression ami rcsul­taut cast shou ld he of the same quality asthe final imp ression as far as ext enslous,hard and son ussuc details, and integrity ofthe occlusal surface are concerne- d. Thi sImpre ssion shollld 1)(' l'()I1sidered as a tri al

impression for tile filial. Tray size is cvalu­ated. patient compliance with il l...tmct ionsnoted . ease of placement disco vered . andthe patient's ability In sit still during Ihe setof the alginate evaluated. EWI)1hillg thatcan he learned Fr om th is impression willaid the clinician in making an accurutc flnalimpression.

Sometimes Ill) stock tray will adequately111the mouth, indk :iting tha t a custom t raywtll have to he iucluded in preparation forthe final Impression. Modtficatiou of tlu>stock tray wi th wax or co mpound lIlay hpm-cessary to allow the impwssion of hordertissues or high palatal vault. All tlll'SI' issuesmust be e"alilait'd whe n the prcltuunuryimpression is made so that the clinician « Ill

concentra te 0 11 accuracv o f the ha rd tisS1U'Sill the final impression.

Alginate can ht' expected to give ovcrex­tended borders due 10 its co nststency wln-nproperly mixed. Und er JlO circumstancesshould the powder-water ratio h( ~ cbangedto reduce the viscosity or the mix. ltathe r;the amoun t of algina to required 10 make a' Iuality impression should be carefully csti­mated and only thai amount placed ill thetril)'. Alginate 1I111sl Ill:>placed into thr- criti­cal areas: rest seats , guid ing planes, soft tis­Slit' undercuts, etc. One cannot count onthe material llm\i llg 10 these are as of itsown accord . The material call he placed

with the finger or inje-cted IIsing a syriuJ?:e.but ill 110 Instance should the trav Ill: 'placed in the mouth unti l all critica l arr-asare wi ped wi th alginate, Borders should befilled IIsing a syri nJ?:e , A plastic 3.') ceMonojct syringe wn h 10 to 1.5 cc of al~.

nate will work well in most situations, Thecrit ical areas are buccal 10 the tuberosit iesand the ret romylohyold space, placeswhere voids are ofte n found ill the com­plf'kl l impres sion . AnIJII I( 'r ad van tage ' Ifplacing alginate in the 1I10u th before seat­ing the tray is that Ie-ss man-rial (the totalmix minus the 10 to 1.'5 ( 'I: ) 1J("t '(1 be place din the tray. resulting in increased visibilityfor tray placement.

\ \ l lt'llevpr possible. th(> stock tray ismodifk-d by adding wax or compound toallow a minimum of 0.2.'5 inch of alginatearound all cri tical structures . A C'()l1ln IOl Iproblem with alginate is ovt>rseating or thotray, rpsllltillg in less than the re-quire-d 0.2,'5Inch of mute- ria] ove-r the' occ lusal sur faces.Stops can he placed in thl~ tray Ilsing hard\\,LX or dental co mpound to restrid till'm·('TS(·;Itinr;. Unfortunately; the area of till'stop will often be distorted due to the min­imal alginate present. The required occlus alspacing may he obtained hy placing theempty Iray ill the mouth. scaling it 10 COII­

tact with the occlusal surfaces, and evaluat­ing the relative l X)SI!iOll of the handle to thelips whe-n the tray is lifted the 0.2.5 inch . 111making the impression , the tray is seatedtothat lifted position and lu-kl in place unti lthe impn-ssion is set.

\\1wll the imp ression is removed fromthe mou th. it must he rinsed and light lydried. then inspected for h ';ITS and any cvi­dcncc of the material Im'aking Free fromthe rimlock or retentive holes. \\11en usinga rtmlock t fit)~ excess alginate-should be cutfrom 1111' borders with a sha rp knife so that

J

Advanced Removable Partial Denture s

the edge of the tray can be seen and the re­tention of tile alginate verified.

Alginate is clearly an abused impre ssionmaterial, hut it is the material of choice forboth preliminary and fina l impre ssions forthe removable partial denture . Seldom isth e alginate mixed for the manufactu rer'srecomm ended time. Likewise , it is ofte nnot allowed time /;J!" a comple te set beforeremoval from the mouth. Many Inaccurateimpressions can he traced to the pati ent'sinuhility to remain motio nless during thesett ing phase. \Vhcn th e t ime in th e monthhas been alte red hy using very co ld wateror not mixing for t he usual flO seco nds , thepatient is forced to remain motion less forlonger than necessary. Since alginate docsnot set all at once hut in scattered islands,any movement hy clinician or pati ent du r­ing the selling pe riod rUJl S the risk of re­orienting the partially set material andp roduc ing a distorted imp ression. Ideally,the set shou ld begi n promptly afte r thetray is in its proper pos ition and any bordermolding has occurred. Algina te mixed withthe proper mcasuru of rOOl n-te mperature(65°F to 70°F) water will allow roughly aminute for loading the tray and placing itin the mouth be fore the se t hegins .Optimal gelation time shou ld be between:3 and 4 minutes using 68°F water. The pa­tien t is instru cted to remain motionlessduring this time . The initial imp ressiongives the clinician the opportun ity to testthe patient's ab ility in th is regilrd to in­crease the prohabtltty that the fina l im­pressio n will he accurate. Should the pa­tien t move du ring the fina l imp ression, itmust he remade and the pati ent informedagain of his or he r part ill this procedure.

If the mixing of the alginate is incom­plete, a reduction of up to :5W7rJ in th estr ength of the ge l can be expected. On the

4

other ham!' alginate mixed beyo nd themanufacturer's sta ted tim e will have a re­du ced gel strength since t he form ing gelswill he broken. Mechanical mixing devices,including vacuum mixing, are w ore apt toprovide consiste ncy and thereby accu racy,and should be considered as essential in­strumentation . Hand mixing for the fullminute requi red by most manufacturers isnot that easily accomplished awl. as a re­sult, the n lixing time is seldom fully uti­lizcd.

Alginate adhesives mus t be consideredessential for all final impressions, hut sinceth ey are not l'iL~y to remove from the tray,they are not required for the diagnostic im­pression. w hen a stock rimlock tray is used,howeve r, ca re must he taken to force the al­ginate into the rimlock with the spatulawhen loading the tray. Once this has beendoric, the algina te is not likely to pop free ofthe lock. Nevert heless , the impressionshould he ca refu lly inspected befo re pour­ing so that if a separation has occurred, theset algina te can he r<-'placed in the lock ofth e tray. \Vhile this maneuver would hi' un­acceptab le for a fina l impression , it willnorm ally produce a cast that is accurateelH 111gh fl)Tdiagnostic procedures .

Once the impression has heen removedfrom the mou th, the following series ofsteps, pe rformed in th is order, will maxi­mize chances for an accu rate diagnosticcast:

l. Rinse the impre ssion under runn tngwater.

2. Using a cotton tip, gen tly clean the toothimpressions. (Plaque and othe r oral de­bri s, iflef t in the imp ression, will reducethe su rface hardness of the resul tan tcast , since the surface hardening agentsin the alginate must come into contact

Patient Evaluation, D iagnosis, and Tr eatment Planning

with th e den tal stone for max im umhardn ess to he uchtcvcd.)

3. Blow excess fluid from the impressionan d evaluate the imp ression under goodlight for tears and defects.

4. With an indelible pencil or other marker,trace the outline of the proposed den­ture o n the alginate. Since ti le patient issti ll in th e chair, exte nsio ns can bequickly verifi ed. Should contours seen inthe mouth and essen tial to the construc­tion not be present in the impression,the decision to remake the imp ressio nwill not req uire all additional appoint­ment. Attempts to identify denture baseextensions from a stone cast davs afterthe imp ression was made often lead toproblems wtth exten sions and will neverbe as accurate as those det ermined viath is method of lh:av\i ng on the algina teimpression .

5 . The technique used to pour the prelimi­nary imp ression is immaterial. Any ap­proach that results in a dense cast withno voids and a bas e suitable for mount­ing in the den tal surveyor wi ll suffice fordiagnostic purposes. As a minim um, thecast should be neatly t rimmed and allblebs re moved, since this cast may wellhe seen by th e patient as well as by th etechnician. A neat diagnostic C,L~t with acare ful deSign, properly drawn, goes alo'ng way toward ind icating that the clin ­ician really does know the standards. Myexperie nce has been that te chnicians areimpressed when they see a quality d iag­nostic C'L~t.

Preprosthetic Therapy

Determining the leve l of mou th prepara­tion required is an essent ial e lement of thestate -of-the-art removab le part ial dent ure .Mouth preparatio n is usually interpreted tomean th e creation of rest preparations onsome of the remaining teeth . Unfor­tu nately, reviews of cases submitted to thedental laboratories show that many mouthshave not even th is level of mouth prepara ­tion.

For the modern HPD, mouth prepara ­tion v..i ll cove r any therapy req uired tobring the mouth to optimum health and tomodify t issue in such a man ner as to makethe final prosthesis ideal. Obviously, a re ­movable appliance C,Ul be made to accep tthe mouth as it presents. In fact, most o fthe HPDs seen in any review of prostheti ct reatment \\111 fall in to th is ca tegory, wlthocclusal p lane discrepancies , malocclu­sions , little o r no reconton ring of teeth, andthe like . A discussion of the basic the rapiesfor mo uth p reparation at thi s point in thetreatment planning process is necessary tohilly develop the concept of ideal mouthpreparation.

\\-'hile the sequencing of the actual careis a cri tical issue, the sf'llueTlci ng of consul­tat ions is not. Th e prosthodontist will al­most always manage the res torati ve dentalexam ination and caries risk assessment.

Nut ritional evaluation for those patie n ts\..-ith obvious active caries may be referredto a nutritionist although there are COIll ­

purer software programs available so that adiet survey, completed ove r a 3-day periodhy the patie nt, can he analyzed withoutspecial traini ng in mo st cases (eg, FoodProcessor Plus 6.0 E SIIA Research , Salem,O regon).

5

Advanced Removable Part ial Dentures

TIlt' pe riodontal examination is a differ­ell ! mutte-r, since most prosthod on tlsts havea network of pe riodontists with whom theycxclnmge refe rra ls. No matter how the dataare gathered. a baseline of pocket dep ths,fnrca tton Involvement , plaque scores. mo­hilit)' levels, and geneml pe -riodontal softtissue conditions must he made. Baselinedata of this magnitude p rovide the clinici anwith a starting point for referra ls ;L'; well a"protection for med icolegal matters.

Endodontic referrals arc apt to he morecouunou, especially those rq.!;ard ing exist­illg endodontic restorations. He-t reatment

docisious can greatly a/li. 'd the treatmentplan, both ill regard to ahutmcut selectionand to total cost of care.

O rthodontic and oral lind maxillofacia lsurgical consultations are almost alwayscase specific and lIlay not always he neces­sary, although to plan tn-armcnt withouttln-m the clinician must he assu red thatthey will not contribute to the ca re of thepatie-nt. A large number of cases wi ll re­qui re minor tooth movem ent to aligJl thearch and to establish the ideal occlusalplane. Often these con sultations cau best1)(, done after a prel imtuary tn-atmr-ut planand desigJl have been estahlished.

6

Alollg with the periodontal examination ,the evalua tion of existing restorations andtooth co ntours is critical to our trea tment.In far t(NI lllallY instances. restorations ofmarginal qual itv are left in till' mout h antith e part ial lmilt around them.

011('(' the abo ve information has lx-cngathered. the clinical findings can 1)(' SUIll ­

murize d as a part of the patients record andIncluded ill the treatme nt plan le tte r. A di­agnosis ami prognos is of the mouth withand without treatment can also be ostub­ltsln-d. At this point , the dingnosttc casts.radiographs, and periodont al chart in).!; arereviewed together, and the cast is "sur­veyed" to determine the BPI) options. Thetreatme nt plan and the patient's inlortncdconsent le tter can only I )(~ completed afterthe te ntative dt'sign of the flual appliancehas been cs tabhsln-d .

Is all this n-ullv nece ssary? Must a writ­len tn-at uu-nt plan ami consent let te r begiven to the patient? Should we make anorthodont ic co nsult a part of our chain ofdiagnostic procedures? The answe r tothese uud similar question s is, of course ,most ('ertainly yes! The type of treatmentdcscrtlxxl in this book-s-the partial dentureat the most advanced len ..I---d ocs requiremorr- work, both in plannillg ;u l{l execution.TIlt' results art', very obvi ously, \\ul' th ourtime and our be st efforts.

Removable PartialD enture Design

E vt-r since the publicat ion of D r \ \ :Fruntxs study of the variations in par­

tial ch-utun -design (] Prosthet De-nt. 1973).I have been troubled by the seemingly tota llack of co nse-nsus 011 the design of a con­ventional pa rt ial denture . J can un derstan dthat then' would be some different ap­proaches 10 any partial design, hu t to findtha t there is apparently 110 co mmonly heldap proach that would re su lt i ll a minimumof variations is I roublmg. It ma)' well bethat the average clinician simply dol'S nothave sufllcicnt repetitions of similar par­tially edentulous situattous to develop aconsiste nt philosophy fo r de,signing a par­tial denture.

For allYsituat io n where there are inade­quate repetitions or when ' the ( 'O Il SP­

(J!1('I1('{'s ofoverlooking a particular step areuuacccptuble , the developme-ntor a check­list, not unlike that used hy the pilot of anairplane, is i ll order, The checklist that Ihan ' used and t aught for lllallY yean; isbased on what I be lieve to be the most logo.teal approach to det ermining tl.e design ofany re movable partial situation. It focuses

011 clinical rather than laboratorv decis ionmaking uud is broken down into tile follow­ing catcgoncs, always in this order, since itranks the co mponents. or elements of de­sign, by clinical importance .

RPDDesign Checklist1. Abutments and rests2. Con nectors . major and minor3. Resin retention-t. Hctcntiou. clasp or at tachment

Elements of Design

Abutments and Rests

'11 .(' re-lationship between tile al mt uu-nttooth and the framework is the most im­portant of all design and co nstruct lou CO Il ­

sidcratlons. In keeping 'lith this thought.the sr-lr-ction of the remaining tee th to heused as abu tments becomes critical. Allabutment is deflued ;,LS any tooth that hears

7

•Advanced Removable Partial Dentu res

Cingulum Occ lusal Incisal Proximal (crown)

Fig 2- 1 Positive rest forms « 90 degrees).

the vertical and oblique loads placed lIpon

the partial through positive rests. Positivere sts arc defined as rests that form acuteangle s wtt h the minor connectors thai COIl ­

ned th e m to th e majo r con necto r. \Vilh arest/con nector angle of less than no de­grees , the partial cannot get away from thetooth and the tooth cannot move away fro mthe partial (Fig 2-1).

\Vhe never possible, missing anter iorteeth arc to be replaced with fixed partialdentures, le aving the RPD to re place pos­terior teeth . Attempting to rep lace both an­te rior and posterio r teet h on the same cast­ing is a comp romise that may affect bothesthetics and abutment stability. As au ad­ditional benefit of anterior fixed replace­ments, the abut ment castings will he givenideal con tou rs to support the posterior par­tial and to allow the elimination of buccalclasp arms. A variety of precision and semi­p recision attachments can he inco rporat edin these abutmen t crowns to eliminate an­te rior clasping.

Selection of the abutme nt teeth beginswith an evaluation of the strength of eachtooth. As a general rule, we must consider

8

the strongest re maining teet h first and thenprogress to weaker teeth <L~ we deci de nponthe nu mber of teeth lleu~ssary to .~ llpP() li

the pa rtial. \-Vhellie r or not a tooth is ultt­m utely selected to be clasped as wel l asrested is Immaterial at th is time. Tt is alwaysprefe rable to indlHle mrrre ahu tmentsrather than fewer; since the only negativeaspect of" extra ab utments is tha t they makethe l:a~ti ng more complex ill geometry and

, thus decrease the likelihood of a perfect fit.Obviously, the number of tt-'t-'th to he re­placed is related to the number of nlmt­me nts needed for support.

The type of rest preparation to he placedupon the selected ab utment tooth is gener­ally obvious: occlusal rests for posteri orteeth and cingulum rests for incisors. Sincethere is often inadequate ename l presentfor cingulum rests, espe cially on rnandf bu­[ar incisors, the se rests are most likely to bemade with either bonded etched metal orwtth bonded composite.

A tooth that is contacted by the p artialbut not through a positive rest cannot heconsidered an abut ment. \Vhat m ighthappen in this sit uat ion can be illustrated

Rest projection'..R:0.... . ....tt-- Height of

contour

Fig 2-2 Posit ive rest wit h guide plates.

by a Class I mandtbula r partial where alingual plate is used as the major con nec­tor; afte r a period of time, a clinical eval­uation shows that the incisors havemoved out of contact with the pla te . Th eeffect of a positive rest can be ob tainedwith min or connectors (guide plat es )alone , hut on ly if they touch the tooth onopposing sides and above the height ofcontour, since the tooth is then nut ableto move away from the parti al. This situa­tion is rare and usually limited to themanagement of existing crowns withporcelain occlusal surfaces in cases wherepreparing an adequate rest may damage acrown that need not otherwise be rc­placed (Fig 2-2).

A factor that will affect the selection ofabu tments is the quality of the remainingtooth, both rcstoratively and peri orlontally.Crowns must be considered for tee th thathave multiple old restorations with mar­ginal leakage. Teeth that are healthy butmobile may need splin ting, especially ifthey are terminal abutments. Teeth that arcunlikclv to remain for unv reason for the ex-. .pected life of the partial, ic, 10 years, must

Removable Partial D enture D esign

Fig 2-3 Post-co re w ith ferru le (>2 mm).

be extracted before definitive cafe beginsor the framework must be designed withtheir replacement in mind.

Teeth tha t are malaltgned relative to theplane of occlusion may also be consideredcompromised abutments and will often rc­qn ire minor tooth movement to make themudoquatc supports for the partial.

Endodontally compromised teeth thatrequire posts and cores must have ade ­quate tooth structure to allow at least a 2­H IH I f(~rnl1e effect (Fig 2-:1) . Any previouslytre ated tooth that has had the fill exposedto the oral emily for any H 'aSOJI must beconsidered for rctrcatmcnt before heingaccep ted for use as an abu tment.

Connect ors

Once the abutments have been selectedand the need for restorations (if any) veri­fied, we move on to the second design con­sideration, that of choosing the connectors,both major and minor. Since the options forthe major connectors are arch specific, it isbest to consider them independently.

9

Advanced Removable Partial Dentures

Fig 2-4 Broad palatal strap .

Maxillary Major (onneeto"

11)(' majo r connector of choice is 0111.-' thatwill, whenever possible , ('O W T m-tther tilt'ante rior nor the poste rior pala te . Studieshave shown that the co nnector conunonlvculled the "hroacl palatal strap" is most ac­ccptcd by patients. Th is connector erossesIhl' palate in the area of the mesial of thesecond premolar to the distal of the firstmolar audrnust he a minimum of 18 mmto have sufficie nt rigid ily with o flt heillg to othick (F ig 2-4 ). A broad palatal strap mea­suring, for example, 18 1I 111l in width amibavillg a cross-sect ional thickness of 0.,5

nun \\; 11, for all practical purposes, he rigidi ll norm al function . Vnles:s anterior teethare lwing replaced by the pa rtial, this de­s i~1 is compatible with all posterio r re­placement situat ions. III .SHII.d im IS wherean isolatedlate ral incisor i.s hl'in g replaced,the cast lng can he extended us a cantilever

10

Veneeredmetal pontic

Fig 2-5 Cantilever from palata l st rap.

from the canine to kee p the ante rior palate(speaking area ) unco vered (Fig 2...'5). 111distal t'xh..-nslou sltuat tons, the majuf eUII­ncctor is brought posteriorly to now intothe hamular notch area, thus ,L<;<;n ri ng max­i nnun eo\'t'rage of the ede ntulous ridge.An altc mattvc d(' <; i,l,'l l ofl-ell elllployt't i forthe maxillae is the anterior-posterior ba r,which. I believe, place s metal i ll , lit' leastacceptable portion of the palate . TIIC ant e­rim har will Ill' ill the spe aking an-a amithe posterior ba r will often be too fa r pos­te rior for pat ien t comfort . The wSll lt i ll ~

0pell cent ral palat e will have all extendedbo rder thai call lead to excessive food col­lcctlon unde-r the partial. Potent ial fu rt he rtoo th loss within the life of the partialmustalways he considered in the major co unce­tor design, since the teeth in questionneedto have a lingual plate contact the easting ifthey an.' to he added to the partial withoutaffecting the quality of the prosthesis.

•Removable Partial Denture Design

Lingual bar Lingual plate Sublingual bar Labial bar

Fig 2-6 Mandibular major connector o ptions.

Mandibular Major Ionnectors

Se lecting a major connector lex the man­dible should he far easier than for the max­illa. Choice s are limited 10: lingnal bars,sublingual bars, lingua l plates, some combi­nation of thes e three, and, in isolat ed in­stances, labial bars. The con nector ofchoicewill be that which covers the minimumamount of soft tissue. The standard lingualbar does have space considerations thatmust be observed. The superior border ofthe bar must he :1 mTH from the gingivalmargin of the remaining teeth to minimizesoft tissu e irritation. There must be 4 rum ofspace for the casting below this point inorde r to have a rigid major connector withminimum bulk The commercial clasp pat­terns used by our laboratori es are very closeto 4 linn in ocd usogingival width. There­fore, 7 nun uf space between the gingivalmarginal tissue of the remaining teeth andthe functional depth of the floor of themouth is essential If a lingual bar is desired .When less space than this is available, theclinician must choose either a lingual plate,

where the snperio r border is at the level ofthe cingulum and will contact the remain ­ing anterior teeth, or the sublingual bar.The sublingual bar has the same relation­ship with the gingival tissues of the rem ain­ing teeth, hut the har is rotated 90 degreesand placed on the anterior floor of themouth (Fig 2-6). Wtth this connector; thesoft tissues can be left uncovered when .5rnm of space remains in the coverage area.In the few situations where the remainingmandibular teeth are severely lingually in­clined, the enti re major connector can bebrought out into the lnhtul vestibule. The di­mensions of the bar must be increased forrigidity since the arc will be longer. The softtissues arc given the sallie Scmm clearanceas in the lingual bar.

Minor Connectors

rn the ideal minor connector relationship,the "marginal soft tissues are uncoveredwhenever possible; 6 mrn uf clearance fromthe marginal tissues in the maxilla and :3 nunin the mandible are considered adequat e.

II

•Advanced Removable Partial Dentures

Bead retention-,Internal -.­finish line

Externa lI fmrsh nne

OftCII he clone when teeth remain on oneside of the arch only. as in maxillary obturu­tors fix lu-mimaxtllnry resec tions. The useof multiple guid ing planes and the ~Ilide

plates of the framework that contact themgreatly Increases the stability and the Inc­ttonal rete ntion of the RPD .

Resin Retention

Fig 2· 7 Meta! base in cross section (maxilla).

The ruiner connectors arc to he placed on lyont o prepared tooth surfaces . They will taketho lonn of guide plates and fest struts and,whew Ill"t"essary. lingual plates. Numerousstud ies han ' shown that soli tissues that arenot covered hy the pa rtial will he healthierthan those that are covered. regardless ofthe oral hygicne of the pat ipllt. Metal di­mensicus for minor connectors are basedpnmurt ly on ha\ing enough metal P R'St' ll t

so that the rests will not fr acture with timeat the marginal ridge. TIle h'llide plate-s canhe (Illite th in (O..S mm) because they take Ii L ~

tic o r 110 llexillj!; stress ami arc not apl 10 heill occlusal contact. The approach arm of ti leminor connector must have a miuiuuun of1..5 IIllll of metal, both uu-siodistully andhllC('()lill f!;llaHy, to ensure adequate strength.

(; Il iding planes are created whe neve rpossible. They wtll most likely he foundontile proximal surface s o f abuuncnt teeth ad­jaccnt 10 ede ntulo us area". Th ey can beprcpun-d in the enamel of these abutmentsor call he added to the touth ill the fo rm ofbonded resto rations or specially desiglledcrown s. In special situatio ns they arc addedto lill~lal surfaces of tf'f'lh to isolate th epath of inse rt ion/removal. This will most

12

The third ('1('111('111of removable partial do­sigll is our- tha t is almost always lefi: to thelaboratory techn ician to se lect, eventhough it is a de cision that is clinicallybased. For 1 1l( ~ must p,u1, the choice of 1"(' .

tc nt lon for the denture teeth am i associ ­ated haw n-siu is simple. w hen it is certainthat the edentulous area wtll need to be n '­lined d uring the life of the partial, then thl'standa rd raisl'd mesh is selected . Such sit­nations wi]] he limited to those involvingd ista l extension bases and an-as of rece-ntextraction. In ( '\ '('1)' ot her instance , a nu -tnl

base wit11 app ropriate retentive lu~s orloops is indica ted. The in te rnal finish 1i1lC'

for these nu-tal bases will he a but t jointsli~htly 10 the buccal of the ridge cn-st (Fi~

2-7). Metal coverage is preferred becauseil places highly polished met al over tho ~i l1 ·

gival margina l tissue rat her th an til(' thinflash of resin that is commonlv found withthe standard rutscd retentive mesh. \V!lell

mesh must he used. the laboratory must heins tructed to use a minimum of (Jill' thick­ness of baseplate wax as the rel ie f padrather Ihan the usual 24- to 28-gauge \V:lX .

T he angle of the inte rnal fin ish line is acritical component of the rete nt ive meclra­nism. For 11.(' rulsed mesh. the mtemul llncis fOTIIl( 't1 by the shape of the wax rdid pad(Fig 2-S). For .1II ideal internal finish line,the angle fOfll u'(l in the wax must he w ry

•Removable Partial De nture Design

Critica l internal finis h line

Fig 2-8 Creation of raised mesh.

.. .~.Wax relief;::: 1 mm

Fig 2-9 Reinforced acrylic ponti c

for single tooth replaceme nt.

There wi ll be no f lange on buccal

acute so that the resultant contour in thecasting will trap the resin in place and re ­duce the percolation that occurs wtt h ther­mal changes. Resin bonding agents, p rop­erly placed, will overcome the potential forresin -m etal separa tion , but thei r usc is notpresently a p,ut of the normal proces singp rot ocol in most de ntal laboratories. Theexte rnal finish line must also provide anacute an gle to lock in the resin and red uceleakage. The finish line must extend fromthe approp riate line angle 10 the occlusalsurface so th at the denture tooth can beplaced in a normal position with a smallamount of resin between it and the finishline ,

For Sing le tuot h repl acement, there arcvarious options available to the clin ician andthe technician. Most co mm only, some formof re inforced acrylic po ntic is chosen. Thiscan be hest descri bed as metal ridge cover­

age with a post extending into the denturetooth. Additional metal beads will enhancethe retention (Fig 2-9). Under no circum­stances should raised mesh retention be se­lected for the single tooth, as the amount ofretention created in the constricted meshspace is inadequate to re ta in the denturetooth. Wh en space is lacking, a metal back­ing, 'waxed as part of the casting bu t havingthe attributes of a fixed pontic, is indicatedto provide additio nal support against the

13

Advanced Removable Partial Dentures

Compositeveneer

v

Extension of lingualbar or plate

y

Fig 2-10 Cross se ct io n of ve­neered metal ponti c.

•

Fig 2- 1I Short flange with re in­forced acrylic ponties.

forces of Incision (Fig 2-10). When the oe­clusal surface of the pontic is an integral parto f the casting, the 0Plxlsiug occlusion. ifthere is any, mus t accompa ny the mastereast to the lulxnutory \ \ 11('11 the opposingocclusion is a denture tooth, the anatomy ofthe occlusal surface of the mel..d ponticshouldmimic the selected den ture teMlth.

Th e most cfflcicnt \\~IY to Ill,lllaf!;t' the sino.gil' tooth replacemen t is to select the den ­ture tooth before the master cast is sent tothe lab for the framewo rk. The tooth isgro und in to /1 1 the edentulous an-n. .01 cs­theuc try-in is arranged . ifappropriate, ant i amatrix, made of either firm plltty o r of phs­tcr; is for med to positively position the de n­ture tooth 011 the master cast . The technicianwtll utillzo II J(~ matrix and the denture tooth

when \\~l,ing the framework. and the resultwill be a retentive fonn keyed to tlte Idea ltooth position. Obvious ly, this technique ismost often needed for the replacement ofanterior teeth alld is esse ntial wh('n two or

14

more adjacent anterior teet h arc 1"M 'illg re­placed O il the partial. \\ 'hell a denture tooththai matches the shade of the adja('('111 nat­ural teeth cannot he fou nd, a compos ile ve­11( '('1" (Visioge lll (ES PE, Norristown. PAl orsimilar material) can he.' pIaL'('C1 in a properlydc.'Sigll{'(1 metal pontic. These mate rials call

be blended and xtairux] to match all\lo~i anytooth. They an-, howr-ver; (Illite brittle inshear and. as a result. must han ' metal at thein ci sal to protect thc wnoc r.The partial del l­lure cas ting e m he 0.3 mill thick at the in­cisal or occl usal and still be rigid enough towithstand incising forces. \ \ 1K'ne\ 'er pcssi­blc, the single tooth replacemen t should I M~

planned to exit from the tissue as a fixed poll­t il', without any resin flange. When two adja­cen t teet h are replaced, a \(' 1)' short fl<llIgelIIay IX! required to provi de for the lutcnlcn­tal papilla (Fig 2- 11). Often th is short nangccan be kept \"('1)" thin and made to closelymatch the Sl im )llJldin~ attached giJl~i\awithminimal tinting of the h:'LS(' when Kayon

•

resin (Kay-See Dental , Kansas Ci ty, MO) isused (Earl Pound Technique). For heavilypigmented ginbriv<l, the flange can he packedin clear resin with appropriate tin ting so thatthe pat ient's gingiva can he seen through thethin flange . The red fibe rs normally found instandard dent ure res ins must he re moved bysifting the polymer through a 2 x 2 gamesince the presence ofthe fibers in the area ofthe att ached gingiva can never he anatomi­cally co rrect and will spoil the esthetic effectof even the most carefullv tinted resin.

Clasp Retention

The fourth , and final , conside ration ill thedesign of the removable partial dent ure isthat of clasp retention . Some clinicians be­lieve that clasp selection is by Elf th e mo stimportant conside rat ion in design . How­ever, clasp types, he they l-bar; wire orcast, circuutfercn tial or reverse back ac­tion, or allY of t he many others that havefound a place in prosthodo ntics, do not ap­pear to have any clearly defi ned effect onthe clinical success of the partial de nture .\ Vhat is more important is that the claspbe pro perly made to be stron g, retentive,and esthetic, and to do no har m. \ Ve willbase on r sele ction on th ese factors aloneand will consider the typ e of clasp to hethe least important component of our ad­vanced part ial denture.

Since the laboratory plays such a largerole in the design ofthe standard HPD, it isnot at all strange that it may em phasizeclasp constru ct ion. Our technicians arcoften forced tu create castings with little orno evidence of preparation of the remain­ing teeth . The undesirab le un dercuts thatmay exist force the technician to deviseways to wor k around them, resulting in

Removable Partial Denture Design

clasps that arc excessive in number andgenerally uncsthctic. A laboratory -designedHPD will usuallv have more retentiveclasps than one designed by a prosthodon­tist , since careful month preparation can beexpected to create parallel guiding planesthat will give frid ional retention . The num ­

bcr of clasps, especially th ose that might heesthet ically unacceptable, can also he re ­duced by the way the casti ng is managedwln-n fitting, finishing, and poli shing. Thesetechni ques will he fully discu ssed late r inthis text.

\V1lCn retenti ve clasps are con te m­plated , their lengt h, taper, and cross-sec­tional width-t hickness ratio mus t be takeninto account, as well as the alloy froinwhich they are made and the degree of re ­tentive undercu t in whtch they are placed .AU these facto rs will describe a retentiveclasp arm of any configuration that can beexpected to function below its proportion allimit. Factors that result in dtstortlon of theclasp arm from allY cause mus t be alteredso th at the clasp will perform as desired fort he life of the part ial.

Given a mouth that has had ideal mouthpreparation, either subt ract ive or additive,there are only four forms of ret entive clasparm s that need he used: (1) circumferentialcast , (2) circum ferent ial wire, (3) infra­bulge I-bar, and (4) infralm lge Lbur.

Circumferential Cast Clasp

Th is clasp is the most commonly used of allthe clasp forms and is easily const ructed bythe labo nu ory and adjus ted by the clini­cian. \Vhile it is stro ng, it is also rigid andpotentially un esthct !c. It is therefore tndt­cat(~d for the posterior part of the mo uthand , because of its rigidity, best used intooth-borne sttunttons.

15

Advanced Removable Part ial Dentures

3mm

1.5 rnm {=f:-:::)

2:1

o1:1

Fig 2-12 Embrasure space for two clasp arms.

A modificati on of the circumfcn-ntinldas» co mmonlv found ill a varictv of sit ua-, ,tions is the dou ble cmbncsure clasp . whichis not hing but two circum fe rential claspshack to back. Th is clasp, used primarily infullv dentate sextants, is nn ncccssa rv ill, ,couvcnuonul HP Ds hilt does have a placeill so me maxillo facial p ro s the ses, Theamount of rete ntion gained from t l lt ~ ante ­rio r p rojf'ct ing arms of the e mbrusurc claspis usually exce ssive, and when that untcrtorcomponent is on u pn-molur; it wtll becomerigid due to its red ucedlength. The buccalclasp an n is ap t to he unesthctic ;L<; wel l. I II

the well-prepared mo uth, th e poste riorcompone nt 0 11 tl n- molar provlrles ado­(Iuat e rete ntion fo r the conven tional par­tial. Th e embra sure clasp th at passesthrough a contact an-a will often ' hrm k inservice becaus e there is seldom enoughspal"C c reated through the contact areas ofthe two teeth at the e mb rasure. As u resu lt,the clasp is ofte n found to be ill hypcroc­elusion. Adjustillg the metal to allow too thcontact with the opposing arch weakens th eclasp by making it th inne r at the bucc al ex­tension of th e marginal ridge than it is fur­tln-r along the clasp ar m. Thi s thin una sets

lip a fle xure IXli1l1 ill the clasp and. utk-r re-

16

Fig 2-13 Width-thickness rati os for two castclasp patterns.

pcatcdmovemeut of the clasp ann in func­tion. a stress fracture develops. Repair ofthis broken e mbrasure clasp is d ifficu lt. ifnot impo ssible, to accomplish with allYhope of long-termsuccess.

To en-at e adequat e space fo r the mostcommonly use d clasp pall ('Tll , the clinicianmu st pn'parc a cha nne l measurtng 1.,'5 JIlIll

hy I.;) l lll ll fo r one clasp eo millg thro ughthe e mbrasure and I .;) mill vcrticallv bv ,'3.0mm horizontally if two clasps are runthrough tha t same cmbmsun- (Fig 2·1 2).Whcu maxi mu m flexibility is required. ae.L..t ci rcumferent ial clasp patten! with awidth-thickness ratio d ose to 2:1 (How­med ica pattern 3 \ I A.fO is an exa mple )sho uld be req ues ted (Fig 2-13). This mighthe th e case if a cast clasp is used ,L" all em ­brasurc clasp for a Class " mandibu lar sit­uation where the m e of a wro ught clasp isnot possible. w hen maximum li gid ity andret ention is required. as ill the case of amaxilla ry clasp where less tha n 0.010 incl.of n-n-n tivc a rea is a\"ai lahle in the terminalthird at the desired location . the n a clasppallen! with a ratio closer to 1:1 would hedesirable.

The convr-ntlon al approach to the l'<L"tcircumferent ial clasp n-quln-s that a brae-

•Removable Partial Dentu re Design

Mesial restWire clasp

Dista l plate

Solder -----1~~

Fig 2·14 Elimin ation o f li ngualbracing ar m (reci procation) withguiding planes (red).

ing arm be used to provide rec ip rocat ion.This nonflexing arm is t raditionally placedax low on the tooth as possible to within 1mm of the giugiva (that is if the height ofcon tour is at the level o f the gingiva, as itmay he on the lingual of it maxillary poste­rior tooth). The need for this bracing ann ,customary since the days of banded claspsmade of plate gold where both arms C1I­

te red unde rcuts , has never been clear tume, espec ially if the clasp pattern had thesame width -thickness ratio as the ret entivearm and was of similar length . The idealbracing ann should be made from a patternhaving a wid th-thickness ruuo that up­p reaches ]: I.

There are othe r \vays to achieve recipro­cation that are not clasp dependent. Thesewould include precise guiding planes 011

the ruiuor connectors to the rests as well asthe natural contact of the tooth to the adja­cent tooth. For the so-called hracing arm tofunction as it has been proposed it should,it must contact the abutment on a surfaceparallel to the path of insertion In such a\vay as to hold the abutment tooth in posi­tion as the rete ntive clasp ann passcs overthe height of contour and the rest scatsfully 'I'his situation nor mally only occurs

when a milled surface has been preparedon a casting for the abutment, since the nat­ural tooth is unlikely to have parallel wallsopposite the retentive clasp arm. Once thepartial is fully seated, the prepared guidingplanes provide late ral bracing in a way thatclasp arms never can (Fig 2-14).

Circumferential Wire Clasp

The "wrought wire" clasp, as it ISuniversallyknown, has long been considered the claspof choice for Class I and II partial dentures,especially for the mandible. It is obviousthat a structure that i..s cold rolled , ;LS allwires are , is going to be more Ilcx tblc than ucast clasp of similar dimensions. In addftton,because it is roun d, th is clasp will beroughly three times more flexible than ahalf round cast clasp when loaded otherthan horizontally, as it WOldt! be as theprime retentive element on a mandibularhtlaterul distal extension partial. The reten­tive properties of wire arc dependent onalloy, length of the active clasp ann, andgauge. The means ofattachment of the wireto the framework also has an effect on theflexibility of the clasp; in the most ideal sit­uation, the wire is attached some distance

17

Advanced Removable Partial Dentures

Heigh t of contour

Recontour Ideal

Fig 2-15 Tooth co ntour for retentive clasps (wire or cast).

from where it is expected to flex. 111is wouldnonnallv he on the resin retention area J\inch hack from the tooth. Both precious andnonprcciou s wires can and have been usedfor retentive clasp ar ms. There is ge nerallya 1- to 2-ga llgc difference between a prc ­cious wire and one that is an alloy of N i-C ror sim ilar material, with the nOTlpreciollswire being stiffer. In fact , bot h an IS-gaugeTiconium wire (Ni-Cr) am i a Baker OR-2(p recious metal) arc four times more rigidthan a 20-gallge [elenko Sta ndard wire . AnIS-gauge Jelenko wire is two times morerigid than a 20-gallge wire of th e same com­position . T he Jelenko Stan dard wire hasproven to be the alloy of choice (Au 6:31/'0,Ag 11%, PI 10%, I'd 2%, and Cu 1.'3%). Anywire with sim ilar composition could be ex­pected to have similar perf ormance.

To get maxim um flexibility from the cir­cu mforcndal wtro clasp , cvmy e ffort musthe made to keep the bend placed in thewire in two plan es. H istorically (and beforemouth preparation), wires took the place of

18

plate gold clasps . They we re bent to co n­fo rm to the unmodiflcd tooth con tou rs and,as a res ult, were bent in the th ree planes ofspace , as the clasp made an ulrrupt bendfrom the ma rginal ridge toward the gingivaland was th en contoured arount] to themes ial of the tooth to en te r the undercut.As each successive bend was made, thewire flexibility was reduced . Acc urate toothmodification to reduce the undercuts onthe proximal two th irds of the bu ccal xur­face allows th e clasp to exit from the Hau gearea close to the gingiva and ente r the re ­tentive area in the terminal on e th ird to adepth ofO.Ol to 0.1.5 inches (Fig 2-L5).

The selection of wires is based primarilyon act ive length according to th is simpleru le , which allows cadi wire to pe rfor mbelow its p ropor tional limit: Clasps with anactive length < 7 mm should be of 20­gauge , those S to 10 mm should be of 19­gauge , and those > 10 nun will require an18-gauge wire . At these distances and thesegauges, th e wires will give app roximately

•Removable Partial De nture Des ign

Height of contour

\

There will be no..-------buccal clas p arm

~~j:;1~~~;- o.oto- ircnundercut

o c

Fig 2-16 Lingual retentive wire clasp above lingual plate.

th e sallie amount of re tent ion aIHI re mainbelow their proporttonalltmtt . \Vhile it mayhe possible 10 place some wires into under ­cuts > 0.15 inch and still have th em func­tion wit hout dist ortion , there is no clinicalevide nce that th ts increase in undercutdepth is of any value. The wire clasp can heused successfully on the lingual surface ofmust mandibular premolars, in conjunctionwith a di stal guide pla te tha t exte ndsslightly beyond the distal facial line angleand a mes ial rest , to provide n-tenfinu with­out any display of buccal metal. In these sit­uations, the clasp an n will be very short andmust therefore be of 20-gauge or finerwire. The major connector must be a lin­gual or sublingual bar, at least in the area ofth is clasp, so that the requirement for :lnun of space at the superior margin of thebar is essential In the maxilla. the majorconnector is open ed to the lingual as a mat­ter of course whenever possible, so thatfinding a lingual surface for the wire reten­tive clasp an n is not norm ally a problem if

the tooth contours provide any retentiveareas of 0.010 inch or greate r. There is noneed fix a buccal bracing arm in these situ­ations. When the major connector cannotbe opened for any reason, it is still possibleto utilize only a lingual clasp arm if suffi­d ent too th height exists to permit the wireto sit on the occlusal border of the lingualplate and enter the proper undercut. Theonly disadvantage to this design is the sligh topening of the major connector beneaththe clasp tip (Fig 2-lG).

Unlike cast clasp arms that can be ex­pected to break if they are deformed andthe n recontoured more than a few times,wire clasps (especially those of high-goldalloys) will withstand repeated rcadap ta­tion withou t any change in their retentiveproperties. Since these clasps are moreflexible , they have the disadvantage ofbeing far easier for the patient to deform iftheyarc used as han dles to remove thepartial from the mouth. Patients must bewarned tha t deformation of a properly

19

Advanced Removable Partial Dentures

placed wire clasp can only occur if thewireis loaded heyond its proportional [iIII it andthat this call happen on ly if tho clasp is dis­torted by the patie nt. SOllie putieuts insist011 hiting their partials to place rathe r thanplacing them wi th the fingers of bothhands. Patients must he shown that theycan US(' the flanges of the denture base asa purchase point for rf"lllm l llg the rk-n­tun'. Sometimes the placement of a simu­lated Class \' cavity on a denture toot h wil lgin" the pat ient a purchase po int to applya dislodging force .

Inf"bulge Clasps

Illfrallilige clasps have Imlg 11('(' I I advocatedas all ultemattve to the wire ctrcmnfcrcr rtial

clasp for Class I and II situa tions. Theyhave been proposed as a more esthet ic al­te rnative to the cast ci rcmufeu-ntlal claspas well. These clasps call come ill a numberof forms and can be either cast or wrought.The most co mmonly used iufr abulge clasphas been the l-bar; wh ich is to he placed atthe greatpst convexity of the tooth meslo­distally ,LS seen From the h0 I17.o 11tal. \\llellcombined with a proximal guide plate atthe edentulous side of the prime abu tment

20

0.0 1()'-inchunde rcut

F ig 2·17 Short wire I-ba r todistobuccal retentive area.

and a rest at the other end of the occlusalsurface. 110 b racing arm is required . This isbecaus e the toot ll cannot be displaced bythe action or the re tentive clasp an n.Depending 0 11 the contact of the gllideplate, stres s relief ca n be created wi th thissystem for the Class I situation.

\\'ht'll til(' l-bnr clasp is made of a suit ­able length and gauge of wire, additionaladvan tages are possible. Since the wire isadded to th.. casting hy so ldering afte r theframe h:LSh~'~ ' 11 finished and polished , it ispossible to plan ' the clasp arm n"'ry closeto t ilt> buccal extension of the guide pla te(Fig 2-17). \\'itll this distal posit ioning. theclasp ur tu become s shorte r an d mus ttherefore 1)(' of a higher gauge 10 retainflexibility (normally a 20-gauge wire wtllbe chosen). Thl' guiding plane and platemu st exte nd fully to the line anglo, ami apositive rest O il the opposite side of tlieabutment urust he used to provide rc-cip­rocation if till" distally placed l -bar is 0 11 atermilia] abutment . Ir this I)pe of claspingis used o n the ant erio r abutment of a Class111 partial dr-uture. the need for preciserecip rocation is not as grea t because theposte rior abutment will restrict d istalmoveme nt o f the partial.

•Removab le Partial Denture Des ign

Height of contour

~~fI.~:::::::::;,I.,\7.~~~;;;;;;;'~~.... 0.0 1O-inch

undercut

Fig 2- 18 Tooth-bar clasp re la­

t ionship.

Fig 2-19 Contour indicat ing t heneed for L-bar clasp.

Cast Wire

Height of contou r

0.010-inch<........~,,"""1 undercut

Th e contact between the l-bar and theretentive area must not be a point contact .Inste ad. th e wire is contoured i l l such a wayas to p resent a line contact o r a su rface con­tad . \Vhen a cast l-bar is used, the surfacecon tact is created in the blockout and wax­ing of the framework (F ig 2-18). 'n1l'SC ex­paneled contact areas provide a margin ofe rro r fo r the technician , since placing aclasp lip at poin t cont act on a repeatedbasis is an unreasonable req uest .

\Vhile the l-bar clasp is by far the mostcommon or the infrabulge clasps, there isan occasional need for an Lbar whe n theonly available usable undercut is immedi ­ately adjacent to the ede ntulous area andwhe re even a light-wire I-bar wtll be 100

short and therefore too rigid . By hr ingingthe approach ann up to the midbuccal o f"the tooth and then bringing t ll(~ hase of theJ, distally to the reten tive area, sutllcicntclasp length can he developed ill most situ ­ations (Fig 2-19). This clasp form can becreat ed in either cast metal or with wire ,again rem em be ring to choose the appropri­ate gauge based on the active length of theclasp .

Othe r forms of bar clasps have been ad­vocated over the years, primarily the T-barand occasionally a U-har. These forms haveno place in the modern HPJ) and are gell­erallyunesthctic and difficult. if not impo s­sible, to adjust-c-espccially if they are madein cast metal.

21

Advance d Removable Par t ial Dentures

There is om- major co nrru mchcat ton forthe infrabulge clasp. Th e height ofcontourof the soft tissue in the area of t ilt> proxi4mal approach arm and the degree of ....ofttissu r- undercut call make the ba r claspsunacce ptable . If the height of co ntour isw ry dose to the buccal marginal tissue ,the approach ann will have to stand outfrom the nssue [x-cuuse it cannot be in anundercut relative to th e pat h of inse-rt ionas ddpnni ncd hy the guiding planes . Ifthat so rt tissu e umk-rcu t is seve re, theclasp may ab rade the buccal 1I1l1l'O Sa inno rmal function.

Eve n the most cas ual glance at any tex ton removable part ial dentu res will ldcn­ti~\' Ulan} othe r clasp forms: ring clasps.backaction clasps, " C~ or fish hoo k clas ps,am i on and 0 11. TIlt'se cla sp fo rm s have allbeen created to work a round contoursthat have not been adequately modfflodwtth appropriat e 1I10nth p reparation or. insome cases, teeth that need minor ortho­donnato retu rn them to a normal positionin the arch. If th e re is no usabl e mesialunde rcut for a ci rcumferential wi re clasp ,unde rcuts 011 the lingual su rface wil l have

to be used or ti lt' tooth mod ified withsonu- form of additive mout h pre paration .Given qu ali ty mouth p repa ra tion. 110

other clasp for ms, beyond the cas t andwrought circumfcn-ut lal clasps am i tln- 1­liar and Lebar clasps, pit her wrought or('ast, are indicated .

Th i're arc two other gene ral catego rieso f cust retentive eh-monts !hat willlx- con­sidcred late r (C hapter H): the rotationalpa th of insertion pa rtial and the hingedconnector (commonly referred to :l.S a"Swinglock"). These two special types offrameworks ma v include conventiona lclasping in addi tion to the ir special re ten­tin' de ,'ices.

22

Design Specifics: Class I-IV I\ \ 'ith all understandi ng of the componentparts of tlu> partial den tu re. we can nowlook to specific design considera tion s foreach of the four haste classifications of theRPD . T he re will be lIlany arr-as of overl apin desigll , hut the inten t of this section is toidentify basic principles of design fo r eachclass tudcpeudcntly keeping i ll mind thefour compon ent parts of partial denturethe rapy,

Before any sred ne designs call he es tab ­Hshcd . a quality dia gllostic cas t must heavailable for sllfvp)i ng, '111P cast must accu­rutely represent all n 'maillillg teeth amithose soft tissue-covered an -as that will bewithin the dent ure space . T his would in­clude ret I'Or . tolar pads, 1'1"(-111 11 11 extensions .vestibules when bar clasps are be ing con ­sidered, am i the like .

Finding the Path of Insertion

TIll:" first stc p will always 1)(' to determinethe path or insertion ami removal. Here theemphasis is 011 the path of rt'IlIO\1lL sincethe goal will be to limit the possible dt rcc ­tlons that the partial can exit from tlu­mou th through prepa ra tion of ha rd tissues.The pat h of insertion is, of course, tlrc T(' ­

ciproca l orthe more important pa th of re~

moval and is most often presented ,LS bei ll/-;

of some Importance. In all but one instance .the path of removal should he parallel to thelong axis of the prime nbunnenn s). TherL'wtl l be occasions. usually i ll C lass IV situu­tions and especially in those where a rota­tional path of inse rtion is plan ned , when thepa th of remova l is primarily tk-tenuined bythe soft tissue height of contour,

Tile path of inserti on/ re moval is frozenill space hy the prepa red gu iding planesand the cast plates that to uch them.Undercut s on hard or soft t i s" llt~ exist onlyrelanvr- to that path , so tilt ing till' cast O il

the: sUf\ (')'or ill order to alter the rel ative

heights of co ntour to obtain retention will1I0t produce real undercuts unless the pathis con trolled by the planes. Civen the fric­tional ret en tion that paralle l guide pla tescau provide, there is seldom allY 11('('(110 heconcerned about re te nt ion . If there an' nousa ble n-te ntt ve areas anywhe re 01 1 the de­sin-d abutmen t teeth , then they must hecreated hy e ither subtrac tive or additivemouth llrep aration.

Class I RPD

Abutment Selection and Rests

Only wln-n the canine is the prime abut­ment (ic, the abutment adjacen t to the dis­tal extension base) should a singk- abut ­men t he chose n for the Class I partial. Afirst premolar used by itself ax the onlyabu tment doe s not provide sufflcicnt sup­port to replace the lIIissillg molars und thesecond premolar. \Vhen the first prem olaris tile prime abutment, it must [ ravr- an oc­clusal res t and the adjacent canine musthave cithor a distal-incisal or it cingulumrest (fo r the mandible , this rest cannot bemade dl't'p enough an d kept ill cnunn-l. soeither houded metal or lxmdcd compositemust I ll~ IISf'cI to create the rest scat ). \\1 lenboth pre mola rs re main, their bony supportm ust he evaluated. If the)" han ' cxcelk-utbone h-eels and the opposing arch is a ('0 11I­

pletc denture. the ca nine re-st may Iw elim­mated. It'ming the two premolars as theabutments. Since it is rare to replace oll ly a

Removable Partial Denture De sign

Fig 2-20 Multiple abutments are used whenpossible,

second molar 0 11 a Class I HPJ), the on lyopt ions we fl{ '("( 1 co ncern ourselves with arethose ju st nu-ntioncd . The Class I RPD willhave a single abutm ent if the abutmenttooth is the- canine, and two abutments ifthe first premolar is the prime abutnu-nt . Ifthe second premolar is the prime abut­ment, then there will he e ithe r two or th reeabutme nts, based 011 the level of bon)' sup­port (Fi!!: 2-20). The Il< lsition of the occlusalrests on the premolars is immaterial. al­though soun- would say that a mesial reston thc p rime abutme nt is supe rior to a d is­tal rest. \ Vhile there lllay well be l lu-un-ti­cal differences here, tlwre appe ars to ht ~ riodifference clinically in th e well-made andm alntalnod 1\I 'D . 'I'hc path of insertiou/ re­moval will lit' chosen to allow parallelism ofthe distal sur faces 01" tile prime abutments.

The gllidillg planes ('(('..\1("(1 on the p rilll l'

abutme nts r equire a basic decision n oganl­ing stress relie f Two tech niques have lxx-nproposed OH'r tilt.> years, Kratochvil slIg·gcstcd that tilt, ~lIi din~ plane be prepa redto be ;lS long ax possible. with the stress re­lief coming fr om a fuucttonal relief of the

23

•Advanced Removable Partial Dentures

00

Long

Oil

Fig 2-21 GUiding plane/guide plate options for Class I parti als.

Ideal Constr icted

Fig 2-22 Ideal paralhsm of guiding planes to allow unres tricted rotation.

casting be fo re the altered cast irnpn-ssionwas made . Kroll. 0 11 tht· other hand. de­scribed a shorter ~lI idi llg plane ext endingfrom the marginal ridge roughly one third(If t i le way d ()\\1l 111P tooth, with theocclusallimit of the guide plate being the ~ngi\~llexte nsion of th is shorter guiding plane (Fig2-21). Here, the stress relief is created inthe hlo ckout of the undercut gingival 10 theguiding plane. The guide plate is effectiveill reciprocation hut can also rotate into th eundercut ra ther than bind on the guidingplane timing loading of the posterior den­tu re bases. T here is no clinical evidence thatwould favor one of these approaches overtile other. TIle decision il Ia)' w('11 rest on thequality of the laboratory support, since thereduced-length gtlidillg plane/guide plate

24

req uires greate r attention to detail in bothblockout and fluishlng of tile cas ting.

III either approach. the parallel guidingplanes, contacted by the guide plates of thecasting, res tri d the path of insertion/ re­moval to whatever angle of diw>rp;ell<:l' W,L5

established in the mouth pn 'paration phaseof the trcatn u-nt. The closer to 00 degreesparallelism, the greater till>frictional rests­tnuce to dislodgml'llt wi th the potential forstress reli e f still viable. For the C lass I par­tial denture, parallelis m must he consid­en-d in unotln-r plane of sp;lee. I II order fortill' partial to rotate ffl'ely around its ful­crum, the guiding planes must be. parallelto each other from till)oc clusal vie-was theyare in t}n - sagiuul. That is, the}' IllIIS! lit' onlil t' same plane across the arch so they can

act in all identical fashion under occlusalload (Fig 2·22). For any of the otherclasses. the effect of the planes is enhancedlw Iwin g in different planes as S{"(' II fromthe occlusal.

The sa me considerat ions exist for theopposite sid e:' of the mouth. with the o nlycompromise coming when ti l t ' d istal slopesof tln- two prime abutments are 1I0t parallelami can not he mad e so through sub tractive11 101111. pwpa ratioll . when this ()('Cllrs ( 1ISI1­

ally when the can ines are prime almt­IIH'IltS), th e be st option is to favor theweake r of the two prime abu nuents. T lwother (stronger) abu tment will he n-eon­t01\l'('(1with additive mouth proparut ton to

allow both sides to be paral lel.

Connectors

As statr-d before. \~-hen{'n>r possihk-, themaximum amount of soft li..sut' should T<.' .

main IlllCOH' T("(! by the RPJ). This wouldrequire, for exam ple, th e use of th e lingualbar O\1.'r the lingual plate . If. h OW( 'H 'r, the reis illadt'l!nate space or if there is tilt' IXlten­ttal for loss ofsome remaining anterior teeth

du ring the life of the partial a lill~ 1;\ 1 platewill he tlu- prope r choice Sf) that ad di tionst-au he m.u le .<;1 rcc cssfully II Illay lx-possibleto ('(lI ll hi lle a l ingual pla te in the inciso r ureawith a lingual bar distal to tilt' canines ill­

stcnd or covering all the lingunl surfaces.Wlreu space permits, th is dt's ign is p rv­fcm-d lx-causc it offers the potc-nt iul for lin­gual n -tr-ntive clasping ami no show o fmetal 0 11 the buccal surfaces of thr- abu t­mcnts.

The maxillary Class I major connect orvaries in the placement of hol1l the anteriorami the posterior borders . As the number ofteeth to be replaced with the part ial in­creases. the natural incl ination wtll be to in-

Removable Partial Denture Design

Fig 2·2] Minimal coverage of anterio r palate re­quires large guiding planes for pos itive results.

crease the coverage of the major connectorso Ihat il approaches a co mplet e dentureoutline . Since there can he 110 pe ripheralseal Oil 11K' partial den ture, there is litt levalue in extending tll(~ poste rior bonk-r tothe vihrating line. The glandular portion ofthe posteri or soft palate offers no real sup­port to the parti al . am i therefore sho uld beleft UIlCOWf('tl. Th e edentulous ridges,however, do sUPlx)J1 the part ial and sho uldalways be covered to the hamular no tch, ei­the r in rcslu or with metal. Anterior cove-r­age is dependent 011 the teeth remaining. Ifonly the six ann-riors arc left . going tn fulllingual coverage offe rs the option of ('asyaddition of teeth ..hould some he lost, uswel l as p rovi{lillg the potential for uddi ttoual

frictional rr-tcntion on ,my guiding pram'sthat can Ill'established . Finding tooth st1'1 IC­

turc o n the llugual o f maxillary anteriorteeth that ca n he p repare d to parallel guid­in)4 su rfaces is, un fortunately; U1K'OI IIIl IOII .

when the remaining six an terio r teeth arehealthy and not mobile. it is certainly Icasi­ble to open the anterior area by projec ting aci ngulum fest on to a prepared acute restpwpamtion from the distal. Th e anterior

2S

Advanced Removable Partial Dentures

border must tlu-n blen d into the ante-riorslope of the rugae an-a and end posterior toa major m gae . For this approach to 1)( ' de­pendably success ful. the canines mu st havesufflclont d istal structure to allow for guld­ing planes of at loas tS ]J11ll (Fig 2-2:3 ).

Mino r connectors wi ll he of standard dl­mensions. with care taken to see tha t atleast 1.2 IlUll of me tal thickness at ti l l ' mar­ginal ridge is available to support the rest s.

Resin Retention

Since the ner-d for pertodic reline of thedistal extension base is expected, especiallyOil the mandibular arch, the resin ret entiono f choice is a raised mesh with > I IIUI I ofSp<K't' for resin below tilt' mesh. III somesituations O il the maxilla. where th ew hasbeen minimal resorption of tile edentulousextens ion (und th ercfon- m in imal roo m for

the casting and the replace ment dent ureteeth), a metal base with rou-n ttvc he ad s a.s

an intrega! lla l1 o f the cas t ing is the only vi­able option. Obviously th is bas e cannot hpn-lmed. howeve-r; in the mat ure edent ulousridge with the suppo rt of the palatal cover­age, no reline lII ay he needed durin~ thelife of the partial.

~I odi fication spaces arc managed withme tal hast's and bead or post rr-tr-ntton

wherever possible . Only very rece nt cxtrac­lions cou ld he considered I()J' mesh n-t cn­

lion, ou t caution must 1)1>taken for a sing le

tooth replacement because the amount ofmesh n -teut ion available fix the singletooth is often Inadequate. It is ~eu('rally

wiser to add a tooth to till>existing partialdentu re tem po rarily; or 10 co ns t ruct all iu­

tc rim partial fix the initial healing periodawl th en cons truct th e new Hl' D with e i­ther a reinforced metal ]Jo.st or a veneeredpont ic form for the si llg;l( ~ too th.

26

(I" ping

The t: Til' of re tentive clasp to he used is de ­te ruu m -d by two facto rs: the uvuilahi litv of aretr-u tfvo area on the tooth and the cltni­ciun's prefere nce . Til e options lIlay be «las­sificd as follows:

• Oulv a mesiobuccal reten tive a rea-wirecircumfe rent ial clasp to 0.015 inch.

• Midfactal retent ive an-a with appropriategingh <:ll contour-c-l-ba r to 0.010 inch (ei­Ille r cas t or wrough t).

• Only a cltsto laclal ret entive arcu-c-Lbarto (J.n I 0 tnch (pn -forablv wrou ght).

• I\ o facial rete llLive areas are prese nt­lingual " i re circumferent ial d :LSpS to0.<))0 inch or rccontour abutment with

either snbtr ucuvc or ad ditive preparation.

' In either arch, one retentive clasp pe rside ,\ ; 11 provid e ade qua te retention if themaximum frictional retention is es tahltshcdth rough mouth prepara tion and curoful fit­tin g o f the casting.

III d l()I)sing the re tentive clasps for themandibular Class I RPD. co nside rationmust be gin-"n to cs tablishmg ..tres.. rel iefIIt'C:mse the partial will always rotate infunction. The maxillary HPD may show n-rylitt le rota tional movem ent due to the sup­port of the hard palate and the ge nc rally su­perior ridge con tour. The we aker th e abut­ment teeth and the supporting ridge, thegreate-r the rota tional movement that musthe allowed in the flt of the e:L\tillg. This re­lid tau he ob tained ill the bloc kout of themaster cast or in till' int raoral fittin g of theframe (to be discussedlate r). Along with thefit of the frame. tile flexibility of the rctcn­tive clasp arms selected plays an importan trole in stress relief so that a light-wire re­tentlvc clasp in any or tile appropriate clasp

Light wire soldered toframe, 0.010-inch undercut

Fig 2·24 Elimina.tion of buccal bracing arm withlingual retentive wire .

forms is indicated when the support is poor.Thb decision muv sacrifice some retentionami stabilitv to n-llovc the abutment teorhfrom the full load of mastication.

In the Class 1 HPD, th ere is 110 need toconsider the use of a so-called "h md llgclasp" becau se t!le combtnation of n -sts/mmor connectors alld guide plates am!tooth contact:.. " i ll provide the nt"<.'t 'sSaJ)'n -ciprocation . Even if lingual circurufcr­cnt lal clasping is chosen. it is Hot neC<'ssaryto complica te the ca.sling and show 1II1 ­

si/!;ht ly metal wit h a buccal hral'i ll~ clasparm (Fig 2-24).

Class II RPD

Abutment, and Rests

\ \ 'lulc the Class II partial design is oftenconsidered a mixture of the principles ofChss I and Class III partial designs, specialconsiderat io n must be given to the potentialfor rotation at the fulcr um line that " i ll r nu

from the distulmost rigid contact s of the

Removable Partial Denture Design

Fulcrum line

Fig 2·25 GUiding planes restricting rotation in theClass II partial.

pa rtial with the abu tment tee th on eachside of Ille arch. One might imagine that ro­tation aml the resulting stress relief willoccur naturally without allYeffort . In truth.a decision as to the desirability of allo\\ingmotion around the fulcrum Jille must hemade l)(.fore mouth preparation begins.For the must pa rt, there is 110 I\{'("I to planfor ...tres:.. relief for the Class II RPD be­cause the n-muiniug teeth. if prope rly con­tacred 011 p repared surfaces (and ill parti cu­lar 011 gu id ing plane surfaces), will be ableto SllppOrt the teeth IWing replaced as acan tileve r (F ig 2-25). .Mastication will mostoften txx'ur o n the den tat e (Class I I) sideduo to lncroused efficiency in managin/!;food part id es, so the distal extension sidewill receive only minor load ing, Only whenthe abutuu-nts are weak and few in nu mbermust we conside r red ucing tile length of theguiding planes and functional relief of thecasting to allow limited rotation and partialloading of the edentulous ridge. When theca.sting I I; ts I)("C1I rel ieved. the Sllpport of theedentu lous area is obtained through the al­tc rcd cast imp ression. In the maxilla ry arch.

27

Advanced Removable Partial Den tures

Fig 2-26 Stopping major co nnector sho rt ofretromolar space.

uddittonal SllPI)( lrt for ti le wcakem-d tee-th isobtained by cow ring a gu-nter portion ofthe palate , and an alte red cast Impression isnormally 1I0t needed.

Th e distal extens ion side of th e partial istrea ted cxact lv as in the C h<;s I s itua tionwt th no exceptions. The nnmugeun-nt of thetooth-supported side offers a few optionsusually dependent on the num be r, strengt h.und position of the available abu tments.When the den ta te side is complete , ie-, nomodific-ation spac('s, an embrasure clasp 0 11

the flrst molar is the rctcutton of choice ,T his clasp must be ca...t. since the co nstrue­tion of an embrasure clasp made of " i re istechnically very difficult and the long-te rmdepcndalnhtv of such a clasp wry lllud. inflllcs iioll. The embrasure clasp is placed onthe first molar rathe r than the second he­cause t ile mandible curves into the ret ro­molar spact.' starting at abou t the secondmolar, which req uires tha t the major eon­m-eter going hack to a second molar standfar away from the tissue , ('rt'ati ll~ a f()(I(J

trup that patients do not appreciate (Figs2-20 and 2-27), The first molar is more apl

28

BIOCkout/required

Fig 2-27 Major connector forced to stand awayfrom tissue in retro molar space.

to allow the placement of l l ll ~ major con­nccto r in a com fortable position . Under nocircumstances shou ld a premolar be used inplace of the molar, since auy clasp placed 0 11

it will be shorter and more ri~id and onenune-sthct lc as we ll.

The need for addi tional abutments on tJIt~

tooth-bor ne side must I~ considered. At theve l)' minimum. an uddi ttonaluunor ('0 1l 1ll'C­

lor and res t must he pl:K't-'<1 as far forwardfrom ti l(' em brasure clasp as possible. Thisrest/con nect or courlnnatiou has bceu call edall indi red n -t.nucr; and it was assumed thatit wo uld counteract the upwanl rota tion ofthe eden tulous b ;l<;C. Th is untir otation {It... teesprings from dcnnstrys past, a.s far as partialdenture design is ( "On ( '('OI('(1, when 110

month preparat ion for guiding planes wasdcue. In the nu xk-m BPD, the guidill)!;planes ami the in timate co ntact with l itecasting through the guide plates prohibits IU­

tationnntil the part ial has 1lI0 W '(! beyond thecontact of the guiding plane and the nssocl­

utcd guid{~ plate. 0 111y at that point ca n thedenture rotate and the "indtn-ct n-tatncr"co me into anttrotanon al contact . So, while

•Removable Par t ial Denture Design

Fig 2-28 Configuration of broadpalatal strap in cross section.

80%

true indiTed retention is a thing of lilt' past,the use ufan additional rest/minor CO III I("<.1or

sonu- distance from the embrusnn- clasp ises sential to provide a thinl point of Ir[I'Il'IICe

for seating the framework <tilli ng fitting ortlu- frame, making the alte red cast Impn-s­ston. and re-rd atillg the framework <Ill lingfuture relines orthe distal extension liaso.

The mesial of Iii" mandibular llr.\! pre ­molar and the d ista l of the maxillary firs tpremolar are o fte n used for thi s th ird pointof contact. The mesial of the mandibularfirs t pre molar is ideal from a geollK'hic

standpoint, but . unfortunately the amountof tooth struct ure at tilt" marginul ridge lIlay

1I0t allow the preparation of an ideal, acuteocclusal rest. TIl(> mesial of the maxillarvfirst premolar would also he Ideal, hu t dis­clusfou ofte n occurs at tile con tact o r thepremolar and the canine, limiting the avail­ahli' space for minor connector am! n-st.

When a modtfl cutlou spaccts ) i.~ pWSl'llt ,we have the potc-ut iul 10 develop additi onalIricnoual ret ention ami recip rocation hylll;L"imizing the gu id illg plane snrf~ l<:t·s adja­cent to the edentulous sp acers) through ci­

tlu-r sub tractive or uddinve tooth pn'para­non. At the \ 'e,)' minimum. a rest and~uid i llg plane would be placed on the iso­luted molar abutme-nt and the tooth at (heanterior e xtension (If tile edentulous space .

Add itional abutments would be added ;tsn-quirrd if the suppo rt From the two origi­nal abutmeuts appeared to be inadequate.

CnidiHg planes for t ill' Class n partialdenture should be as IOIl~ us possible . pm­vidcd that the casting is planned as a can­tileve r. If stress relie f is lnd icnted. the cast ­ing will be adjusted tut ruorully

Connectors

\Iajur ami minor connec tor design 0 11 thedentate side of the pa rtial, in IMJth the max­illa and the mandible. will he that of tl l('

Class III HPO. EWI)' attempt is made tocover ashttle gingival ttssuc as possible. Thl'dtmenslons of the castings and their relation10 the so li tissues arc tlu- sam e as for theClass I situat ion, while the thi rd po int ofcontact (indirect ret uim-r] in the maxi lla Illaymqlliw ti ll' major CO Tl1I('d lJ f to be movedtoward tI ll' anterior. Tbe m inor connector tothat rest mus t blend into the rugae area orthe maxilla so that the sl)('aking area is Hotcompromised . Placing a smal l part (0 11 1..'

fifth ) of the major connector onto the slopeof the anterior palate and the remain ingfour fifths 011 the more posterior horizontalpa late will strengthen the <''O l"ting;, as the cor­rugation in the metal allows for a thi nne rcas ting with tile sallie ligid ity (Fig 2-28 ).

29

Advanced Removable Partial Dentures

Add clasp itnot present

Fig 2-29 Conversion of Class II to Class I withloss of molar.

Mod ification spaces for llIi s s ill~ 'Ul te riorteet h pre sent a special problem in that theycomplicate the design of the casting andorh'lI req uire that metal he place d in thespl'akiu~ area of the ant erio r palate. \ \111:'na la teral inciso r is missill~, it m ay be possi­hl{~ to ca nt ilever it u ff the rest ami minorcouucctor 0 11 th e canine, hut when centralnnd laleral or two central inci sors are miss­ing. a full anterior cas ting " ill he required .A le-tter solut ion to th is problem is to re­place missing anterior teeth with fixed orbonded part ial dentures and lean ' the HP J)to replace only posteri or te-e -t h:

Resin Retention

Tlt t ~ rcstn retention for till' too th-homesido 01" the Class II HPJ) favors the lise ofnn -tal coverage of the rid~c whenever l X)S­

siblc. according 10 requirements men ­t ioned ea rlie r. If only a sillgle tooth is IX'ingreplace d, special consklerat lon IU IISt be~n'n to metal reten tion because the spaceis often res tricted. Usually Stlllle fon n of an-tcutive post is tlesiglll'(lto f.,11 within the

30

dent ure to o th. When the desired tooth P "sitton is obvious, then the post can he run­domly pla('('d hy the tech nician. \\111.' n thetoot h needs to IK' ill some irregular positio ndue to l,!; tlll't ie require ments or ab normaltX:c1US<11 relations, the n the den ture too thmust lx- ground into place hy the clinician.verified in the pat ien ts mouth, and sentaloug with the master cast in SO IlK' so rt ofmatri x so that the technician k"lIOWS exact lywhe-n : the too th must he placed.

A filial consklcn uion for the C h ss IImandibular HPJ) is the pot en tial forcouvcr­sion ann addtttonaltooth loss. TIIl ~ Isolatedposterior' ahl l l lllt~nt on the tooth-borne sideis On ('11 a weakened teeth, both rcstorutivclyand pcriodontally, and lllay Hot last tlte Ii li ~

o f tln- partial . III aut tctpation of till' loss o fthis tooth, tile partial should be designed asif it WCT{' a Class I RP D. with raised rctcn­tivc mesh, a mesial rest on the pre-molar thatwould become the prime ulmtun-nt 0 11 that

side of t lu- arch , and with the potential forfll'xihle eh"pillg 011 the prime ahut uu-nt. Inaddition, tilt ' inte rnal mill external flnish iu f,!;lines mus t he posi tioned as if the poste-rioralnrtn u-nt did not exist, ie , at the distolingualof the premolar that " i ll ht'<.'t)JI Il" t ill' primeabutment. The retentive mesh. suitably T{'­

infonvd , tln-u n il IS dista lly to th« isolaft-'dmolar am i its clasp assembly (F ig 2-2H) .\Vh ell th e molar is lost , the re st , clasp. andgll i d l~ plutc- an ' cu t off and the resin hast ) isextended to cover the total denture space(hiring n-ltmvrcbasc procedures.

Unlortunatc-lv, the maxillary arch cannothe treated ill the same fashion for conver­sion since the major connector in the max­ilia " i ll 1101 have a finish line asse mblv thatcan 1)(' converted to a Class I. Attempts tosolder Oil flnishillg lines and usso ctatedmes hworkare technically w ry complicated,ami the cost seldo m justif ies the conversion.

•

Fi g 2·]0 Lo ng o nlay rest o nmo lar restores occlusal plane foropposing coroplete denture.

Clasping

t\gain, the clasp n- qurrcments for the distalextension side of the Class II a re ick-u tical10 those of the Class I. 0 11 the tooth-homeside , th e re is a major decision to h e made .Since i t is rare to Ilnd a mand tbulnr situa­lion where more than one clasp pe r side isnee- ded for retention, the clinician mustchoose betwee n clasping O il the fulcrumline or ante rio r to it. In most cases. the pos­te rior abutment 011 the tooth-Lome sidewi ll he a mo lar. since if i t were a p remolarthe case W 01 11d he considered a Class I. Th eadvantages are d early 011 the side of clasp­ing on the fulcrum line. ir-, the molar 0 11 thetooth-home side and the terminal abut­munt on the other side . Clasp selection forthomolar is ge nerally limited to a c-ircum­fcn-nttal clasp, either east or wir e, with thelingual ann being n-tcnnvc. Th is is lx-cuuscthe re te ntive arca is most apt to be !()lI1l(10 11 tha t side of the tooth due to its nat uralinclinatio n in the arch, Since th is chesP wi llhe.' the termina l of ti ll' HPJ), some rccipro..cat ton " i ll he requi red to main tain thetoot h in the arch and pn'\"ent it fm m mov­ing away from tile partial, Th is can I M.~ donein two ways : (J) " l th a conventional guide

Removab le Partial De nture Design

Occlusal plane

plate/rest and bracin g an n combin atio n or(2) with the use of an ext ended gu ide plate(one th at extend's slightly from th e mesial tothe buccal und lingual surfaces} combnu-dwith an oversized occlu sal rr-st tha t extendsto the dlst ul fossa. This lo ng res t has th e ad­d it ion al advantage of allowiu~ the rcstom­tion of the plano of occluslou with the restif the distal abutment has Indeed migrat edmesially undltnguallv (Fig 2-:30).

If the molar is so sevcn-lv tilted th at theretentive area is , ·el')' deep and \"el')' nearthe O('(.'I II_~ll surface, with mino r o rthodon­ties not all option for whatever reason, itmay be best not 10 clasp th at too th . Inst ead ,conside rat ion should be ~\"('n to retain ingthe ~uid i llg: plane an d the extended oc­clusal res t and moving th e retentive claspan te rio r 10 111(: fulcr um (10 the premola r).The cla....P choice in this situation can h e d ­ther a clrcnmfcrcuttal clasp or a ll infmb­ulge clasp. The re ten tive a rm " i ll beanterio r to the fulc ru m. so a " i re circum­fen-ntiul clasp ann is Sdl'ck d over a castone because the potential for greate r move­mcnt of the pa rtial in fun ction in that areadictat es a more flexible clasp. As in ot he resthetic areas. a wire l-ba r clasp. se t to Ihedistal, Hlay he the best cho ice ,

J I

\,

Advanced Removable Part ial Dentures

I n the maxilla, a case call he made fix theIIS 8 of th ree retentive clasps if a modifica­tion space exists on the dentate side, sincethe force of grmi ty adds anoth er dimensionto the retentive requirement. Here, themolar clasp will most likely he a cast cir­

cu mfcrcntial and the clasp on the distal ex­tension side an I -bar; since this clasp is lesslikely to be visible whe n the patient smilesand speaks. The l-bar clasp has been PfP­scntcd as having to be placed midway onthe tooth mcsiodistally in orde r to funct ionwith minimum stress on the abutment.While this lllay he true in the mandible,there is not enough movement possible ona well-Htung maxillary casting to make anyclinical difference. For this reason, the l -bar

clasp call be set as far to the distal as possi­ble as long as the re is a mesial rest and a dis­tal guide plate. If a wire I-bar is used, it ispossthle to place the clasp almost in contactwith the buccal extension of tho gllide platebecause this clasp is added to the frame­work alter the frame has been finished andpolished. A cast tnfrabulge clasp must heplaced farthe r from the guide plate so thatspace is available to finish and polish theclasp, lnakillg the clasp potentially n lore vis­ible on the tooth . The third clasp , placed onthe ante rior ab utme nt OJ I the tooth-sup­ported side , should also be a wire l -bar

clasp fix the reasons given. If no modifies­tion space exists, there will he an increasedreliance on the creation of multiple 6,uidingplanes to restrict the movement of the par­tial denture.

Class III RPD

This classification of partial denture couldreally be called a "removable fixed bridge."III most situations, it uses the same abut-

32

rncnts as would a fixed partial dentu re re­placing the same missing teeth. The de­sigH options, at first glance, might appearto be endless, but in truth can be reducedto only a few b asic options as long as theclinician is willing to prepa re the mouthideally Four obvious treatment conside ra­tions govern the choice of t he removablepartial denture in the Class III situa tionover a fixed part ial denture . The first andmost mflnent tal reaso n is cost. Th e secondrelates to those situations where the len gthof span of t he edent ulo us area and theperiodontal support of the remaining pos­sible abutment teeth combine to bringinto question the long-term success of afixed partial denture . The thi rd reason isst rictly one of esthet tcs . Th ere are in­stances whe n the need to replace the in­terdental papillae ill the ante rior of themouth make the fixed partial denture 1Il1­

acceptabl e. While it is true that ridge aug­mentation in any of its many forms cancreak an ad equate ging ival base , therestoration of the pap illae is not alwayspossible. Last, there wil] ulwnvs be tllll.sesituations where the loss of teeth was ac­comp anied by traumatic loss of the alveo­lar pro cess as well. In these cases, the needto replace missing soft tissu e reqllires tileuse 0(' a flange of such dimensions that theapp liance be removable to allow the pa­ticnt access for proper hygiene. The goalof removable partial denture treatment forthe Class III pat ient must he to make theappliance conform to the principles offixed partial de ntures as much as possible .

Ab utme nt Selection

The choice of abutments is generally obvi­ous: one abutm ent un each end of an eden­tulous area. This general statement is mod-

Removable Partial Denture Design

Path of inse rtion/removal

RPD is partiallyseated

Fig 2-31 Anterior gUiding planes preclude rotatio n awayfrom tissue.

ifk-d hy adding abutmen ts when the poten­tial support of tIll' tee th is in question.Whenever this question arises, it is lx-tterto add another abutment because udell­tional frictional retent ion can be obtained.Unlike the case of 111(' fixed partial den ture,in which splinted abutments bri ng pote n­tial problem s of embrasure access and co n­nector rigidi ty, double-abutting ill the re­movable part ial situation causes 110

parti cular proble ms. Rem em be r, abut­mcuts must han ' posith 'e rest preparationsto maintain contact betwee n the partial andtee-t h ove r the life of tile part ial. These idealn-st shapes Call usually be crea ted with sub­tractive mou th p reparation in the pos teriorof tilt) month, but additive mout h prepara­tion is often requtn-d for the an te rior h'l'l h.

In additio n to !'it' lt'cling th e almtnu-ntsalltl planning thei r res ts. the potential forparalle l gniding phuu-s mus t be cvuhnue-dthrough careful consideration of the pa th ofiusc rtton/reurovul. The goa l of the mouthprep aration for the Class III east' is to max­imize the Frict ional retention of th e gllidh lgplanes/guide pla tes to totally eliminate tilt>11< '( '<1 for any anterior clasping. l 'osn-rior

clasping. one clasp 0 11 each side, is mort"than sufficient when the ante-rio r portion ofthe part ial is co ntrolled h)' the gUidingplanes. Th is partial dent ure cannot rotateout ofthe mou th. hut mus t t ravel down theguiding plant' unti! the posterior re tentionis uo longer effective (Fig 2-31). For thisn-ason . the guiding planes created Oil theabutmen t teeth must he as long as possiblein the all tooth-ho rne case.

Connectors

.\I ajor connector design for tile mandibularClass III HPD rem ains baslcallv the sameas for the ot her classes. Again, wheneverpossible in the mandihk-, th e lingual hal' isselected over the lingual plate to reducethe amoun t of soft: tissue ('()\'erage. As i ll

tile Class JI, co nside ration must he given tothe convers ion of the cast lug to a distal ex­tension base when the choice ofa posteriorterminal abutment is q uestlouablc.

Selp(1:ill~ a deSign for th(' maxillary con­nect or that will provide adequate strengt hwithout hulk and gin ' the pa tient maximumcomfort is more of a challenge. Tht> b road

JJ

•Advanced Removable Partial Dentures

palatal stmp des ign form s t11(~ basts of allmaxillary major connectors. Xlodlfkat ionswil l depend on the numbe r aud posltiou oftIle P{lt' llh l](H1S areas, Major connectors canIHe' kepi to a tlnckm '55 ( If (l.5 Ill III if they art'plan ned so that t!lt')' cover a portion of theslope of the m gae area as wel l a~ the vault o fthe poslt'rior palate; this form s a corruga­lion in the basic form. wh ich increases therig idity of the connecto r; Agaill, cantileversfrom more poste rior rests can he used to ru­place single anterior teeth and stillleave thespe-aking area of the palate opell .

Resin Retention

Since there is seldo m any 1\('('(1 10 rel ine aClass III HPD, resin ret e ntion will he metalridge coverage with rete ntive heads , loops,or posts and the occ asional metal pontic.These metal polit ics can be veneered o r, ill

the posterior wh ere they willnot be visible.le ft in me tal. The ful l metal po nt ic shouldnot exte nd buccally as it wonkl if it WPI"!'

being veneered. By keeping it lingual to tilebuccal line angle , its preSl' lICe can be d is­gUis{'d .

Clasp ing

Cla.sp ing is limited to the posterior abut ­ments of the Class III Hl'D whe never pos­stble , ln-cnuse the poten tial for pa rallelguidi ng planes adjacent to Ibe edentulousspaces is great and \\; 11 eli minat e the I}('{'dfo r anterior clasping in all h ilt those situa­tions where the clinica l Cro\\1 IS are so sho rtthat no adequate gllid ing planes ca n be cn-­ated . As the crowns gd shorter, the need tohave parallel planes increases- a real chal­lenge i l l sub tract ive mouth preparat ion .Guid ing planes thai a re adchnve haw theadvan tage of allr)\\ing machined milling to

34

create "perfect" parallelism. The cla-sP ofchoke for the posterior will be the cas t ci r­cumferential p lace d into a O.OIO-inch un­dcrcut for the terminal thi rd of tho act iveclasp a nn . 'I'l l(' need for ante rio r daspiTlgca n be st be dd ermined afte r the castinghas be r-n f itte..l. Should ret en tion ilppt>ar ill­adequate at that time, one or 11I011. ' distalwire l-ba rs can be added to the frun u-workinto a O.OIO-ineh und ercu t.

Class IV RPD

T he Class IV partial denture patient classifi­ca tion R·pTt'Sf'llts a ~lIP of patie nts forwhom the advent of ossl.'ointegrah 'l. l im­pluuts has greatly reduced the reliance onthe removable partial dent urc. Most of thes ep atien ts go tlmmgh a stage of treat ment inwhich a cast pa rtial denture is essential . eve nthough the final prosthesi s may be implantsuppo rted a nd ret ained . 111e cost of a cast­ing is Insignificant when comp ared with thepc sslblc problems oflong-ter mall-resin pro­vi sionnls . For these patients, :L<; well as thosefor vhom no impl ant-supported or fixedprosthodontics is possib le or affor dable. theCke...s IV RPD represents a challenge both illdesign an d construct ion. A special tnlt· ofpart ial de nture . I Ising a rotational path of in­scrt ton/removal, has great pote ntial in theClass IV maxillary situation and will he ad­d ressed late r (see Chapt er H).

Abutm ent Selection

For the most pa rt. the pa tu-nt with an extcn­sin~ anterio r edentulous spael' willne-od thesuppo rt of all the remain ing teeth. Thosewith smaller edentulous an'as will require atleast Ille teeth adjacent 10 the edentulousarea and the first molars. Again. the more

•Removable Par t ial Dentu re Design

_ Possible fulcrum line

)'~,,- Excessive cove rage

Fig 2-32 Extensio n in palate may ro tate away from tissue in function.

teeth being replaced on tlu- partial and theweaker the quality of the ubut tucnts, citlu-rpcriodon tally o r rcstorativelj; t ile more teeththat must be involved as abutments. For theother classific ations . the path of Inse rtiou / re­1ll00",U was planned to he in th e long axis o fthe abutment teeth so it<; 10 load them \'( '11 i­

eally as much as possi ble am i to reduce 10

the ve ry minimu m th e .uuount o f too thstr ucture lost to mou th prr-puratton for guid­iug planes. For the Class IV situatio n. CO I1­

siderationmust he 6>"i.vpn to the undercuts in

the !lange art-a because. ifa full flange is de­sired , these soft tissue undercuts will have tod raw wi th the posterior gniding planes. It isoften im possible to m ake this ulignmc-ntwi thout cr owning the abutment t£'l'lh.Another solution is to p lan 0 11 a sho rt nangeonly- one that extends just to the Iwight ofcon tour of the edentulous ridge when tlwpath of insert lon/rcmoval £\\ors the abut­ment teeth . Decisions O il this dilemma areoften based 0 11 the need for a full fl :lIlge tores tore lip support.

(cnnerters

Mandi bular major connectors for this classi­flcation offe r the same options as the other

mandibular desih>1ls. They are more apl 10be fulllingual plates. since the necessary ad­ditional Frict ional retent ion call be obtainedfrom the pre pa ration of paralle l guidingp lant's on the lingual su rfaces of the rem ain­ing teeth. The continuous lingual plate givesthe III ,LXiIllUJl) contact with these surfaces.

Muxtllary major co nnectors wi ll oftendiffer somewhat [rom those used for othe rclassifications. Since the edentulous area isapt to lw extensive, ie . greate r than thatwhich would normally be replaced with afixed partial denture, rotational movementsaround an axts that will run between themost uu-sial rigid contact of the Frameworkami the an te rior abutment on each side canbe expected. As r otation of the II:L.;e towardthe tissue takes place , allY po rtion of themajor connector that is posteri or 10 this ful­cr um will have a tendcncv to move awav. .From tl. t\ tissue (Fig 2~32). The further pos~ter ior the casting extends , the gn 'ate r thepote-ntial for breaking contact with the softtissue. The sp.}('t' that may he opencd nphen' can act as a f(xxl tmp dll riug mast ica­tion . To reduce th is rotational open ing. theposte rior extension of the major connectorshou ld he limited ami should never extendbeyond the posterior d asp iTl f!;.

35

Advanced Removable Partial Dentures

\\1 1i le it may ap pear that the " l'"!' ovalor anterior-posterior bar configura tion isapprop riate for the Class 1\' situation. thepalatal extension of the ant e rior spgmentcan still interfere with speech unl ess it iscarefullv hleuded wtth the contour of th euun-rior rugae area.

The rotational pat h Class 1\" option R "­

quires add itional decisions Oil major CO!l­

m-ctor (k~sign (see Chapte r 9 ).

Resin Reten tion

Most Class JV cases will n-quirc raisednu-sh ret ention because tho e-dentulousspans arc apt tu be extensh 'l ~ and thereforeTllay Jl("( "(1future relin es to keep thl' partialstable. Since the external flnishing line ofthe maxillary part ial willlie ill the speakingarea. some consideration should be ~v(,Jl tohlt>ntling the junction of the metal and there-sin in such a way as to eliminate a ridge illtilt" area where speech is fonm-d. This llIayrequire moving the finishing lint" posteri ­orly or hrinbring it almost to the dentureteet h. depending Oil the palatal contour.

Clasping

A conventional Class IV partial wil l have itsprimary retention Oil the molar teeth (usu­ally the First molars), oll e Oil each side .These clasps will often be cast clrcum fe ren­tlal. eit her coming from a ruodiflcuttonspaCt' o r as all embras ure clasp . III the max­illary arch, the an terior edent ulous areaoft('11 (('(Illires an addi tional clasp to offset

36

the pul l of g ravity and sticky foods . \\"llt'n100 Ig para lle l glliding planes are obtainableadjacent to the edentulous area, the castingIllay he n -tenfive wi th out the third clasp.Since the ani prior clasp is likely to l it.' vi si­blc ami possibly nnesthettc. the castmgshould !){" evaluated without the anteriorclasp. \\"11t'1l additiona l retention is re­quircd. the third clasp is added i.t 'i a win- 1­bar soldered to the casting.

Tile mamhbnlar Class IV wtllnot usuallyneed a th ird clasp if guiding planes arcwell-planned 'lilt! executed. If the guidillgplanes an ' inadequate, the same approachfo r th e third clasp should be used.

Th is chapte r has covered th e basis of I"e­movable partial denture design. Th e keysto SIICCt'SS are careful and exacting prepara­tion of a 1J('<llth)' mouth and co ntrol or thetooth-frame n-lntionship through atte-nt ion

to detai l in the labo rato ry, Th e clinicianwho follows the principles established herewill find desib'1l decisions reduced to a min­imum. The anatomv of the mouth ami thenumber ami locat ion of the missing tr-othwi ll grc>at ly Influence the dcci..slon. !e<l\l ngpe rsonal preference as only a llIod if)illgfactor. Prosthodonttsts do HOt. us a mil' ,wear (('Illovah le partial den tures and sohave 110 ('t,t·ling for the pa tient's rt'"spo ll.'\ t' 10

th e addition or .'\ 0 much material in themouth. Clinicians can, however, lllak" acasting or two to fit their mouths and atleast cvaluuto the placement and conf lgura­tion of tilt' major co n nector. Many o f theIdeas expressed he re have come fr om justthai cxpcrk-ncc.

Mouth Preparation

M o uth preparation, us described ear­lier, co vers e,"prythillg we do to pn>­

pare the mou th for the actua l coustr nct tonof th e removnlile partial den ture. Hex­torat lvc procedures asso('iatetl wt th the re­maining teeth a rt" obviou sly a n -sponstbthtyof the prim ary clin ician. hilt 1II0st ot heran-as of mouth preparation fall under th emanagement of specialists or g(')lt'ral prae­ttttoncrs with expertise i ll the areas of peri­odontal therapy. cndcxlontlcs , crt hod ontics.and oral and maxillofacial surgery.

For the most part. mouth prepa r.ltion islooked IIpOIl ;lS p reparing a few n -st seats,pe rhaps a SlIJYI'y{-'(1 CroWII or two, and tlu-ngelling Oil with the final impression for th eC:,lStillg. Since mou th preparat ion is thefoundution for all we plan to do later on. itis essential that a planning phase he dcvel­oped . All possible ch anges required to bringthe mouth to all OptilllUIll stale of healthmust be ldenttfh-d, with the remaining den ­tition properly aligned und positioned, sothat the result ing partial denture ca n be asideal us is hu manly poss ible. Mouth prepa­ration for the vta lr-of-thr-urt HPJ) n 'qnires

d iagunslic procedures that include, but art'not limited to, the following:

• Survey of the diagnostic east with selec ­t ion of tilt' path of luscrtion/n-moval.

• Ik shaping of stone teeth to ide-al con­tours for subt ractfve mouth pn'paratioH.

• Diagnostic waxing of any areas re-qui ringaddit ive mouth pn-pnration .

• Diagnostic set- up of teeth to he replaced.

• O rthodon tic set~ llp for teeth req uiringminor tooth movement .

• IUdge mapping fo r gill~\'l l surge ry amiimplant s.

• C rea tion of a prep aration guide (va cuu m­for med ) for surve yed crowns .

• Cen tric re lation records, and Illoullii ngof d iagnostic and o pposing C;l..ts (wh e reindicated).

• Impressions, jaw re lation records, amiesthetic S(·t-up of oppos ing arch (if to­ta lly o r partially edent ulo us).

Only when these extens ive d iagn os tieprocedures haw' been comph-n -d . the de­finitive treatment plan developed. a treat-

37

Advanced Removable Partial Dentures

mcnt plan letter for Informed consent writ ­ten and sigm-.I by the patient . and all co n­suits Finished, should the act ual Im -wrstblemouth preparation lx-gin.

Surveying the DiagnosticCast

\ \ 'hell the diugucstic cas t has beenmounted in the surwy table, the easiestway to begin the survey p rocess is to standover the cast und. using the parallax of theeyes , att empt to look down the long ; l\eS ofthe abutment teeth. The p rime abut­mentis), should they exist (as i ll C I:L'iS I andII situations), will deter mine the path of in­scrtion/removal for the partial since theguiding plane established OJI the distal sur­fact' of the p rime abutment will be the keyto the remai ll i ll~mouthpreparatio ll . Th is

posit ion is found hy tilting the c ast in thesagittal plane. Once the anterior-posterior)Xlsition has lx-cn dete rm ined . possible re­tcntt ve are-as can he equalized by tilting thecast in the frontal plane . Before tripodiugthe cast, all proximal surfaces that wtll haveguiding planes ami all poten tial n-tcntiveundercuts are vertfled using the analyzingrod in the Slll"\'l'}llr. Minor adjustments tothe tilt are then made and tripod marksplaced on the cast . Tile t ripod marks shouldbe in such a position that they can all heSCCII at one time. Vertical markings 0 11 thesides of the land an-as. while they do allowaccurate repositioning, ar e much more dif­Ilcult to use because they cannot all he seenat one gb ncc. \ \11('11 the marks arc \d elelyspread out , one Oil the ltngual of the ante­rior area and the other two on the linguallateral surface s of the retromolar pads or

38

tulx-rositir-s, the east can he easily repo sl­t tom-d bv clinician and technician alike.

At this point the lead is placed ill the sur­\'p)n r and the ent ire Iwight ofcontour ofal lteet h that will possihly hp contacted by thepartia l is marked . Edentulous areas requirethe idcnt tflcatlon of tlu-tr heights of COll4tom as well. \ VHholit Information on bothhard and soft tissue undercuts, there is ill­

suffi cient data on which to base the designand the mout h preparat ion that wtll heneeded.

A reasoned design m-r-ds to be carefullydr.I\\11 on the diagnostic east before diag­nostic mou th preparat ion can ~n. Itmakes sense to use a color code that is fa­miliar to )1Jur laborutory \ Iaking: a neat andprecise drawi ng on a stone cast is 1I0 t aseasy as it would appea r, and most d iagllo.s­tic ousts see n in the cleutal laboratory \\i11have d rawings that arc ch ildish at ht'sLNone of tis has a natural talent fur drawingin three planes. All our previous effort s i lldra\\i llg have bee n dOIl {, 0 11 the two dimr-n ­sions of a piece of pap('r. To simulate thetwo-dimensional drawtng with which weare familiar, the cast is br aced against theclinician s stomach uml rotated with Olll'

hand whtle the other hand draws . III thisway th {~ pe ncil stays in the (1Jlllfortal>l(-' two­plane position while tho third plane is mall ­age d \ ; 01 the rotation of the CiLS!. Just a littlepract ice will allow PH ' n the "non-art i-st" tomake a credible d rawlll /-?;. There is an atl(k dvalue to had ng a neat ly co nstructed designdr;.t\\i ll~: technicians are much mere likelyto gin ' their best effort wln-n the materialssubmitted to them an- of the highest qual­ity. The well-drawn design 011 the diagnos­tic cast rvmforces the level or quality de­sired in the final prosthesis.

Perhaps the most important step in th ecoustructtou of a re movable parti al denture

is the preparat ion of th e diagnostic cast .The process is broken down in to subtree­tive mou th preparation , that is, the red uc­

tion of existing to oth contours to SOHle p re ­determined klcal sta te , am i additive mouthpreparat ion, the diagnostic waxing of co n­tours that m ust he altered with fixed appli­ances , be th ey crowns , bonded m etal gu id­ing planes or bonded composite res t sc ats.

Subt ract ive mouth p reparation is donefirst, usi ng the same Inst rumentat io n thatwill be used in the actual tooth recontour­

ing. The armamentarium wil l include:

• Both tapered and nontapered diamon dcylinders of rnediumlfine grit fo r the

preparation of th e guiding planes

• Hound diamonds for occlusal rest prepa­ra tion in ei ther 3D, lOD , or 12D

• Inverted cone for cingulum preparationin 37 or 39 size

Using the actual clinical diamonds onthe stone teeth docs not harm the dia­mo nds and o ffers the opportunity to prac­t ice th e p reparatio ns. The stone tee th areto be p repared to ideal conto ur eve n

th ou gh it Illay Hot be possibl e to d o so inthe m outh. Once the practice subtractivemonth p reparatio n IS co m plete d , adecision on the clinical possibility of cre at ­ing th e same preparation on the naturaltoo th is made on a tooth -to -too th basis.Obviously, there "in be lllallY instanceswhen com prom ise s will have to he madebetwe en th e ideal and th e possible . For

soruo of these situations, th e actual de signmay he changed , or thodontic min or tooth

Mouth Prepara tion

movemen t requi red, or additive m outh

p re paration und e rt aken to achieve theideal sit uation.

The sequcncc of su b tractive mouthpreparation must always he guiding p lanesfirst , followed by re st seat preparation .Once the stone teet h have been prepared,th e de sign is redrawn to its origina l state.

Dimensions and depth s of res t scat prepa­ration should be ideal, once again, withpossible co mpro mises or changes in d psignco rning afte r intraoral reevalu at ion .

Addit ive preparatio n follows with the dt­ag nostic w' L\:iug of crowns and bonded con­tou rs. The surveyo r blade is usedto create"mi lled" gu iding p lane surfaces on t he wax­ups, again, to ideal cont ours. When fu ll

crowns are de sired for the ab ut men t teethin Class III and IV partials, the proximalgu iding p lan es wtll he extended as far aspossible so tha t maximum frictional rcten­tton can be o btained (Fig 3-1). The COJl­

tou rs of bonded resto rations are waxed di­rectly on th e diagnostic cast . The de sign ofth e base of bonded castings will be identi­

cal to those ofthe bonded fixed partial de n­ture (Maryland bridge or Rochette style ).The contours ofbonded composite res tora­tions, usual ly cingulum res t seats fo rmandibular can ines and gll iding planes, arealso waxed to id eal contou rs. Retentive

areas fo r clasps are to he brought as close aspossible to the ginf-,riva, leaving a minimumof 1 mm of space between the proposedclasp arm an d the soft tissue , a task easilyaccompl ished in the wming o f a crown h utnot always possible in natural tooth st ruc­ture or bonded met al or co mposite . Sinceth e c row n gives liSthe potent ial for c reati ng

th e jdeal abutment contou r, thought mustbe given to the timing of the undercut.

The relationship 01" the heigh t of co nto urto th e de sired unde rcut depth determines

39

Advance d Removable Partial Dentures

Buccal

Fig 3· 1 Guiding planes fully exten ded.

the qual ity of retention that \\; 11 occu rwhen the retentive clasp dislodges from thetooth . If there is some distance (a gradualtransition) borwccn the heigh t of contourand the desired undercut (0.01 to 0.0] .')Inch), then the re.~ ult ing retention will beapt to be weaker but last for a longer timeas the clasp moves toward the height ofcontour. If the unde rcut is steep (tha t is,wt th litt le distance between the O.O I-inchpoint and the height of contour), then theinitial retention is apt to be greater, h ilt itwill uot last as long (Fig ,1-2). The gradualundercut is best suited for a distal extensionsttuatfon (Class I) in the mandibular arch.This will allow a certain amount of stressre lief in the clasp-tooth relationsh ip. Th esteeper undercut area is more apt to beused in a tooth-home situation in the: max­ilIa where the patient \vi ll appreciate maxi­mum retent ion against the force of gravity.Th(~sc decisions on contour are made atthis time so tha t a diagnostic record of theideal contour of the abutment teet h will heavailable throughout the treatment phaseand not have to he rede signed at each sub­seq uent step in treatment.

40

Lingual

The final step in the diagnostic prcpa ra­tion of the mouth is to position the replace­ment den ture teeth. The dent ure teet h willhave to he orde red from the dental uranu­Far-ture r at some time during treat ment, sothe earlier, the better. The criteria for shadeselection \\111 he the same lIO matter whenthe selection is made. The mold can bes t hpdeterm ined from an analysisof the diagnos­tic cast as soon as it is recovered. The de­finitive denture teeth can therefore hereadily available to the clinician at the timeof diagnostic: mouth prpparatioll. All alter­native is to lise teeth from a mold guide fordiagnostic p roced ures and !J1ing in the ac­tual denture teeth later on; however, ifsome tooth mocltllouf on is necessary, thecontinued rccon tourtng of the mold guideteeth may 11e unaccep table .

A quick W,L'\ procedure fix isolated miss­ing teet h can he accomplished by selectinga tooth from the mold guide awl impress­ing it in alginate. \Vhen the alginate is set.the denture tooth is rem oved and moltenW, L'\ poured in the mold. The wax tooth ismodified to fit the ede ntulous area on thecast and waxed to place.

0 .0 10 inch

Mouth Pre pa ratio n

•

He ight ofcontour - - -

Gradual Abrupt

• •· ,· ,· ,· ,· ,· ,t

Fig ]-2 Quality and quantity of ret ention.

\ Vith the denture teeth in position, th edia~lIosti<: procedure is complete ami thepa tien t ca n he- shown the rccontounxl cas t,L<; a means of describing the trea tment plan(anothe r n -ason fo r a quality drawing and aclean and neat cast).

Clinical Mouth Preparation

Subtractive Mouth Preparation

Th( ~ uctuul subt ractive month preparation ishCgllll llsing th e diagnostic ideal mout hp reparation from the cast as a template .Pn'paring parallel gllhling pLI1 H'.~ ill the1110 111 11 cunonly he accompllslu-d witIi prac-­Iice, C huk-iaus trained in Ihe e ra of mu ltiplep illlt ,< lge restorations will recall the pa rallel­iug devices that were attached to tl'l'th nottnculvcd ill the restoration so that the ( '011­

tm-angle ha ndpiece could be ke-pt in thesame plane throughout till' prepar ations.Th at t~Pl ' of device is not usable for thepreparation of gu iding planes. since teeth

Fig ].] The long axis of a prime abutment is usedto establish the first gUiding plane.

on bo th skk-s of the arch are involved . TlU'be st guide available to the clinician is there fe rence of lilt' long axis of the prime ulnu­meut und the angle of the pn-dctcnnincdguidiug plane to that long axis (Fig 3--.'3), Ifno prime uhu tmcnt exists, the tooth that of­fen; the clinician the greatest \isiIJility andacccssibilitv is dUN'1l to act as the indicatorfor the first guid ing plane . After the firstpa<;s with thl' d iamond cylinde r, the result­ing guiding plane is visual ly evaluatedagainst the prepared surface of the stonec ast and , if the p lanes appea r to he kk-nt lcal.further reflncmcnt of tile proximal surfaceis carried out . From that potnt Oil , the clini­cian refers 1lack to the origina l gll iding planoto set the angle of the diamond cylinder Iw­fore moving nu to the other abu tments .After allthe g llid illg planes have been pre­

pared , an alginate impression is made andpoured in foist-set plaster to serve ~L'i a chockcas t. T his cast. when recovered. is placed onthe surH~'t J r, and the guiding planes areevaluated for parallelism. Any discrepanciesare adju sted 011 the cast and then correct edin the mouth .

41

Advanced Removable Partial Dentures

Fig ) · 4 Buccal and lingual extensio n of gU idingplane.

Hr-membcr; gnid ing planes for Class II ,III , and IV shou ld he as long as possible vcr­ttcally without compruuustng tile enamel .I II some sttua tious ill the older mouth, tltcgui di ng planes e m be taken in to dentin , Bypreparillg the tedh without uncsthcskr. thep atient can indicate when the tooth be­comes scnsiuve and till' exte nt or the gu id­ing plane can be reevaluated. The huccolln­g ual (1i11U'II.;iun of the ~ l it ling plane in thesethree situations shou ld extend just aroundthe line angle in most cases . This slight ('x­

tension, tlu: tn m ing o( the "c-orne-r;" "i llgreatly enlumcc rr-ctp ro cattou mid providethe brucing co mponent that used to be de­pendent on the b racing clasp ann (F ig 3--4).TIlt' only ( 'xl'(~plioll to the lnrccal cxteusicnof th is plane wonlr] he Oil tlH~' mesial proxi­mal surface o f a tooth ill (he anterior por­tion of the mouth, where the ~ lide plate ofthe partial could he seen and he ul1('sthet ic(most likely in the Class IV).

For the Class I Rl'D, the clin ician willhaw to choose b etween the shorte r ~u id in~

plane \\ith the stn-ss relil·fkh uilt in" ami thelon~(' r guiding: plane that will n-qut n - func­t ional adaptation of the guide plate Oil thecasting for the same amo unt of stress relief

42

-------- -----=.~ . • , - , ~

Both of these t1t 'sigm have hccn provell to1)(' effective in allm\ing some level of stressrdi('[ Tile shorter gu iding plane, wi th itsbnride plate toucbing tile tooth only at thegiugival extension of t ll( ' plant '. requires amore prr -clsc leve l of laboratory support :this is unfortu nate beca use it would appearto ulTer control with the least amount of ad­jU.;lillg at the ehair. \ \ 11('11 the laboratory'support is loss thau ideal, the longergllidingplane and plate will bo more apt to providecontact of these surfaces. The Class IV situ­atiou has uften lx-cn described as a Class Iill n-versc and , if stress rdif'f is tndt catcd(wln-u the remaining ubunncnt {f'eth areless than ideal suppo rts). the rk-ciston ux tothe prime guiding planes on the mesial ofth e most anterior tr-r-th \\ ill han ' 10 bemade OTi the s.um: basis as for the Class I.However; when a rota tiona l pa th RI'O isplanned . the proximal undereut mu st bemaiutuincd, thu s e liminating the gnidingplane adjace nt to the edentulous area.

O Il C(' tht' g.liding plant's have h ('C1\ P!'>pared ami verified. ti l l' occlusal rest scatsan' prepan-d. The tendency has alwaysbet'll 10 make th e rest scats too small ami toleave them with sha rp angl t~s or with 11T 1 ~

dcrcuts to the path of inscrnorvrcmoval(especially in the east' of th e isolatedmandibular molar, where the rest may drawbv itse lf: usunllv to til(' mestolinznal. hilt

.. .. h

willnot draw with the oth er guiding planes ,reslliting ill a cas ting tha t will not fllllyseat). The res t spa ts are to be one thi rd thebuccoltngual dnm-usion of the too th . Therest st-at must he deep ouough to allow for1.2 HU ll of mot ul ill the rest. A round dia ­mend with the same diamete r as the de­sired rest seat should he selected. TIl(' oc­clusal rest has historically been presentedas l1('ed ing to he " Sp OO l] shaped." mcnuingthat the sea t is deeper in the center of the

Mouth Preparation

Fig J·S Ideal rest seat dimensionsfor the isolated mandibular molar.

-

Sharp exitFig 3-6 Prope r rest seat contourat the marginal r idge.

Rounded exit

tooth than it is at the marginal ridge.Unfortunat ely, this results in a marginalridge without adequate space for metal andin a casting that will eventu ally break rightat the marginal rest-a difficult repair situ­ation. The rest scat on any isolated tooth.and especially on a single mandibularmolar, should exte nd at least to the centerof the occlusal surface so that the rest candirect the occlusal forces down the longaxis of the abutm ent (F ig :3-,'5).

After the bulk of the occlusal rest seathas boon prepared, attention must be paidto the junct ion of the glliding plane and therest scat. The sharp line that results fromthe intersection of the two surface red uc-

tions must be rounded (Fig .3-6) . To leavethis sharp angle is to risk a casting that wi llnot fully seat , since the thin, sharp edge isunlikely to stand up in the refractory. Ifeven a slight defect in this area is createdduring the fo rmation of the refractory castor in the waxing of the framework, a posi­tive bleb will result. Clinical studies of thefit of parti al denture castings indicate tha tthe marginal ridge area is where the great­est amount of contact can be expected.

\Vhen placing occlusal rest seats inamalgam restorations, there is always thepossibility of weakening the alloy in thedepth of the rest or along the verticalwalls. Should the amalgam appear to be

43

Adv anced Removable Par tia l Dentures

Fig 3-7 Rest pre pa rat io n e x­tended beyond alloy margin.

Dist a l Fac ial Fig 3·8 Incisal rest is used pri­marily on distal aspect of mandibu­lar canines.

compromised, it mus t be redo ne withgreat er extensions . An alternative wouldbe to consider a casting. If the re is Ill) op­pming occlusion or if the occlu sion is witha dentu re tooth, the rest preparation canhe extended beyond the margins of tile oldalloy and the de pth of the preparation canbe reduced (Fig 3-7) . Th e demands of thethickness ofthe rest remain, but this spacecan he developed, at least in pari, at theexpense of the opposing denture tooth .Occl usal res t prepara tions in existingcrO\\11S arc anothe r area of concern, sincethere is no way of evaluating the thicknessof the occlusal metal or metal-porcelain.The patient must be informed that if a per-

44

forut ton occurs l!llring mou th prepara tion,the crown must he remade. Sometimes adesign change can elim inate the need toprepare a cer tain tooth . Often, thou gh. thetreatment plan will have to include thenew crown as a distinct possibility.

Incisal rest seats arc prepared in thesame manne r as for the occlusal rest. Thediamond of choice is the tapered cylinderrather than the round bur since the idea lincisal rest is one that is rounded bothmcsiodtstully and buccolingually, withoutunde rcuts, of course, to the path of inser­tion/removal. Here again, the "jllnd ion ofthe seat with the guiding plane must herou nded (Fig 3-8) .

Fig ] ·9 Pro per angulation of inverted co ne dia­mond stone for cingulum rest on maxillary canine.

Ci ngulu lll rests, limited to muxillary ca­nines for the most part, a rc p repared wi th adiamond Inverted CO liC (Fi~ :3·m. The sizeof tilt' COile is determ ined hy the hulk or( ' II<.lIlW! in the ctnguhnu. Th e gn-ater thea mount or e namel. tilt" larger lIlt' rest seatca n be. It is also possible to au gme-nt therest seal wi th bonded ('omposit(' lo en-ate an-st witha floor or 1.5 mill . Th e n ',L'>0I1 a di­amend is chosen OH'r a ca rbide invertedcone is that the diamond leaves a mo rerounded Internal angle . Irthis un-a is sha rp ,the sa me problems can arise :L'> with themarginal ridge. The shape or the rest scatas S{'{'I I fro m the lingual is one o r all ill­verted "V," which follows the natural shapeof the cillgu lulll and requires the minimumreduction o f tooth structure.

Ci llgn lllill rest seals on maxillary uutc ri­ors an' often required and, i f su IHd e lltcnanu-l exists be low the con tact of themundibnlar inciso rs, they a re p re pare d'li th the same inverted {"(JIlC a the ca nine,tllc o nly difference being tilt' hupe or therest. It is mo re apt to he strai~"t or se mi­lunar, as it follows th e natural contour of

Mo uth Preparation

Natural HOC

Desired HOC

Terminal one thirdat 0 .010 inch

Fig ]-10 Required red uctio n fo r the proximaltwo thirds of a ret entive clasp arm. HOC = Heightof contour.

the Iillgllal gingival surface. These rest scutsoften require uugmentution.

Addit tonul reduction is often requi redon the buccal and ling ual surface s o f pos­tenor kdh to drop the height uf contourcloser 10 the g ingiva (especially on lin­guall), Inclim-d mandibu lar poste rio rs ).The approach arms of minor co nnectors" iIl IU'( '{ ! a minor gu iding plane gill/-,ri\'a) tothe margin al ridgt' for ad d itional frict ionalre te n t ion . When ci rcumferen tia l cl asparms ar e planned. the p roximal two thi rd smust lie at o r slight ly ahove t ile hei gll t orco ntour. Sinco the tooth at tile line anglonormally has the con tou r rising to th e mar­ginal rid gc , reduction in this a rea is re ­quire d to bring the proxi mal portion to ­ward the gingiva a nd out of possibleoc clusal iutcrfcrcucc (F ig 3- im. Tl ll'SPcontours a rc l»-:st l'pti lleetl with a uou tu­pored cylinder, As gllid ing planes enter t ilt'lingual embrasures on their way 10 thesupplemen tary rests. it may he 1U'('('ssary10 change to a finely tapered. d iamo ndcylinder just to get into the constrictedspacf'. The guiding planes can still he kr-pt

45

Advanced Removable Partial Denture s

Embrasure rest,~3 )( 1 .5mm

Fig 3-11 Ungual mouth prepa ratio n fo r embra­sure clasp.

pumllc! to the proposed path of inscruou

by s li~ht ly tihin~ the handpiece 'iO that t ill>ta pcrr-d cyiindcr cuts at 90 degrees (paral­lel to othe r gniding planes).

Em brasure clasps rcq llire p reparat ion himlditiou to the n-s t SI'.d . Depending uponthe con tact urea of the marginal rid~(' s amithe opposing occlusion. all access IIIl1s1 b('established for the clasp ann to hoth enterand exit the rest area. The exi t to th e buc­cal sur face is usuallv the 1Il0...t criti cal. III ei ­

the r Clt...c, a minimum of 1.5 nun of space ,both vr-rticallv uud hort zo utallv; must he. .create d . A tapered diamond cylinde r isused to (Teate tilt' spa('C, cHtting at 1..3 nun0 11 the cylinder for automat tc con tro l of thedtmenston. Th e lingual approach to tht 'margina l ridgC' offers the posstbilttv of aminor ~ll id i llg plane that should always 1)('used , since the e mbrasure che...p assemblyoffe rs Jill I.tlu-r l)(ls.... ibilitvof a gni(!ing plant'( F i~ :3-11). The rest sca t area is to he shan 't Ibetween the two adjacent teeth 10 conservetooth structure uud still have adequat espace for tlu- rest. Under 110 circumstanceshould the contact act ually he broken. If it

is broken by mistake , a re sto ration wtll havc

46

to he placed o n one of the ('o lltacting te-ethto restore contact . \\ 'hell a rostnctr-d Sp'l('t->is ld t for the embrasure clasp, fracture ofthe retent ive clasp arm can be expected .Th e ph sttc pattern uSl't1 tu wax the clasphas a c ross-sed ional urcasureuu-nt of ap­proximatr-ly L") 111In; should any reduction

be Ilcce ssary on the occlusal portio n of theclasp, all area of stress concent ration willoccur ami fractu re call be expected afte rrepeated flexure . Repair of a broken chesPann in the embrasure a rea is d ifficu lt amicannot bo depe-nde-d OJ1.

ClI iding planes are usually 1101 preparedon anterior teeth lx-causc n ·shapillg of theproximal surfaces alters the shape of thetoo th 10 the point where esthetics is ('OIIl ·

promised. Occasionally, a minor j:!;uidingplane call he created O il lingual surface swhe-re gingival recession or crown length.l:ning leaves the full unatonuc <.TO"1 1 ex­posed .

When inadequate spacf:" is available furan anterior replacemen t. the adjacen t teethmay he n-contoun-d to eq ualize the ponticspace with th e adjacclll teeth . When thespace is so constricted that a ll esthetic re­still is uot attaluable. orthodontics or a lhl't lpart ial dell (uw replacement lllay Iw theonly Ilpt i(lI lS.

At till' coru plct tou of tilt" su btracti vemou th pn-parat fon . th e surfaces thai havebceu recontourcd Ill ll....t he f inished andpolished. Sint.'( ~ these prepa red surfacesshould be the onlv area.... where contact he­t W('CIl the- tooth andthe Frame takes place ,there arc Signi ficant ad vantages 10 polish­ing with e-it he r a f ine diamond or fine whitestone followed by rubber po iHts sud disks.The chances of alginate sttcktng und tearsare reduced. Since the rcfractorv materialreq uired for stellate alloys is large grained ,tho exact duplkuttou of irrcgular surfaces is

not possible. The resultant cast ing will heapt to have an inte rnal surface that is nat u­rally rough, so every effort should be madeto redu ce this surf ace roughness.

Additive Mouth Preparation

Befo re any preparation is undertaken foradditive contours , the subtractive compo­nent of the mou th preparation must hecomplete to include final polish. It is ohvt­ously easier to crea te a casting in harmonywith th e contours already estab lished onthe teeth than to make the casti ng first andtry to create guiding planes on the teeth tomatch thos e on the casli ng.

Additive mouth preparation can he bro­ken down into three diffe rent approach esto obtainin g ideal contour: bonded metalcontours, composite contours. and moretrad itional surveyed crowns and pon tics.The actual con tours establishedustng thesemodalities arc the same , only th e means ofcon necting them to the abu tment teet h rlif­fe r. Both bonded metal con tours andcrow ns req llirc mouth preparation ofenamel surfaces as a part of their construe­tion. All bond ed restorations require thep resence of soun d tooth structure, prefe r­ably enamel, to which to bond .

Bonded Metal Contours

Bes t sca t areas , guiding planes, and attach­me nts all lend the mselves to honding toenamel. They offe r a high level of pre­dictability hut arc technique sens itive . Themo re attention to detail du ring the p repa­ratio n of the enamel, the greater the long­term success.

Th e cingulum rest seat, to be placed onth e lingua l slope of a mandibular canine ,

Mo ut h Preparatio n

is the most conunonly used bowled co n­tour. Th e mo uth preparation for th isres torat ion is limited to a horizontal notchcut in the enamel in th e gingival th ird ofth e lingual slope. This minia ture cingulumrest serves as a ve rt ical stop when seatin gth e cast ing at cem ent ation and as a posi ­tioning de vice to re late the res torat ion inits proper positio n. Since the ena mel onth e lingu al of the ma ndibular canine isthi n, th is groove will not he more than 0..3mtn in depth to he ce rt ain to stay inenamel . Although not really ne ces sary,on e can redu ce 0.2 nun o f enamel overalland leave a finish ing line so that th e resul­tant cas ting , which will be app roximately0.4 mm thick, will have a smoother inte r­face with th e surrounding tooth structure .

\ Vhen guiding planes are incorporatedon the casting, microgroove preparat ions,as recommended bv Scharer andMarinello, arc placed in the enamel usingthe smallest-dia meter sligh tly tapered car­bide hur (Fig :3-12) . These grooves offerlateral resistance to dislodgment and havebeen shown to greatly increase rho success­ful bon d between casti ng and tooth .(Precision attachmen t castin gs are d is­cussed in Chapter 10.)

Fi nal imp ress iOl ls fill' bonded casti ngsarc made in e ithe r silico ne or polycthcr,since they arc poured in the re fractorymateri al that is compatible with t he alloyto be used. These ref ractory ma terials donot , as a ru le , set against alginate . TIle im ­pression need not be full arch bu t mustco ntai n th e ot he r prepared abutments sothat any guiding plane area on the castingcall be made paralle l with the existingguiding planes. If the base of th e casti ngextends to th e gingiva, a retraction cordshould be placed to assure accuracy inthat area.

47

Advanced Removable Partial Dentures

Paralleledsurface

Fig J ·12 Microgro ove preparation for bo ndedcastings.

Til t, bo rders of the l'<L~ting art' o ut lined ,

and a small piece of sheet W ,LX, availabl efrom Kerr Laboratorv Products Division atI}..') IllIII thi ckness, is adapted to the o utline

and waxed 10 place hy ;ultlill?: a sma llamount of vpry hot wax all ar ound the bor­dcr; Th(~ contours of till' n-storutton areadded to thiswax base. FOf a cingulum res t,the hiN ' mu st have a wid th of 1.2 II lIn wi tha rouuck -d internal angle . T ill' res t mustfo nn all acut e angle to the pa th of inse r­tiou/rcmoval so that it will he "positive"n-st . Decisions on the contou r nnd extent ofan y gllid ing planes must he made relative10 1he classification of tho "dpu t1l1011S situa­tion am i the established con to urs o f theo ther abutment teeth .

The \ \',LX-U P is sprucd with a round \"LX

spme uttachcd to the lingual surl;u.x: o f thecingulum. As a final uddt tiou, a ph ..tic bris­tie from a toothbrush is attached ncar theinci sa l o r occlusal margin to ad ax a holdi ngdevice for the ea.~ting rimi ng fillhhing and

48

.II' Plastic bristle

Refractory

Sprue lead

Fig 3·1 J Sprued wax pattern on sec tioned re­fractory cast.

cementutton (Fig 3-13). Since the patte rn iswaxed agains t a refructorv cas t . 110 al h 'lIlptis made to rt ' IIlO\'P the pattern. The refrac­torv cast is cu t wit h a die saw so that oulv a. .miniunun of stone is present. The spnlL' istln-u attuchcd to the base of a casti llg riugand th e s('('OI1(1 stage of th e investnu-nt is

poured . 111(' mate rial of chok e fix thebonded t'<L\ti ug is so me for mof Ni-C r alloy(He xilhum or similar alloy).

The completed casting is fini shed amipolished and. if it has a gnid ing plane , rc­

turned 10 a master cast for fina l rnillingusi ng a milling machine. It is then preparedfor eit her uucrorctcnt ton through an <'lclr­

ing p rol'CSS (as for a Murvland bridge) or formacrorctcnnou Iising co untersunk pr-rfora­lions (Roc het te). Either elccrroche micul oracid preparation of th e inte rn al surface is

acceptable to etch the metal. Cart' must hetaken not to contaminate the etched sur­fact" unce tln- ddling.: is complete. T heholding device, cast fro m the plastic bnsth -,

is used to holdthe casting d'l ring ceme nta­tion with a chemically cured composite.Light-cured composites can be used withthe perforated design. On ce the res in iscured under rubber dam, tile holdin g de ­vice is cut fro m the casting and that area isstoned and ru bber-wheeled to finish therestoration .

Bonded Resin Contours

Rest seats and guiding contours can also heestablished in composite alone . \V'hile it

IlIay appear that a restoration formed incomposite would be likely to fracture whenstressed repeatedly, experience of over 15years has shown this not to he th e case.\Vlwn the abutmen t tooth has been prop­e rly managed, under rubber dam, and thecomposite placed according to the manu ­facturcrs directions , t his becom es a viableand less expensive alternat ive to thebonded cast contou r.

The rest aw l/or guiding plane can beprepared in a hulk of bonded composi te , ,LS

if it were enamel, or a template can beform ed from tile diagnostic wax-up toshape the composite as it is being bondedto the tooth . To cre ate a working template ,th e diagnos tic wax-up is duplicated in den­tal stone using alginate or reve rsible hydro­colloid . On the resulting cast, a vacuum­formed dear-plastic template is adap tedand trimme-d to contact the abut menttooth, as wel l as adjacent teet h on at leastone side, to allow precise positioning du r­ing composite placemen t. A stone core ispoured against the ou ter surface of tiletemplate to he used to force the temp lateto place once it has been filled withcomposite .

Afte r placement of the rubber da m, thetooth is etche d and prepared according to

Mouth Preparation

.",,--- Die stone

....'---a..J\-_ Vaccu m-formedtemplate

-.-.;f---- Composite rest

Fig 3-14 Template fo r co mposite cingulum rest.

the direct ions for the specific light-curedcomposite being used . The template isfilled with composite to app roximate theamount required to cre ate th e restorationand forced to place lIsing the stone core(Fi~ 3-14). Once the template is fullyseated, th e core is removed and the coin­pos itc cu red llsing an intraoral light sourcethrough the template . Th e template is sim­ply peeled away when the curing cycle iscom plete. Th en tile excess composite is re­moved, and the borders are finished andpolished. Use of the templat e resul ts in asuperior finish because the bulk of therestoration \\ i ll not need to he touchedafter curtng. For a single simpl e cingulumrest scat, however, shaping a bulk of previ­ously bonded composite is the most p racti ­cal way to create the desired form.

When the compos ite used for theseres torat ion s is a nncroftll . the poten tial forwearIs reduced. Unfort unately, all com ­pos ites are somewhat brittle ; therefore ,when the abutment toot h is mobile, thebonded metal rest oration is chosen be-

49

Advanced Removable Partial De ntures

Surveyed (rowns

Fig ] -15 Subt ractive mouth preparation beforecrown preparation.

1'11(' third awl final form of addit ive mouthpn-paruttou is with the surveyed crown.This descriptive term has 101lg been appliedto any crown or pontic specially <."OlItoUI'('(1

ami placed in conjunction with an abut ­nu-nt for a removable partia l denture. UIl-

fortunately, tilt" C m \ \11, ,L<; ob tained fromthe dental labo ratory, is likely not to haveIlll' desired form as far us the part ial d('I1­ture is conce nu-d. eveu though il mOl)' beideal iLS a sin~I I'- tooth restoration. Theteclmiciunfs) who construc ts the Cro\ \ 1 1

most likely will not haw had partial den­ture experience ami so will f"I\ 'Or the eo n­tou rs of the natural ( '1"0\\11. The mod iflca­tions required hy the ideal abutment maynot he a part of that teclmicinn s training;and, since the partia l denture (',lsting maywell he cons tructed in a different labo ra­tory, it will he the clinician s duty to controlthe contour of the <.'mWII ,

Befonol)f'gillliing tilt' mouth preparationphase or crown construct ion, the cltn fclanmust have gone th rough the diagnostic::process of de\"elopillg the ideal contour forthe abutment tooth in que-stion . Tht=' cilui­clan must then prf'pan' the toodl as if nocrown we re to he co nstructed: CHt a guid­ing plane, prl.'pan~ the rest se at , a nd makeall other modifku tions of contour; Onl\'then can the act ual c rown preparutlonbegin . The init ial sub tractive mouth pnopa_ration \\; 11 ens ure that there has hccu ade­Ijuale tooth redu ction to allow the for ma­tion of the «leal contou rs ill the final c r ownwithout compr onustng the restonutve rna­terials (Fig; 3- 1.5),

As a general m il', for veneered C rO\\1 IS, ad i,sapp eari llg ma rgin or a metal collarshould be used rather than a porcelain buttmargin, since additional forces wi ll heplaced 011 the CW\\l1 hy the partial denture ,A~,tin , it is essential that all asp(-'(: ts o f idealsoft tissue m,llIa~('mellt he employed forthe surveyed crown. \.Iarhrjn placement ator above the gillgi\<'l.1 margin, respect forthe biologic width . ami careful manipula­tion of ret ract ion co rdm ust he a part of thetreatment .

Original confour

Preparation outline

Area of additiona lpreparation

caus e the hulk of the ali-compositerestoration is morcltkelv to fracture whenthe tooth is loa<l(,d d u ring inci sio n . Therest will he held hy the par tial denturewhile the tooth will be apt to IlIOH' in th ed ire-ction of the force appl ied. with the re­sult of increased fract ure caused hy ashear of the bulk of the com positethrough the rest scat itself.

Both of t1 ICSP bonded options offe r a n-l­ati vely non invasive approach to idealmouth pn-paratiou with excellent n' lXlrtsof longevity for low cost. As previouslystate-d, they require ample ename-l for qual­ity hOlld in~,

50

The final impression for the crO\\11 \\111need to include mo re of the mouth thanwould the usual single-tooth impression.Th e entire den ture-bearing space mu st heavailable on the master C'L~t. This wi ll insurethat the plane of occlusion can he estab­lished independent of the maxillary teeth incomplete dent ure (C D)IHPD situations byusing the junct ion of tile middle am! distalthird of the retromolar pad as the posteriordeterminate of the plane of occlus ion, theanterior dctcnntnate being an ante riortooth tha t has not bee n p repared for acrown. Th e full cast \\111 also allow the ere­ation of a stable record base for jaw relationrecords sho uld that he re-q uired. For anysitu ation re(luiring multiple U OW1lS, a pa­tient-approved set-up of the CD/HPD is es­sential so that the plan e of occlusion, as we llas tho relative position of the oppo sing de n­ture teeth, has been definitively estab­lished . Obviously, all other abu tment teethmust also he present on the master cast soth at the addit ive mout h preparation can hein harmony with the previously comple tedsub tructtve preparation.

Th e only res triction on the dimensionsand contour of the master cast is tha t itmu st fit into the survey table. O ften th is de­mand creates a problem when the distanceof the base of the cast to the mounting ringis great, making the use of the dental sur ­veyor and possibly the milling machine dif­ficult if not impossible. S Ollie modtficauonof standard techniques is ge nerally re­quir ed , especially if the final impression issent to the dental laboratory rath er thanbeing poured in clinic.

Th ere is a distinct advantage, however;to pouring the cast, trimm ing the diet s),and mounting this type of C,L~e in the den­ta l office: it allows the repositioning of themaster east for final determination of the

Mouth Prepara tion

path of inse rtion/ removal and the place­me nt of the three tripod ma rks OJl the cast.To expectthe cle ntal laboratorv to completeall these steps and not lose control of thecase requires a high level ofcxpcricnco andexcellent and long-term communicat ionbetween clinician and tcclu uctan .

Until such time tha t a specific dentaltechnici an has been suitably traine d andhas demonstrated compliance with the re­qui remouts of a specific clinician, the "sur­veyed" crown is to he waxed to full contourand returned to the clinician for the actualshap iug of all areas of crown-partial den ­ture contact .

Since the ideal cont ours of the survcvcdcrown have been estab lished in tile diag­nostic waxing ph ase of tr eatment plann ing,it should be a simple matter to copy th econtours. Because of the crit ical natu re ofthe "surveyed" surfaces in the long-termsuccess of the treatment, it is essential torC\1C\Vthe modificat ions to the fuli contourW ,LX-UP usually required to create the idealcrown . Th e first step is to repos ition themaster cast in the dental xurvcvnr andree stnbltsh t he tilt of the cast to the origi nalpath of insertion/removal. It is to this pa ththat we IllIISt evaluate the co ntours of thecrown as returned from th (~ labora tory.Dusting the wax with zinc stearate (or babypowder) will allow the analyzing rod of thedental surveyor to create an easily seenheight of contour.

Usillg the blade that is normally a pali ofthe components available for th e surveyo ror a wax milling bur in a dent al milling de­vice , the guiding planes are estahlt shed par­allel to any previously p repa red planes inthe enamel of the noncrowncd teeth .Cui(ling planes can be cut as flat planeswith or withou t a gingival ledge. Th e ad­vantage of using the gingival ledge is th at it

5 1

Advanced Removable Partia l Dentures

l edge rest

GUiding planes

Fig ]· 16 Guiding plane extensions,

fuuct ious as a rest and clhninutes th e needfor an occlusa l res t preparat tou. This is ofparticular value when est bet ic demands re­quire full porcelain occlnsals. Th e guid ingplane is not restricted to the proximal sur­face. In fact. the greatpr th e exten sion ofthe gu iding plane 0 11to the lingual or buccalsurface for n 'ciprocat ioll, th t· greater theFrict ional re tention poss thilfttes (Fig :l-16 ).

Only afte r all guiding plant' surfaces ha velx-cn contoured can we proceed to theplace-ment of rest sea ts am! n-n-ntive con­tou rs. It is essential that the junct ion of theg llitlillg plane ami rest is rounded and thatsuffk-ieut W,LX has been n -movr-d to allow anunt nnun of 1.2 mill fo r allY clasp/re st as­scmbly Host preparation s ill cn)\\1IS shouldhe 0 11C th ird the occlusal table, which willt>!'t e n Illake them large r than they would hpif cu t into enamel. The large r and smoothe rthe n-st preparation. the gn':.Ilt' r chancethat rl«- pa rt ial denture will he in sohrl co n­tact with it. Que of the probk-ms we facewith (o\"(ory crown that will have a conven­tional clasp ann or arms is tln- detenuiua­tion of[ust where the height ofcontour L'> toJ,l ' located in the wax·up , It is most desir­ab le that any ci rcumferential clasp lie as low

52

on the ItMlth as is possible, bo th fo r esther­ics am i to maximize the re tentive nature ofthe clasp arm . Since the die stone that rt"p­resents the WIl~i\,Li marginal tissues hasbeen n -movr-cl fm m the d ip, an un triuunedsecond IX tUf of th e mast er Impn-sslon isneeded so that either clinician or tcclunciancan know the relation of the margin of thecrown to the WnW,·a. Wewould like to placethe inferio r border of anv clrcumfi-n-utlalclasp a full millime ter above tln- marginaltissue. The average c.....st d,L~P an n measures1..5 nun o<.'C!llsogingivally, so that the heightof contour must he at least 2,,5 1T1lI1 ab ovethe tissue , Since we have the oppo rtunit y tomake tilt' crowncontour truly ideal, a clini­cal, not labo ratory, decision 1IIIISt he madea.<'; to the relation of the survey lim' to thef inalp osition (If the clasp wh en tile partial Isfully sealt·tl. Th e greate r the distance of theheight of contour From the final clasp posi­tion, the longe r lasting; the retent ive effectof the clasp will he . The flexing of tIlt' claspwtl l he mon- g rad ual, both on insertion amiremoval. hut the initial retention will he re­duced. It would S('P Ill then. that for alltooth-borne partials the hpight of contourshould 1)( ' close 10 the final position. per·haps 3 10 :1 5 mill from the margin al tiSSIll' .This posit ion will gi \"(~ a retentive fo rce thatis shorter ad ill).!; hu t of gn-atp r initial value .Fo r thos o situations where "nnw 1(,\,(,1 ofstress n-licf is desired, it makes more S ('Il S( ~

to raise the height ofcontou r to 4 to 4,:5 nunfront wl«-rc the ma rginal tissue is known tobe (Fig 3-17).

In addition 10 the c reation or veri ficatio nof the hei ght o f contour; the clinician m ustalso determine the maJWII of the cut bac kfor porcelain application. It is essen tial thata margin of metal exist beyond any ext on­siun of the part ial framewo rk so that hl'u ideplates . rests. and minor connectors contact

Fig 3- 17 Options for retent iveare as. HOC = Height of contour.

HOC 3.5 mmfrom gingiva

Steep

Veneer cutback

Mou t h Preparation

HOC 4.5 mmfrom gingiva

Gradual

Guiding plane

Fig 3-18 Options for cutb ack.

Standard veneer Surveyed crown venee r

only the metal of the crown, not the porce­lain. This margin need only he 0..5 mm. Theresulting margin of the cutback will not bewhere it would be placed 0 1\ a standardmetal-ceramic restoration, so the techni­cian needs to know exactly where to star tthe removal Of W 'L\:. The clinician must out­line the margin wi th an explorer so thatthere is no misunderstanding (Fig :3-18).Since the cutback wi ll he a uniform reduc­tion of the wax, allO\ving a uniform thick­ness of porcelain, it is essential that the waxcrown has the exact contou r desired in thefinal survcvod crown.,

Even if the original cont our was idealand the cutback proper ly done, the applica­tion of the porcelain venee ring , which mustbe done to excess because of the shrinkagefactor, offers anothe r opportunity to alte rthe height of contou r and potentially ren ­der the crown unusable . Fo r that reason itis advisable [or the clinician to evaluate thecrown after the porcelain is contoured atthe bisque hake stage. .Minor corrections ofcontour can easily he made by adding addi­tional porcelain before final stain and ghl'l.e.The porcelain 111IIst he ve ry smoot h fromthe he ight of contour down to the final P'"

53

Advance d Remo ....able Partial Dentures

sttio n o f the c-lasp. If it is no l, a dark lineoften becomes visible as the porcelainwears the metal of th e clasp through re­peated inse rtions and removals. Obviously;011<.'(' tilt' cl inician and technician really UIl ­

derstand each other, the tcclmlci .m cansimply create an exact copy of the d iab'1los­tic W;lX-lIp.

T he clinician has two options rela tive tocom binin g these crowns ami the partialdenture framework The em\\1IS can eithe rht~ cemented permanently before the finalimpre ssion for the framework or they canbe picked "P in the filial impression (wh ichTIlIlSt then be mad e in a finn-se-tt ing elas­tomcr-likc Iurprcgum). Hcsln dies must heconstructed and he in the Impr ess tou whenit is pOlln·1! xo tha t they will bo pn'seu t 011(he master east. It is impractical to Includethe single surveyed (')"{)\\11 0 11 the maste rcast . hut fo r those situa tions where thereurc mult iple surveyed crowns ami b ridges.with pn -ctse milling of the ir guid ing sur­faces . it is essential that the CnI\ \l IS he pre­sent 0 11 the master cast. TIlt' master cast

S4

will selYC as the lllilling eas t so that a stah lebase is uvuilable on which th e final millingof the gllid ing planes is completed. The ac­cUTac)' or the refract ory cast is Increasedbecause the actual crowns, not stone n-pli­("<L<;, were a\ ullablc fi l l' duplication. Thefinal fit of th e partial framework to tilt'milled surfaces should therefore he en­hanced. These special impression p mct' ­dures are essen tial to the use of fixedrestorutlon s with pn-cision nttaclu m-nt s andwill be d iscllsst·d further in Chapter 10.

Mout h p « 'para tion , in the largest S{' IlS<' ,

when well-planned and executed, \\111 sim­plify tho actual construction of the ud­vanccd partial denture and ensure its long­tcn n SHCCI'S.S. It is unfortunate that theg reat majority of rem ovable part ial don­tures arc made wi th litt le or limited n·gard

to this crucial com pon ent of can', He­me mber, it is essen tial to establ ish all as­poe ts of the mouth p reparation on the di ­agnost ic cast before any att<'lIIpt is made togo to the month .

Final Impressions andMaster Casts

F ina! impressions for removable pa rtialdenture fram eworks are mad e in irrc­

vcrsihlc hvdrocolloid in ei ther modifiedstock trays Of custo m trays. Algina te is pre­fe rred over silicone O [ polycther materialsbecause it will tear rath er than dis tort.Remember; th e silicone -type imp ressionmate rials we re designed for the impressionof prepared teeth , whe re a minimum or un­dercuts will be found. The removable par­tial dentu re impression will often includeunprepared teeth that may be severelyt ipped or rotated, leming large undercutsthat could well distort by tearing the im­pression material from the tray and Tll aynever he noticed until the casting docs notHI the month . Since the contact surfacesbetween HPl) and teeth are to he smooth ,rounded, and well-polished, there is noneed to reproduce minu te detail as with thefixed prosthodonuc impression ma terials.To lise th is te ar phenomenon , th e clinicianmust carefully evaluate th e final imp ressionunder good light. As described in Chapter1, in th e section on preliminary imp res­sions , th e final imp ressio n should he rela-

t tvely easy because the majority of poten tialp rob lems we re identified during th ose firstimpressions. Using the d iagnostic cast , theadaptation of the stock tray can he evalu ­ated; if the mandatory 0.25 inch is not avail­abl e , a custo m t ray is made wtth adequaterelief to assure the 0 .25 inc h of alginate . Allcustom alginate t rays m ust have multiplerete ntive holes p laced in them using a no. 8or no. 10 round bur. These retentive holescombined with algillate ad he-sive will assu reth e retention of th e im pres sion material. Itis obviously mor e important in the finalthan the preli minary imp ression to m ix thealginate properly, place it into critical areas,and allow the complete set of the material.If the preliminary impression is taken sen­ously, however; there wtll be no diffe rencein the techniques employe d to obtain an ac­curate master cast .

The final impression is to he pouredusing the double-pou r techn ique . Th is ap­preach offers the bes t chance of pouring am aster cast withou t d istortion of the algi­nate. Since onlv a small amount of stone isadded in th e first pour, th e re is a m inimum

55

Advan ced Removable Partial Dentures

Minimum denta l stonein first pour

Alginate Tray

Fig 4·1 Cross sect ion of ideal alginate with a minimum of 0.25 inchof impression material.

load placed on the alginate as compared toboxing and pouring the entire C,L~t at onetime . Once the stone has readied the initialset, the addition of the base p resents no op­portuni ty for distort ion. The only potentialp roblem arises whe n inadequate retentiveblobs of stone are placed on the first pour(F ig 4-1). Without th is retention, there is apossibility that the master cast will separatein the flask during boilout and flask opening.

If a vacuum mixing devi ce is available tothe operatOlY' the clinician can pour thefirst pour right at the chair and thereby as­sure tha t the impression has bee n correctlymanaged. The impressi on with the firstpour should be placed in a humidor 01"

some type for the initial set. The base canhe added anvtimc thereafter. Die stone isindica tell for the maste r cast, not for anyincrease in accuracy but for greater resis­tance to abrasion .

w hen the cast is recovered, it should betrimmed as soon as possible so tha t anvblebs can be removed casilv When the castis shaped with the model trimmer, a thinslurry inovttahly covers the cast and, if it is

S6

not removed, will affect the accuracy of thecast. The slunv can be removed with a softbrush and running wate r; this should hedone immediately. Dies or othe r criticalareas can be protected from the slur')' bycovering them with a latex or silicone mate­rial before trimming the cast. The castshould be trimmed to the smallest possibledimension without compro mising the criti­cal areas. The smaller cast will allow agreate r hulk of duplicating agar in the flask.Underc ut areas, blebs , or other rough areason the tongue side of the mandibular castshould he removedto redu ce the possibil­ity 01" learin g the agar. The distal extensionede ntulous areas that will require an al­te red cast trav should be clcarlv marked so. .that the techn ician will know exactly wherethe borders of the tray will end.

A final task tha t is un ique 10 the maxll­larv master cast is that of head ing the out ­line of the major connector. To reduce thetendency for food to impact bE'T~eatb themajor connector, a bead line is scraped intothe cast following the out line, In general, awidth of 1..5 HU ll and a depth 01" I mm will

suffice to ensure a positive contact with theunderlying soft tissue. The beading extendsto within 4 to 6 mm from the marginal gin­gival tis sues and there phases out com­pletely. The bead line is to be roundedrather tha n sharp and is usually createdwith a discoid carver or a roun ded curette.

The master east must be resurveyed and,dependi ng ou the arrange ment with thelaboratory, the design of the frameworkneatly drawn. If the clinician is unable tomake a precise drawing of the des iredframework, it is bette r to leave the mastereast unmarked and send the diagnostic eastas a reference for the techn ician along wtththe work authorization form. \Vork autho­rizations vary depending on custo m and ju­risdiction, but the more thorou gh the de­sign and instruct ions, the greate r thelikelihood that the tech nician will be en­couraged to return ,i casting of the highestqu ality.

For the most par t, jaw relation recordsarc made on the framework after it has beenfitted to the mouth. There will he occasionswhen the mast er cast must he mounted be­fore const ruction of the framework canbegin. These situations always involve oc­clusion, especially when the space availablefor den ture teeth is limited or when compo­nents of the framework must be in contactwith opposing teet h. \Vhen anterior teetharc being replaced with the part ial dentureand a steep vertical overlap exists withoutany Significant horizontal component,mounted master casts are essential.

Wheneve r possible, the master castshould he related to the oppos ing cast with­out the imposition of any recording mater­ial and the casts shou ld be mounted by theclinician to assure acouracv; when insuffi-,d ent teeth remain for positive positioningof the casts, a record base is constructed

Final Impressio ns and Master Casts

and a record made, usually ill cen tric oc­elusion. The recording material should hecompletely plastic when the record is madeand have a final set that is rigid. Bosworth'sSupcrbitc Paste (ZnO ) or Blue Mouss e aremost often used. If the master cast is sent tothe laborato ry without being articulated,then witness lines are placed between teethof the master cast and the opposing castwhen the cas ts are in the desired occlusion.At least two ma rks per side are required toallow the technician to place the cas ts inthe exact position. Any mounted cast mus thave had notc hes placed on the base of thecast to allow the east to he repos itioned onthe mounting plaste r, since the master castwi ll have to be removed for blockout andclnplicalion.

Th e construction of a record base for apart ial de nture master cast is not with ou tsome risk of damaging the abutment stoneteeth . A combin ation of W (LX blocko ut , plas­ticized polymethyl meth acrylate (P:\fME),and autopolymertztng orthodontic resin(DentsplwCaulk) , used wit h the followingtechnique, \\; 11 permit the construction ofan accurately fitting I )<L~e without injllly tothe master cast.

First, the master cast is surveye d and soft{issue undercut s, if they exist, arc identifiedby circling them with a pencil line. The out­line of the desi red record base is alsodrawn . It is not essent ial that the base con­tact all the rem aining tee th, but some pointsof tooth contact are critical (at least th ree,wide ly spread when possible). A smallamount of baseplate wax is flowed into theginhrival crevice of the teeth to be contacted.Auv undercuts in the denture base areagreater than 3 rnm are also blocked out withwax. The cast is then rehydrated by placingthe base of the cast in water awl allmdngthe moisture to pen etrate the entire cast.

57

Lynal

Advanced Remo vable Partia l De ntures

Orthodonticresin

Fig 4-2 Blockout with wax and Lynal for sprinkleon base (cross section, lowe r midline).

Th e east mus t not be submerged in water;as the accuracy of the tooth portions can healte red with the dissolution of the stone ,Once th e east is hydrated, tinfoil substitute ,diluted 2:1, is pa inted on , Caulk 's Lynal orsimilar plasticized resin is added to any un­dcrcut areas and aroun d the necks of thetooth that will be contacted bv the recordbase. Th e 1.\11al is mixed thicker than is rec­ommended by the manufacturer, to theconsistency of peanu t butte r, so that it willstay where placed. Orthodontic resin is im­mediately added in a "salt and pepper tech­ntquo" to complete the record base (Fig4-2), Th e autcpolymcriziug resin " i ll bondto the Lynal, and the result ing record basewtll bc retained by the intrusion of till' plas­ticized resin into th e undercuts. There is noneed to place the cast ill the pressllt"c potfor curing.

The base can be removed as soon as theresin is hard ami trimmed. 1\ wax rim canbe added with the intent of haVing a sup­porting table of wax 2 to :3 uuu out of nc­elusion . The recording material is mixedand placed Oil the table, and a cen tr icrecord, at the des ired occluding vertical eli-

58

mcnston. is qutckly made. The casts can hemounted on the art iculator or submitted tothe laboratory with the record for urtlcula­tion . Th e labo ratory te chnician can make amou nting record Frein the articulator to en­uble the mounting of the refractory cast tothe opposing cast for the waxing of the oc­eluding portions of the framework.

~ ,.,,.,~ W! ~~~~'~Altered Castlmpressions I

Made only after the casting is finished,the altered cas t imp ression is an att cmpt tocombine the SllppOlt of the abutment teethwith the support that can be obtained fromth e edentulous ridge. Original1y, alteredcast impressions we re made on any ede ntu­lous area that had no posterior abutmen t,eithe r maxillarv Of mandibular. Since thenmxtllary HPJ) is so well -supported by themaj()f connector, litt le additional suppo rt isgained with an altered cast imp ression for amaxillary distal extension area, especially ifthe fina l impression was made in a customtray. The difficulty of capturing the totaldenture .~pace of the mandibular distal ex~

te nsion in the fina l impression has madethe altered cast imp ression essent ial for allmandibular Class I and II situations. Withthe usc of an alte red C<L~t impression, t heelmir-ian nced IIOt be ovcrlv concerned withthe accuracy of the edentulous areas andcall concentrate Instead on making the bestpossible impression of the teet h to he COII­tactcd by the partial denture. Tt is essen tialtha t the full exte nt of the denture space inthe distal extension ofthe edentulous ridgehe captured so that the outli ne of the de ­sired altered cast trav can be drawn as apart or the deSign. Th e technician can thenret urn the framework with tho altered cast

I

tray ill place, with its bo n k-rs 2 to :3 nunshort of the desired final cxt r-ustou of theden ture base in the edentulous art-a.

The altered cast tmv is constructed 0 11

the master c..ist afte r the casting lras been

completed. Dill' thickn ess of baseplate wax.the same as for the relief for the retent ivemesh, is adapted to the muster cast to theoutline of the desired altered cast tmy ex­tension. The retentive mesh area is heatedover a Bunsen hunte r and the fram ewo rk isseated onto the cast. The hot metal of themesh mus tmelt the rcl tcf'wax ami allow thecas t i ll~ to fully seat. 'Vith the tip of a spat­ula, tlu: ,,",LX that extruded up t lJ rou~h sumeof the 1I 1csh holes is removed to allow theresin or the trav to lock onto tho frmm-work.The trav resin is mixed ami a small amoun tis n ·II1O\"(..d from the mixing jar and imme­diatl'ly placed into the retent ive holes thathaw lxx-n cleared of wa x. The fluid ity ofthis n -sin would 1I0t allow il 10 1)(' 11.\('(1 as~·f't II) form the tray, but it will now into theret entive an-as eas ily ami p rovid e the re ­qut red reten tion. The remainder of the travresin is added when it is 110 longer tacky andthe tmy is formed. The tray must he kept tothe dimensions of the ideal dent ure base.To form the ideal den ture border, the lraymust he uniformly short and he slight ly 1111­

dcrcout oured to make space tor the im­pression material to capture the borderwithout becoming bulky. 'Vhell the occlusalportion of" the tray is kept th in. it will oc ca­sionally he possible to make the flnuljaw re­lation record at the sallie appom tment ,l~

the altered cast impression . If at that timethe patient is unable to d ose tile tee th intothe desired occlusion for tlJe n-co rd be­cause of tl1(' thickness of the tray or tile gcn­era l lack of intcrocclusal space, the jaw n-g­isl ration must be mad e at a sepa rateappointment.

Final Impressions and Master Casts

TIl(' altered cast hnp rcssiou is made onlyafter the framework has been fitted to themouth and the full se ating of the l'<L"t illgverified (t i l<> actua l fitting of the frame willbe discussed in Chapter 6). Wit h theframework seated firml y on the abutmentteeth. the extensions of the altered cast trayare evalua ted. They are to be 2 to 3 IIUIl

short of the re flec tio n of the border tissues.When the tray is prope rly exte nded. the reis 110 need for !'o rder molding :l~ a separatesl<' p. The wash impression "ill al.~() giveideal bord ers if the tray is in t i le pn1lwr po...slt ton relati\'c to the tissues.

Tlw ch() i {'( ~ of impression materialto heused lo r this impre ssion does not appear tobe critical. Earlv stu dies indicated thatmouth-tcuq x-nuuro wax imp lt"A"sions placedthe den tlire h:l~e tissues ill their most Sli p'"

pOJ1 iH~ state. This mate rial is seldom usedbecause il requi res a good deal of expert­en('l' to read the filiality of the impn·ssioll .Polycthcr illlpn-ssion materials offer the'option of Yal"}in~ the viscosity hy blendi nghigh- and low-visco sity materials into onemix. Th.. firmer the underlying tissue. thehighe r the percentage of high-viscosity im ...p ression mate rial. \\l len a good deal of 1IIl ...

SUPIXlrtl't1 so ft tissue is found on the rid~e

cres t, the mixture is altered 10 lise agrea te r p roportion of low-viscosity mate r­ial. \Vhile a wash of alllow-viscosity urate­rial willmake an imp ression of this Il Il SIlJl ­

ported tissue wit h a minimum of pressure,it willtcud to Ii:IVl' poorly rounded bordersbecaus e it is no t thick enough 10 create thebest bonier contours.

Excess saliva should be removed fromthe month, hut there is 110 reason 10 havethe mout h totally dl"}'. Th e tr.1Y is 10ad('(1wi th just enough material to make lip forthe spa('t'r. and a ll additional 20% is addedto assure full borck-r co ntours . The n ' must

59

Advanced Removable Partial Dentures

he 110 excess material at the internal flnlsh­ing line, as th is material can now up intothe guide plate area when the frame is

seated. when pladug the framework in themonth, the cltmcian must make sure thatthe frame is fully St'ah't l and that no pres­sure is placed 011 the tray itself The flll~ers

are placed OIl three widely separated reststo maintain the frame in its opti mu m posi­tion while the bord ers are developed andI he material sets.

When fully set , the impression is re­moved from the mou th and trimmed to n-­

ilion' any exeess impress ion mate rial .There will normnllv be a thin extension ofthe material into the ret romolar space onmandibular Impressions and an extensionof material onto the soft palate fur the oc­ca sional maxillary impression . Since it is al­most imposslhle 10 fully border mold theretromolar space on the altered cast tray.the dctcmunattou of the extent oftlte resinborder in this area is arbitrary, Rl' lIll' lllht'rthat there is 110 ru-ed I(]I" 1'1111 extension intothe ret romolar space in the removable par­tial denture as the n' would be for a com­plr-te denture. The retention of the part ialde nture is not dr-pcudcnt on th is border, Ifa large undercut exists distal to the mylo­hyoid ridge, the dent ure base Illay II( ' pro4

lnbited from entering the undercut . as itmight ill a complete denture, sim'(' theguiding planes dctenninc the path of lnscr­tion. It is acceptublo for the lingual exton­ston of the Hauge 10 tcmunatc at the softttssuc height of contour as determi ned bytlu-se gu iding plum-s. The patient \\; 11 hemore comfortable with less resin in the1I101lth, and tile support of the extensionbase \\;11 not be compromised, since it isthe ridge crest and the exte r nal obliqueridge that arc the supp0l1ing; stru ctures forthe d istal extension.

60

AllY bo rders of Insufflcicut width can berecreated in \ \ <LX if they are exte nded tothe pn-dctcruuned limits. Since this bor­del' width is arbit rary in ti le removablepartial denture, there is no nr-ed to l 'U lJ 4

firm the width in the patien t's mouth atthis time. Should exe('ss wax flow onto tileint e rna l surface of the impression whenthe borders are being; cn-ntcd, it can easilybe removed without damaging the accu­racy of the impression .

A filial verification of the distal extensionimpression must be made after the base istrimmed ami shaped . At this lillie the d in­ician must be confiden t that the frame fullyseats and that all impression material thathas flowed onto the framework has bee nremoved. Special consideration must hegiven to removi ug any material that extendsbe yond the internal fillishing line. A sharpblade should he used to trim the material inthis area so that no plll1 i ll g or tea ring of theimpression material occurs. At this point ajaw relation record can he made if req uiredand if adequate space for the reco rd exists.

Pou ring the altered cast impression canhe t!('lpgalt't l to the technician . but the din­ir-ian must w rit)' th at th e Framework is fullyseated 0 11 the master cast and that stickvwax has lx-cn added to hold the cast amiframe togethe r during the Il(lxing and pour­ing of tilt, stone . Th is means that the origi­

nal edentulous porti on of the master castmust have boon removed earlier and thatadequate rctcnt ton has \ 1(' ( ' ]1 cut into theremainder of the master east. Bath er thango th rough an elaborate boxing p rocess. theclinician mayelec t to pour the ultercd castimpression in two stages , much as was donefor the master cast. The bo rder roll of thealtered cast impression must he preservedin the hoxing and pouring of the imp res­sion. A line is drawn Oil the impression \\i th

•

an inde lible ma rker ju st at t ill' I'MJill! whe rethe bo rder contou r is complet e . Boxing ma­terial is placed at this line to create a landurea ofS nun, th e impress ion is filled withvacuu ru-nnxed stone. and retentive blobsare placed (Fi?: .-1 -3). The base ca ll beadded later; after the initial set, withoutfea r of d isturbing th e tooth-frame relat ion.The altered cast impression is poured instandard vellow stone rathe r than in thesame d ie ...tone as wax used f(JI' the origin almaste r cas t. The softer vcllow ...tone is f:ITeasier thun d ie stone to remove from theprocessed denture base with the lise of tilt'walnut shell blaster and sto ne solvent.

Jaw Relation Records

\\11f'1l suffk-tent Intcrocclusal spal'C ex ists,it ma ke s sense to m ake th e jaw relatio nre-cord before po uring the altered east im­

p ression. thus S;l\; ng the patient an add i­tional visit. T he reco rding mat erial 01'choice is again one that is completelyplus­tie to start and tha t sets hard quic kly Theocclud ing su rface o f the tray is prepared hycutti ng a few c rossing grooves ill the resino r. when ,I gre at deal ofspace exists , addinga wax occl usion rim to reduce the space forthe record ing material. Since there wil l h ( l

natu ral teeth in contact ill all dentate cases.only a ve l) ' small amount of ft'con ling ma­te ria! Ill,,('11 he placed. Th ree wd l-d e fllll·t1and " idd y se parated point s ofpositive COII­

tad " i ll allow al"<.'urate articulat ion of thecasts. Once th e stone has set and the O;LWco mpleted and trimmed, the cast with theframework and tray ill position is artfcu­

luted wi th the op po.sing cast alltl mountedin tile articulator before th e impre ssion isseparated fro m the l ';LSI. Wh ('n the 0Ppos-

Final Impression s and Master Casts

Retentive blobin yellow stone

Impressionmaterial

Boxingmaterial

Alteredcast tray

Fig 4· J Double po ur for alter ed cast impre ssion(base is added later].

ing arch is a complete d(,111 moe, th e jaw re ­lation records are made al a separale ''I"poi ntmcnt since there are ot her proceduresth at must he complet ed as a part of th is pa­fient treatment .

No compnnuisc in t ile quality of th e finalimpre ssion or maste r cas t call be allowed.The clinician mu st be pre pared , and mu stpn 'pare the patient , for the inevi table ro ­makes tha t will occur. Once patient... under­stand th at only pcrfccnou is acce ptul .lc OIL

this critical sta~e. they will sec that it is intheir best Interests to coop('rate fully. In ad ­dition. technicians must feel comfortable intelling; cl inicians th at an apparent e rro r hasbeen identifi ed (Il l ti l e master cast. Their ad ­vice must always he welcomed, even thOllgltthe nat ural reaction to tho requested re­make is one o f irritation. It is th rough thisteam approac h th at partials of the h ighestqualtty are mark- on a routine h;L<;L<;.

6 1

dLaboratory Construction

of the Framework

T he laboratory phase of removable par­tial denture cons tru ct ion IS just as im­

portant as the clinical phase. Because of tileexpensive equipment requ ired to C,L~ t ste l­late alloys, the clinician is totally depende nton the dental technician to construct theframework. As a result of th is situation,dental schools do Ho t prepare their stu­dents to make frameworks an d , unless theclinician has had laboratory experience he ­fore dental school, he or she will under­stand the procedures necessmy to createquality frameworks only in the most basic:SCIISC. Xoucthclcss, the clinician hears theultimate rcsponstbtlt ty for the quality of theprostheses placed in the mouth and somust care fully interface with the laboratoryto maintain this stan dard.

Clinicians have, unfortunately, oftenused the labo ratory as a scapegoat for prob­lems that arise duri ng treatment. Problemsin cliuic-laboratorv relations can most oftenhe Iraced 10 lack of communicat ion and theunwillingness of the clinician to review th elaboratory procedures at the appropriatestages in cons truction. For example, the

clinician should always have the blocked­out master cast and the waxed-up refrac­tory cast rcmmcd for evaluation beforespruing and casti ng the framework Thisevaluat ion is well worth the de lay it pre­scnts, as the re will always be cases forwhich the clinician is unable to adequa telydescribe wha t is desired in the final prod­uct . The inte raction between the clinicianand the technician is equally Significant forfixed prosthodontic res torat ions in the situ ­ations described in ChupterS in the discus­sion 01" addit ive mout h preparation.

The ph ases of RPD construction in thelaboratory can be divided into:

• Design transfe r• Hlockout and du plicat ion

• \Vaxing• Sp ruing, investi ng, and casting

• Metal finishing• Addition 01" wtre clasps (where iudi ­

rated)

• Addition of the altered cast t ray (whereindicated)

The actual construction techniques and

63

Advanced Removable Parti al Dentures

Critical area

Externalfinish line

Position of extern alfinish line

Fig 5-1 Placemen t of internal finish line.

materials are usually propri etary, havingboon devel oped by the dental laboratoryindust ry and the metal manufactur ingcompanies. The alloys are generallychrome based, although iron and titaniumalloys have been proposed and are in lise.Vitallium and Tlconium arc the most com­monly used commercial allovs in Nor thAmer ica. These Lwo alloys use di fferentinves tmen ts and d iffe rent d uplicatingagars but are oth erwise quite similar intheir construction techniques. TIley showsimilar results in materials testing as well.The composition and characteristics ofthese alloys are available in any text ondental mate rials and shou ld be a part ofthe knowledge base of the clinician in­volved with prosthodontics at the ad­vanced level.

Design Transfer

Construction in the laboratory begins wtththe transfer of the design from the diagnos­tic east or the work authorization to the

64

master cast. Specialists who are comfort­able with thei r ability to make a precisedrawing OIl the master cast need to he surethat the color COlle theyempl oy is known tothe technician. By placing the design on thetripodcxl master cast, one area of potentialerror is eliminated. Special care must betaken in the out line of relief pads for reten ­tive meshwork. The extent of the internalfinishing line must be clearly marked 1..'5 to2 1t11l1 from the gingival murgtnal tlssue sothat this area wtll he in metal rather than inresin (Fig ."'>-1). Heights of contour must becarefully marked with the surveyor lead onboth hard and soft tissues so tha t no areasrequiring blockout arc missed.

Perhaps the most critical area of designtransfer L~ the accurate drawing of retentiveclasp arms. The te rminal third of all cir­cumferential cast clasps must he accuratelyplaced at the desired undercut depth, al­most always 0.010 inch (0.250 mm), De­pending on the steepness of the undercutandthe amount of mouth preparation, un­dercuts in the terminal third or the toothsur face Hlay require blockout even thoughideally the entire te rminal third of the clasp

should he contad ing the tooth i ll tht· U II ­

dercut area. A master east must be rej ec tedif the available undercuts are inade-quate i lldepth or positio n o n the toot h. lk-fon - de­eidin~ that the m aster cast will not be ac­cc pt ablc. the path of inse-rtinn/n-movalmust he reviewed to assure that the' ca st is.in f act. at the proper tilt on the' SllfY(')l:)r.

Blockout and Duplication

J) f'l)(, lldin~ Oil the proprietary techniquesspecific to the alloy being usod fo r theframework. the designed master ca...t mayhe sprayed with a model gloss to scul theea st and prpse rve the d rawn de sign ,Obviously, care must be taken not to ove r­spray since any accumulation ofthe protec­tin ' (.'oating would change the dimensionsof the maste r cas t and may result in an un ­usable casting. Most modern te-chniqueshan:' e liminated this process .

Blockout wax. e ithe r the comnu- rciallyavailable ble nds o r homemade , is thenplace d Oil the stone teeth to he'gin theblockout proeess. It is essential that nohlockout \V; LX he placed above the Hill' in­dica ting the height of contour O il any areaswhere the cas ting is Inte nded to touch theteeth, Oil gU iding pla nes , rest seats , andclasp arms (F ig ,5-2), The reason for stress­ing this sl'culillgly benign step i... that thecontours of the stone teeth will tncvttublvbe chungod by the process ill arc-as whe reacc uracy is essential to the fina l fit of tilecasting. The technician removes tln- excessblockout wax using a vertical hladl" in aSIll"\"P) i ng instrument , somet imes evr-nonethat is elec t rically heated, to increase thepos _sihilily of creating a smooth surface Oil

the refracto ry {'; ISt. Wax placed ahon ' the

Laborato ry Constructio n of the Framework

Preparedguiding plane

Height ofcontour

1""e-Wax

Fig 5-2 Relation of guiding plane and blcckourwax.

he ight of co ntour in areas of toot h-frame'contact IIl IlSt also he removed. III a ll at­lempt to do so, the technician wi ll e itherleave a small amount ofwax, thereby mak­ing th e master cast ami resultant refractoryslight ly larger than it rea lly is, or, in at­tempting 10 remove all the excess W'lX.

scrape some o f the stone and therebymake th e m.Lstcr cast slightly smaller inthat an-a. III either situation, th e at'(.'uracyof the master east has been compromised.II is far be tter to he vcry careful ill the ill i­hal placemen t of the hlockout wux undnever have 10 deal with the problems tltatari se ill its rcmovul.

The blockout is gcnerally done at 0 do­gree.~, parallel with the intended path of'!n­sertion/renmvnl. It is possfble 10 alter thi sangle I»)' Sllllstitlltillg a blade that has a 2- orf i-degree angle . Th is t)l)f' of d iverge lltblockout is used primarily for certain t)l"ll.'Sof p recision attachment situations. In Ilsingil blockout of oth er than 0 degrees, fric­tional re sistan ce to di slodgment is ill­e\itably Inst, fon,jng Increased re lnmce onclasp re tention.

65

Advanced Removab le Partial Den tures

Retentive clas p10 0.010 inch

Blcckout wax

Fig S-3 Blackout ledge fof" clasp placement.

Some laborato rie s 11....1' a technique inwhich a I('dge is created in the blockoutwux at the inferior bo rder of clasp an us.Th is ledg(' is duplicated in the n-Fructoryand servos ; ts a shelf onto which the plastic­clasp palt('1"Il is placed during the \vax-np.It should he obvious tha t till' ledge must heplaced \\i tl. ca reful rega rd for the undcrly­ing d ra\\i llg of the clasp arm (Fig 5-.1).Since th e placement of th e plastic clasppatt en) to a precise pos ition O il the n -Iruc­tory cast is not an (';I.'>y task. the Il·dgeshould he placed slightly (abo ut 0.5 111 m )below the llm- that represents the inti-rtorborder of the clasp . This \\; 11 ensure thatthe clasp will reac h the des ired unde-rcutpos ition.

\\1len tln-abut me nt n-cth have ht·t·u R'­

contoured \\;111 the blcxlout wax to tilt' ex­te nt prescnlx-d. tile relief pads are addedto the master ca st. A full tlnckr ICSS of base­plate W ,LX (rollghly l uuu) is the minim umfor the re lief of tilt, re tentive mesh .Commercial laboratories often choose tolise a thiuuer relief wax ill the belie f that

66

kt'<.'ping th e meshwork closer to the eden­tulous areas creates more room lor therapid placement of the denture teet h.Whi)t ~ this is true, a relief pad that is toothlu c reates tnsuffk-lont spaee for qu alityresin under the meshwork as we ll as an ill­

temal nnishill~ line that does not have ade­quate de-pth to retain the resin ill the criti ­cal area next 10 the abutment tooth. Therelief pad thickon-ss also dctenniues theamount of space that wi j] be available forthe Imp ression material of the uln-n-d c-d...t

impn -ssion. Again , I JlII Il is the mi nimum

,"p' K"t~ 11 )1" impression, In addi tion , the rec­o mn u-ndcd procedure for a reline of th edistal extelision buso involves first removing

a uni form amount of material to e-nsure agood bond of the added rosin to the olddenture base. \\1lt'1l less than a millimet erof resin exists under the mesh work, the re­duct ion of the material often n-sults ingrind illg completely through to the mesh.TIll' th ickness oftlu- relief wux pad mus t hepresc-rlhod bythe clinician, not det e rm inedarbitrarily by tho laborat ory, es pe ciallywhe re ove rdcuture abut ments and im ­plan ts are Involved (to be discussed later).The relie f pad mu st he sealed to the master

cast so that it dot's not separate ill tile du­plicati ug procedures to follow.

To complete the blockout procedures.wax o r caulking mate rials arc place d in allundercuts that arc not part of the frame ­work. Hloc kout of thes e 1100H'SS('l lt ial areasi." Import ant , nonetheless. since the entireeast must he removed from the du plica tingmold without tearill~ the aga r. AllY under­cuts other than Ilu-0.010 inch for the claspretention have the potential to d istort theagar, The fully blocked -out cast i ~ placed illa saturated solut ion of dental stone to behyd run-d before (hlllikating it ill tile refrac­tory material.

Tile duplk ating a~ar is commonly onetha t is p rovided hy ti le man ufactu rer of thealloy system and is chosen fo r companbilnywith the re fractory ma te rial. For example . aphosphate-bonded tnvestnu-ut dot' s 110 1 setagainst a water-based co lloid, so a glycerill4

based duplicating agar is used for thehigllt' r-heat alloys. The agar is usually kepiin all elect rically lu-ated dispe nse r, fromwhich it is pOUH'11 through a con trolledvalve into tht· dup licating flask at a pre­scr ilx-d temperature ami to which it is ro­turned after rc('o\,('')' from the se t re frac­tory at the end of the duplicating pr<x'("ss.

The duplicating material doe s have an expi­ration point hasod 011 the number of lim es

it has been broken clown ami reheated.Clin icians Heed only assn n- tltt'mst'!ws tbutthe laborato rv dol'S indeed record thenumber of cycles and replaces the agar atthe ap prop riate times as directed hy themanufacturer,

TIlt' flask used to contain the du plicatingaga r is desi~lll'( l with a met al base and anomnetallk-side ring th at fits into a channe lon the base . The blocked -out master cast is

placed 0 11 the base , and the ho t (tempera­ture depending OI l manufact u rer) agar isslowly po ured into the flask np to !he levelof the top of the ring. Th f" entire tlask isplaced into a circulating cold-water bath ,whew the metal of the IXLw co nducts theshrinkngc or the cooling agar toward thebase to result ill all accurate mold . \ \11CII

the aga r is cooled to roo m le m pe ra tu re , theflask is removed fro m the hat h. T he m astercast is care fully removed from the mold byplacing a kntfo hlad t ~ ill th e cast bas e atboth sides and lilting ti le east vert ically out

of the mold wi thou t si ressing the agar.1l<t\ i ng the sides of the base of the mastereast triuuned to dh'e l"'Ae slightly toward thebase will make' re moval easier.

Laboratory Construction of th e Fra mewo rk

T he liquid-powde-r ra tio for the rcfrac­\(>')' cast is cri tical for the accuracy of thecasting. T he dcn stty of the set re fractory de­te n nines , to a great exte nt , t ltl' expans ion ofthe inves tment mold. It has been d a.inwdthat a ehall~( ~ as little as I cc ofliquid in theliquid-powder ratio cnn aflc-c-t the clinical fitof the framework. Because o f the h igh east­ing temperutures of the stel late alloys , th ethermal shrinkage wi th CU lling is signifi4

cant. O ur ahility to Sliffici('lli ly expand themold is limited. By decreasing the amount

of liquid to powd e r, the expansion o f themold can be increased to offset the the r malshrinkage. Unfortunately. the thickening ofthe mix th at results from the dlangt~ ill theratio m akes the mass too thick to pour intothe agar mold without fear o f trapping air.Tile technician who uses the man ufac­tu re r's recommended ratio wi th ex act mea­

suremcnts of both liquid and powder wi llgene rally p roduce a mold \\; 111adequate ex­panslou. Beware o f the tec-hnician who isca re less with the m easurem ent of the liquidor perha ps oH'rIOCl"-" water ill the bo ttom ofthe mixing bowl. A mix that has too muchliqu id in the ratio results in a mold that can ­not expand sufficiently to match the eX4

peered thermal shrinkage.\Iost techniques for the casting of these

HPJ) alloys call fo r ti ll' desicca tion of therefractory cast in all oven to remove excessmoisture, followed by dipping the cast ill aba th of hot molten !J1"e S\\. Lx . T his W ,LX sealsthe lx>res of lile refractory and makes it less

susce ptible to abrasion. 11 also eliminatesthe Jl("("{1 to soak the re fracto ry Ci.L<;1 be foreaddillg the first layer ofpaint-ou investmen tover the waxed Framework. Conuncrctalmodel spmycan also I M~ used for these pur­IX)Ses. Two light coats of spmyare n-quired.wi th a 2- to 3- lllinlllf" d [)ing time lx-twccucoat s.

67

Advanced Removab le Partial Dentures

Waxing

At this point, the design is again trans ­ferred, from the maste r cast to the rcfrac­torv cast, to form the outline for the waxinr-, 0

of the framework. The clinician has everyright to expect a casting that conforms toth e design placed on the master cast.Commercially available plastic patt ern s areused whenever possible to maintain stan­dard dimensions for ma jor conne ctors,clasps, ami fiuishtng lines. Bests are apt tobe hand-waxed to blend in with the plasticpatterns. The clinician needs to have seenthe patterns and evaluated the ir shape andthickness to he able to truly prescribe thecomponents of the framework. Becauseclasp patte rns have such a major effect onthe perform ance of the cast clasp andcome in such a variety of tapers and width­thicknes s ra tios, they must be selectedwith care.

The plastic: patterns are quite flexibleand can easily he stretched when removingthem from the cards on which they come orwhen adapt ing them to the refractory cast.They also have a memory, so they must beheld in place with some sort of adhesivethat is compatible wtth the entire process.A mixture of acetone and the plastic pa t­tern mate rial \\111 create a tacky liquid thatcan he painted onto the refractory and towhtch the patterns \\ 111 adhere. The tachliquid should have only enough viscosity t;)glue the pattern in place. Excess materialpainted on the cast will result in a change indimension of the resultant casting.

Once the tacky liquid has been applied,the patterns are cut to length, and occa­sionally shape, and adapted with either fin­ger pressure or with a soft pencil eraser (orsimilar instru ment). Sharp instruments

68

Plast ic pattern

Plastic mesh

Fig 5-4 Junction of plasti c pattern and han d­waxed minor connector.

may create cuts or grooves in the patternsthat may influence the performa nce of thefinal casting. The sections of tile plastic pat­tern s will have to be joined with wax. tryingto maintain the contou rs of the pattern.Since till' resultant casting will not comeout of the casting process as smooth andprecis e as a cast Cro\\11 , the wax is alwaysadded in slight excess to allow for Hnishingand polishing of the surface . Where clasparms join the minor connectors, care mustbe taken to assure that the tape r estab­lished will not create a thin area in the ac­tive portion of the clasp or at the junction ofthe plastic pattem and the minor connectorwhich will often be thinne r than the pattem(Fig 5-4) . This thin area, in between twothicker areas, can only act to concentratestress, and, thus, a fractured clasp can bepredicted in the future.

The blockout/relief pad established theinternal finish line, so the tech nician nee donly worl)' about the accurat e placement ofthe external finish line. This line, usually aport ion of a plastic pattern, should extendto the occlusal portion of the line angle ofthe abu tment (Fig ,5-,5). This position " i ll

•Laborato ry Const ruction of the Framewo rk

Internal line

<§>;;'"0"0"./t""'''-- - - Externa l lineo

Fig 5-5 Placement of external finish line.

permit a small amount of denture baseresin between the denture tooth an d thecasting in the completed prosthes is.

The tips or cas! clasp pa tte rns shou ld ex­tend to just beyond the terminal extensionof the tra nsfe rred design to allow a smallexcess of metal. no more than 0 ..5 rnm, fewfinishing.

D istal extension meshwork will require atiSS1J(~ stop to be ad ded at the end of the re­lief area of the refractory, either distal ormesial depending on the situation . Thestop should be roughly :1 X :1 mm andshou ld be placed on the crest of the eden­tulous ridge or slightly buccal to it whcr­ever a rel atively flat area can be found. Theslop indicates a complete seat ing of thecastin g in that a rea fo r fitti ng and finishing ,It will be re moved as part of the alte redcast procedure in situations where th is f)1)eof impression is requ ired .

Wlule the plastic pattern of the mesh­work is adequate for the V,L~t majority ofsituations , there arc occasions when theresin re tention should he created freehandin wax. I ,oops or stri ps of one-half round 8­or lO-gauge wax can be place d Oil the relief

area of the refractory and waxed in to thefinish line area. This app roach is most ef­fect ive fo r maxilla ry tu be ro sity are as,where space for res in is at a p re mium. Thelarger retentive areas of the hand-waxedresin retention may create a stronger linkto the processed resin , although the shapeof the commercial pattelTls appears to beadequate . H oweve r, the patt erns do notprovide adequate re tention fo r res in inconstricted spaces . Shou ld mesh be rc­(luired in the space of a single tooth, ells­tom \vaxing of th e retention is desirab le be ­cause the small latt ice arrangemen t of theplastic patterns will no t provide sufficientre tention .

At th is point , the re fractory cast and th eblocked-out master cast are to be returnedto the clinician fell' re view. It is essentialthat this re view ta ke place fell" every caseuntil the technician tru lv understands thequality level expected by the clinician. Fo rcomplex cases and all precision attach mentpartials, it mus t he standard practice . Th etechn ician see s that the clinician caresabout quality and is knowledgeable aboutlaboratory techniques . Misunderst andtn gs

69

Advan ced Removable Partial Dentures

that inevitably occur O il desir;1l ami con­struction are most often the fault of theclink-ian being unable to describ e in wordse xactly what is required. It is on ly co mmonsense that the W<1.~-up should he reviewedbe fore spruing and investing. It In s beenIlly ('xlx 'rie nee that so me i1.~r)t"t-1: of tile wax­lip will need to be wfint"l! in about 25% ofcases, and that percentage makes the in­('011 \ enicnc-e wort hwhile .

Spruing, Investing, andCasting

TI J('.w~ ste ps in the laboratory const ructionof tilt, removable partial de-nt me are indus­trial i ll nature and gene rally follow the pro ­priet ary Instructions of the nu-talmanufac­tu n -r; TIll" clinician does not han' a role toplay here except for Ix'ill~ uwure of thep l"< )(1.'SS, especially the sp n nng. since thevariat ion in spruing tl't:!lIIi'IIWS is gwat­with p\'t'ry technician doing things a hit dif­fprPlltly, As all example, the labora tory withwhich I have worked for IS vears li st'S ahelix ill the spnte leads. usually two or threeleads for a mandibular casting ami four fora maxillary (Fig 5-6). TIll' technicians fel' lthatthe helix doe s two thill~s that dramati­cally affect the quality of the casting: (1) itads as a reservoir for the metal muss thatreduces the po tential of a suckbuck. and (2)it slows the !low of the molten metal, how­ever briefly, reducing the turbulence andthus n '(hleing porosity. Sp rue I('ads withoutthe helix are sometimes used ,1." an add i­tional lead for complex casting co nfigu ra­tions. These sprues an' always slightlycurved to slow the metal flow,

The clinician should always examine theresultant casting and any broken ea~lings

70

Fig 5-6 Helical sprue leads reduce turbulence.

for evidence of porosity <.1.S a quali ty-controlc heck on the laboratory II is possible, hUInot practical. to x-ray a cast ing USill~ all oc­

clusal fil m to visualize porosity, ilS was stan­danl practice for subpe riosteal imp lants.

Wh ile tln-rc is little that the chmciun cando , Ix'plll" slu)\\i ng inte rest, about thecasting of the part ial den ture framework.the trcutnu-nt of the cas ting after it haslx-cn cast is a critical p rocedure that d ra­matlcallv affects the ultimate Sl lC'tX'SS of thepartial denture.

Metal Finishing

Metal finishing is an <Ill-e ncompassingterm cover ing the steps from the act ualcasttng of the partial denture fmmework tothe fully finished and. polished framework.It is <Ill <' l,,!,)('("t of the process that histo ri­ca lly has 1)('('11 left: entirely to the dlscrc­lion of the technician. wit h the clinician

acce pting the fbushcd product withoutquestion. Th e finish ing and fi tti ll~ of th el, lstillg is th e most impo rtant phase-of con­struction. and it is here whe-re an accuratec,lsting l';. 1II easily be rendered unaccept­able if the inte rn al surfaces tha t contactthe te-eth are alte red in any way. The stan­da n! means of flntshiug the cilstillg, oncethe sprucls ) has been re moved with a cut­oITdisc, is to elcctropolish.t hat is, stri p thee-ntire cast ing electronically in o r der to rc­

move a small amount of nu-tal from theI ' r l t i n ~ surface. This p n x't'ss reduces theamoun t or flno finishing ami pol i.'ihillg thatwill btl required. Unfortunately, the re­moval or eve n this potentially ve ry sm allamount or meta] (40 to 50 microns ) will re ­du ct.' the fridional reten tion that couldhan ' lxx-u obtained with the pa rallel guid­ing plant's established thro ugh mouthprepa ration . The on ly WilY to control th iselect rochemical p roc't.' ss is to 1I0 t allow it tooccur at all.

All tooth-co ntacting surfaces-a-guidepla tes . minor connectors. rests . andclasps-c-must be protected from the elec­trolytic dcplatmg prOC'eSs hy coa ting them\\i th a high -fusing wax or a subs tuucc suchas fingl' rnail lx>lish tha t will not allow con­tad with the add ha th. SlJippi ll~ or deplat­i ll~ oc curs when a metal is placed ill au addhath att ached to an e lect rode and a C(J Jl ~

trolk-d microamperage is passed throughthe metal via the electrodes and tln-hath . Acommercla l unit with temperat ure am] am­perage control and timer; which has adamp O il the electrode to hold the frame­work. is used. Obviously, all the ingredif'llisof the svstem contribute to the rail' of dis­soluttou of the sur face of the frameworkand so are susceptible to illlpmpt'rly cali­bmtcd compon cnts or careless technicians.T his syslf'1Il works in n -vt-rse as compared

Laboratory Construct ion of the Framework

10 a die~platillg unit and is simila r to theunits II.,;t,<I for microc tching of bonded ca st ­

ings.On ce the co ntact surfaces han ' lx-en

protected , the fram e can be safely placed inthe hat h :.lil t I kept there until the normaldark color of the as-cas t alloy is replaced hya d ean and shinv surface. T he fram e is nowready for pn-liunnary finishing and fittingto the cast . On ce again, the clinician mu stdemand that the contact surfaces an' nottouched ill allY way hy the techntclun andthat IlO fitting of the fram e to the mastercast take place in the laboratory TIl(' tech­ntcian is Instructed to finish and po lish tlt('Iramowork ill a standard fashion , !t'avillgthe fitting to t h (~ clinician. The reason forst ressing this polut is th at the tcclmlcian. illattempting 10 fit the frame to the mast e-rcas t. wil l illl'd tahly remove more nu-talfrom the contact surfaces than is required.which dec reases the quality of the tooth­frame relati onship. Once a casting ha... lx-euplaced on .1 cast , the east surface will IX'abraded and no longer accurate , so thatsubsequent fitting wi ll he clone to a casttha t does Hot ({'p resent the month.

If the cast ing is not fitted to the muste-rcas t in the lab o rato ry, then thi s respou st­hilit)' wi ll H'St with tile clinician . T lu- slate ­o f-the-art easlillg will first be fitt ed to theteet h by tho din k-ian, and only when allacceptable relat ion ship lIas been obtuiucdwill the cast ing hl~ placed on the mustercast. Should tlw cast he scraped ill thepn x'ess, it is uot a co nce rn Iwcalls(' thiswill Hot a11( '(.'t till' tooth -fram e relatlou­ship. If it is 1I0t possible to fullv seat theeasting ill th e mouth, the master cast mu stIX' re made lx-cuusc there is nu W <I\ ' to ac-

o 0

curately de termine if the ca use of tilt' mis­fit is a ll iuaccumte imprlC'ssion or a labors­tory error,

71

Advanced Removable Partial Den tu res

Bottom ofguide plate

Areas coveringgingival margins

Fig 5-7 Intern al view of casti ng, indicat ing areas requiring high

polish.

The laboratory must be instructed toplace the highest-possiblc finish on thecasting gingival to the contact area of theguide plate (Fig ;'')-7). This will require care­ful use of stones <UHl rubber wheels so asnot to abrade the contact areas. This qualityfinish is requi red, since plaque retention inthis area has the greatest potentia l for tissuedamage. In fact, this is the only area of thepartial denture for which there is a physic­logic reason for polishing. All other surfacescould [ust as well he left in the as-cast state,except that the technician, clinician, andpatient expect the appliance to be highlypolished, ,LS this is the customary finish foranything that goes into the mouth.

The clinician has two options for seatingthe casting on the master cast when theframework requ ires the additional steps ofadding wire clasps or altered cast trays: (1)the casting can he return ed to the clinicianfor the fitting of the frame and the fittedcasting sent hack to the laboratory on themaster cast, or (2) the technician can be in­structed to place the finished casting on themaster cast in the lab, always at the expe nseof the stone teeth. The int raoral fitting of

72

the framework can be done just as easilywith the wires and the tray in place.

ss ~ :sw.Additioll of Wire qasps , .1

Wh ile it is technically possible to cast towires, this procedure is primarily used forgold base castings and high- gold-conten twires. When stellate allovs are used for theframework, the wire is best soldered to thefinished Framework some distance from thepoint of flexure. Casting a stellate alloy to awire clasp or soldering the clasp directly tothe minor connector will result in a b rittleami more rigid clasp and increase the like­lihood or subse que nt clasp failure.

Wires for retentive clasp arms are mostofte n round in cross sect ion. It is possible,however, to use a half round clasp wire.There is no clinical evide nce that this formhas any advantage over the simpler shape.In fact , the half round wire is much moredifficult to adap t to the tooth; 'any hendacross the flat surface is a technical chal­lenge . The desired position relative to the

Laboratory Con struction of the Framework

Notch in

guide plate ---t-t- - lI-..,

Soldering spot

Fig 5-8 Position of w ire clasp on framework.

height ofco ntour has been indicated on themaste r cast and mar ked with a single Hnc.

The technician should he able to CUll tourthe wire exact ly to this line. For the wi r e I­bar, the clinician III l1sl ind icate just howmuch of the foot of the clasp should contactthe tooth . Usually a gpntltl bcllt12 toS nunfrom the tip of the clasp will give suffk-ieutlinear contact Lo ensure a positivp con tactof clasp Oil toot h. The tips of ei the r fon n ofwire clasp should be rounded befon- sol.d ering th em to the framework. since accessto the tip may he Itmttr-d once the clasp isin place ,

Thc wire clasp is adapted to th e mastercast wit h the framework III place,Occasionally the guide plate is notche d atthe point where a clrcumfcn-nttal clasp ,, ; 11cxtt the resin so the clasp can be positionedexact ly as designed. T he tan~ of the clasp isdirected down the guide plate and onto thelingual surface of the (';L'i ting. It ,,;11 tcn ut­nate in a positive contact a rea. either a re­tont tve mesh square that has been filll'<! indu ring the wax-up or a n-tont ive bead thathas been flat ten ed wi th a dtsc afte r casting

(F ig 5-8). In ei the r instance , the wire mustmake a positive contact with the casting ifresistance brazing is to be used to solderthe clasp. Our studies have shown that anSOO fine solder will prod uce the best jo int swhen used ill conjunction with a non­precious or a PC P (platinum, go1l1, and pal­ladium) wire. Softer wires (.'illl'h as thej elen ko Standard Clasp Wire) a re be tte rsolrk-n-d with a 10 R,h am] COIlH'lItionaI6.50sokk-r;

Hcsistance hrazing, which uttlt zes astep-down tnmsformer and a ca rbon tip toheat the solder while a copper tip com ­plc tc-s the circuit through the casting, is aquick means of soldering stellat e alloys andis used extens ively fo r repairing partialdent ure fnu ncworks (Fig 5-9). Like all sol­deri ng operat ions, the brazing is an artrather than a science and conside rable ex­pericucc is requi red to create a depend­able joint. Fortunately, the wire ,,; 11 also beretained hy the n-stn , but to do this, theportion of the win : e mbedded ill the den­ture base must have so me bends for physi­ca l n-tcnt ton.

7]

Advanced Removable Par tial De ntures

Copper tip

Solder Carbon tip

Fig 5-9 Resistance brazing to attach wire clasp to frame .

Addition of Altered CastTrays

Mundtbular distal extensions will requi re as('(.'(lntlar)" impression to relate liI(· suppo rtof the soft tissue to that of the hardt1m>ll~h th e framework. As stat ed pn '\i ­ollsly, ce-rt ain maxillary situations wtl l alsorequire a secondary impre ssion, The goalin the construction of tlu-sc 11':1\:s is to makea l ray to a giveIl outline of standard thick­Il l ' SS and with adequate n-tcution 10 theInuuc. All sharp areas mus t Ill' roundedaml .l l lY relief W:lX completely removed sothat tho tray can be inuncdlatr-ly placed illthe mouth without the need for alteration.T he borders 1II11st he uniformly short ofthe desired final denture base exten sions

74

so that the alte red east impression ca ll besatisfact orily made on the first aHe mpl. Itis reasonable to expeel thai if the cltnlctanclearlv ou tlines the desired exten sion ofthe trays and prescribes the thidllcss de­sirl:'d . tl. l 'St ' t ravs will co nform to th.. workautIIorization.

\\l lilc not us important as the uuunte­

namx- of tlu- hard ami soft tissues of th eora l emi ty in the long term. the qnalitv ofthe Iabomtory phases of constructtou die­tate s much of the potenti al for SUl'('( 'S5 ofthe R'lIlovahle part ial de ntuR', F iJl(lillg thestate-of-the-art dcutnllaboratory and build­ing a working relationsh ip wi th the teclrul­clans will always he a major factor ill thotreatment of patiellts need ing a rl'lliovablepartial dent ure. The more comp lex the par·ttal. the gn 'ah 'r tll(> need for technicians 10

be fully Involved in the process.

Establishing theTooth-Frame Relationship

SInce Ihe laboratory ted mtcinn has nottouched the tooth con tact areas of the

Framework du ring the recovery and finish­ing procedures. the responsibility for fittingthe [runn- devolves cnti relv on the clinici an.

\\'lnh- this may he interpreted hy sonn- asUllltl'('('s ~"1ry am i time-co us u uu ng . the re is110 other way to ohtain the h ig)l('st -(Ilial ityfi t of till ' cas ting and to ret ain the frictionalfi t of the guide plates on the prepared gntd­ing planes.

There :I fC three phases of this Httillgprocedure: ( 1) correcting tooth contact sur­faces , (2) o htain ing static fit ill the month,and (3) establishi ng a functional Ht .

Tooth Contact Surfaces

Since the :L<;-( "1L<;1 surface of a ste llate c:L<;t i ng

is quite ro ugh due to the porosity ami grainsize of th e refractory, th e first step is to ex­amine th e castin g unde r magnification andto carefullv remove all th e blebs on thetooth contact surfaces. primarily the gUide

plates. Because the stellate alloys are somilch harder than gold alloys, the adjust­ment of the contact spots is not easily orquickly uccomphshed . Special burs a reavailable for tlu-sc alloys. (T he Brussck-rCompany makes all Ecseries bur for thestraight handpiece intended to run at10,000 to 15,()(XI rplll. These burs ( '( lIlle in a

variety of sizes nnd i ll both regu lar and Huecut. There are also fully sin tcrcd diamondstones that are intended for lise withchrome alloys .) T he goal at this point is toremove the positive imperfections withoutehaIl J..,riug tile contact surf ace of th e guideplate. Once the blebs have been removed,the contact surfuccs are sandhlas tod LC I leavea un tfonn matt e surface to make the Idcntt­fication of int raoral con tact points easier.

Static Fit

The second step i ll the fitting proce dure is

to obtain a static fit ill the mou th, wherebythe casti ng fully seats OIl th e prepared

75

Advanced Remo vable Part ial Den tu res

teeth . Using magnifying loops and a sharpexplorer, this fit is verified visually. Theseating process begins with the use of a dis­dosing materi al to identify areas of pre ma­ture contact. Historically, disclosing waxesor a mixture of gold rouge in chloroformwas used to idcntifv these areas. Both havebeen dtscont tnued-c-the waxes becaus ethey were a mess to apply and to clean upand the chloroform-rouge mixture becauseof conce rns related to the volatility of thechemical and its toxic nature. A convenientsubstitute has been found in Fit Check er, aCC product. This very thin and quick-set­ting silicone, inte nded for evaluating the I1tof crowns, works equally well for frame­works. It klontifies contact points in a staticfit only, since it sets chemically.

For the casting that is difficult to seat, itis gooe! to rememb er those areas most aptto be in hypcrcontact. Our stud ies haveshown that the area most likclv to have con­tact is at the marginal ridge, where thetrans ition from the guide plate to the restoccurs. If the tooth preparation has left asharp line angle here , chances arc excellentthat the cause of the casting not seat tng canhe traced to this area. Unfortunately, iden­t ification wtth the Fit Checker in this areais not as obvious ,LS it is OIl the flat surfacesofthe guide plate. It is always possible thatthere are still some minor blebs at th is crit­ical junct ion that were Hot identified in thefirst step.

Functional Fit

Once a satisfactory static fit is obtained,usually afte r a number of adjustments ofthe guide plate surfaces, the fittin g of theframe is complete for all but Class Tpartial

76

dentures. For the bilate ral free -end situa­tion, functional rcltcfis required if the clin­ician wants the supporting areas of theedentulous rklgcs to hear some of the loadof mastication. Remember, if no funct ionalstress rel ief is created in the casting. eitherthrou gh the short gu iding plane concept al­ready discussed or the use of taperedblockou t, the C<Lsti ng must be relieved toallow some rotation movement around thedistalmost points of contac t .

How much stress relief is desirable?The r<· is 110 d ear scientific answer to thisquestion. It may be best to tailor theamount of moveme nt to the displacementof the areas of major support for the den ­tun; bases. When the ridge tissue is firmand healthy, lill Ie relief is needed to protectthe abutm ent teeth hom luxation. llow­ever, when the sllpporting tissues areweaker, the amount of possible base move­ment in funct ion is incre ased and theamount of stress relief must he increased.As a general rule, if 2 mm of rotationalmovement is possible at the distal extensionof the rete ntive mesh without binding onthe abutment teeth, stress relief will havebeen established . The longer the ede ntu­lous span , the greater the amount of stressrelief that must be created in the casting.

To rotate the framework, the tissue stopmust be removed from the distal extensionof the meshwo rk. If it is not removed, itwtll, <Iuite possibly, dig into the soft tissuebeneath it and restrict rotational move­mont . Next, a small squa re of Mylar-basedart iculating ribbon (Accu-Fih n 11 or similarmate rial) is cut and placed in the casting inthe area of the guide plate. This mate rial isgenerally about :30 microns thick , notenough to have any effect on the proce­dure. The casting is seated and rotated byplacing a vertical load on the distalmost

part of the meshwork or Ihe altered casttray (if one is attached at th is point ). T hedn-tncorporutcd in the \Iylar ribbon trans­fcrs easily to bo th casting and tooth to iden­ti fy the areas of heavv con tact with rotation.. .Th e l'< l~ ling is adju sted. ulwavs with ca re1101 10 remove unv more metal than is ab­solut r-ly llt 'ct'ssa l)~ unt il the desired 1Il0n ' ­

uu-nt is obta ined. The \Iylar has justPIIOllgh elastic ity to adapt itself around thetooth. I t, and the toot h. must he completelydry to lay down a crisp mark at tlte point ofcontuct.

T11 l ~ combination of parallel or "milled"gu iding planes, accurate final imp ression,am ! attention to dela il ill 11 1I ~ laboratoryshould creat e a cast ing that call be fullysea ted without eliminating the frictlonul rc­ststancc to removal of the framewo rk. Eventhe finest ea."ting can be scvc n-ly eOlllp ro­mixe-d hy ca reless fitting of thl' Frumc. Theclinician must ge t in the ImlJit of tR'alingthe part ial denture l,<-e; tillg with the samecare ,L~ would be gin'lI to a Crm\1 1 margin .

,\1Ial should one do if th e framework

does not completely seat 0 11 till' abu tmentteeth? III some instances it may lx- possibleto ret rofit the e.l.~t ing to the abut ment toothby honding on resin to contact tlw frame.T he most obvious example of rl'l rol'i tli ng is

when the casting fits everywhere exce pt for{)1I t: or two rests that fail 10 con tact theirrest 'scats . \V'hen these rest seats are illenamel il is both convcn k-nt und accept­able to etch the existiJlg rest seal. ptillle ther-nan u-l with any suitab le how ling agellt,and then place composite resin Oil the res tarea ami seat the framework. In most in­StaJK'('S , sufficient light can he transfe rredto the l.'o m pos ite by V"l l) i ng the :lI1gle of thelight sou ree to ach ieve a stable mass ofresin. Exce ss material th at lila\' have ex·tmd('ll over Ihe casting is pliminah'l! and

Establishing the Tooth -Frame Relationship

the framework is removed. Adclitionulhghtcuring is dOll<' be fore allY fintshlng prnef'­durcs an' unde rtaken. T he quality of fit ofthe IW W rest seat will he perfect becausethe spat V\1lS made to fit the existing cast ing.Other areas of the framework are not useasy to ret r ofit . hilt llsing ch emically curedcompos ites, guiding planes can he hn lllghtinto contact with the guide plate. OIlT n-­ce nt studies ban .' shO\\11 a dramatic in­creas e i ll fnc tlonal ret en tion with theseretrofitted con tact s. T hese co mpositeret rofit s ha\"( ~ stood np remarkably wdlover a ll 8- to lO-year pe riod .

In addition to filling the frame to tireteeth , the Frame must also he brought intoocclusal hunnony with the na tu ral t('d lL.The clinic ian must evaluate t ile naturaltooth stop.'i without tile partial casti ng inthe mou th ami assure th at the prpse llce ofthe casti ng has not altered th is relat ionship.Since the occlusal ami incisal rests are rou ­tinely ovcrcontourcd in the wax·llp . it is tobe expected that 0 11 some OC(.,L5iullS thecast uu-t al ruav , \"(, 11 inte rfe re with co m­plctc closure to centric occlusion. Til('elm­ir-ian should first evaluate th e thickness ofthe offendin g rest by measuring. hot h atthe cen te r of the rest and at the marginalridge nu-n. the tlucknoss of the Jlll' ta!. Tl. t·re st should never he reduced lx-youd 1.2HIm for fea r of subsequent fracture, some­times mout hs or years later. When thls d i­mcns ton is reached, furthe r udjustmeut1ll 1 1.~1 be doIl l' Oil the opposing toot h.Obviously, careful mouth preparation willredu ce the 11('('(1 fer these adjustments.

Since the occl usal surface of the rest " i llhave to be finished with rub ber wheels awlpolished after adjus tment , the met al shouldhe sandblasted 0 11 those su rfaces to maketh e idcutiflcation of the d ie mark s from tbeAe<':ll -F ilm (·'L"ie r to slXlt. It is lIot e.l\Y to

77

Advanced Removable Partial Dentures

return the labo ratory finish to the l';lStingwi th standard chairslde finisllillg stones andrubber points. T he hardness of the metalreq uires that a high -spl.'l·d dental lathe heused to quickly restore the metal to its orig­tnalluster, The repolishing of these occ lud­iug surfaces is a laboratory function andsho uld he completed before the positioni ng0 11 the denture tee th begins.

Th e additional time and effort requiredto establish the ideal toot h-frame relat ion­ship 1IIl1st be added to the total cost of cre­at ing till' ve ry Finest part ial dentures .Without this level of attention to the finalfit , the goals of ost bct!c to ot h replacementwi thout visilile anterior clasping and thesubstttution of frictional retention for claspn -teut lon cannot he achieved 011 a routinebasis. As the parti al den ture lx-comes moresophist icated wtth the uddftion (I f precisionattaclmu-nts and implants. the ability tocont ro l the interface lx'( "()IIIl'S ('\1.' 11 moreeswnt lal to creating partial dentures of thehlglu-st quality

Poor Casting Fit

lnevi tahl y, the clinici an must face the prob­lcm of a casting that cannot he brought intoan acceptable fi t in the month. Oft en it will

78

not he possibh- to determine the C, IIIS(' ofthe plxlr fi t. Th e fit of the frame on th emaste r en:..t \\; 11 ofte-n show that the labora­

tory pha...<> of construction has produced aframe that Ilts th e east ill an acceptablem anne r. If t h is is true, o ne ca n on ly con­

d ude that the error Wi.L<; not in the laboru­tm) . The clinician must then review 11)(·procedures for making the maste r lmpres­ston. I Iccl d Ial the Inaccurate master cas tcall most often be traced to patient 11I0\'( ' ­

nn-ut du ring lite se llin/!: of the al~llak ~d

or to separat ion of th e algi nate from thetray dm;ng removal of the impression. If0111.' assumes thutt he alginate was prepack.aged und mixed for the recommendedlength of tbuc and that a careful clouhlc­pour technique was usr-d 10 create the IIl ;L~4

tcr cast. there really is no othe r pla("( ~ tolo ok.

-T hf' removable partial denture frame­work is not an easy <-,L<; ting to make withprecision . Tl.l' g('olllelry of the Fnune undthe variations that can occur just Fnnu dif­feren ccs ill r-xpanston based un placcuu-ntin the l'i.lsting ring make the framework farmo re com plex than in the casting of acrown. One could well e"11ed to rind I outof S or 10 castmgs unacceptable if onesstand ards of acceptance are high. It onlymakes s{'lIse to reward the excellent n-clmi­dan if one is fortunate enough 10 find one.

Completion of thePartial D enture

Onee the framewo rk !I :L'; been properlyfi tted and found to he acceptable,

the n' lIIai lJ i Jl~ steps in the construction ofthe advanced Rl'D are- no t all that dill crcntfrom tlu- standard RPD. Ce rtainly, attcn­tion to detail in th e colori ng of tlu- denturebase ami the creation o f metal occlusal SH r·

faces mont o ur at tention. TIll' insert ion ofthe HPJ) should go smoothly if the IpH'1 of<fl wJity I.;Ls lx-en mainta ined throughout . Itis ch-arly i ll the maintenance of the pa rtialwhew the long-term success of the treat­1Il( '1l1 willb e det ermined.

Jaw Relation Records

Jaw relation records arc uonnally macle onlyalter the framework has been fit ted to litemou th ami brought in to the desired occlusalrelationship with the opposing arch.Hemr-mlx-r; if the master ca st can be relatedto the 0Plxlsing cast by simply placing thecasts i ll occlusion wi th wear [accts for re fer­enoe. this wi ll always he the IlIdl.ud of

choice . O nly wln-n this stable relationship isnot ob tainable should a reco rd he made.The most positive n-cordings are made in amaterial that is tr uly plastic for the reco r dingand then rapidly sets to a hard surf ace.Registratillll materials using zinc oxilil" wi theugenol (ZnOe ) il" a base are most U ft( '11

used. Boswnrt hs Super Bile or Blue Moussehy Parkcl l an- excellent examples of this~pe of material. T hey [('<p Lire a base of IIan iwax, trnm uod to he 2 to 3 mill out of occlu­sion. as a platfonn for the actual reco r ding.The set ting lillie can gcnerally he decn-ascdby addill~ a small amount of water or ulco­hoi to the mix. 0 111'1' set , these mate rials cunbe trinlllwt! with a sharp knife so that on lythe tips o f t111 ~ opposing cusps are vistlilc(Fig 7-1). Since the opposing CIISP tips aremore likely 10 have been accurately re pro­ducc d in the opposing ca st than ill the ful locclusal surface, the reco rd should he eil\ ilyverified when llsing this technique . 'I1Il.'hard wax base should net contact the soft tis­sue in a Cia.",,, 111 situation. Onlv on te r mi­nally edentulous arr-as is it 1U~'(~ssary to 01.­Iain some support from the sort ussue.

79

Advanced Removable Partial Dentures

Wax platform

Zinc oxide - - - -If

-47'-- --- Rec ord base

Fig 7- 1 Zinc ox ide reco rd withonly opposing cusp tips recorded.

Res in addition

_ _ _ -'V---- ' Fig 7- 2 Auto po lymeriz ing re sinsupport for record added to pos­terior meshwork.

Since t ln- Z nO l' p'1.~tes art' truly plasticfor a short time afte r m ixilll-!:, the recordc011111 thcorcticallv be made wi thout auv. .po su-rio r SllppOrt. A comprom ise between110 support am i a fullt issue base l'(),-eragecan Ill' made by pladll~ an island of all ­

topolymcri ztng resin under llit' plncowhe re the t issue stop is (or was) loc ated ,afte r the caxt has been coated with u sera­ratin~ age nt (Fig i -2 ). Th is will ree stablishthe tissue stop support of tho distal exton­sion fram ewo rk as well as sen..e as a base forth e strip of hard ,,",1.'1: that SUPlx, rts therecording mate rial.

11H're is litt le evidence to suppo rt tltt'making of a facc-llOW reco rd for the remov­uhle partial de ntu re C<1.~(~ with natural teeth

80

."'- -. -...-.- - --..• . --

in th e ()ppmill~ arch. Onlywhen th e 0Plxls­ing an ..h is a complete dentu re could an a r­gumellt he wade tor the use of'an ea r-bowor other arbitrary mounting. T he gn-at ma­jority of removable partial dentures sent toa conuucrciallabomtory for set-np ami pro­t'('ssing will nse a plane line art iculator.Protrusive records to set cond vlar iuclina­lion un- also of littl e II Sl' because tilt' planeline articulator is 1I0t adjustable.

Jaw relation records for a removable par­tial denture oppo sed hy a complete den­ture req uire a much mo re bwclved tech­ulq ue . 111("s(' records arc most often madeus a pari of'a separate appointment d lJringwhich anterior teeth will he positioned amithe basic records taken. When an altered

Wax platform'--------,

Completion of the Partial Denture

Space forrecording

..-- .___..,-J material

Fig 7·] Use of cone in wax or compound to establish occluding

vertical dimension.

cast impressio n is involved, thai impress ionm ust be made before the jaw re lat ion ap­pointment. On occasion , a suitable recordca n he made in conjunction with the al­te red cast impression'as describ ed earlie r.

Th e relatio nship sought [or the CD/BPDsituation is ce ntric relat ion , not ce ntric oc­clus ion as with the other partial denturetypes. Eith er a processed de nt ure base [orthe opposing arch or one made with a co rn­biuation of p lasticized resin (I .yn al or sim i­lar material) and fast-setting orthodontic:res in needs to be available for the centricrelatio n record. The recor d must capturece ntri c jaw re lation, a post erio r, unstruined,patient-assumed posi tion at a vertical d i­mension of occlusion that allows th e estab­lishment of an esthetically pleasing b eeheight, adequate speaking space, and somemte rocclusal space at rest, much th e sameax is requi red for a co mplet e denture .

The first step is to establish the verticaldi men sion of occlusion . A quick an d de­pcudablc method for find ing an d cap turingth is position of mandible to maxilla involve sfirst e stab lishing a length of W ,L\: rim thatwill extend sho rt of th e len gth of th e re -

faxed upper lip by2 toS nun. The patien t isInstructed to d ose to first contact and th eface he ight is evaluated . The patient mustappear obvious ly overdosed at th is time.This docs not in any way sim ulate th e ve rt i­cal position of th e anterior tee th, as too thp lacement is independent of the jaw rel a­tion record. A COliC of wax or co mpound ,warmed in a compound heater, is added tothe wax rim in th e midline of the maxilla.Th is cone is direct ed to contact the inci saledge of on e of the man dibular anteriorte eth, usually a centra l incisor (Fig 7-.3).When no natural anterior teeth ar c presentin the lower arc h , a den ture too th (incisor)is arbitrarily p laced on to th e resin retent ionin the central incis or area. The COlle is longenough to ensu re that the vert ical di n len­sion of occlusion is exceeded at first con­ta ct. The patien t is instructed to close , incentric rel at ion, into the cone until the clin ­ician tells the pa tient to stop-when theface looks neither ovcropcncd o r over­closed. The clinician th e n evaluates the es­thetic face height and repeats th e proee ­durc as ncccs s,uy. The cone is allowe d toharden to p reseNe the te ntative vertical di-

81

Advanced Removable Partial Dentures

nu-nslon record. After the ('OIIl' has ha rd­e lll·1! so that it will not d isto rt , allY ex('PSS

material can he removed so that onlv theinci sal edge of the tooth remains in therecord.

'111(' contact o f the COllL' and tln- inciso rtoot h will normallv be vts ible to the clini­d an so that tile speaking space can be ccul­uated . The amount of Sp;KX-' seen whensibilant so unds are spoke n will usually g1\'eall lndtcutio n that the 1U'(,('ssal) ' "speakingspace' Ila.s been created . Un fort un at ely,."pI'I-ch is not a gorxl Jllea." lI n ~ until all theteeth an' p rese nt in the dentures of bothard l('s and the pat ient has had lill ie toada pt to the He\V contours. Tlte cl iniciancall, however; eas ily evaluat e t lH ~ lnteroc­clusal spaee at res t hy looking at Ihp rela­tio nsh ip of the t ip of the cone and the op­posillg tooth. even if the lips haw to heslightly parted by hand to gain a line ofSight. One could expect to see anywherefr om I.,') to 6 or 7 III1lI of spa('(' al rest. withthe Class II I pat ient ha\ing the lea...1 andthe Class II the most. Finding thf' ideal ver­tica l dimension at rest requires the bal.mc­illg of these diffe rent factors. Since it isquite ch-ar thai the re is 110 exact vertical di­mcnsion of occlusion, till' clinician needonly lind an est hetic and comfortable di­nu-nsion and then verify that posit ion late rwith the trial set -lip .

T he cone, as it contacts the mandibularinciso r, will also serve as a vi:..nul indicatorof'ccntrtc relat ion for the actual recording.To mul«- the record as posili\'(' und as fool­proof as possible fo r ot hers to mount castsinto the articulator; one ca n place a molardcntun- tooth on each side of the maxillaryrim i ll the area of the first and second 1Il0­

lars (Fi~ 7-1). The eusps of these denturetee-th will imprint on th e n,('tm ling materialwith a minimum of pressu re and lean! pre-

82

Record base

Wax rim

Fig 7-4 Lateral view of maxillary reco rd base withcone and posterior de nture teeth.

cise iudentutlons so that, with the cone asthe third polut of reference , a positiverecord can he easily veri fied visually, bothin the mouth and when mountin g the Il1 ;L'i ­

te r casts. Instead of lIsing a new denturetooth for this P1 1'l)OSI \ unused teeth. alwaysava ilable in the ofllce . can he cut in halfhori zoutallv so that no mterfcrcnce \\illoccur when placing the ex ..c lusal portion

onto the maxillarv rim. This method is ul­\\<I)"S Sllp('rior to cutling grolw es in the rimand (':\.v ('cting the recording mate-rial toflow lip into the grOl)\"CS.

.Placement of Denture Teeth ITill" occlusion desired f or BPD situationswhere t!le opposing arch contains natu ralteeth restored i ll allY mann e r is one of con­tac t in cent ric occlusion only. Dlsclusion.bot h in lateral moveme nts and in protru ­sion. should 110 1 occur on the de-nturetee th. if al all possible. " 11en denture b-et hmust he in\'o IH'l1 in disclusion, as when acanme is replaced, some form of metal cnv-

Complet ion of the Partial Denture

Fig 7-5 Denture flange begins distal to the most anterior tooth.

e rage on the denture tooth must be consid­ered to eliminate th e rapid wear tha t can beexp ected with res in again st porcelain , nat­ural te eth. or restorative materials .

For those situations in which the oppos­ing dentition is a complete de nture , thepartial denture occlusion should be similarto that of standard comple te dentures­som e form of \vorking and halancing con­tact s over a range of 1 to 1.5 tnm from th ecentric position. Protrusive contacts areoften -not possible to ob tain without drasti­cally altering th e vertical and horizontaloverlaps o f the an terior teet h, wh ich wtl lmost likely he unacceptab le esthetically.

Before p lacing the firs t denture teethonto the part ial framework, considerationmus t he give n to the contou r o r th e resinflange . Since severe res orpt ion of th e resid­ual ridge is un likely to occur im mediatelyadjacent to an abut ment tooth , the Iirstden ture tooth wil l he much more lfkelv to

appear natu ral if it is butted to th e rid geand th e flange is begu n in the interp roxim alarea between the first and second tooth(F ig 7-5). A denture tooth of sufflctc nt oc­clusogingival length must he chosen toallow a natural t ran sition betw een it andthe abutment too th. Often this implies atoot h wtth a well-fo rmed an d colored rootsurface (as is found on the Ivoclar poste riortooth, for example). Should the abutmenttooth he clasped with a circumferentialclasp, th e dentu re tooth wtll hav e to hecarefully contou red to create spaee for theclasp to exit w ithOIIt e<msing an es thet icallyunaccept ab le d isplay o f base m ate rial.Should too much of the dentu re tooth beremoved fo r placement , the re sulting un­natu ral de nture IXL~e ca n be removed witha cavity preparation in the re sin and a mi­crofillcd composite p laced to simulate aproximal res to ration afte r p rocessing andfinishing the part ial denture (Fig 7-6) _

83

Advanced Removable Part ial Dentures

Denture teeth

Fig 7·6 Use of composite restoration to disguise clasp exit.

W ith the C D/ BP I>, it is 1I0t ;th'~ IYS pos~

sfble to position the denture toot h ill theideal posit ion that would he IIsC'd ill aC I)/CD sit uation. Ih 'lllai ning natural teethwill often r('quire the use of dtasrcums orerowd ing of the denture tee th to properlyiJlknligitate wi th the opposin~ complet edentu re. The mr-sful aspect of the first de n­ture tooth should not be comp r omised.

since auy extm "'paCt' here will fill wit h baseresin and be es thet ically unacceptahk-, cs­pt 'dally if the abu tment too th has a circum­I"..rcnt tal clasp. (T h is will occur prima rilywhen that too th is the pri me abum u-nt fo ra Class I or II situnt lon, because ante riorclasp ing will no t normally occu r Oil theClass I II part ial.)

T Il(' sa me mesiodista l considerat ionsmentioned abo ve can he expected to occurwhen the partial de-nture is 0PIXlS('(! hy nat­urul teeth. with o r without a partial den­tun-. In addition, the co ntour of till' oc­clusal surface of the denture toot h willofte n not harmonize wit h the occlusal sur­face of the natural too th. To obtain ~ood es -

84

tbetics with maximum cent ric co ntact , thede nture tooth may11<'1.' <1 tCI be placed h i 11)' ­

pcrocclusion and then gro und into a solidcentri c contact . \ Vh c'I1 this lIl'l'd arises, theclinician IIlIlSt verify thai a d('lItllre too th o rthe sa llie dime nsions as the natural 10011.

has lx-r-u select ed. Th p manufacturer's n -c­ommendcd mo ld, as taken from the moldgUid(' ofan)' ante rior tooth , cannot be used.as it will always be too small to allow opti­mum occlusal contact . Instead. the choiceof the poste rio r tooth mold will he madeonlv 0 11 Ihe basis of the mesiodi stal an dbuccoltugual dtmenstons of the op posingnatural tooth. In the .~ a ll H' manne r. thechoice o r cusp height is based on the COIl ­

tou rs of thr- opposing tee-th.In mo st instance s, a l -uun hyperoc clu­

sion that is adjusted into contact will he sa t­tsfacto ry The occlusal surface of th e ad ­justcd tooth must he n -con toured torecreate tln- occlusal uuatomv, usually h)'reestablish ing the groO\"t·s am i fossae withall inverted cone bur; D enture teeth shou ld

he positioned am i g lUlIIU J into sut tabl.. 0(:-

clusal co ntact on e at a time ins tead o f set­ting all thr- tooth into hyper occluslon atonce . since so me tee th will req uire agrcan-r or lesser degree of hyper occluslonthan others.

As tln- posit ioning of th e teeth proceedsposterior ly (o r anteriorly in the ca....e of theClass 1\'). the creation of small, rundom­lzcd dlastemas will usually result in a life­like appearance of any teeth that an.' vi si­hie. Likewise if ante rio r te-eth art'im'huhl, they will need to he sck-cn-d, andd,' cisiollS made as to diustemus or crowd ­ing, on the basis of the dtnu-nstou of theedentu lous area. Beca use ante rior di­astemas are unlikclv to occur i ll nile archonly, the most common placement will hein all an-a wtt b some level of crowd ing.

Hemr-mlx-r, it is H 'I)' unlikely that allY pa­tient n"l' liring anterior tooth n-placr-mr-ntin tln- mandible would han ' perfectlystraight incisors unless the patient is \ 'pry)'OIl1lg or has a tooth-arch discrepancy thatwould indicate the Heed for dlastemas.Obviously; the patient can be expect ed ton ' III( 'IIII)('r the prespnt'{· of dlastem as butlIlay 1I0t n-eal] the crowding.

Second molars would he placed in themandibular partial de nture only when theopposing arch co ntains second molars thathave the po te n tial for continued eruptionor the oppo.~i ll~ arch is a compl ete dentureand the patient is severely Class III. III themaxilla ry arch the second molar lIlay bepartially visible ami therefore should he re­

placed.For the n-movablc partial ck-ntur o op­

pOSI·t1 hy a co mplete denture (almost al­ways C J)!HPJ» ), some decision on the oc­clusal sche me of the combined prosthesismust 1)(' made. There is no 1'\idl'Il('l' thatone fon n of occl usa l arrangement Is SlIpe­

rio r to anv other. hilt for esthe tic reasons

Completion of the Partial Denture

some form of cuspcd tooth is usunllv indi ­cated becau se a llat too th may he difflcuhto harmonize with the remaining naturalteeth . PerllapS tile lmgualized arrangemen tis the most ndaptnblc.

Final w;lxill~ uud waxing for try-ill.should that II( ' indicated. must be idcntlcul.except that the final waxing Includes seal­ing the pcrpln-ries. Unfortunately. w;l\ ingfor try -in is often done i ll a casual numner,which does not allow the clinicia n to fi lllyevaluate the final form and esthe tics o f tIlt'denture , TIll ' wax-up IJIIlSt always be " val­uated off the cast to en sure that adequatethickness of has f ~ material will he avatlubloafte r finishing uud poltsluug. Any areas ofpo tential sore spo!.'i, as migh t he found ad ­

jacent 10 a sharp mylohyoid ridge . shouldbe overwnxcd an d then rcco ntourcd i ll thefinal resin once any proble ms of pn'ssllrt'SIX)ts han - (w e ll eliminated. Any lla ll~(,

area for which t inti ng of the denture base­material is plan ned must be waxed to e-x­ading contours. since the tint ing \\; 11 II(~

supe rficial aud easily alte red by recontou r­ing . Those flange marg ins that will be visl­hie must he waxed to a Yt'I')' thin marginand should II(! slightly curved as they p ;L'iS

vertically, since a straight line will tend tobe 1lI0rt' visible than a margin th at flowswit h the con tours of the tissues. A~ a [luulstep in the waxing of the denture base , alltraces of wax must he removed from tIleexposed denture teet h. This is normallydone wit h a sharp ca rving inst rumen t, suchas a \Valls carver. Further lise of the flamewi ll result ill a Ilash of wax, so i l should heavoid ed. Th e object of this final w;lxillg isto create a surface thai will require no flu­ish ing, o nly a light po lishing. since any fin­ish ing ope-rutmn will remove so me of theou ter surface of 11u-> tooth and tln- tinteddenture base.

85

•Advanced Removable Partial Dentures

Denture flask

F shadeinterproximal

E shade over all

H shade onroot eminences

Fig 7-7 Dentu re base tint ing guide for fair-skin ned patient (DrPound).

=",...,..,.......,..,.-,'-,...,..""""",,,Flasking, Tinting, a,ndPacking .

The laboratory procedu res of flasking andpacking the removable partial denture aremore complex than those of the completedenture and, except for the tinting of thedenture Lase, are not high ly technique sen­sitive. Since there Illayoften be many smallareas of isolated base resin, a split packingof the flask is used . The technique of splitpacking impli es that a sheet of ce llophane,wtth resin on both side s, is kepi betwee nthe halves of the flask up to the fina l closu reof the denture flasks. This procedure en­sures tha t the resin wi ll not pull out of theinte rproximal areas or from around clasparms during trial packing. At the final clo­sure, the cellophane is removed and thetwo resin surfaces are moistened withmonomer to ensure a complete hond o

Th e tinting of the llange is one of th etec hniques that makes the difference be­tween a stan dard den tu re anti a state -of­the-art prosthesis. As part of the tinting ofthe den tu re base, conside ration must be

86

given to opaquiug the cast ing in areaswhere the grayness of the metal may showthrough thin sections of the flange. Resinsassociate d with the 4-:\I ETA bondingagents can be used to bond on a thin layerof opaque that is suitab ly colored , but ex­perimentation with coloration wtll he re­quired between clinician and technici an.

Certain ly, tinting to accurately matchthe patient's gingival color is a matter of artrather than science and, unfortunately,som eth ing that ca nnot be done at thechair. Superficial tints are available butthey a re only temporary in natu re .Definitive tinting requires that the tintedre sins (availab le fro m Kay-See Dental ~I fg

Co, Kansas City, :\10, for Dr Earl Pound 's"sift in" technique) be placed in the flaskand blended from the outside inward be­fore th e regular base materi al is add ed (Fig7-7). Th e clin ician interested in developingth is aspe ct for the "advanced" partial den­ture must create a series of shade tabs inconjunction wi th the dentallaborato ry thatwi ll process th e resin. Th e Kay-See kit con­ta ins five vials of colored polymer thatrange fro m a very light pink used to tint

Dentate cast

Completion of the Par tial Denture

Plasterremount base

Fig 7-8 Remount cast for RPD.

area s of Hnnlv attached nssuc over thenecks 01" tee th , to a dark, heavily pi~~

mented co lor that is compatible withdarker lint ing pattt'ITls. The kit also co n­tains n'd flocking thai call be placed in theareas of unattached gingh '"i.t to simulateblood vessels. The short lloc'king that isco m moulv found in den ture h,L....· mate rialsdot's 1I0 t look natural , especially when itappt'ars in the marginal gill~oiva ill a ran­dom patte rn. as can be expected with stan­dan I packing techniq ues. This t)p e offloeking does, however, add colo r to ot he r­wise purtially tran slucent materi al. Wh e ntho tint s are p laced in the outer surface oftho base and backed lip with the standa rdresin, the end result can be indist iuguish­ahh · from natu ral tissue . Since a naturalappt'aralll'l' of the \lsihle denture base iscritical to ideal esthetics, mash 'I)' 01" thetinting pmcess is an essential ('o mpo nelltof an advanced len ' ! of p rosthodont lc care.The instruct ion s that come with the tintingkit provide sufficient gllidam.'(' for choos­ing the appropriate colors hut do not covertile fine poin ts of their applica tion .

Because the denture base adjacent tothe dent ure It'd h has been carefully w,lxt,dto the desired contour, the final finishing ofthe finished denture base should requireonly the removal of the O,L<;h From thepacking and the possible slight reshapingand poli shing of the dent ure bo rders.Finishing aud IX llisl.ing of the junction oftilt' denture tooth and the base should lit'kept to a minimum for the most esthe ti­cally pleasing result.

Should the part ial denture be Class I orII and opposed by a complet e rk-nturu, aremount cast mu st he mat Ie for the Hnlslu-dp rosthesis. Occasionally, the den tate por­tion of the master east can be salvagt d indeflasktng 11I lt, more often than not . thecast is dest royed in the process. A se-condpour of the dentate portion of 11K' fl nal im­pre ssion is perfect ly adequate for tilt' rc­mount C'L<; !. The finished part ial is placedon the dentate portion. and a pl aste-r hase isadded to suppo rt the distal extensions (Fig7-8). Any undercuts present in the denturebases must he blocked out before pouringthe plaster 1.,\.<;('.

87

Advanced Removable Partial Dentures

.Insert ion

Because of the care taken to make the al­tered cast impression, there should be littleadjus tment of the denture base at insertion.F'lange.~ of tooth -home segments should beshort of any undercut areas. Pressure-indi­cator paste will identify areas of possiblesubsequent sore spots, but it is important toremember that the correla tion of a visiblespot in the pressllre paste and a subsequentarea of soreness is not 100'l(). Therefore,some thou ght must he given be fore remov­ing dent ure base material. The most com­mon areas that require adjustment areareas of tissue undercuts, below the heightof contour, normally found adjacent to theterm inal abu tmen ts (Fig 7-D). The guidingplanes will dictate the path of inse rtion.The resin in these usually minor undercutsmust be relieved even if the undercuts donot initially hinder the full seat ing of thedenture. The soft tissue ill these areas isusually quite thin over the bone and tightlyhound. To avoid traumatizing these tissues ,the partial denture should never be fullyseated at first. Rather, pressure-indicatingpaste is paint ed on the resin, and the partialis seated until the first slight resistance isfelt or the patie nt feels pressu re. The par­tial is removed and adjusted, and this care­ful procedure is repeated until the partialfully seats without any feeling of p ressureor rubbing expressed by the patient. Bystart ing the flange of the den tu re base dis­tal to the first de nture tooth as was de­scribed ear lier, some of these problems canbe eliminated.

Retentive clasp arms lIlay have been dis­tor ted in the deflasktng process and may re­quire adjustment at insertion. Bathe r thantrying to overadapt the clasps, the pat ient is

88

Fig 7-9 Cri t ical undercut area generally requiringadjustment before seating th e RPD.

better served by leaving the part ial on theloose side with the explana tion that the ini­tial goal is to have the part ial only minimallyretentive. Since all prosthodontic patientswill have at least one post iuscrtion visitwithin the first few days, furt he r adjust­mcnt of the clasps can he done at that timeif the patient finds the initial retention in­adequate. Most patien ts wtll understandthat having the partia l too rigidly attachedto the remaining teeth is not destmble inthe long run.

Occlusal adjustments are almost alwaysrequired at the insertion appointment.This should he looked on as fortuitous he­cause the absence of p remat urities oftenmeans tnfraoccluston, which can only becorrected by the addition of metal oc­clusals . The patient should not be releasedif t he natural tee th arc not back in COlitactwith the opp osing occlusion , unless sometype of overall onlay casting has been de­liberately selected to increase occludingvertical dimension. If the patient has a par­tial de ntlife in bot h arches, the partialsshou ld be adjusted one at a time to naturaltooth contacts before attempting to place

Completion of the Partial Denture

Adjusted occlusion Silicone mold Preparation

Wax sprues

Fig 7·10 Sprue leads atta ched to build metal oc­clusal surfaces.

bot h partials i ll the mou th for final adj ust .men t. Anv casilv visible natura l tooth con-, ,tad ca ll he chosen as a witness mark 10 hesure that nat ural tooth contact occurs,both in cent ric occlu sion and ill excursivemovements.

A po stlnsertt on \lsit within 3 days of theinsert ion appuintment is essential to com­plc-te the insertion procedure. If all aspectsof co nstruction have been uccompl lshcdwith care, the re is seldo m need for allY ad­

dtt lonul I)(Jst inse rt io n apI)()illtllll'lltS. T ilepa tient can he placed on a wcll-dcfhn-d re­call program at this po int, realizing thatonlythrough regular recal l and rocvalua­tiou cnn the full li ft) of the part ial de nt ure[x- assured.

Metal Occlusal Surfaces

\ \l len the removable partial dent ure is op­P O S( '(! hy natura l teeth or fixed n-storu tiuns.consideration must be given to p mted:illg

Fig 7·1 1 Silicone mold to dup licate occlusal sur­faces.

the occlusal surfaces from the incvtt ahlewear that occu rs. There are Illany tech­niq ues for fabrieating met al occlusions.Perhaps till' most dependable method is toallow the patient to wear th e new part ialdenture for u mouth or so to be ce rtain thatthe chosen occlusal scheme is approp riatefor that situation. At that point, the patientreturns and the part ial is placed back on there mou nt cast, if one has bee n made fo r ud­justlllt'll t at iusortion. Sprue leads of 6­gauge round wax (or similar W ;LX forms) areadded to Illl' oc clusal table, one at the mostposterior cusp aIH] one at tho most untortor

(Fig 7-10). Th eil a stlfcone mold is mad e orthe occlusal surfaces of the denture led h toinclude the sprue leads. Using a resin fill ­ishing bur; the occlusal surfaces of the dell­ture tee th are red uced by a un iform 1 111111 .

including tho groon's_ A Scnnu-dccp (1. ' 11­

tral groO\-e is cut into the teeth (and, illsome instan ce s, extends into the denturebase materi al). Th is groo\·e should he wideenough to O(1:Upy a thin! of the bucco­lingual \\idth of the teeth (Fig 7·11 ).

89

Advanced Removable Partial Dentures

Pattern

Retention groovecut in wax

Sprue--/-l~

Fi g 7- 12 Sprued wax pattern w irh retent iongrooves.

The occlusal sur faces of the dentureteet h and groove are lubricated with a St'P­arating materi al, and the silico ne mold rs)are replaced on the partial. Molten tnlaywax is Injected. using an eye dropper, intoone of the spmc leads until \ \,LX is S(>("II

coming ou t the opposi te spm c. wlu-n thewax has c{lol(',d, the silicono molds are re ­moved ami allY voids or de fect s are ('01'­

rected with uddttt onal W ;LX. I II partials lorwhic h no remount cast was made, the W;LX

contacts mil he verified in the mouth.Wlrcn the desired occlusal contacts are ob­tained, the \\,LX occlusal block is teasedfrom th e den ture and sp rucd from the un ­derside of tilt' ce ntral groo\"( ~ with suffk-icntspnw leads to assure a complete cas ting.Before inn'sting the WiL'\: paltcm s; a n-teu­

t ive groove is cu t into th e bulk of wax thatextends into the ce nt ral groove (Fig i - 12 ).The pu'1X)S(' of this groove is to ensurephysical reten tion of the G.lsting in the den­ture base. A 4 \IETA-~ve hondin~ agen tcan he applied to the e<l"ting as an addi­tional ret ent ive measure. T he partial dr-n ­ture is cleansed and rein se rted , and tln- pa­tien t is dismissed. Since it will take only aday or two to invest , east, and finish the

90

cast ing. the patient can use the pa rtial in anormal fashion cer-n if mastication is some­what compro mised .

\\~h (, 11 the castings have h C('1I finished.the pati ent returns and the partial is placedO il the remount cast (i f one oxlsts) to com­plete the p rocess. The tooth-colored resinthat \\i ll he used to join the casting to tileteeth wi ll he \iSCOllS , so additional space forthe re sin will need 10 be created by n- mov­iug u small amOUIII of tooth substance ove r­all. The emoting is tried into the prepa rat iolland if tile occlusal contact s are satisfactory,tooth-colored resin of the app rop riat eshade is mixed ami placed in the groove, Oil

the other prepared surfaces. and in the rc­tent in ' groove O il the casting. The casting isforced to place by d osing the urt lcularor 10the original occlusal vertical dnucnston.EX(1'SS tooth-colon -el res in is removed antithen a stout rubber hand is place d aroundthe articulator 10 hold the casts ill occlusionwh ile the articulator is placed i ll the pres­sure pot. After f1 11 i.~h i llg awl poli.~ hillg, th emetal occlusal surfaces can he expected toadd conside rable lili:' to the re movable par­tial denture. T he only potential pro blemwith this procedure Is that then' will he m i­croleakage at the metal-resin interface th atwi ll. in time, le ave a dark line i ll the res in.By using a hon ding <lj!;ent, this line can beclimiuntccl or Wl'atly redu ced .

Depending OJ I the opp osing occlus ion,the met al occlusal su rfaces need not coverthe entire occlusal surface of the dentureteeth . They may, in fact. lake the form ofla rgt' C hL';S I resto rutious. \ \11('n tile oppos­ing occlusion is a complete denture. th e lin­gnal cusps of th e poste rior t("('11i can bemade in metal lIsing the same technique. Alingualizl'd occlusion that virtually climi­nates occlusal wear for the expect cd Itfe ofthe dentu res call be created for the patient.

Long-Term Maintenance

L ong-te rm maintenance o f a part ial t1CII­lure constructed to the highest standards.as described in this book. will he minimaland limited to the occasional readjustmentof retelltin- clasp anus and precision at­tachments. Hcsilicnt attachments can heexpected to need replacement 0 11an annualbusts. Helmes of di stal ext ension bases andareas Ill' recent extraction will he requ iredwhen indicated. An evaluation ur lhl~ fit oftho resin dentu re base must lu: a purt oftheunnuul recall appoinlmelll.

or far grea ter importance in the recalland uudutcnancc phase uf treatuu-ut is thecouttnucd management of hotlt the pert ­odontul ami resto rat ive components.Excellent studies indicate tha t the lift· ex­pf·<.1ancy of a remova ble pa rtial denture canhe increuscd towanl20 years if the suppoI1­i ll~ structures can be maln taiued . He-

Completion of the Partial Denture

me mber, the part ial den ture patient has al­ready demonstrated some degree of inah il­ity to man age his/hr-r own disease p mc'('ss,"ill 1 the exception of t rau matic and congcu­ital n ced s for care. In the first year after ill­sert ton. tln- patient should he see n at ei ther3 or 6 mouths to evaluate the n'sponse ofthe tissues to the partial denture. An t"SS('Il­

ttal part o f this recal l is the evaluation of thepat ien ts ulnlity to dean not only the T\.'­

maining teeth, hut the partial denture aswell. The lise of a solution of vege table dyeto stain the partial will gene rally indica tethose areas where plaque remains . Ollcu ,the clin ician will find that the patient haslost the dent ure brush that is normally pl'O­vidcd at the insertion ap pointment am i isIryi ng to cle-an the partial with a standardtoothbrush thut mav not have bristles of suf­ficicnt length to gel into all areas. Th e stan­dard of clinical r-are has not been met unti lpa tiellts ha ve proWll their alu li tv to keep thepartial free From accumulations of plaque.

91

Repairs , Additions, andRelines

M any of the necessary repairs and ad­d itions to a removable part ial dell­

ture will bv nccc ssitv I~ made in the den -. . .'ta l laborutory, It is Incum ben t 0 11 theclinician, however, to he knowledgeable i llthe area of framework repairs am i to fullyuudcrstund the clinical requtn-mcnts IHX'­

l'ssar)' to pre'pare the prostbests for thelab­oratory n-pnir.

Pick-up Impressions

Th e clinician will be responsible fo r rr-lat ­i llg tlil~ part ial to the mon th ami fi ll' captur­ing this rc-luttouship in th e pic-k-up impres­sion , rq.~anll (' ss o f the t)11P o f n 'pair Of

addition. To he certain that the part ial den­lure is fully seated during the hnp rcsslou.the clinician will often be n-qut n - d10 holdthe partial in positio n while tilt, im pressionis lX'ing made. This requin-nn-n t m-cessi­tutcs a sect ional impression. Fortunately,repairs are aImost always confined to onespecific area of the denture, so that a pick-

up impressio n that covers only the 1111<1<1­rant in qu estion "ill allow the purtial to heheld firmly in position. In some Instances.an assistant will be req uired to seat the traywhile the clink-ian maintains the compo­nents in positioll. \\1IL'n a pick-up impres­sion, almost always made in Irreversible by­drocollotd . is fully set , eye ry attempt shouldbe made to remove both the impressionand the partial together; Should the algi­nate separa te from the partial, the clinicianHlUSt he ce rtain that the prosthesis hasbeen fully reseatcd ill tile impression. Tlliswill sonu-timcs require sma ll am ou nts 01"im p ression mat erial . \vhich Hlay have ])('('11

bent under t lu ~ part ial during rcinsert ton,to be cut from th e impression before thtl\x lur ing of thl' rq l<lir cast.

when pouring t ile repair cast, only t i le

p0l1ioll of tIlt' a rch that relates to th e actualrepai r Heed be reproduced on the cast . Aslong as there is sulllc tent COilS! struct ure toensure that the technician call (('IIIO \"(' andreplace the S<'gIlWllt(S) accurately, the re isno a<I"antagL' to I la' i llg a larger coast. In fad ,it is often easier to wor k with a partial L':.L'i1,

93

Advanced Removable Partial Dentures

since st'atiug the repair on amlolT the castis factlltnted and the po ssibility of cast fmc­tu n - reduced .

Resin Repairs

T he Heed to repair only a resin portion ofthe prope rly constructed removable partialdent ure is usually related to an accident i llwhich the patient has dropped the part ialami SOJ Il (~ pa d of th e de nture l-ase frac­tun-d. \ V'hen the broken part is available, itcall usually be reposit ioned exact ly basedOil the Fracture line. It is then a simple mat­te r to submit the denture ami the fracturedresin to the lab o ratory for repair. Oc­caxionally, the patient wtll attempt to repairthe fracture using the dreaded Super Clue .Once this material has been placed on theresin, accurate repositioni ng of the twoseglllt' llts is u sually impossible. In this in­stance, the Super Clue is removed wi th anacrylic bur ami the rem ainder of till' den­tun- base is prepared for a reline impres­sion .

App roxtmatelv I mill of dent ure resin isremoved from the entire tissue sur face oftIl(" fractured denture base. and the missingor broke-n area is re formed Ilsin!-!: !-!:ray orgree-n slick modeling compound. Once th eborders (If th e defect have lx-cn c'orrccrod,1 IIllll of compound is removed from thetissue slde of til e add ition and a wash relineImpression is made ill the aff('ded de nturebase. The wash impression can he made in

any free -flowi ng im p ression materi al. Thecomple ted reline impression is submittedto tilt' laboratory; a cast is poured al!:aillStthe impression, and the reline and repairare completed at the same time, eithe r in aI lask or a reline jig. By comhining the repair

94

wi th a rr-lim-, all accurate tissue su rface is

ob tained regardless of the fract u re site.Another common repair situat ion is the

fracture of an isolated den ture tooth, al­most always caused by inadequate frame­work de~i~ 1 ami construction. Since them use of tlu- Fract ure is in the framework.no successful. long-term repair can ill>made without either remaking the specificre ten tive componen t or IIsing 0 11(' of themodem resin-to-metal bond ing agents (4­~IETA) . Since the cos t of f('lI1 akilll!: am isoldering 011 a pro per retentive clement "l"preaches till' cost of a new casting. thebonding agl'llts offer an inexpensive andapparent ly dependable me thod of slugletooth repai r. TI ll' proper use of these bond­in g; agents is te-chnique-sen sitive. the man­ufactu n-rs instruction s must he followed tothe le tter.

Metal Repairs

Th e most common metal repairs arc associ ­

atcd with Fractu red clasp arms. For themost part , these fract ured clasps can he n-,placed with a wrought clasp. Emhmsurcclasps ami clasps emerging from some sin­gle-tooth edentulous spaces are t]n: {'M'('P­tions to the rule alit! may no t be n-pamhlo.Whenever possible , a fractured cast cir ­cumferoutful clasp, the most commonlyused clasp. should he rep laced wtth auinfra blll!-!:c wire- clasp, since the replace­ment clasp will be contained enttn-ly in tileresin of the dent ure base and 110 1 involvethe occlusal surfaces (Fig 8-1). \ \ 'In-n infra­bulge clasps are added as the repair clasp.the technician IIIl1St he rem inded that theapproach ann of the clasp must not contactthe gingiva if the p artial can he expected ln

•Repairs, Additions, and Relines

Broken clasp

Fig 8-1 Replacement of a circum­feren tial clasp with a wire l-bar;

Tape 0.3 mmFig 8-2 Adhesi ve tape square usedto keep repair clasp off t issue.

rotate into the soft tissue, as it would if itwere a Class I partial. Instead , the claspshould he pos itioned so that it is slightlyll\vay (0.2 to 0.:3 mill) from th e soft tissue(F;g 8-2).

Before making the pick-up impression,the cause of the clasp fracture, if known ,should be evaluated . It may be that theclasp was poorly designed or const ructed,that without so me additional mouth prepa~

ration the situ ation cannot he improved,and that the repai red clasp \\111 itself frac­ture in the future. This is most commonlvseen ill circumferential clasps where insu f­flcicnt space for the clasp was created dur­ing mouth p reparation and the clasp arm or

shoulder was adjusted to allow full occlusalcontact of the opposing teeth. The adjust­ment created a thin spot that became apoint of stress concentration and resultedin the fracture. The th ickness of the metalat the fracture site can be measured and , ifit is less than 1.2 mm, add itional mout hpreparation must be accomplished beforethe impression. For similar reasons, othertooth contours arc modtflod to the idealform, line angles arc rounded , and exces­sive und ercuts are reduced as an essentialcomponent of the repair procedure.

After all ind icated mouth preparationhas bee n done , the pick-up impression ismade . Again, the need to maintain the par-

95

Advanced Removable Partial Denture s

Fig 8-3 Ungual access for circumferential repair wire.

Hal in its ideal n -lation to its support ingstruct ures is essential, since the fracturedclasp may eli minate the poss ibility that thepart ial will stay i ll place for a full-arch im­

pres sion.Huthcr than sr-nd the pick-up tmpn-ssiou

d ln-ctlv to the tcclmician. the clmicianIllI ISl pOllr tile cast ami remove the dentureafter the stone lms se-t so that the contoursof tile stone ab utment tooth call hl' sur­vcycd and the gauge and position of the re­placem en t wire clasp determined amimarked 0 11 the cast. The same standards ofclasp construction discussed in earlierchapters apply to the repair clasp:

\Vllen the clasp in question does not!l:lve an adjace nt acrylic nan ge of suitablepropo rtions to allow the place ment of aninfrabulge chesp, the n -palr will requ ire actrcumferenttal (..lasp. This rep'lir wi ll ill­volvo the opening of tlu-occlusal surface ofthe denture tooth udjaceut to the repair sothat the wire circum ferential clasp can hebrought transocclusully to be emlxxkk-d intile lingual resin of the den ture hasp (Fig

96

8-:3), A~ a resul t of the prepa ration of thetransocclusal groove, the occlusal surface ofth e dent ure tooth wtll uood n' pair as well.To ensure tlmt the repaire-d partial dent urewill huvc proper occlusal contact in t h i ~

area, tlw opposing den ture or east of theOPPOSill~ teeth should lx- sent to the lubwith tlw n-pair cast so that the tcclmici uuC<.Ul restore the occlusal surfaceis}involved.

Ti ll' fractured e mbras ure clasp may her epaired by sectioning the lingual minorconnector a few m tlltmct crs below the 0('­

clu sal surface before making the pick-upimp ression so that the minor connectorweld is not placed in all area of occlu salload (Fig H-4). The lalxirutory can thenblock 0 11 1 the cast and du plicate, wax, andcast a replacemen t em brasure clasp. Th isclassp, wln-n finished and polished. C:.Ul hewelded to the framework to complete therepair. Unfortunately. the cost of this ~l>e

of repair is high and totally dependent 011

the weld for longevitj-Iu most of these sit­uations, it is advisable to re make the partialden t l i re .

Repairs, Additions , and Re lines

New casting

2==::,~~:=~_ Solder joint

Fig 8-4 Repair o f em brasureclasp,

Investment

Repair cast - - - -t"t+-

Fig 8-5 Replacement of brokenocclusal rest.

Waxed rest

-.i~- Sprue

Solder joinl

The same proced ure of sedinning themin o r COlli lector first is used for anot he rC0 1l1 1110n r(-'pair situation, that of the- Frac­tun -d occlusal rest . This tn>t· or fract urecan almost always he blamed 01 1 inadequatemout h preparation th at leaves a marginalridg{' reduction of les s than the 1.2 lI l1l l

ment foued be fore . Tile tech nician ca ll wax

the replacement re st direct ly Oil the lubri ­cater! n-patr cast . The rest is sp med with asmall round wax spm e lead. and a smallamoun t of appropriate c1l<; ting investmentis pain ted O il the wax (Fig; 8-5), Once theinvestment has set, the en tire asse-mblycanbe teased from tile repair cas t and added tosome othe-r partial d entu re framework cast -

ing fo r final investment and cas ting. T ilefinished res t add itio n is polished and joinedto the partial using 800 fine solder with aresistance brazing device as a heat source.Th is type of sohIl'r ing is an ali Iorm and re­quires constdcrahle skill and experfcuco.High-qualit y laboratories with a reputationfor rernovahle partial denture fram eworkscan he expected to have such skills avutl­ahle 10 the chuiciau.

The addt tfou of a den ture tooth to thepart ial to replace a natural toot h los t todecay o r periodon tal d isease is also a co m­mo n re pair situa t ion. o fte n one that couldbe considered a real emergency if th e too thhappens to he all ant erior. The tooth can be

97

A dvanced Rem ovable Part ial Dentures

Solder

Replacementtooth

"'If-- Nr-Cr wire

New cas ting

Solder joint

Fig 8-6 Addit ion of retention and denture toothto lingual plate.

replaced as an addition after the naturaltoot h hit'> been extracted and initial healinghas tukr-u place or, and this is often the prp­Icrn-d way, as an Immediate replacementfollowed by the extraction. In ei ther caw,the l'xisting framework must hi' c..rpable ofsnppo rting the addition. As discussed ea r­Her; 011 1' indication for a lingual plate iswln-n the potential for toot h loss exists.\\111'11 a lingual plate is present, tilt' best re­sults a re obtained by d ri lli ll~ Iwo smallholes ill the plate and soldering a smallloopof wire, usually one or M , Cr, .md Co, intothe holes so that th e loop is internal to thereplacement denture tooth (Fig cS-6). Thisfonu or retention will he as strong as onethat is part of a new partial fnuncwork\ \1lt'1I110 lingual plate exists and the re is in­sufficien t adjoining resin to retain the de n­tu re tooth , a cas t additio n is indicated (F ig8-7). As in the replacement of the brokenembrasure clasp. the cost or a quality repairIllay approach th at of a new c..lstiu g. Again.and O il a tl'lIlpomry basis, the -1 -:\1ETA

98

Fig 8-7 Addit ion of cast retention to lingual bar.

bonding agents can he used to add a toot hto the metal framewo rk.

Fractures ofmajor connectors can I I( ~ rc­paired by IIsing 800 fine solder and tlu- rc­ststancc hrazillg device. O b viously, themandibular bar will be the eastcst majorconnector to weld. since it offers eilsy ac­cess ove r a limited d istance. vlaxlllarvmajor connecto r repairs are seldom worththe effo rt. The need for a major connectorrepair results more often from distort ionrather than from outright fracture of litemetal. Th e pat ient who drops it part ial andthen step s 0 11 it can expect it not to fit allthat well [rom then on . In an emergencysituation. tl](· maj or connector call he Sq);l ­

rated \\11 11 a th in disk at the point or t ilt'

perceived bend . if bo th segmen ts fit t ilt,

mouth in all acce ptable manner, it is worthmakin g til l' pick-up impression and selldiugthe case off to the laboratory for wplding.Beyond this. major connector repair is notpractical.

Restorations UnderExisting RPDs

It is Hot unco m mon for abutment tee-th to

req uire some form of restoration du ringthe life of the- partia l denture, The two- orth ree-surface alloy restoratio n that [rae­tures at the isthmus is difficult to placeunder an existing partial and maintain pos­itivc co ntact with the rest. III these ill­stances, the tooth usually requires re­pre paration of the box form 10 wid en. ordeepen. Of some combination of the two, toensure that al l adequate bulk or amalgam ispresPll1. These re storat ions may also hemade in composite if th e cltnfcfun is (' 0 111­

fortahle with its lise in the poste rior. Sincethe composi te filling call he lay(·n·1! into

the cavity; the final contact with the rest orothe r COlllpolIl'n ls of the part ial c..m bemad", after the R 'IIIO\ ,tl o r the r nblx-r da mand mat rix. Ligh t activation or tln- c:ompos­tte is usually po ssible in a t\\"o-sta~(' pnx't-sswhere the material is first adi\·alt'C.l withthe partial in place . This will usually set thematerial sufflcie ntlv to allow n-mov't11 o r theparti al denture wit ho ut d isto rt ing theres to ration. Additionallight Cllri llg with IIrepa rtial out of the mouth completes therestoration .

For 11105(' situuttons in which a completecomposite restoration is not indicntcd. acombiruu lou of alloy and composite can 1)('used to support an occlusal rest. Afte r theadditional mou th preparation, the alloy ispacked in the usual manner am i then adovetailed bo x in the area of the rest isformed (Fig 8-8). Chemically curing COIII­

posite is placed i ll the box. and the partial isfully seated iu the mouth until completelycured. This combination of restorativ e ma te­

rials will allow the creation of a positive res t

Repairs, Additions , and Relines

Composite

Amalgam

Fig 8·8 Composite and amalgam combination toretrofit rest.

seat contact . SO llie limn of mtcrofillcd re sinis Ind tcuted in these l"t' ll< lir situations rathe rthan anv of the hcavilv filled materials.- -

Crowns Under ExistingRPDs

In n lany situat ions, res to ration of the toothwit h amalga m or composite will not be ad­eq uate to sup port t11(' pa rtial o r to properlyrestore the too tli. Some tHle ofvcru-crcd orall-metal (Town will he ne eded. (;011 ­

stru cting a cr own lim ier an existi ng part ialdentu re is not al l ('asy task and , if it is not

done to perfoctlou, th o part ial will not seatpassively Oil the tooth afte r cementati on ofthe crown.

It is essential thut sufficie nt tooth st ruc­ture be le ft to allow for bo th retention amires istance fo rms. since th e pote n tial load­ing of the uhu tment tooth can be expectedto be grea ter than for an uninvolved tooth.If Inadequate tooth struct ure remains , tlu-nconsideration should he gi\ -en to eit he r sur-

99

Advanced Removable Partial Dentures

gical crown leugthcning or orthodo ntic ex­trustou. On ly as a last resort shou ld en­dodont ic treat ment wt th post ami co re beconskk-n-d. since the failure rate for th isapproachwtth partial denture abutmen ts ishigh .

In almost all these repair situat ions, thetooth will be prepared for a full ('m\\11. T heclinician must \"erif)' that sufficient toothstructure has been removed to allow a min­un um of 0.5 1I111} of metal on thl' axial wallsand lip to 2.0 111111 on the occlusalsurface ifan occlusal rest is invnlved.

As ill other repair situations, the imprcs­siou must he made v..ith the partial denturein its proper relationship tothe support ingabut nu -ut teeth. This requires a section alimpression wi th the cl inician holding thepartial ill position while the assistant seatsthe sectional tray. The actual imp ress ion ismade hy removing the retraction cord andinjff1ing the low-vi sco sity imp ression rna­teriul ofchoice completely aronud the mar­gin of the preparation. A small amo unt ofImpression material ca ll lx- Injected ontoti lt' n-malude r of the prepared toot h. Anexcess of mate rial might rest rict the fulls('ating; of the partial.

Th(' partial denture is st'ait'd ill themou th, ami additional mate rial is syringedonto the p repa red tooth ami into tl](' spacebetween the tooth and the partial. Oncethe space is filled wit h the low-viscosi ty rna­terial , the sectional tray can ht' sea te-d. T]listray must extend 011 either sicl( ~ of the re­pair area so that there will he snflick-nt nn­pression material to lock the parti al into theimpression. ' n il' impression and the partialmust he n-movcd at one time because thechance of being able to accurately reposi·tion the partial into the impression is U11­

likely. The master cast is then poun-d, ci ­

ther by the clinician if the parti al is to be

100

returned to till' patient, or by the tcclmi­d an if the partial is to be kept in the lebo ­m tory for the construction of the (' 1'0\\11.

\\1u'n pouring th e master cast, it is cri ticalthat the stone lx-poured directly against allparts of the partial denture wi th th e ex('('p­lion of clasp arms, precision attachments,and undercut s in the resin areas. T his " i llallow a pos itive- seating of the casting d ur ­ing the co nstr uct ion of the repair ('m"11 .

If the patient can do without the partialden ture for the time that it takes to coin­

plete the n -p.iir, then the tcchulcfun III'I'd

only margina lc ~ the die and W,lX the crown tofit the fmnu-work. This is usually dono byfirst \,axing a th in coping to rho margins.Th e casting is then seated on the cas t. allt lmolten wax is no\\,('(1in the space lx-twccnthe coping ami tln-eas t in~, using a ghss (' )"l' ­

dropper that 1m'> been warmed ill the flameto prevent the wax from cooling ItM) cplit'kl):

The most difllcult part of the re-pair iswaxing tlu- area where the clasp, shouldthere be one , wtll lie . ~ot only will tilt' wax

need to flow a~aill st the Int e rnal art-a of t lu­clasp arm , hilt u retentive contour \\; 11 huvcto he built into the wax-up. T he undercutformed From this contour- will have to n-lat eto the path of insertion ami provide the re­qu ired O.OIO-ineh dime nsion for the tr-n ui­nal thi rd of tlte clasp ann. If the crown is tohave a porcelain veneer; the task !>ecOlIH'S

even mow difficult, since th e porcelainmust he overbuil t originall y. As a res u lt, tlwframe cauuot bo removed from the crownwithout l'rad llring ofT the dry porcelain.

The solution 10 these problems is to sac­rificc the n-teu tlve clasp ann and make tll{!facial contour 10 ideal dimen sions. Alterthe porcelain H'lIeering is co mple-te. withappmpriah' undercut in place , a repairclasp is added to the partial using th e tech ­niqucs prevtously descrtlx-d. T ilt' resuhill~

re pair ( T O\\ 1 ) will have an ideal fonn am iwill ofkn he an imp mWlllent, hoth func­tionally and esthe tically; OWl' tilt' originalabut me-nt tooth ,

Should the patient require til(' uS(' of thepartial de nture du ring tln- rql<lir pe riod.t ill' clink-ian will need In pour and n-co vr-rthe final Impression and construct a 1t' 1ll[)(}­

1<1I')' restoration in the shape of the or iginaltooth fonn . A vacuum form made from adia~nostic cast before mouth preparationcan hl' used to make th e tempo rary,Another technique uses a putty mat rix thatis made of the tooth before pn-pnnufon.

\ lissillg tooth structure can [n- restoredwith soft W lLX before the mat rix is adapte- dto the lool h, After p repa ration, tho mat rixis fII Jt.<1 with tooth-colored res in am i seated011 the preparation . Unfortunately, someudjustn u-nt of the temporary is almost al­ways req uired to seat the partial den tu re.An-as of pn' lllatllre co ntact are best Idenu­lied using till ' ~ lylar-h,Lst'( l articulating rib­bou place-d inside the partial contours whenthe fram e is seated onto the h'mporaI)'Cro\\1I . Points of heavy contact show up

easily and are adjusted.Th e pa tien t is allowed to wear the partial

denture hilt is asked to returnonce the d ieI1;L\ lx-on t rim med am i a " ",LX ('()ping has1)('('11 dipped onto the die. The pat iellt waitswhile the W 1L\; pattem is devdoped usingthe molten wax as p reviously described.Sim'p the fuciul surface will IH ~ shaped toide al contour:.., the patient will Hot beneeded a~aiJl unt il the CroW II is completedand 111,· repair clasp added . At this tunc, thecrown is ce mented and the part ial seated.Occasiona lly, desp ite one 's best efforts.SU IllP adj ustment of either the cast ing orthe clasp is required. Again, ~Iylar tape isthe method of choice for identif)ing pointsof prem ature contact . Since the clasp will

Repairs, Additions, and Relines

be made of wire. and as often as possihle inthe l-bar f(JrI 11, t llt~ adjustment of the claspis not difficu lt.

Relines and Rebases

Peri odic n'lilling of the distal extensionareas of the removable partial denture is all

esse ntial compom'nt of the maintenancephase of therapy. Relines of recen t extrac­tion areas are also required. T he clin ician isIaced wtth (!('cidillg between a laboratoryreline and out' done at the chai r. Uullkecomplet e dentures, whore a labo rato ry re­line is preferable in all hilt vel)' tempo rarysituations. the part ial den ture reline is lx-stdone ill the mou th. The reason for th is d if­Is-renee lies in the fact tha t the part ial den ­ture casting I1 'L\ a different relationship tothe ah utun-nt teeth when it is be ing relinedin a flask than when it \V.L';; ori~illally

p nx -es<;<..d.\\1lell the part ial denture is processed in

the denture flask. it remains on the mastercast so th at the too th-Frame relation can notchange, {,W 'II if the technician should notget the flask completely closed when pack­ing the resin. The result of any error herewould he a prematurity in the occlusion,which is easy to correct . In a laboratory rc­line , however, the partial denture dol's notstay OJ] the cast but ends up in the 0 1\ ](' 1'

half of the flask. NO\\', when th e tech niciandoes not g(' t 1111> flask completely closed ,the too th-frame re-lationship is destroyedand the comple ted reline will not spat com­pletely 0 11to tilt' uluumcnt teeth.

To avoid :lIlY chance of this disaster 0(.'­

curri ug, a n-sin that cures e ithe r compk-n-iyor part ially in the mouth is used . This al­lows the clinician to fu lly seat and maintain

101

Advanced Removable Partial Dentures

the casting 0 11 the abut ment tee th while theresin polymerizes . The partially light-curedresin . Astron (Anstron Dental. \ \1 lt"'t'ling.IL) or a similar material, is an excellentchoice for the HPI) reline. as it is q uitecolor-stable over time: also, becau se it onlypartially cures in the mou th . the clink-ianneed not fear locking in place around abut­ment tee th.

Regardless of which reline approach ischosen , the p repa ration of the partia l den­ture hase for the n -l tnc impression is nearlyIdentical. For the reline material (ei the rn -stn or impressioll material) to flow freelywhen the partial is seated on the tet'th, theclinician must l x- certain that adequate­space exists between the base ami the sup­po rting ridge. Just be-cause the partial den­turn rocks or the pat ient complains ofmovem ent, it cannot he assumed that auniform space exists unde r the base .

To register the tissue-base relation, athin layer of specially p repared algi nate isplaced in the base and the dent ure issea ted compk-tcly, Th is alginate hi a mix­ture of one scoop of regular-se t alginatewith two units of hot water. Th e resultantmix will be the consistency of soup. so itwi ll not displace tissue bu t wil l set quicklybec ause of the hot wate r. when the part ialdent ure is removed from the mou th . thetissue-base relation is easily seen and anyareas of contact are marked before the al­ginate is removed . The alginate can he tornto evaluate its thtekncss. Often there willIH-' 1 to 2 mill of space over the ridge, espe­d ally in the mandible, hut no spact' wi llexist in the lingual flange area. The cllnl­dan wil l need to rclfcve the contact area'sso that 1 mm of spa('(>. at the veryk-ust. isprt'sent overall. III "ome instance s. this wi llmeau that the underside of the raisedmeshwork is com pletely exposed . Tilis

102

RelineincludesI borne,

Reline maintainsoriginal border

Fig 8-9 Creation of uniform re lief after alginateevaluation , with finishing lines .

space is critical for the free flow of the im­pression material or resin.

A decision must also he made as to theadequacy or the border extensions. Thelight-cured resin cannot hi' expected to cre­ate a proper border roll if the existing bor­der is unrlerextendcd more than 3 mill. rrthe existing borders art' greatly underex­tended , a rebasc of the partial denture cast­ing should be considered. which would ( ' 11­

tail a pick-up impression as describedearlier. If the existing bo rde rs are properlyextended. a finishing line should be cut intothe n-stn bo rder to provide for a butt jointof th e IH~W resin with the old. This will rc­duce the possibility that repair resin willpe el away later, whic h is often the casewhen a \1' 1). thin flash Drresin exists at theborder. The goal of the parti al denture re­line should he to add a uniform laver ofnew resin overall ( Fi~ 8-9). The same fin­ishing line shou kl becreated for an imp res­sion to he used in it laboratory reline if thatopt ion is chosen. .It will gin' a positive linefor culling away any t'X("('SS imp ression rna­tenal lx-forc pou ring the n -pair cast.

•

The light ..cured n-line material \\ill setto a finn hut resilien t mass in the mouthwithout the gencnnion of he-at hili, as \\i ll!all resin materi als, with a strange taste .When inserting the part ial i ll to the mouthwi th the fe line resin in p lace, a smallamount of the resin should he placed in theclmtctaus mouth so tha t th e initial set of th ematerial can be evaluated. \\l len the massatt ains Ihe consiste ncy of bubble ~1II1 , it issafe 10 remove the pa rtial de nt u re becausethe addition is heyuud the stage of possibled is to rtion . Afte r t rim ming any gross excesswith scissors (neve r with a ku lfe ), an O:\.)'gPIl

harrier is pain ted Oil the reline su rface am lthe final emf' is made with a light unit. 1\

Simple light source such as that used 10make trays is perfectly acc ept able to com­plctc the cure .

To complete the reline p roc ed u re , thecltnictau must be prepared to adjust the 0 ('­

elusion. especially if the 0Plxlsing arch is aco mplete.' denture. Smce the loss of ridgl'support I )(.X:Urs OH ' r an extended period ofti me, lHi~ration of the opposing denttt lonor prost heses is to ln- expected. This wouldrequire a clinical remount procedure if aco mplete den ture is involved , since intra­ora l adjustments Oil unstable buses willnever give the quality of occlusal co ntactstha t can be developed on the articulator.

While the base support must he evalu­ated as part of the ann ual recall examinu-

Repairs, Add itions. and Relines

tiou . the act ua l nee-d for a reline on a ma­ture ridge should not occ ur more oftenthan once en 'l)' -t to 6 years. \ Vh cn a solidtissue-bas e relationship exi sts, concern overthe stress relief built into the design ofthepart ial becomes purely academic; rotationof the part ial during function can he ex­peered to be within the tolerance of the pe­riod ontal membrane, thus eliminating de­str uctive torq uing of the ubu tmcn t teeth.

As part of tile recall evaluation, the wea rof tllP occlusal su rfaces of the denture teethmust be evaluated ami the addition ofmetal co nsidered . As discussed earlier, it

may he appropriate to evaluate the wearpotential of the resin tee th over a period oflime and only concert to metal when a totallack of contact is found. Convcrslou tomet al is best clone immediately after t Ill' re­line of the denture basets).

Civcn what we now know about theneed for conttuual maintenance of evenour la-st efforts, the repairs, additions, andrelines of all 1)1)('s of removable partialdent ures become a critical component ofthe stutc-of-thc-urt part ial denture. Event holl~h we have made eWI)' e ffort to designami construct the strongest possible par­tials. we know that we wil l be required toperformthese se rvices. with the he lp ofourtechnicians, ou a routine basts, aloll~ withequal efforts in co mbating caries and pe ri­odontal disease.

103

Special Prostheses

T h ~re ar e three special modificationsof the partial dent ure we are lJ)ing 10

create that are different enoug h to merit aspecial chap ter. The strut rest has p roven tobe a valuable tool in the support of multipleabutments with compromised bony sup­port. The hinged partial denture offers ameans of managing failing or severely com­pro mised dentitions almost 10 the lasttooth , and the rotational path of insertionpartial permits the esthetic replacement ofmissing an terior teeth in most Class IV sit­uat ions .

The nsc of the removable partial denture tosupport multiple teeth with mobility haslong been questioned. Certainly, fixed pros ­theses offer a more dependable means ofjoining loose teeth into a single unit. Therewill be situa tions, however, when the re­movable partial will be called upon to offermaximum supporl to the remaining teeth ,

either for financial reasons or because ofthe number of missing teeth in the arch .The best treat ment for these situations isobviously some combination of fixed andremovable prostheses where ideal con­tours- guiding planes and rest p repara­tionsc-can be created on all remainingteeth . Carefu l, wcll-planuod mouth prepa­ration of multiple teeth, coupled with idealcasting control, can offer excellent supportto weakened dentitions and has beenshown to actually reduce mobility overtime .

To achieve these results, special mouthpreparation is required . Perhaps the mostcommon modifica tion of conventiona lp reparation is the use of the "strut" or con­tinuous occlusal rest p reparat ion. Insteadof a ser ies of mult iple regular occlusal rests,th is continuous rest runs from tooth totooth as a channel in the cente r of the oc­clusal surface of the remaining: teeth and isjoined to a proximal guide plate at eitherend of the block of contacting teeth . Thechan nel nee ds to have a width ofS rnrn anda depth of 1.2 mm for adequate strength

105

Adva nced Removable Parti al Dentures

Guidingplane

Fig 9MI Design of co nt inuous o r "strut" rest withterminal guiding planes.

(Fig 9-1). The buccal and lingual sides ofthe preparation must he slightly tapered ,wtth rounded internal angles to facilitate acomplete seating of the partial. These sur­faces must draw with the prepared gnidingplane surfaces and therefore mu st hereevaluated duri ng the surveying of thecheck cast before final impressions (Fig D­2). When an extens ion of this rest is placedon the last tooth in the arch , norm ally a sec­ond molar, this amount of metal will createa rigid rest despite the cantilever from amore anteri or tuoth.

Since the rest will he in occlusion withthe opposing arch along its total length,some modification of the waxing techniqueis requi red to minimize the amount of oc­clusal adjustment on this very hard alloy.The laboratory can mount the refractorycast ami wax directly to the opposing occlu­sion, or the rest can he waxed on a mountedmaster cast and transferred to the rcfruc­tOlY dnring the final waxing of the pa rtial.Th e advantage of the latter technique isthat it allows the clinician to create the de ­sired occlusion on the master coast ratherthan try to descr ibe it to the technician.

106

3mmf------j

1.2mm I W

Fig 9-2 Cross section of continuous rest.

\Vhen waxing the occlusal strut to be trans­ferred, a hard waxshould be used to reducedistortion during removal from the Iubrt­catcd cast and its placement on the refrae­tory. After finishing, the surface of th is spe­cial rest should be sandblasted so that anyeccentric interferences to a smooth disclu­sion can he easily identified during the firstfew days of wear. After the adjustment pe­riod, t he final polish can be easily restoredusing rub ber points and a rag wheel withappropriate polishing compounds.

When this special rest is prop erly con­structcd, it \\ 111 stabilize loose tee th both incentric occlusion and in eccentric move­ments . This is because the teeth cannotmove independently h om the partial whenit is fully seated wtth Ideal tooth -frame con­tact. \Vhile this rest may not be "esthet ic,"it nor mally appears as a ser ies of occlusalamalgams to the eye of the patient.Anterior teeth involved with this type of.~pl i nting wtll require positive rests, eithercingulum or incisal, to mainta in the tooth­frame relationship (lining occlusal loading.Simply plating the lingual surfaces will notserve to "splint" mobile teeth.

•Special Prostheses

.•..... ~. .•

Attaches toframe

Fig 9-] De signof hinge.

Late ral view

Fig 9-4 Design of latch.

'111C hinged miljor connector, commonly rc­[err ed to as a "Swin glock" (actually apatented name and technique), is anotherspecial prosthesis that offers excellent splint­ing capabilities as well as a means of reten­tion when normal tooth con to urs are notavailable for any reason. A barrel-shapedhinge with retaining dimples is attached tothe major connector \\1Ih a mino r co nn ectorthat will, in most instances, exit from anedent ulous area (Fig 9-:3). On the oppositeside of the arch, a retaining latch of somesor t extend s in a similar fashion via a minor

Occ lusa l view

connector (Fig 9-4) . Connecting these twoterminals is a bar w ith projections to the gin­gival enamel of the enclosed teeth that.~wings from the hinge and snaps into thelatch. \\'1Ien the prosthesis is in the dosedand latched position, all the enclosed teetharc locked together (Fig 9-.5). The bar por­tion can take many forms , OTIC of the popu­lar oplions being a plate that runs from thevestibule to just incisal to the dcntocnarneljunct ion. The oute r surface of the plate has agingival finishing hue and rnicrobead reten­tion tor a thin resin venee r (Fig 9-6). \ \-11enthe plate is opaqned with the proper shadeand suitahly colored with resin stains, thtsgingival apron blends in as natural gingiva.

107

Advan ced Removable Partial Dentures

Latch

v

Fig 9-5 Frontal view of hingedmajor connecto r.

Resin extensionto teeth

Resin retention

Fig 9·6 Veneered labial plate.

The laboratory has two op tions for COIl ­

strud ing the hiIl~cllatch combtnatton . Themost com mon tcclnuque uses the patentedcomponents, h inge and latch, wh ich ar eadded to the wax-up of the partial and re­tained in the casting by means of rete ntivecont ou rs in the metal. A more soph isticatedand potentially more pmcise approach in­volves two castings. The first casting con­ta ins the bas ic structures o f the partial den­ture and the hinge an d latch . After th issection has been cast and finished, it is re­turned to the master cas t and reduplicated;the cas tin g remains in th e duplicating a~ar

and th e refracto ry mate rial is pouredagains t it. On th is second refractory, the bar

108

component is waxed to the h inge and latch .It is sprucd and "cas t to" the first cas ting(Fig 9-7 ). A precise hin~e and latch results,since the freedom of movement is createdby the thickness o f the oxide layer thatfo rms on the first castin g when it is placedin the fum ace to burn o ut the second (liarsegm ent) refractory Using th is tec hniq ue ,it is poss ible to make smaller and more p re­cise joints than one can achieve \\1Ih com­me rcial components .

The Swtnglock concept was ori ginallypresented as a techniq ue req uir ing nomouth pre paration ofany kind . Subsequentclinical studies have demonstrated that restpreparations are needed to assu re that the

First casting onsecond refraclory

Fig 9-7 Double cast ing for hinged co nnector.

Second wax-upsprued and cast

Special Prostheses

ent ire assembly doe s not slip ~ 1Il!:ivally onthe teeth. Since th e lJ in~t'(1 f!;ale e llix tivelyholds all the teeth it touches in contact withthe main cas ttng. mesial migration of thesetr-r-th will not occur, A sin~le , positi ve restfonn of allYt)pe on each side of till' cas t ingwtll keep it from sett ling . The hill~t'd pros­the sis h,lS the same re'tllin'lIll'llts for th emanagement of allY distal extension h..ise(especially 0 11 tile mandible). Since theseca..ting.s arc far mo re complex (han thestandard partial de nture fruuu-work. theclinician ca ll e .''1lPl'l to he ehargpd a fel'75 % to 100% higlw l" than fi ll" a routine par­tial den ture c'Lsting.Tl lt ~ hill ~('d appliance has two major in­

dlcat lons . Th e most commcn uso is in CO Ill ­

p romised mand ibular situations wln-ro onlya few anterior teeth remain. \ \1 11 '11 oue orhoth o f th r- ma ndibular canines is missing,it is often next to impossib le to obtain ade­quare n -tcntlon hy claspi ng a lateral incisor.In tln-sc situations. the re mutntng t("C.'tl. areoften compromised periodontally, whichmakes splinting them into om- multtrootodabu tment advisable. It i.s critical , 1I00\'('\'('r,

to provi de a pos itin~ rest sea t on the tcmn­nal abutm ent o n either side to ehmluatcthe possibilit y o f sr-tt llng. The othe r indica­tion , fo und far le ss o ften. i.s for maxillary sit­ua tious where th e remaining teeth arc allon the same side of the arch , often ill amore or less straight line . This situatio n isoften found ill ruudllofacial patients whohave lost half of the maxilla as the result ofa maxillary tumor. The sp lin ting: e ffect ofjoin inf!; all the remain ing teet h is often theon ly means of supporting and maintainingthe p rosthesis.

Special problemsexist for the hinged ap·pltancc thut an ' not found in the rou tinepartial denture situation. There mus t heenough of a buccal ves tibule remaining fo rth e labial bar. When this space is minimal.the hal' lIIay Ila\'( ~ to IK~ changed to a n '­nccrcd pla te in o rder to have sufficn-utstrength. Till' labia l har is so metimes Olljt-c­tionablc to till' patient because o f th e hu lkin the lip . '11 ](' on ly alternatives to t h(~ liSP

of the hing('(l appliance for the se t."OllIpm­

miscd situations are sp linted, fllll -<-'o\"( ' nl~e

restorations of all rt'maining teeth \\i th at-

109

•Advanced Removable Part ial Dentures

Posterior

v

Conventional c lasping

v\Retent ive projections

Fig 9-8 Rotational path partial casting fullyseated.

tuchments, the lise of implants, or somecombination of the two. Some elde rly pa­tients who are compromised hy arthri ticchanges in their hands wil] have troubleopeni ng and dosing the lock mechanismand wi ll require both tra ining and patienceto he able to utilize this design. In some ex­t re me situations it lIIay he necessary to re ­move the gate and replace it with someform of light wire clasping, even thoughthis may be unesthet tc and provide on lylimited retention .

Rotational Partial Dentures

The rotational path ofinsertton part ial den ­tun: is a special prosthesis normally used inmaxillarv Class IV situ ations where ante riorvisible clasping is objectionable . This spe­cial de.~ign utilizes rigid projections intomesial p roximal unde rcuts on th e primeabutments (those adjacent to th e ante rior

11 0

edentulous space) to retain the anteriorpart of the part ial (Fi g 9-8 ). Since th esep roject ions are no t clasps , in that they donot flex, th ey must he placed into the un­de rcuts by inse rt ing th e partial first in thean te rio r and the n rot at ing the poste rior ofth e casting to p lace; the rigid projectionsact as th e rotational pointt s), hence thename "rota tional partial denture" (Fig 9-9 ).Became the posterior part of the castingmust he rotated to place , any p roject ionsthat might inte rfe re with the rotatio n m usthe eliminate d fro m the design. This usuallyimplies that there he 110 modifica tionspaces in the posterior segments and thatthe major connector he open from the restin the an te rio r 10 the posterior mi no r co n­nector for the posterior clasp (Fig 9-10). Ifthe modificat ion spaces were presen t, theadd itional potential gllicling plane su rfaces,properly util ized , would make the rota ­tioual design unnecessary because anteriorclasping would not he required.

Special Prostheses

Fulcrum poin t

F ig 9·9 Ante r io r co mp o nentseated, before rotation.

Fig 9-1 0 Class IV rotational par­tial,occlusal view.

Projection incontact on mesial

Rotate to place

Retentiveprojections

The prime ab utme nt teeth must havewell-defi ned, positive rest preparations.Anv move-ment of Illcse teeth over time \\;11result in the possible loss oft he partial's re­tcntion as well ,LS in its inabilit y to com­pletely sea t onto the abutment teeth . Th isdesign provide s anterior ret e nt ion , sincewhen ti ll' partial is fully seated . the anteriorsegment ca nnot rotate d OW II and o ut of themouth due to th e rigid project io ns i ll theante rior undercuts. The postt' rior part ofthe castillg is held ill place by embrasureclasps 0 11 eit her the first or second mola r,bilaterally. The positive rests Oil the prime

abutments provide a solid stop againstmovement toward the tissue. 111e result is aretentive partial that rep laces anterior teethwithout the show of clasps in the front ofthe mou th.

T1u~ projection into th e pr oximal under­cut can take the fonu of a clasp-like an n ifthe tooth involved is an ann-no r; or a part ofthe minor connector if the prime abu tmentis a pre molar (Fig 9~1l) . Special care mu sthe taken in the laboratory t fl ensure thatt htsp rojection is in no way altered. either ill theblockont (of which there should be noneunder the projection) or i ll tile electrolyti c

III

Advanced Removable Part ial Dentures

Height ofcontour

Mesial of canine Mesial of premolar

Fig 9-1 1 Rotat ional elements, no blockout.

stripping and finishing of the metal. Thisprojection must contact the tooth for the re­te ntion of the anterior segment to he nc­ccptablc, therefore, the casting must be fit­ted first to the mouth and then placed onthe cast without regard to possibly scrapingthe cast. The clinician can expect to find in­terferences to the rotation of the casting.These must he identified and adjusted in­tmorally Iising S( lI11e IIJnn of disclosing rna­te rtal. Care must he taken when adjnstin gthe rigid p roject ions; as opposed to a clasp,they will be too short and rigid to bring intotooth contact.

Since the anterior segment must he ro­tated into place, the anterior flange can onlyexten d to the height of contour of the eden ­tulous ridge and must be tapered to a veryth in margin to avoid creating a ledge thatwill accumulate food (Fig 9-J 2). In cases ofanterior ridge destruction there lllay be noanteri or undercut. In this situation , theflange is fully extended to provide lip snp­port and the resin rete ntion of choice is araised retentive mesh, since ,Ul V large softtissue defect can he expecte d to eventually

112

need a reline. In mature ridges without lossof contour; the metal base with suttulile re­te ntive devices for the dent ure teeth is p re­fer red. Depen ding on where the metal ofthe casting ends on the facial giJlgiva, thecasting may require opaquing and tinting ofthe denture base . Since the resin in thelabial flange willmost always he on the thinside, some experi me ntation with the tintingwi ll be required. There will not he the nor­mal dep th 01" denture base resin to hack upthe tints and, as a result, the colors will notappear as one would expect from the tintingof a standard denture base.

It is also possible to reverse the rotat iondirection hy placing the rotation points illthe posterior of the mouth. This design hasbeen advocated in the literature for ClassIII mandibular partial dentures where theposterior abutments have migrated mesially,lemi ng large proximal undercuts. Higkl, castmetal is extended into these mesial under­cut areas and the pa rtial is rotated to placeon that axis. No guiding plane is possible 011

ti le distal aspect of the anterior abutments,so reten tive clasping is required on the se

Special Prostheses

Heigh t of contourof anterior ridge

Iv

Flange outline

Fig 9-12 Flange extension for Class IV ro tat ional partial.

teeth. There is no disadvantage , ei ther func­tional or esthetic, to post erior claspi ng, so Isee no advantage to th is des ign and cannotrecom me nd it .

Th e pat ient will often re qui re some extratim e and inst ruction in the place men t ami

removal of the rotational p ath partial.\Vhile some loss of retention over time canbe expected, the amount of actual wearfrom the fr ict ion of rotation is really min i­mal so that the partial should he serviceablefor a no rmal period of wear.

113

Precision Attachments

T he precision attachment den ture haslong been conside red the highest

form of partial denture therapy. It L'0l1l ­

hine s fixed and removable prosthodonticsin such a wav as to create the most estheticpartial possible . It also has the reputation ofkL~t i Tlg far longer than the conventionalpart ial. What possible biological reasoncould exist to SUpp Oit this repu tat io n? Ithas long been my belief that the reason th isprosthesis is, in general, so successful is thatthe clinician and the laboratory simplymust take greater pains in eve,}' aspect ofconstr uction just to get the p recisionattachment part ial into the mo nth. Sincethe cost of this part icular I hemp)' is apt tobe far greater than for a conve ntional par­tial denture, there is a greate r likelihood oflong-te rm follow-up care an d higlHlualitymaintenance . If the more conven t ional par­tial dent u re , o ne that is clasp-retained , isconst ructed as described in th is text, thereis no inherent reason that the attach men t­re tained partial should he supe rior.

The precis ion att achm ent part ial shoulddiffer only in th e means of its reten tionwhen co mpared to the clasp -retained par­tial dent ure. The on ly reason for utilizingthis mech an ica l device is to re p lace the vis­Ible clasp ann. All other functions of theparti al can be performed by conve ntion almeans if they arc unders tood and the par ­tial is const ructed to the h igh est standards.

Until just the last few years , the use of aprecision aunchme nt required the construe­tion of one o r mo re crowns a..s part of thet rea tme nt . \Vith the advent of resin-bondedmeta l components, a whole new era hasopened for the attachment-reta ined partial.TIle demand for what might he called "fash­ion magazine" esthetics, so apparent in ourmod em society, has made many of our pa­tients unwilling to accept visible anteriorclasping, and so we see an increasing needto offe r this type of p rosthesis. The combi­nation of these two seemingly unrelatedstatements will create a de mand for a moresophisticated partial dentu re, one in which

11 5

Advanced Removable Partia l Dentures

~ood tooth structure will not han ' to hI" sac­rificed to allow maximu m cstln-ttcs.

Since the const rucriou of the p rt"eisionat tachmen t p artial denture is techutcallydl'lllanding, the need for the clink-ian toflllly unde rstand the implicat ions for thedental laborutorv is critical to success . It isto that ('11(1 that the subject is presen ted illSO Ill!.' de tail in thi s chapter. The sheernum ber of attachme-nts 011 the marketmakes a truly comprehen sive evaluationnext to Im po ssible. A soli,l llllllt'rstanding oftil(' usc of six baste catl'gnrit's of attach­nu-nts wi ll p rovide the cltutctau with too lsIn evaluate oth e r attachment systems asthe}' CO Ull' OJl the ma rket and 10 choosethose tha t offer the greatest potential forlong-term SI ICCC SS.

Common Clinical ProceduresIA number of clinical pnx"(...lures t.'O lI lI llOIl

to the lise o f any attachment system mustbe mastered before a real I(,\"('I of confi ­deuce can he achieved.

Diagnostic Procedures

Spacl' will almost always be a major con­sidcmtton and a problem for precision at­tuchurcnt selection and 11St ' ; therefore, adiagnostic wax-up and sd ~ l] p is essentialfor ('w ry caSl~, Hegardless of what is foundill the opposing arch, th i.s diagnostic pos i­tiollin g: of teeth on bases tha i will allowverification in the mou th must he done sothat tooth position can Ill' evaluated. bothby the clhucian and the patient . The finalposition of all teet h and the dent ure Last:'mus t he k Il O\\11 to e nsure that the spact'

116

rcquiroun-nts of the attachment systemunder con snk-rat ton can be mel. \ \ 'hell in­sufficien t spat'e is available. ei ther till' sys­tc m sr-lcct r-d or the oral en virounn-ntmust change, th rou gh surge ries , or tho­{Ion tics , o r too th modification . The clint­cian will 11('("(1 all up-to-date. ccmprehen­sin' cata log of attach ment sys tems thatInd icates all dimensions of each unit. IIIchoosing a ll attachment syste m, the I01ho­ratory mu st he a willing collaborator: itmust hOI \"(' expe rience wit h the chospnsySIPIl\ or he willi ng to cxpc rimcut a longwith the clinician . Attacht nc ut s lufer­national , tho Prcat Corporat ion , AI'.\l ­Sterugohl . ami Ccndrcs & Mctuux allhave current cat alogs. most of which CO Il ­

ta in rcchnknl guidance as wel l as prec ised escriptions of a wide variety o f att ach­men t syste ms, These catalogs should heavailable, in a current edition, fro m theden tal Iab oratorv,

The Pick-up Impression

The cl in ician must devel op a teclmlque formaking a final impression for the n -mov­able part ial denture framework that in­eludes picking up the com pleted fixedco lltpoue llts fr;'!l1 the mo uth in s Heh ;~ waythat I II( ~ position of the unit s remains ;\('CII­

rutely related to the remainder of themouth. I l a vi ll ~ the actua l CroWIl S on themaster cas t allows p recise positiollill~ ofthe attaclunent compollen ts, a task thatmay 1I0 t ht> possible when working 0 1] astone replica of the Cro\\11, due to th(· prob­able fracturing of thin pmjt>e1iolls of stom-.It also a llows the maste r cast to 1)1' IIs('(1 asa mill ing ca st to provide a stable platformfor m illing metal surfaces of ti lt' fixed l 1 )111­

ponents. This procedure will req uire <l ('IIS~

tom Impression tray and an imp ressionmade with a relatively rigid mate rial. IlSU~

ally a silk-one or a polyether, The fixed un itswtll han ' 10 he complete ly retentive on thetoot h because of the inherent fit of th e cas t­ing, or, if there is a potential for IllOW IIU'n t

during the maste r impression. Ihey willhave 10 he te mpo rarily cemented to keepthe m f rom moving. Th e cen u-nt tngme-dium for th is procedure must be onethai will allow the unit to he removed fmmthe mouth wi th th e final nuprossiou, sincerep lacing a unit in an elastic man-rial run sthe risk of creating an inaccu rate rclatlon ­ship, :\ small head of Fit-Checker, placedjust iutemnl to the margin, will usuallyrnaiu tuin t lu: castin g-tooth re-lat ionship. Anequally small head of Temp-Bond (Kerr,Homulus. \oIl) with Vaseline also can heused. When th e impression is rem ovedfrom tlu- month and is foun d to lx- accept­able, resin dips th at han ' been made pn-vi­ous ly an.' placed into each fLX('( 1 un it, am]the impression is boxed and poun-d.

TI I('sf' dies are made wi th all autcpcly­IIl t'ri ,dlll!: res in, such as Duralny (RelianceDental. Worth, I L), wi th a retent ive wireproject ion to lock them into the de ntalstone of the master cast (Fil!: tn-t ). Th ecompleted crown is lub ricated und theresin is add ed up to the marg in . A wire thathas lx-cn serra ted is inse rte d into tho resinmass, and the resin is allowed to set. T hel'' irt ion 01" Ihe wire that p rot rudes from thecrown is ln-nt into some ret entive limn toreta in it in the slone . The crown mu st sea tcompletely 0 11 the resin die with the mar­~II protected and he easily removed Fromthe cast iL~ needed, T his is particularly trueif the crown has a po rcelain butt margin.Tlu' maste-r cast must always be pou red inimp roved (lip stone to gainmaxi mum rests­taucc to fract ure and ab rasion .

PrecisionAttachments

Retentive cuts

L

Duralay inlubricated crown

Fig 10-1 Pick-up die with wire retention.

A vel)' real pot eu ttal exists for fractu ringany porcelain butt margins that lIIay hep respnl whe-n the- impre ssion is removedfrom the rna...tr-r cas t. Fo r this n-ason, theimpressio n tray must always be custom­made of regular laboratory tmy materi al.T hese resins, unlike those th at are light uc­treated . can be hea ted with an alcohol torchand softened enough to peel the tray ofTthecast without fea r of damaging the fLxL"(1compollents, Stock metal trays, pe rfectlyadequate for most framework impressio ns.will ( 1)\101lsly not offer this option andshould not he used. Once the tray is re­moved, the impre ssion material can he t 'as ­

ill' separa ted from the cast.

Pick-up of AttachmentComponents

The clinician. with th e aid of the cluurs ldeassistan t , must dewlop a technique forjoining attachment com ponen ts to ti l('framework directly in the mouth as wel l ason the ca....t. With the adven t of light-act l-

r17

•Advanced Removable Partial Den tures

vated resins, such as Palavi t (;LC fromKulzer, the clinician can maintain the ap­propriate p osition of the various compo­nents while the assistant places the resinand activates it with the light. If any load isto be placed on the at tachment during re ­moval from the m out h, a used den tal burcan be adde d 10 the composite mass tostrengthen it. Each attachment system willrequire slightly different pick-up tech­niques, rcqutnug some level of experie nce10 routtnelyjotn the attachment to the cast­ing \\1IhoI11 int roducing erro r. In m any in­stances, it may be appropriate to join the at ­tachment 10 th e framewo rk ou t on th ebench. Generally speaking, it is easier tomake a quality resin bond on the bench andthen take it Lack to the mouth to verify theaccuracy of the relationship. These steps ofverification are essential to success wit hprecision attachments. Some attachments,such as clips for bar-clip attachments, willbe picked up using a laboratory autocuringresin having the same coloration as thedenture base.

Other attachment systems will requ irethat some portion of the unit, eithe r thematrixor patrix, he joined to the removablepartial denture casting in the mouth. Thesame approach as was used for ce rtutntypes of repair impressions will be needed .In other words, the clinician must relatethe components while an auxiliary placesthe resin and cures the mass. As with therepair, either an nutopolyrnenzlng resin likeDuralay or a light-cured resin like Palavtt

can be used. The light-cllred resin is moreexpensive but quicker to lise. Attachmentsystems can be soldered to the frameworkor joined in resin alone, the choice depend­ing primarily on the amount of availablespace and the possible need for retnevabll­it)". \Vhen space is at a p remium, the sol-

118

tiering option is definitely the technique ofchoice.

Tn addition to these specific tcclmtques ,altered cast impressions and precise jaw re­lation recording systems must he availablefor the constru ction of the precision attach ­ment partial den ture . The altered cast im­pression will be made after the attachmentsystem has been joined to the framework,since the object of the altered cast is torecord the support of the soft tissue in rcla­lion to the abutm ent teeth through the fitof the casting. Adding the attachmentsafter the altered cast impression could alterthis tissue-tooth relationship if any move­ment of components occurs.

Crown Preparation forIntracoronal Attachments

\Vhen mtracoronal attachments are to beused, the preparation design for the abut­ment tooth will have to be modified humthat of a standard full-vene er crown prepa­ration. To create a crown tha t has normalemergence profiles and dimensions, someform of box preparation that will relate tothe dimens ions of the chosen attachmentmust be made . A review of pulpal anatomyis essential to pre clude ovcrprcparation ofthe abu tment tooth . This may reqllire thepreparation on the bench of extractedteeth with dimens ions similar to those ofthe actual abutment tooth. The presenceof secon darv dentin and the determinationof its depth become critical issues . W hen

considering the prepara tion depth, theminimum thickness of the alloy, usua llyaround 0.5 mm, must be added to the di­mensions of the attachment matri x. If thisreduction places the tooth at risk for over­p reparation , the choice of attach ment sys-

Resin template

Diagnostic cast

Preci sio n Attachments

Diagnost iCpreparation

Fig 10-2 Preparation guide for incacororat attachment.

tern mu st he reevaluated . The usc of anr-xtracoronal uttaclnucnt inste ad of an ill­tracoronal is an obvious solution 10 theproblem.

The sto ne tooth representing till' abut ­111( ' 111 Oil the d iaj.!;llostic cast must he p re ­pared 10 accept the matrix plus the mini­m um spac-e nl'(.'('ssa ry for th e go ld of thecrown. The matrix can be tried ill place onthe prepared tooth using the ho ldin j.!; de­vice that fits into the dental Sl ll"\·( 'yor and ,once adequate spal't-' has bee n created , ate mplate can be quickly construct ed thatwill transfer the preparation for m 10 themo uth. T he prepared sto ne tooth und theocclus al surfaces or adjace nt teeth arepain ted with a ll alginate-based separatingagPllt , and uu uutopolymcriviug n-siu isplaced into the cavity and onto the occlusalsurfaces of the adjacent teeth (F ig 10-2).\ \ ·hpn set. the template can be trimmed ofexces s resin ami ta ken to the mouth to ver­ify the dlmenstons of the matrix cavity byplacing it onto the adjacent teeth and mod­i ~'ing the prepamtlou unti l it a(,('t'pts theform . Th e use or th is simple pre paratio n

gu ide reduces the risk of overprepanuionof tho tooth and gua ralltl'es that there hasbeen e-nough red uct ion In allowth e matrixto he placed within the uornml contours ofth e abut ment too th.

Converting an Existing Cas t RPDto a Provisional Resin RPD

One of the most d iffic ult tasks the clinicianwill face ill the construction of a precisionatta chment partial denture is main tain ingt i ll' patie nt's existing part ial th roughoutwhat llIay he a long trcutnu-ut time. \Vl lt'lIorthodont ics and perhaps even ort hog­nathie sllrge I)' are involved ill addition toimplants, treatment tina- ca ll extend toyeaN, Trying to m ake quality provisionalfixed resto rations that will support an exist­ing removable part ial denture for thailength of tim e maywell he impossihle.lt isin the lx-st inte rests of tilt' clini cian ;L~ wd las tilt' patient to co nvert all existing metal­[ mille partial denture to a qual ity resin ap­pliauce made ill co njunct ion with any n --

119

Advanced Removable Part ial Dentures

Portion to becut away

Fig 10-) Preparation of an old RPD for conver­sion to a provisional removable appliance.

quired fixed provisional res torations. \\1Iilethere are mallY ways of creating these pro­\tsiouals. it is important to bear in mind thecost to the pa tie nt. The follo\\ing tec hniq uecreaks a quality Iong-te nn provisional atmininuuu cost to the patient.

"111e first step is to prepare the existingpart ial denture for a special type of pick-upimpn-s-...ion. Any component of the parti althat contacts the remaining teeth is cutaway with a large cut-off disc, leadllg atleast 2 to 3 mill of space 1* 1\\'('('11 the par­tial und tile tr-oth (Fig 10....1 ). T llis will allowtile impress ion material full access to thetoet h. A higlr-viscosity polycthor or siiicoucimp ression material is mixed and placed inthe part ial. Tlte part ial is cnrrfod to placeand maintained in a po.<,:i lioll of maximumocclusion with the 0Plxlsing arch. without

regard to the abutment teeth , until set.Before rt'!llm; ng the partial de nture, a se-c­

e nd Imp r ession. alginate this tnue. in astock dentate tray [preferably sect ional], ismade over the partial and the remai nder ofthe tlt'utnn'-hearing area. Special care is

120

taken to ensure lhat alginate is wiped ontoall remaining te-eth and into the space ere­ated between the part ial and the teethwhen the framework was sectioned .

The two impressions are re moved to­gethcr and poured in yellow stone. \\1 lt' 1lthe alginate port ion of the Imp ression is rc­moved From ti l(' cast, the elastomcric im ­pression inside the old partial is left in placeunti l the east has (,t"'(' 11 mounted in tln- ar­ticulator with the opposing cast. Once tilemounting is complete. the partial dcu tun­is carefully removed from the cast, !ea\;lIgthe hnp resston material in the part ial. Atthis time, allY diagnostic waxing for thefixed provisional component is done ac­cording to sta ndard techn iques . Hestp repa rations and gu iding planes are pre­pa red , and undercuts ideal for infrabll ige I·hal' clasps arc created. On ce the w;lxillg iscom plete, that cast is duplica ted and theparti al denture replaced on the duplica tecast .

Flanges are cu t away from the partful tocreate space for the retentive wire hal'clasps. These clasps are adapted lISing Ni ­Cr-Co wires and waxed into place on thecast. Addit ional W'lX is added to co mple-te­the desired form of the provisional partialdent ure . Since the resin p rovision al \\i llneed to he thicker than the old framework.at least Dil l.' thickness ofbaseplate W~lX musthe added 10 ull areas of hare framework.The out l!ne of the provis ional wtllm-ccssur­ilv co ver a )!;n'a!('1" p o rt ion of the mouththan did III(' o ld met al-based partial (Fig10-4). Fo r t ll( ~ mandibular provisional. slw­cial caw must he taken to wax the lingualplate an-a of the major co nnector to p m­vide for adequate strength in the resin.Bec au se the pick-up impressio n was madein maximum occlusal contact , the n - is 110

need to urticulan- th is prece ssing cast .

Fig 10-4 Final waxing of converted cast partialdenture.

in a block and placingit hack in the mold orpouring tooth-colored resin in to the toothne~ati\"t·s in til e eh..tomeric material . Th eflas k wo uld then be placed in a pn.'ssurcpot for the cure of the new den ture teeth.Th e S( 'j.(ltIl'nt of" \('('\11 will have to be takenont of" the mold nud the excess resin re­moved before placill~ it hack into the moldfor final processing. In e ithe r case, the pro­vis ional partial is packed in a high-impact ,heat-cured resin ami processed and fin­ished in the normal manner.

The originaJ Illw.tt'r east, nitl. ils waxedprovisional res toration , is now used to cre­ate an eggshell fixf'd provisional for ,-dinin gin the month. Additional wax is added tothe Ill:lJWnal one thir d of the teeth to beprovi siouulized to assure adeq uate resin at

the maJWll, and a putty mold of the \ \ ';lX-UP

is made. 'Iooth-colon-d resin of the appro­priate shade is painted into the plltty, USII­ally with both Incisal and bod y resin, andt he mold is placed in the press1ll"e pot.Since th e fixed provisional restorat ion willbe required to snppo rt the removable pl"O-

The co mpleted w axed part ial is placed intile first ha lf of th e proce ssing Ilask in a nor­mal manner. Th e seco nd half of the n;l"kingis the key 10 making this technique possi­ble . Th e exposed denture wit h its addedwax contours is cove red with an elns ­tomer!c mold releas e mate rial (Den t-kotcfrom Dcntsply or a ma te rial of similar\\'(_·igh t). Immediately after placing this ma­terial, usually wi th the fillgt'r to aSSIlIT' thatno voids an- created. the second half of thelh ;ki ng is completed lIsiug the normal unxof dental stone. This Imun-dtatc pouring ofthe stone ont o the as-vet no t set stltcono Is

esse ntial to keep them from separat illg dur­ing the bollout and opening of the flask.

\\1len tho Ilasking stone is set, the flaskis boiled ou t in the nonnal manne r. \\b enthe flask is opened. the old partial is castlyremoved from th e mold . After completingthe boil -out , the cas t is pa inted wit h sepa­rato r. A sma ll amount of au topolymcrixingresin is added to the tang of the bar claspsto stabilize th em during pat'king . Th e rea ­son for ...e lecting the tnfrubulgc clasps forth is p rovisiona l dentu re sho uld now be ap­parent. Had a normal ctrcumferentiul claspbeen used, it wou ld have had to cross theocclusal surface of the partial. wh ich lIli~ht

have made removing the old part ial fromthe flask a dilJk ult task.

If the tk-uture teeth fn nu the old partialarc porcelain , they can hn removed (ron I

the denture bases by warming the baseresin with a lI anau to rc h and pryi ng themfrom the softened mass of resin. Thev are

cleaned and placed back ill the ir cavities i ll

the silicone mold release material . Resindenture teeth will normally 1)(' found. sinceporcelain teet h are seldom used for partialdentures. The tcclmicinn has the option ofclIltin g the resin teeth ami their associate-dden ture base material from the old r ad ial

Palate rewaxed10 lull con tour

Precisi on Attachments

Wire bar claspsadded

Extended coverage

121

Advanced Removable Partial Dentures

Resin provisional

Prepared teeth Welded band

Fig 10-5 Fixed pro visional reinforced wi th welded orthodonticband material.

visional, the stresses placed Oil the tempo­rary cement seal will he greatly increased .especially if'thc provisional partial is a C I;L'isI am i can rotate ill function . Any washout ofcement and res ultant carie s " i ll create adisaster that can he at leas t partially ove r­co me by rein forcing the provisional withorthodout lc band material . T1Je [ianr] mate­rial is loosely adapted to the preparationand SIXlt welded in the inte rp r oximal arr-asus well as in the edent ulou s pontic an-as.\ \11£" 11 completely adapted , the hand isplaced ill the mout h and the fixed prm i ­stonal shell is relined in nor mal fashion, rc­s li l t i n~ in a me-tal-rei n forced provisionalfixed unit that has a ~reatly Increased resls­tance to flexure und ce ment seal fract un-mg 10.5).

Sinct' the fixed provts ionuls and the rc­1II00·ahlp provisiona l partial denture we remade from the same maste r cast, they " i ll,wtth a III ill imu tn of adjustment . fit to~d he r.In fad , it is in this state that the reHllillg ofthe fixed provistonals onto the preparedteeth wil l occur. To reline th e fixed provi-

122

sion als without regard to the removablepart ial will almost assure that their relation­ship wi ll change and that Imnc('e sSi.u-y ad­ju stments to the resin partial will he re­qulrod to seat the rCIIl0\11hle pro visionalrestoration. Hather thai I completely fill thellxed provis ional restorations with resin toreline them, only a small amount of resinshould he placed in the e~shen, am i thenthe entire provisional :t..sem ble; fixed andremovabl e, is seated ami directed to placeusing the oo;-lusion wt th the opposing d e n­tt ti on as the guide for pmper placement.The small uddit lon of resin will impr int theocclusal/incisal portion of the preparedteet h and positive ly relat e the p rovi sional.Tile n-movablc pro visional can now be re­moved from the fixed units and the relinin gof tln- fixed provisionals courple tecl withoutthe Interfe rence of the removable partial.

Th e result of all this will be a combinedfixed and removable p rovisional restora tionthat can he udjustod and added to asnee- ded while e ther forms of mouth prepa ­rat ion are made. The onlv chair time ex-

pcudcd will be that needed to make thedouble pick-up impression, so the cost tothe patient and cltuictun will he low. Theollly downside of this provisional comlunn­tion will be the added bulk of the all-resinremovable portion when compared 10 theold metal partial denture. Patients gt'lIer­ally tolerate this bulk whe n they know thatit will only be temporary.

Immediate Temporary ResinRPDs

.Many of the patients whose ultimate tn-..II­mcut will be so me form of a prec ision at­tachmcnt part ial den ture wi th associatedfixed prosthesis ente r OUT practices withfi\iling resto ra tions, some fixed ami someremovable. They are in immediate need ofa provisional restoratio n to carry themthrough the initial phases of troutun-nt .Often a failing flxcd partial den tII I"(' willprt'sent with the loss of retent ion of oneabutme-nt, leaving it supported by only O IIC

abutment. The put k-nt is well aware thatthe fixed partial is loose. The first sh'p illtn'aliu?: such a patient will be to ohtain thebest possible initial impression of the af­fectcd arch. Any att e mp t to remove the de­foctl ve f ixed partial de nture withou t a ux­ahle initial cast of the urch can lead to amajor pro blem if the defective restorationis completely undermined with decay andit is 110 1 poss ib le to maintain it in place fora later impre ssion . The patient is withou tthe fixed partial, ami a conventional provi ­sional p art ial de ntur e, especially if u large1ll11IlI*r of teeth are involved. is some daysaway from comple-t ion.

An almost instant replacemen t call bemade using a com hinat ion of autopolymcr­i"j l lg tooth-colored resin, orthodontic resin,

Precision Attachments

and uonpn-cious Lbar wi n- clasps. Whenthe original alginate impn-sslon is removedfrom the c ast . teeth that will nN'<1 replacingare po ured Immediately in th e appropriatetooth-colo red resin, ami the alginate isplaced ill the pressure pot. The bloc k ofteeth is removed nnr] truu nu-d, and thestone teeth an.: removed From the cast.Wire clasps, again preferably in the f-barform, are adapted and waxed to place withsticky W:lX . The new resin tooth segment issubst ituted for th e stone teeth. and theridge is trimmed as for any immediate dell­ture situation. Am' oh\iollS undercut s o ntile lingual surfaces of the teeth to be COIl ­

tactcd with the denture base are blockedout with baseplate W "LX to n lllghl), 00 de­g rees. Afte r coating the east with a separat­ing nu-dium. the hulk of tile partia l isformed ill ti le Hnc-grainod orthodon ticresin, eithe r pink or d ear, and the en tireprojc'd is placed in the pwssnre pot.

The res u lting part ial dc-utun- can be ex­pectecl to closely approximate the defect fvcrestorutlon in tooth posinon and arran ge­ment. If tln- patient requires the extractionof ucnrestomhlc teeth. tilt' tee-th are re­moved and the provisional partial is seatedand adjus ted as needed . Burlew's Dry Foilis then placed ove r the sockets. L~11al isadded to the partial and it is Inserted . Th eL)11al \\; 11 ad as a soft: balldage for the iui­tlal hculing. TIle purpose of the Dry Foil isto preclude the 1.)'11:11 hd llg forced up intothe socket . OILt__x- the 1';11a1 is into its init ialset , the part ial can be removed from themouth and the Dry Foil easilypeeled out ofth e lxnnl .

Most immediate provisional partial den­tnrcs II("{'( ! only one cla..P ann per side. Asl-bnrs. these clasps are much easier toadap t initially an d are read ily adj usted tothe abutmen t teeth if lIe('Cssary. Any areas

123

•Advanced Removable Partial Dentures

Positioning struts tobe removed after

altered cast impression

Fig 10-6 Cast ing modification for precision at ­

tachments.

of this quickly made provisional p rosthesisthat do no t fit satisfactori ly can he eas ilyreadapted with any autopolymertztng resinintended for oral lise .

Modifications of the FrameworkDesign

At times there IlIay not he sufficient contactareas between the framework and the re­maining teeth to ensure pos itive orientat ionduring the pick-up operat ions describedea rlie r. This wtll most often he true whenattach ment s thai wtll also bear some of thevertical support of the partial denture arcused. In these cases , additional struts areadded to the major connector anr] exten d tothe occlusal or incisal su rface of at least twowidely separated teeth (F ig 10-6 ). The st ru t

124

Vertical supporting strut

Attachment matrix

Fig 10-7 Casting modification to suppo rt intra­coronal at tachment .

is waxed directly on the refractory cast andhas th e dime nsions or a normal minor con ­nector. The struts provide a positive posi­tion of the fra mework in the mouth whil eattachme nts are joined to the casting andaltered cast imprcsslous arc being made .Afte r these two operations a re completedand the [it of the attachments is verified,the struts ar e cut from the maj or connec torand the surface is re turned to a no rmal con ­to ur and Huish.

~..Iany partial dentu re Fram eworks willneed a support post added to the res in re­ten tion area in order to have som eth ing towhich the pat rix can be e ithe r soldered orattached to with resin . Th e exact shape ofth is st rut will be de pendent on the attach­ment system use-d, hut its (lcsign must hereviewed with the lahoratorv because it issuch a critical e lement (F ig 10-7).

Precision At:Systems

Overcoping/Overcrown

The most basil' precision attachment sys~

tern is that of the precision coping. A thin­walled coping cemented in place on theabutment tooth permits an oven:op ing orovcrcrow nattach ed to the removable par­tial den tu re to fit ove r it and p rovide, bas edon a frictional fi t, some degree of rete ntionfor the partial dentu re as well as excellentlateral stability and solid occlusal stop sup ­port. These copi ngs are usually milled tothe planned path or insertion/ removal orwith a slight taper, around 2 10 S degmes,depending on the height of the coping. Theheight of the coping varies with the crown­root ratio and the integrity ofthe re mainingtoot h structure . When vcrv little toothstructure re mains, the coping should beused as a stop only, since lateral fo rcescou ld he un favorable when precise millingis used. Th ese simple att ach ments havebeen used for manv years for exte nsivesplinted fixed restorations , commonly re­ferred to as perurprostheses, with great SUl'­cess . The e ntire .~ llperstrlldllre can he re ­moved by the patie nt , providing totalaccess for clean ing . Moreover, sho uld acoping abutment be lost for any reasonw ith time , the tooth can be re moved andthe overcoping filled with re sin to becomea po ntic. In many cases thes e large restora­tion s can st ill he used even wtrh the loss ofsom e of the or iginal abutments. C roat sue­cess in using th is approach for ove rden­tUfCS has also been wel l-documented.

Ohtaining a ferrule effec t of at least 1..5rnm on solid toot h st ructu re is crit ical in the

Preci sion Attachments

Overcrown ~ 1 mm

Coptnq e 0.5 mm

Tooth preparat ion

Fig 10-8 Vital toot h co ping w it h ove rcrow n(th ickness).

re storation of badlv broken d O\\1 1 tee th forcopings . W hen e ndodon tically t re ate dteeth arc used, thi s ferrule wtll dramaticallyred uce the posstbtltty of root fract ure . Inmany instances, it will he necessary to per­form crow n-le ngth en ing procedures toga in sufficient tooth st ructure sup ragingi­vally, since the coping margin should heplaced at the gingival cres t.

Any pos terior tooth or roo t por tion canbe conside red for a cop ing res to ration.O ften , on e root of an othe rwise pertodon­ta lly involved molar toot h will have suffl­cicnt hone remaining to justify its retentionin the month. When thi s root can be ma in­ta ined, an e ffect ive tooth -bo rne part ialdent ure can be constructed in a situationthat woul d ot he rwise result in it d istal ex­tension base .

Vital abutments, whe n used with co p­iugs, must have sufficient occlus al red uc­tion to allow both the coping and th e over­c row n to have suffi cie nt th ickness towithsta nd occl usal wear (F ig 10-8 ). At least

125

Advanced Removable Partial Dentures

1..5 H Ull IIlUS ! he available , with the copinglIt'eding O.S and the cruwu taking up the re­mainillg space. For this n -ason, the occlusalsurface of th e CIU\\TI should be in metal,porcelain would require at least 2.,'5 mill ofreduction . Th e need for a facial veneer inthe overcrown is a more common require­mont . Slightly less than the 2.S-1ll1ll spacecan be used and it will still hold shade andcontour. Nonvita l abutments an ' oh\i ouslymore udaptublc to the lise of a ceramicovcrcn IWIl .

T he cons truction of a milled copingstarts with a diagnosti c wax-up uud set-upthat will include the opposi ng arch. be it ac0 1l1 plt'le denture or a partially eden tulousrostonulon . Th e design o f the parti al den­tun- is deknllined and drawn on the diag­nostic eas t with indica tions for subtract ivemout h preparation. The stone teeth thatrepresent the abu tments an' prepared forei the r additive or subtructivc mout h pwpa­rat io" 10 a ch ose n path of iusertion/re­moval . ami the vital abutments that \\i ll beused for lv pings are prepared to tln-appro­p riat e dimensions and angulat rons. This di­agnostic ca st becomes the blue-p rint for theactual mouth preparation. Endodon ticallyt reated abutment teeth usually do not re­quire the same level of dlagnos ttc pfl'para ­tion because th e re is much more freedomill ert'ating the desired nulled con tours .Ann lite cast is used as it guide for mouthpreparation , it can be used as a pn-scr ipt lonfor additivt' mouth preparation by l I lt' de n­tal tecimlciau. The stone l'opiuJ!; kdh areprepared . waxed, and m illed Oil a sut"\'eyorII sin~ a blade that wil l attach to the verticalarm of the Slllyeyor. The diagno....tic cast willth en n-prcscnt all the desired con tours insuch a way ,L~ to ensure th at th e teclmlcianwill be able to reproduce tltem ('.xm:t ly int1w final restorations.

126

The actual pfl'paration of the copingabut ments occurs only after all the subtree­tive mouth preparation has been (,( )IIl­

plctcd. III this wa)~ the prepared gu id ingplanes can serve ,L" vertical indi cators of thefinal path of iuscrtion/rcruoval during t ll('

preparat ion of the abutments that wi ll n -­ccivc copings.

The muste-r impression mu st involve allthe teet h in the arch as we ll as all cdcntu­lous land marks that wtll be req uired for theconst ruct ion of th o final partial dcntun­framework, eve-n though the e:t,>ti ll~ willBever be mad!' fro III th is cast. Once tlw dtcshave been trluuned and th e cas ts mounte-din tIJ() ar ticulator, the copings can be roughwaxed. T]H' prepared dies are dipped inmolten wax In establish a thickness or atleas t 1 IIlIll and then milled to the dcstn-dtap{'r wit h till' den tal sun 'eyor or \\i ll. wax

burs in th e industrial milling mac hine ,which must he available ill the dental labo­ratory choxr-n to support the treatment.

\ \ 11(' !l the milling is complete, th e waxedcopings an' marginated to allow for a cop­ing margi n ofatlea...t I mill. The placementof this margin will dete rmine the margin ofthe ovcrvrow u or overcoping. Because orthe ang ulat ion of an isolated tooth relat iveto the pa th of inse rtion/removal tha t tltepart ial den ture must take , it lllay not I )( ~

possib le to mill all sides of the coping totha t path for tlte 1'11 11 length of the ('oping.III such situuttons , the margin of the over ­crown or o\"('I'('opillg: will rise or fill! ae( ~ m l­ing to tlte nnlk-d surf ace (Fig Hl-H), TIlemore surfaces that can he paralleled , ho w ­eve-r; the IlIO l"(' the fri ct iona l n-rcutiou ofthe part ial ca n 1)(, increased .

T he coping is th en sp ruerl and cas t in atype IV gold to reduce long-termwear, fin­Ished, and n-tumcd to the master cast. Thecoping should never he thinner than 0,,5

(

Tooth preparationoutline

Coping margin withferrule effect

Precision A ttachments

Autopolymerizingresin

0 0

Meshwork

Overcrown

Uncovered coping

Fig 10·9 O vercrown margin options.

llllll in any portion . The copings can nowhe milled on the milling device to bringthem into ideal contour; Cn-at care must hetaken in thin areas, obviously; hut thisshould not he a problem ill the hands or allexperienced h-ehuician. TI I( ~ un-tal is hl'stId t ill a sandblasted surface. the re is TlOud­vantage to a high polish, except at the mar­gill with the tooth .

The decision between a ll m'ereupillgthat will have 110 oc clus al anatomv ami anovercrowu with normal occ lusal contours isbased on the position of the tooth in tlu:arch and the available intr-rarch spa(-e, Ingeneral, a second or th ird molar on theruandlbular arch tndicutos the overcoptngas the design of cho tec if occlusal contact swith the opposing de ntition arc not esse-n­lial. Ti,e overcrowu is then waxed , cast, I ln­ishcd . and veneered if indicated . Both thecoping and the ovcrcrown are returned totin' mou th so the final imp ression for thepart ial den ture east ing can he made. Thisimpression must pick lip the ovcrcrowu asit would any additive resto ration, since theymus t all appear OTi the master cast.

Fig 10410 Overcoping attac hed to raised mesh­work.

The coping att achm ent. whether anovcrcopiug or ovcn-rown . wtll lx- solderedto the framework in most situations. It ispossible to attach rr-te-ntive loops or headsto the ()\'(' l"{v ping and ret ain that unit in theresin h;t~e, hu t the Ilt,('d for this app roach islimited to situations whe re there is a greatde al of hucrocclusal space present anr]where the extension of the OH' n -rO\\1 1 intoocclusion would result in an cxccssivclvthick crown (Fig lO41O ) , Th ese on' I"('I"O\\11S

o m be veneered if thcv fall into the areawhe re the pat ient's es thetic deman dswould he compromised hy a full goldCI"O\\1 1, 11111 such eOI )i l l ~-crowll sit ua tions

are most often found in the posterior pal tof the 1I I00 1t l i where a display of uu-tal is uc ­

ceptahk-TIll' coping \\ill, ;11 cve rv Instance . act as

a vert ical stop fiJr :the partial denture. Inmost cases it can also provide frtcuonal re­te ntion. lt is most effective whe n m et! incombination with other att uclnuent svs­terns that provide gn·ater resistance to dis­lodgment or wtth conventional clasping inother areas of the mouth.

127

•Advanced Removab le Part ial Denture s

Bar-Clip Attachments

The har-elip attachment has its origins intum-of-the-cen tu ry dentistry, when th eGilmore clip system was made available tothe profession. It was commonly used withcopings or crowns over vital teeth and laterwith endodontically treated teeth in whtcha post coping system atta ched a solid bar ofabout 8 gauge to the posts. The attachmentmechan ism was a plate guilt, If-shaped dip ,of various lengths, re tained in the res in ofthe prosthesis or soldered to some port ionof the internal fram ework. Th e Dolder barsystem offered an egg-shaped bar that pe r­mitted a certain amou nt of rotation of thepros thes is while still retaining the den ture.This syste m was used extensively in bo tharch es and was equally adapt able to the re­movable part ial dentu re as the completedenture.

Advances in organic chemistry have rc­su lied in the creation of resilient dips ,made of thermoplastic materials, that arcvery inexpensive and can be rapidly rc­placed bv the clinician. Thcv have the dis-, ,advantage of wearing more quickly thanth e gold pla te clips. Th ese plasti c clips areoffered wtth a thin metal retainer housingthat has retentive contours on the innersur face to retain the clip . They are, in turn,held in the resin of the denture with reten­tive contours on their oute r surface.

Bar-clip systems are widely used withimplant-support ed ovcrdcnturcs of manydifferent des igns and arc available from avariety of man ufacturers. The bars , in crosssecti on, can he round, pear-shaped , 11­

shaped , or rectangular. The round and Ihepear-shaped forms are inte nded to allowsome rotation of the attachm en t deviceperpendicular to the long axis of the bar.Among the most popular are the Hader

128

bar, Dolder bar, Cvl -Hidcr; and Ackermandip and bar.

\Vhen used as an attachmen t for a re­movab le partial denture, the bars, ei ther inth e form of a castablc plastic pa ttern or as awrought precious metal hal' that is in­tended to be soldered, are att ached to ele­men ts of the fixed prosthodoutic eompo­ncnt. It is again essential that diagnosticW,LX-lIpS and sci -ups are created to relatethe position of the dent ure teeth to the po­sition of the hal'and to assure that adequatespace cxists-c-not on ly for the bar, th e d ip,and the clip reta iner, but for the teeth andassociated resin that \\111 usually be placeddirectly over the bar-clip assembly. Whenspace is limited, the use of a p rote ctivemetal covering over any thin resin areas isIndicated. This wtll often take the fonn of acast-me tal occlusal sur face for a posteriortooth, since the expe cted wear 01" a resindenture tooth in function can result inbreakage over the dip assembly.

Once the diagnostic wax-up is completeand the teeth to be replaced on the partialhave been tried in the mouth and verifiedesthetically a pu tty matrix of the tee th ismade with a positive scat on the cast toallow both the clinician and the tech ntctanto find the ideal position for th e bar relativeto the denture teeth (Fig 10-11). As part ofthis decision, the vertical position of the ha l're lat ive to the soft tissue will have to be se­lectcd. If the bar is placed on the tissue ofthe ridge, or even slightly above it, e,xperi/ ­once has shown that the tissue \\111, in timq,hypertrophy and will not only come intocontact with th e unde rside of the bar butextend up along the sides of the bar intoany space not occupied wi th th e dip.Perhaps the best position 01" the ba r in rela-tion to the tissue is just high enough off thetissue to allow the tip of a mini ProA)' brush

Fig 10-1 I Putty matr ix over pa­t ient-approved set-up and wax­up.

Fig 10-12 Relationship of plasticbar pattern to gingiva.

Facial puttymatrix

Preformed bar

Precision Attachment s

Lingual putty matrix

• -r-e-r+-_ Ideal dentu re- base contour

Positioningdimple

Wax connectorto c rown

Special clearance

to pass under the bar. The patient must as­sume responsibility for daily stimulation ofthe tissue ,L~ well as keeping the undersu r­[ lee free from plaque . The contours of thebar where it connects to the crowns or cop­ings m ust also be carefully evaluated , as theclearance required for the marginal gingi­val tissue is eve]I more critical than for thebar as a whole (Fig 10-12). The level of thebar in these areas will, almost without ex­ception, need to he raised. In practicalte rms, this mean s tha t the bar must he cutshort of the connector area, maintainingsufficient length for the clip, and thenwaxed into contact with the crown, usuallyin a curved segment. As this connector is

closer to the Incisal/occlusal plane, spacemay become a problem, even if there wasadequa te clearance over the straight lengthof the bar.

Usually the plastic bar pattern is cast toone side of the fixed component mHI sol­dered to the other side after relat ing thesegments in the mouth or from the mastercast. The preformed bar is solde red in sim­ilar fashion, usually with post solder afterany ceram ic component has been corn­pleted. The solder joints must always belarger in circumference than the ba r itself:In the Hnishing and polishing of the bar,care must he taken not to touch the sectionof the bar tha t will receive the clip, since

129

Advanced Removable Partial Dentures

Height 01contour

Btockout wax

Fig 10-1 ] Blac kout of bar and abutme nt cro wns.

any chango in dimension will re-duce the re­tcutive effect of the dip. Otlu-r areas of theha r-e-solder jo ints and tissue surface. forexam plc-c-wil l receive the sallie degrr-e offinish as the fixed units. \\h .'11 the fixed(llmpOllcllts illd ud ing the bar have been

compk-n-ly assembled and Iintsln-d. th eyare picked Ill' ill the final tmprcsstou fo r th eremovable framework us clcscnlx-d eariterso that they arc available to the laboratorytechnician du ring tile subsequent construe­tion ph ases. To facilitate the removal of thenupn-ssion from the cast, the space be­neath the I lar must he blocked out in themouth. Thi s step is eas ily uccomplished byadapt inp; a thin ro pc of sof! utility \V,LX totho unde rside of the bar lx-fou- placing it intho mont h. Th e soft wax will adap t to thetisstn-, and allY excess can be quickly [P­

Illm"ed with a hand instn unc-ut b efo re theirupn -svion. This procedure \\; 11 h(~ far PiL~ ­

ic-r than tr)ing to pack W,LXnude r the bar inthe wet fk-ld of the mouth.

It is not essen tial to liSP the d ip with the

bar. In fad . in instances whe n ' space is at areal premium. the b ar makes all ideal ante­rim rest for the partial. Conventional clasp-

130

ing or other attachment systcllIs elsewherein the mouth wtll then provide the 11( ' ( "(' S­

saTy retention . ru, approach also S(' I"\"('S asa less expensive alternative to fixed pon ticsin many situat ions, most commonly whenmandi bula r inciso rs a re missing and the op­tion is citlx-r to Include them wit h the- Ilxed<'"(lIHIXl llent as lXlnlies or to replace themwi th tile partial denture . As a res ult ofadding tile bar in the anterio r region. thetwo sides an' more effectively splinted andan ideal rest is created. A disadvantagt.' tothis use of the ba r is that the patien t isforced to wea r the partial den ture at alltimes for esthe t ic reasons.

Whether t h(~ cltp wtll he used or not . thebar is to he blo c ked out along with the othercomponents of the remaining tlt~ llt a] arch.The superi or surface of the bar is left fn '(' o fblockout w ax so that the pa rt ial denturecasting will contact the bar along th at sur­face np to the solde r joint area, where aslight amount of relief is appropriate (F ig10-13). 111is blockou t of the bar P[('Sllp­IXlSPS that the bur and associated flxcd co m­poueuts ha\"(' lx-cn picked Ill' from themouth ill their finished state and are a part

Precision Attachments

iTop O'ba,

Fig 10- 14 Blackout of bar anddip,

Fig 10-15 RPD casting-gold diprelationship before pick-up.

Clip and housing

Contact with ridge

of the maste r cast submitted to the laboru ­tory for construction of the fram ework. If ad ip is to he used , it, along wi th its housing:,mus t hi ' in place O il the bar at th{ ~ ttmo ofhlockout .... 0 th at a refractory rep lica theexact sizt, o f the housing will be created (F ig10- 14). Th l~ d ip must he placed in ,...uch a\vay ;l'i to ensure that its midline is parallelto the pat h of insertion. as indican-d by theprep an-d guiding; planes on the ulmtme-ntteeth. pc: nniUing hoth wings of the d ip tohe fk-xcd till' same amount when the d ip isact ivated during insertion und n-movul. 'I1It'

d ip \\tll be reproduced ill the n-tmctorycastto en-ate an opt·ning in th p casting exactly

where the d ip is to he positioned. The outersurface of tile casting adjacent to the 0pcn­ing will n-quin - n-ten uve beads or loops toret ain the attaching resin (Fig 10-1.5 ). Thotooth -replacnuont retention in the an-n (Ifany bar-clip uttacluncnt or the liar alone is10 be metal with lx-ads or other nu-chanknlproject ions. This will always he superior toha\ing that un-a only in resin, since the lim­ited space \\i ll n-qutre the strength of thefull metal ('ow ragt', The metal ('OWr.IW·must extend to the crest of the re mainingridge just <Interior to tile b ar, with the n-­malnder of tilt' denture base in resin of theappropriate colnr. " '!Jen that resin is tlun. it

131

Advanced Removable Partial Dentu res

will he necessary 10 have the lnbonuoryopaflue the facial uspec t of the metal so thatit wi ll not be seen through the part iallytranslucent den ture base.

\\l len the casting is returned from thelab oratory; all co mpollt"lIls arc seated ill themonth if some natura l teeth are pres('ll t , oron the master cast if all contacts arc onFixed units. and its fit is corrected as rc­quircd. If the cast iug contacts only the fixedcomponents present 011 the master cast , c-i­tlu-r tile d ip or thed ip Iiolising, tk'pendingon the system ill uxc-, should he attached tothe frame on the master cast with it smal lamount of autopolyuu-rizmg resin, eitherpink or tooth -cole n-d. df'l>endill~ 011 thearea of attachment. \ \ l lf'n the casting con­tacts teeth 1I0 t associated with the fixedrestorations present Oil the master cast aswell as the fixed components , the d ipshould be attached in the mouth. with allco mponents completely seated. Only afte rthe d ip is att ached to the framework is thealtered cast impression made (where indi­cated ) and jaw n-latton reco rds taken. Theobject is to have till' framework and ,L"SO('i­ated abutments in thei r final relationshipbefore any snpport of the soft tissue is ob­taincd . This wiil ( ' n SUTl' th at no misalign­uu-nt occ urs durill g pmeessing of the den ­ture bases.

Before the flaskiug of the denture bases ,the fixed COlllp01Il 'llls are removed fromthe master cast so they will not ln- sub­[cctod to the bigll P[( 'SSI ITeS of tna l packing.The metal housing in the area oft he d ip isfilkxl wi th a stltconc mold release materi alor a putty to pro tect the d ip and housing.11l(' flllly \\"<1.'\1:"(1 den ture is seated 011 themaster cast, ami the borde rs are scaled.Tilt' first half of the Ilusking wi ll cove r theresin cores that once suppo rted the f ixedcomponents, in add ition to allY exposed

132

an-as of the framework. in the standardfashion. The siJieollt' will make the dean­up of the dip area \"('1). e,L'_Y because lin

ston e willlx- prese nt .The dips, e ithe r metal or plastic, will

event ually wear and will need replacemen t.In gf'lIe ral, the plastic d ips wi ll wear muclrfaster than the metal dips but, since theyan' now in it metal housing. they can be re­placed in seconds allow cost Thei r life ex­pedall('}" can he Imp roved in two vel)' im­porta nt ways. Fi rst, if th e rf'mainingteet h/llxcd untts are nulk-d to UO degrees tothe path of inse rtkuvre moval. the \\ings ofthe dip wi ll Hex {'(lually and minimally asth e d ip is ncuvated. Second. if the patientcall he made to take some responsibility forthe method of insert ion of the precision at­tachmcn t partial (fe, never bite the partial10 place bill uxe only fill ~(' r pressure) , th eload Oil tho dip \ViII he controlled. Thesetwo sllggt'stions are app licalilo to all partialdentures hili are especially pe rtinen t to theprec ision attachment with a resilient com­

pOlle llt.In n-placing the plastic d ip, allYdental

hand in strument thai call fit insid e themetal housing em be IIs('(1 to slide the olddip out of the hOllsing. T he new dip isplaced Oil tile inse rtion tool thai is specificto that d ip and snapped into p lace.Hc-platomc-nt of the meta l d ip will rcqulrethai lite old d ip be ground out or the par­tial by making an access hole over th e d ip,usually just lingual 10 th e rr-placemeutteeth. The hole must hl' large enough toallow ucvcsx to the enttn- dip and its n -­tenttvc cxtcustons . These n -tentfve extcu­sions an' covered with a thin coat of au­topolvu u-ri...ing resin of the appropriatecolor. II'the coati ng resin is a f ilx-rcd w pai rresin , the fibers are removed hy siftiugthe m out through a 2 x 2 gall....e. T he resin

Prec ision Attachments

Initial resin application

Ackerman clip

Round bar

Fig 10·16 Cross section of mand ibular over-denture showing re­placemen t ofAckerman clip (gold).

should he placed on the clip as quickly aspossible and the clip placed in tile p re SSllreIXlt to cu rl' . Once the resin is hard, any ex­ce ss can be remov-ed and the dip placed Oilthe bar, making sure that it is aligned withthe path of insertion and the parti al isseate-d 0\1.' 1' the dip. By completely co ver­ing tilt' n-tentive elements of the clip wi thresin outsidl' the mouth, the climciau willensure that no voids are created when thed ip is act ually connected to tilt' parti al intile month. O nly enough add itional resinneed he added hy picking lip polymer witha \\"d{t,t! brush and placi ng it tltrongh tlteaccess hole to create a solid joint (Fig 1O~

In). The patient is instructed to closelight ly into maximum occlusion to ve rifythe p rope r base-clip relationship and then0IX-'11 th« month slightly while the clinicianholds tln- de nture in place . O nce the layerof re sin has completely cured ill the mouth,the partia l is carefully removed and the re­mamdcr of the required resm uddr-d to fillthe inte rnal contour to it s pre-repair co nd i­tion. The exterior hole is filled to excess.

afte r which the partial is placed ill the pres­sure pot for the en tire curi ng time. By fill­in~ to excess and the n finishing away theexcess, the densi ty of the added resin \\i llhe maximized.

Th l' bar-clip combinatton offers a rela­tivelv inexpensive att achment system thathas been used successfully for a few gener­ations. It is adaptable to many situationsand {Wi)' 10 maintain. Its only n-ul dis.ul ­vantage is tha t il does require a good til'al ofspace, both vertically a litI horizontally, andso ca nnot he used unfve rsally

Intracoronal PrecisionAttachments

The int racoroual attachment that is classi­fied as precision co mes from the man ufac­ture r as two compone nts: a matrix and a P'"t nx. These an : often accompanied hy aparalleling guide that fits into the dentalsun:eyor as w(·11 as devices to act ivate theattacluncut aft('r Iabrtcatton. The matrix is

133

Advanced Removable Partial Dentures

waxed into the crown or bonded into aprep;mltion in tl.e tooth , The patrix is at­tached to the Frumcwcrk in some fashion.usually by solderi ng. In many instances. thepa trtx will have some retentive eOllllxlllelltthat can be act iva ted and readjusted aswea r occ urs.

Th ese attachments. be ing machined toclose to le rances (0.001 inch OJ I tho aver­age), cannot 1Jt' expected to allow for con­trolled f reedom in rotation of a den turebase am!' as a resul t, are used in all toot h ortooth/implant-supported partial dentu res.There are a mn nlx-r of mtraco rc nal attach­me nts that han ' an integral hinged ('o m lxl-­

ncnt intended to nffe r stress relief to a dis­tal exte nsion ha st>. Th e use of this hingedattachment does not. in my opinion. fulfillthe need to dist ribute the maximum load toth e selected almtun-nts. In stead . it placesuu un con trolled amount of force on the tis­Slit' least likely 10 withs tand the load, theedentulous ridge tissues. Since wr- knowthat n'soq1tio ll of tile edentulous ridge is ano ngoing, generally irreversible process, theIlSl' of an y hinged device places an addi­tional maintenance rcqutre meut 011 theclinician. The distal extension ba...e must hekept in ideal contact with the ulIl le rI)ingtissues through relines to minimize soft tis­sue Impi nge ment ami stripping of tissue . Ist"e no need I(Jr th is t)11(' of attacluucnt inthe modem partial dentu re.

T Ile standard lntrucoron al attucluncntsthat contain no moving parts do , however;offer exce llent n-n-n tion and es thet ics forthe tooth-home partial. Since these at tach­mont systems become a part of the crownor po nt ic, they mu st he contained withinthe nor mal con tours of th ese restonu lons.The ;l\erage dinu-nsion of th e mtmcoronalattachm ent is just ove r 1,5 mill am !' allow­ing for a minimum of 0.5 1I1I 1l of met al in

134

the l'TOWn internal to the' ma t rix, it call heeasily S('(' II that a minimum of 2 mill of re­ductiou in the area of tln- att achment is c s­sc nt ial to kee p the finalunit within normalcontours. It may he that bonding the pa tri xin to a p re pared cavi tv ill the tooth wouldrequire less axial reduction than for a C<L~t ­

in g, but th is treatment modality is in its iu­fancy without longitudinal studies to "~ llp­

pori its use.

T IIt' re is general agf('(' II1eut that, in ml­dttiou to the axial SP,K'l~ req uire me nts, tiletooth must howe sufflck-nt cllntcal crownlength to accept a matrix with a minimumvertical height of 3.5 mill. The lengt h ofmust matrice s as received fro m th e 1Il ;1Il1l ~

factun-r is 6 mill, but it is not common tofind a crown capable of accepting the totallen gth . Obvi ous ly the greate r vert ica llengt h of the attach ment complex, thegreater tlte pot ential ret ent ion and stabilityth at C<111 he expected . Th(' I"( ' a re a numberof split attac hments that han >some form orlatch (Sn-m gold GL, I()r examp le). T his canhe effective ill sho rter ve rtica l le ngths ,since the ac tual retentive mechanism is asplit c;'L'i ling with a ridge at its most gingivalport ion (a minimum of2.62 nun is requiredfor th e GL) (Fig 10- 17), Becau se of thesplit casting, the ridge call ('()mpress all it­self am i snap into a recess i ll the matrix.

T hese space requirements mus t hetaken int o careful cons ideration dming th edi agllo stie waxing and positioni ng of ti ledenture teeth . In the younge r patient .where large pulp chambers and a lack orseco ndary dentin are found , it may not hepossible to use an intrucnronul attachment(cxtracoroual attachments will be nff-essaryfor these pat ients). The width of the matri xin a buccoliugual direction will he in therange of3 mill. a dimension that can be ac­co nuuodated in most ulaumen t teeth. For

Precision Attachments

I

~~~~~ Backinq .~F= ..- plate ----. L... .....

Lateral view Inferior view

Fig 10- 17 lruraccrcnal attachment (Stemgold GL gingival lateh). Red denotes space within attachmentlatch area.

example , the widt h of the patrix fo r theStorugold G L is either 2.4:3 nun for thestandard head or 1.77 mm for the microhead.

Before mouth pre-parat ion on the uctuulabutment teeth . all guid ing plane pn 'para­uons 0 11 the re nuuuiug teeth Ihal wtll uotl)t> tn-atcd with crt J\\1IS or othe r castingsmust he made and verified. .\Iaking th e at­tachmeuts and allYguid ing planes on theircrowns 10 match tilt' pa th of inse rtio n/re­mova l as it exists on the other preparedteeth is more p ract ical than mali ng the at­tacluncnt containing crowns first and thentl) i ng to parallel gll id ing planes to ma tchth t' path. Since these at tachments ar u VP I)'

p recise , it is ne arly Impossible to matchthei r path aile r thoyure in place . Th e sam esystem of d iagnostic mo uth preparation assu~estl"d fo r the conventional partial den­ture must be employed with a ca reful veri ­

flcat lon of the check cas t before heginningthe act ua l pre paration of the teeth to becrowned.

It should he OO\ i OliS that all)' maste r eastfor the cons truction of th e crown s must in ­clude all othe r teeth involved with th e par­tial denture . Th e clinician must determi nethe desi red pat h of insert ion/remo val andtransfer this spatial relat touslnp to the tech­nician thr ough the use of three widely SPI)­

amted tripod marks. placed wit h the ve rti­cal arm of the surveyor in a locked position .

Laboratorv construct ion of intraco ronalprec ision attachment crown and ponticunits is 1I0t d ifficult , although some f"xperi­e ncc is m-cess urv 10 use the survevor and. .special too ls to position tlu- matrices pe r­fcctly pamlk-lto the indicated path ofinsor­tion. Senne discussion with the technician isneeded as to the exte-nt of till' po rcelaincoverage 0 11 the abutme-nt l'fO\\1 1S, since thematrix will re q uire a small amount (0 .4 m illminimum) of metal around it th at is free orporcelain (Fig 10-18). Tln-sr- abutments \\ i lloften also requi re milled guiding planes an dappropriate contours to aCt 't'pt rests, all ofwhich will lutlue ncc the cu tback o r themetal for WHeeling.

135

Advanced Removable Partial Dentures

Milled guiding Porcelain

Plane\ : ( OClline

l edge rest

Fig 10-18 Veneer outl ine for intraco ronal attach­menr.

The intraco ronal uttaclnnent wi ll notnor mally be indicated ou the mesial surfaceor anterior teeth because the alteration orcontour \\iIL most like ly, pro\"e to he un ac­ccptable (the canines Il('ing the only possi­ble exception ). Cencmlly speaking, ante­rior ed en tulous spaces <Ire better fllled withfixed pontics than with co mponents or thercrnovnble parti al.

When the crowns have been complet edand have been found to be accept able fixesthetics and occlus ion . the final impres­sion fix the removable framework is made.A finn-se tting elaston u-nc impression ma­terial is used , either silicone or polyether; ina custom tray with ample retent ion (holesami adhesive) to ensure that the impressionman-rial does 110t Sl'parate [i'0I1l the trayduring remova l of th e impressio ll fro m themonth. These mate rials are not Intended toImpn-ss large undercuts, a.s may be foundon unprepared nat ural teet h. Since the goalof tlu- final imp m ssioll is to relate the Ilxodcomponents to the n-matoder of the archand to allow the pick-up of these compo­nen ts wi tho ut distortmg the final imp res­sion . it is often Jl('(.''f'ssary to block out l a~l'

136

undercuts, furcatlons. undersu rface s ofp O ll tiCS, ami allYotln-rarea where the n-sts­tancc to removal is ap t to be so high as tothn-u ten tl«- integrity of the final nup res­siou. Anv number of mate rials can be usedlo r the blockout of th ese unusable an-as:wax , temporary cement , co tton pellets, amial~i nate are examp les that shou ld he con­sidcred.

Ideally, the CrO\\11S and oth er fixed com­POIlt' llts should come out i ll the impress ion:re positioning them in the imp ression doesnot gua ra ntee aecu racy. As di scussed ea r­lie r; resin elk-s should he available to inse rt

in the lTOWTl S prio r to pouring tile maste rcast. Th e modern impression mate rialsused in these situations can be co mfortablvtran spo rted to the dental laboratory with­out fea r of distortion and th e co nst r nct louor the maste r cast left to th e technician. Adi a~nostlc cust must accompany th e fina limpressio ll to in form the technician of theprescribed design of the framework. It isusually nl:'(,,'ssary to m ake an alginate du­plication of the master cast ('t>lltaining thefixed components in ord e r to obtain a d iag­nostic east, since tho master im p ressioninav require ubu rnin u of the uuv to recover

• • •it. It is much e asier to ('onw y specific re-qulrcmerus via a diagnostie cast wi th a neatand careful d ra\\ing of the outline of theframework than to try to describe the de­sired outcome over the phouo or 0 11 thework authori zation lim n.

T he sa me requ ireme nts o f d esign andconst ruction as described for the COIl\"t'Il­tional partial denture must hi' ad hered tofor the precision attachm en t framework.' Vhell the frame and maste r C'Lst are rc­tu rned to the clinician, the fit of the framein tile mout h and to the crown s mus t heverified befo re the patrice s are picked up illresin, either in the mouth or on the master

east. 1'111>d eci sion as to wllt'm lx-st 10 jointi lt' attach men ts to the framework is de­pendent O il many factors am i the w is noone correct way. It must he remembered.II00n 'n ' r, t hai in every ins tance th efruuuvuttachment relationship must beiden tica l from the mo uth to the master eastbefore the co nstructio n can continue . MostIntmco roual attachments will he joined tothe fnuncwork by solderi ng because spaeeis like ly to he a cr itical factor.

T he Ilt of the framework must he rever ­Hied after the soldering; openn ion ill cvcrylustnuco. Only when the tooth/ frame rela­tion mcctx the highest standards can otherprocedures he undertaken, it ', altered castimpressions allcl jaw relation records. Thecompk-tton of the case . once the-se stepsare done . is rel ative ly standard as far as po­sltlonlng o f the denture teeth ami \\ ~lx i ng.

p n x:t 'ssing. and finishing of the base areconccnn-rl. An are a ofspecial cousldcratlonis tht~ p rotection of the patrix conm-rtionwhen the amoun t of resin over or aroundthis un-a is minimal (less than 2 111111 o ftooth str uct ure or base resin). In these in­stances . metal occlusal surfaces are 10 hecoustructr-d. usually i ll !)lx~ IV gold . andadded to the denture teeth to ensure thatsuhse'l ue llt wear wtll not break th roll/-;ll tothe patnx.

At insertion of the intracoronal at tach­mcnt partial den ture, any undercuts to thepath of fusert ton/re moval wil l [ruvu to becarefully idl'lIti fled aIHI rccontourcd tofnlly scat ti ll' part ial. Since the path of in­sert ion " i ll he so precise, the finished par­tlal must neve r he forced to place on initialseating until all possible un de-rcuts in re sinhave lx-en ide ntified and adjusted, The softtissues uf the mouth occlusal to areas of

slight undercut Illay <:om prps.s ami allowthe full spating of the part ial hut "ill not

Precision Attachments

allow tilt, part ial 10 he removed withou tpain or chscomfort to the patient . some­times with ~rt'a t difllculty If pressurc-indi­eating paste is placed on all resin areas amithe partial is iIlSl'rt('t! with light pn'ssurcunti l resistance is felt. e ithe r by th e clin l­cian or by the patient, an-as ofpotential dif­f iculty c't111 he ideutifled withou t fear o f tis­sue i r ri tation.

T here remains onlv the activation of theattachmen t, i ll those attachment svste ms,whe re this posslbllity exists. III general. pa­ticuts should be informed of the intcu ttouto use only t l H ~ lightest activat ion that willsati sfy thei r noods fo r re tention, since thelower the level of act ivation, the better thechance to re- duce distort ion and th e 11('('<\

for repealt'd adjus tments. Activation is uc­

complishcd with the use of specific tools.provided hy the manufacturer; which <lis­tort the patrix hy inc reas ing the opening ofth e split an-asof tlre metal (F ig 10- 19). T hetools an' carcfullv cali brated to ensure th aiovemct tvutj o n does not occu r, a fri~hl('ll ing

situation where the partial d enture c annotbe re moved from the mouth without execs­sin ' force. For this reason it is 1I0t ";Sl' toallow patients to reactivate their uttuch­mcn ts hy themselves. Assuming that eH")'aspect of construction of the in t racoroualprec ision attachment pa rtial has been doneto the highest standards, the uttuclunent sshould need only periodic re activation, un­

de rtakcn as a part of normal recall act ivi­ties, Systematic recall for the se patient s isperhaps as critleal as higl, standards of con­structicn fo r the long-te rm success or theentire t reat ment. Certainly the se two com­pOllents of treatment are far more impor­tant than variations in d esign of th e part ialdenture.

A wide assortment of mtracoronul at­tacluuents is uvmlable to the clinician, all

137

Advanced Removable Par tia l Dentures

Late ral view

Fig 10·19 Reacdvancn of Sterngold Gt auacbmene.

based 0 11 the saun- !!:pne ral principle-s de­scribed here. Dental tech nicians will havethe ir favorites, d,,!wlllli ng UII the ir cxperi­cnco, however, their experience is based onInbrtca t ton Issues und no t on clinical cvalu­anon. Therefore, while one auaclunent sys­tem lIlay be easier to construct . it docs 1I0tlollow that the system wi ll work as well :tS

some other ~1)L' over the expected Itfcspanor 20± vcars. The sheer number or attach­mcnts precludes that any one clinician ortcchnlclan will han ' had sufficient experi­once working with all attachments to define

the se lection in anv scient if ic manner. (S('(',listillg of attachment manuals and 11 1,11111­

fucturo rs at the eud of th is chapt e r).

Intracoronal SemiprecisionAttachments

Because of the \ ·('1)' low tole rances or theprecision attaclum-nt , little stress n-lief ispossible whe n it is used on Class I partialdentures, especially in the mandible. \\11en

01111'a few co mpromised mandi bula r an te-

138

Activa tion 1001

rior t{"('lh are availnblo as ah unncnts. as isso often the case, mallY chulctans elect torelieve the stres s of masttcntton to the ubut­mcnts by splinting an re maining Il'dIJ andt ransferring some of the load to the eden­tulous ridge. \Vhilc it is theoretically possi­hie 10 do that with precision attachmentsthat utilize it 1II00illg C()mpo llt'llt in the P'"t rix, us sta ted earl ier this is not advisa ble.T here is a ~lx~ of at tachment. usually n-­fcrrcd to us a semipn-cision rest attach­men t, tha t ut ilize s all intrucoronal box anda resilient lingual clasp nn u. preferablywrought . for the actual retention. The hot ­tum of the box in the <:rO\\11bas a slight lipawl a rounded base that allows the patrixrest lo rota te slight ly ill function bu t thatwlllnot , bec ause of t1 11 ~ lip. slip distally andunseat (F ig;10-20 ). To d iS<'lIgag;e , the e nt ire

partfulmus t move vert ically the distance ofthe raised lip before the putrtx is free of thematrix. The esthe tic effect of the semi­precision attachment is exadly the same asfor the precision intraco ronal attaclnm-nt:no evtdcncc of the partial denture O il th efacial aspect of the abut un-uts.

Precision Attachments

0.0 10 inch

Porcelain coverage

----- +

Facial view Proximal view Occlusal view

Fig 10·20 Cross sections of semiprecision mcacorooat Attachment,Thompson dowel rest.

TIl(' Th ompson dowe l attachmen t is thebest known of this type of clevicc.Jt is madeby wa.xing the mat rix 10 a hOllw llJade for­Iller ami then creating the patrix rest pat ­te rn ill resin directly in the fiuisln-d castingof the ahut menl. Similar attachment fon nsarc made bv SO l!lC' conuncrcial manufact ur ­ers (Preat l\-L attachment, for example).

Tile semiprccis iou attachment, almostalways created in the dental laboratory ei­ther ill wax or by millillg the completedcasting. can he used \\ith a lingual retentiveclasp arm ill CI.L"S II, III , and IV situationsas well a." in the bilateral distal extensionsitua tion. I lowcver; their use is Hot as eWiYto-defend because th e space they require illthe crown will he the sa llie as till! precisionuttacluncu t, without the retentive effectfoun d in most precision pntriccs. If a pos te­rior isolated uhu tmcnt 0 11 a to oth -bonn­side of the part ial is less than ideal amiwithout a projected lffospan expect ed ofthe parti al, tln- Thompson dowe-l attach ­men t is ind icated for the more anteriorabutment tooth (usually a p remolar). \ \ 11('11the distal abut me nt tooth is lost, the partial

can he quickly converted to a distal cxtcn­SiOH (e ithe r Class I or I[) without having tobe conce rned about the stress re lief of theattachment sy,~ t e lll .

A matrix former can he easily handmadein wax. at tached to a straigh t resin Sp nJc ofsufficient length and dimension to allow itto be placed in the vertical arm of th e den­tal surveyo r. ami cast in any alloy (usually anonproctous partial denture alloy), It is fin­ished and polished ami tJI('1I machbu-d

using the side of a large. nat disk to ensureth at the wa lls of th e matrix will have no nu­dc rcut areas. The original Thom pson dowelattachm en t had both a right ami a left ma­trix former, the lingual walls of which wereset al right angles to the internal wall. Th ebuccal walls diverged slightly 10 allow easeof rotat ion while still pm\iding a gu id illgplane sur face parallel to the pat h of iusr-r­tiou/ removal . The bucca l diH'rgence alsoallows easter placeme-nt of th e attachmentfor insertion by the pa tien t. TIH ~ metal for­Ille r is lub ricated with a sillcoue spray, andwax is added in excess to creak th e matrix.The wax pat tern is removed fr om the rna-

139

•Advanced Removable Partia l Dentures

Fig 10-2 1 Parallel placement of Thompson dowelrest.

trix former aw l reduced to have walls ap­proximately 0.3 rnm tlnck. The Cr U\ \11 pat­tern is cut away Oil the distal aspect to it

thickness of 0.3 nun and the matrix palkrnis added 10 the crown usill~ the slIIy eyor tocany the wux mainx to place . Once the ma­trix has been fully tacked Into place ami theco ntours n -cstabhshed. the former is re­moved from the wax pattern .

Since th is attacl nnent is sc mlprecfslon , it

can he comple tely hand waxed without thelise of tho matrix fo rmer. Tapered burs areused in tilt' \V,lX pattern 10 create the wallsto the same dimen sions anti angles. Around bu r can be used to create the de­pression for the rota tional ridge. Whenshaping \ '':.LX with a bur; i l is obvious that aH 'I)' slow speed IIII1St he used . For th is rea­SO il, a belt -d riven, low-speed and high.torque handpiece is often used. 'I'll(' so­phisticatcd milling mucluncs commonly

140

found in labomtoncs that specialize in thist~lx~ of prosthodonttc work have speciallymade wax-cutting burs that. when used incombina tion \\itl. precise spe-e-d co ntrol.make tho .~hap i ll ~ of the matrix a relativelysimple procedure.

It should he obvious that th p matrix form

must be set pnrulk-l to the path of Inscr­ttou / n-moval as dictated by the guidingplanes prepared 011 any nonrosto rcd teethp WS('nt ill the an-h that wtll he IISed usalmtnu-nts. \\11('11 this attachme-nt is usedfor a Class I part ial de nture, the Internal\\1111s of the matr ix must he set para llel toeach other and at right angles to the mid­sagitta l plane of tho arch (Fig 10-20 , Thispostttoniug of tlu- mat rices is essential toallow rotation of tile bilateral distal cxtcn­slon bases. \ \11('11 the terminal abutme nt isa c au luc. it is often II("<--essal)' to shape till'd istal half of the too th like a premolar toplace ti le distal surface parallel to the distalsurface Oil the opposite side or the arch(Fig 10-22) , \\'1lClI the remaining teeth areto he splinted, as they often nru in thesecases. a premola r can be can t lh-vcrcd offthe term inal canine to contain the att ach­ment. Since the actual retention of the par·Hal wi ll he created using a lingual "ire ci r­cumfcrential clasp. the usc of the premolarpontic "ill allow a longer clasp arm thanwould be possible 011 the canine. with amore natural approach to a uu-sioling ualundercut area (Fig 10-2..1), If the nhunncntteeth are H Ot to he splinted i.K' roSS the arch,donhie abutting must he consklcrcd . wt thadditional rests and guiding planes pre ­pared on the nonspltntcd teeth . T he lise ofthis att achment i ll a nonspltnted mandibu­lar first premolar, for example, would becoutmtndicated due to the possible loadthat could be placed OJ] the tooth iftho dis­tal extens ion bas e were not kept ill full con-

Pre cision Attachments

Fig 10-22 Alteration of contour(canine) to accommodate preci­sion attachment.

Fig 10-2] Cant ilevered firstpremolar to conta in attachment(Thompson dowe l).

Labia l Occlusal

Pontic

.L~I----- Matr ix

Wire retent iveclasp

tact and support through the originalaltered cast impression and subsequentrelines .

The ltngunl surface of the waxed crownts )is prepared to accept the terminal third of alight wire (20 gauge) circum ferential clasprun ning to the rncsiolingual . The entire lin­glial surface can he shaped to allow theclasp an n to lie in a depression in the metal,with the flnal one third passing into aO.OlO-inch undercut relative to the path ofinsertion/re moval of the matrix and the re­mainder of the guiding planes in themouth. The clasp ann is 10 be extended asfar to the mesial as the embrasure contour

will allow to create tile longest possible re­tentive ann (Fig 10-24). Th e height of con­tour must he planned to leave a .l-inmspal'e between the gingival border of theclasp and the gingival tissue.

Once the castings have been completedand veneered, they are picked up from themouth in the final impression for the pa rtialdenture. The parriccs are now formed inresin and their tangs in either resin or wax.At this time, a dociston on the method of at­tachment of the patriccs to the frameworkwill have to be made . If the putrices are tobe solderer! to the framework , the area ofattachment should be ull in metal with the

141

Advanced Removable Par ti al D entures

Fig 10-24 Lingual retentive wirewim full extension mto embra­sure.

Metal coverage withbead retention

....----- Solder strut

Regularmeshwork

Fig 10-2 5 r-tera! coverage ofridge under soldered artachmem.

Internal finishing line distal to the solderan-a (Fig 10-25 ). This would n -qutn- thatthe n-licf wax be placed dist al to the sol­d('ri ll~ area. If the intent is to altaeh thepatrk-cs to the frame wi th resin and keepthem ill resin, then an eva luation of theavuilalilc space occlusal to Ihl' mes hworkmust be ma d e. Remembe r; when space isat a prem iu m, the solde ring lll<'thod of at­tncluncnt is p referred . \ Vith adequatesp:l<'e , IIU're is an advantage to kc·eping theconnect ion in resin so that the att achmentco mponen t can he replaced with minimumdr-stmction 10 the part ial.

\\11('11 the shape of the tang is csrab­lished. the W , LX and resin pattem is Invested

142

and cast i ll the sallie alloy or one slightlysofter than was used fur the CTO\\l l. This isdone so any wear with time will occur Oil

the patrix, whic h are relatively easy to rc­

place, rather than on the matrices. T)1)e I"gold will probably be slightly softer thanthe ceram ic alloy chosen fix the (TOWl lS .

Th e master <'<lsi , with the patn ccs ill place,is now ready for hlo c kout and duplication .The waxill~ of the framework wtll de-pend0 11 the 1Il,1I1lIer in which the palli ees arc10he attached .

Once again, the framework is protectedfrom any internal finishing by the tcclmi­cian and. only after a quality fit is vcrtfk-d inthe mouth. will the putrtces be attached to

the frame, either on the east or in themouth. Care must be taken to ensure thatthe patrices are fully contacting the inte rnalwall of the matrix when they are adde d tuthe f -arne, since it is in this relationship thatthe altered cast impression must he made.Now the altered east impressions are made,even though the clasp arms have not yetbeen added to the casting. The altered castwith its jaw relation record is rcmmcd tothe laboratory for the addition of the wi reclasp arms and completion of the case.

Since there is no Iabiobuccal clasp armon th is type of partial de nture , a Class \"cavitv is cut into the most anterior denturetooth to serve as a ledge where the pat ientcan place a fingernail to remove the partial.The Thompson dowel nttachmcnt offersfreedom to rotate for the Class I partialdenture, wtth ease of adjustment of thewire retentive clasp. The only disadvantageto this I)ve of attachment is the hulk of thematrix and the Heed for 3.5 nun of verticalheight.

Extracoronal Attachments

There are a variety of ext racoronal attach­ments avatlablc to the clinician. Some ofthese are rigid; that is, they do not allowany rotation of the part ial in function.Oth ers are hinged , offerin g a stress-break­ing action to the distal extension base.More recently, a number of resilient extra­coronal attachments have come on themarket that permit a limited amount ofmovement of the denture base for theClass I partial situation. Both the rigid andthe resilient attachments have a distinctplace in the tooth - and tissue-borne partialde nture. The need for hinged attachmentsis less obvious: the rationale for their lise

Precision Attachments

can he questioned if one recognizes theneed to utilize the remaining possible abut­ment teeth for maximu m support and re­ten tion and to reduce the load on the softtissues as much as possible. The conven­tional distal extension removable partialdenture creates stress relief through restplaceme nt, light clasping, alte red cast im­pressions, and careful maintenance, withperiodic relines to keep the base move­ment to a minimum. I f the conventionalpartial denture, constructe d to these pri n­ciples , is potentially as successful as longi­tudinal studies would have us believe,the re seems little advantage to placinggreater load on the extension base throughthe lise of hinged attachments. It has beenmy experience that the hinged attach menthas great potential to become destructiveto the soft tissue unless it is vcrv carcfullv- -mainta ined and replaced as soon as it be-gins to show lateral movement in additionto its plann ed vert ical rotation. For thatreason, I do not consider its usc justifiable.

TIle great advantage of the extracoronalattachment is that it does not alter the nor­mal contour of the abutment crown , heingent irely outside of these contours. Au addi­tional advantage of the ,igid attachment isthat the entire length of the attachment,from the gingivaJ tissue to the occlusalplane, can be used for ret ention, making itinvnlunhle in situations in which the abu t­ment teeth are short.

A simple rigid extracoronal attnchrnontis Olll' commonl y referred to as the pin ­tube attachment (Fig 10-26). For most ofthese , the pin (patrix] ts added to the fixedunit and the matrix (tube ) to the partialdenture. Th e attachments can easily bemade by hand. They are also available fromattacluncnt manufacturers (Fred-Ver texfrom Prcat Corp. Interlock and Tubelock

143

Advanced Removable Par tial Dentu res

Cingulum rest

Tube

Fool

Occlusal view

Fig 10-26 Pin-tube atta chment.

front AP~ I Sterngold. for example), SomeIntraco r onal pill and tube uttachments canhe \IS( "( 1 i l'i cxtracoroual attachments bv re­versing the patrix and matrix S( ) thai, ill­stead of t.a\ing the matr ix in the crown. itbecomes part of the part ial denture (cy lm­drica l slide C~ I attachment from AmericanPreci sion Me-tals). Recent ly, n -siln-ut n -tcn­tivc sk-cvcs han ' been added to the matrt­l'('S of pin-lube attachmen ts. The mostcommonly used of this specia l form is thevertical Hader bar, A similar current Ion u isthe l'n-ci-Vcrt fx from Prea t Corp , which,according to the man ufacturer's claims, canbe used eitheras a rigid attachment-or, re­dlld ll~ by 0.:3 to 0.,5 n un the coronal por­tion of till' patrix, as a resilient uttucluueut .Allof these simple attachment s can lx.' con­struct cd lIS i ll~ the same princ-iple-s \\i th lit­tle cxpcct r-d variation. They diRt'r "mill theolder svstcrus in that the matrix is lined'lith a resilient materi al that call be cas ilvand inexpe nsively rep laced as needed forretention , The mat rices ( V IlW \\i til a pre­cisclv machined metal cover that has n-ten -

144

Pin

~o

Mesh

Fool

Tube

Lateral view

tive contours 0 11 its outer su rface to whichresin can adhere. The metal matr ix coversan ' intended to stay in the parti al for itsnormal life. allowing the resilient Inner nut­

trices to 1)(' replaced.A slightly diffe rent attachment system

that is well-known and has been used formore tlnm :30 w ars is the Ceka uttaclunr-nt(Ceka 1\\ : Antwerp. Belgium ). Th is attach ­ment differs fr om the others in that the pa­trix is a split metal post thai is adjustableand snaps Into a metal matrix uttacln-d 10the proxima l surface of the abutment

crown. This svstem has manv modl flcntlous. .fix use ill a vnrk-ty of situations. The patrtxpost is thread l'd so that it can he screwedinto the hold ing ckwtcc and easily replacedif damaged or W O I1 I. A space r ling is l ISI ,! 1 toallow the pl)ssil)ilily of stress relief, cr('a tin~

a vertical spal't-' or 0.3 mill when the spa('('rhas been removed after co nstruc tion. Thisspa('t-' allows a small amount of rotation ofthe partial denture, which will place someof the load 0 11 the tissues of the denturebase. A recent Ceka innovation is called the

•

Fig 10-27 Ceka Revax attach­ment.

Fig I 0-28 Roa ch attach me nt(ball and tube).

Cekn Hevax attachment. This system placesthe mat rix in contact wlth the gIngival tis­sues in a way that allows easy access for hy­giene, both under the matrix and betweenth e matrix and the axial surface of th e abut­ment crown, so that the ging ival tissues arcnever comprom ised (Fig 10-27) .

A vel)' old system that h as been in usesince the tu rn of the century is the Roachattachmen t. The patrix or this attach ment isa partially split, adjustable round hall tha textends from the axial surface of the abut ­men! crown. The ball comes as a finishedcasting that can be sold ered to th e axial su r­face of a c rown o r cas t to . The matrix of th is

Precision Attachments

~HO",'09

I m----Pa" "

Matri x

_4_--- Tube

..

system is a tube , in much the same form asdiscus sed previously In its ea rliest fo rm,the tube was made from plate gold and wasattache d to the partial denture by means ofa meta l tang that had been soldere d to thetube. The modern edition has a tube wtthone form to be used if the attachment is tohe solde red to the framework, another ifthe matrix is to be attached with resin (Fig10-28).

Since the patrix is a round hall, th e con­tact wit h the matrix is o nly at the ci rcum­fe re nce, which allows for more rotationthan anv of the other svstcms. The in-- -creased stress rel ief availab le with this sys-

145

Advanced Removable Par tial Dentures

\Rodge

\ / crest line

\\

This portion iscontained inwax crown

c >

Fig 10·29 Extracoronal attachment placed lingualto ridge crest,

rem indica tes its lise in compromised den­titions for which a conscious declsion hasber-n made to transfe r load From the abu t­nwn ts to the snpporting tissues of the den­ture bases. The exact amount of rotationallowed wit h the Roach uttuchnn-nt is afact or of the space between the tube andthe axial wall, since th e tube ca ll only allowrotat ion to the point where it comes incon tact with th e crown . In all the svste msthat allow rotati on, the amou nt of move­

ment that is desired is slight; the t l W of the­altered east impression and th e n-liues th atare mad e , when indicated , ke-ep theamount of space between the hast' andt het issues to a minimum. If the pn-cisiou at­tucluucnt partial denture is igno red forlon~ periods of time, no nttucluncut sys­tern will permit control of the rotati onalforces.

Altl'r all flxcd unit s have been waxed tofu ll contour and milled in \vnx for maxi­11I11I11 guiding plane surfaces. the putnccs.of whatever system has been chosen . areadded to tiK' axial surfaces of the abutmentL'rO\\1IS lIsing the special alignment toolsprovided hy the manufacturer.T he put rices

146

Fig 10·3 0 ERA patrtx.castable plastic.

a re generally patterns, made in some formof hard n-sin that is amenable to burnoutand casting in standard ceramo-metu l al­loys. TIlt" a l i~ lIl IL' ll t tool is placed in tlu­dental surn'yor at the same tilt of mustercas t as \\~IS used for the wax milling of thegu iding plane surfaces . It is c ritical that thepath v[ tuscrtton/remova l to be used takesinto account tilt' height of contour of till'

edentulous soft tissues as well as the re­maining tee-t h.

The plastic pattem, or preformed metalpatris , is 10 he placed som ewhat Iingnal tothe cente r of tll(' proximal sur face (Fig 10­29), This skp e-nsures that the bulk of till'matrix will not inte rfe re with th e est heticsof the buccal (' lISP of the replacement den­turc tooth . Th e average patient can toleratea slight excess of contour to the Iingnal be­cause esthetics are not involved . Th e put rtx

(in the pin systems) is to extend fm m a eon­tact with the ed en tulous ridge just Ii ll~'1 l:l 1

to the crest of the ridge to the occlusalplane, This length can be maintained insvstc ms tha t utilize an 0llen tube. If the svs-, ,tern requires a cappe d hom ing, the patrixwill have to lx- short ened to a(,('Ollllll(xbh'

the housing, The decision of which type ofsystem to employ often hinges on theamount of vert ical space available. The P'"trix pin must extend far enough out fromthe abu tme nt tooth that floss or cotton yarncall be passed under the pin and lip to themarginal gingiva. Most plastic patternscome with a self-limiting platform tha t,when waxed into the normal contour of theabu tment tooth, automat ically co ntrol sthe extension into the ede ntulous area(Fi~ 10-:30).

when the tee th hearing the extmcoronalattachments are to he venee red wtth porce­lain, resin, or eomposite, the extens ion ofthe cutback for the veneer is critical. Theveneering mate rial must not be allowed tocontact the matrix portion of the attach­ment. In most eases, this requirement wtllmus e the margin of metal to extend furtherto the facial and lingual surfaces than itwould in a veneered crown not involvedwith the attac hmen t. This extension be­yond the normal cutback is generally in thearea of 1.0 to I,,') n un; esthe tics is usuallynot a p roblem given that the attachment ismost often on the distal proximal surface ofthe abutment tooth.

Fortunately for both clinician and tech­nician, the manufact urers of attachmentsprovide excellent instructional material,gene rally at no cost. Since systems are con ­stan tly being redesigned, the inclusion ofgreat technical de tail in any text is apt to bea waste of time.

After casting, the technician is careful toleave the patrices untouched. any finishingand polishing will decrease the retention ofthe system. The fixed units are finished andveneered and are then included on themaster cast for the partial den ture frame­work ,L~ described earlier. This step is es­sential for the extracoronal attachment be-

Prec isio n A t tachm ent s

Metal housing

Resilientpatrix

Meta l matrix

Fig 10-31 ERA cross section, overdent ure ma­trix.

l'anse the patrices are so small they wouldnot stand lip if impressed and poured instone . By having the actual casting on themaster cast, the technician creating thepartial denture can wax out the contoursand prepare the refractory cast so that theattachment of the matrices is precise andaccurate.

When all remaining teeth in the arch arepart of the fixed component, the matricesare best p icked up on the maste r cast andverified in the mouth . When some of theabutments are natural teeth not nssoctatedwith the fixed unit s, the task of picking upthe attachments becomes slightly morecomplex since the stone replicas of theseab utments may be damaged. ln this situa­tion , it is best to place all the fixed comp o­nents in the mouth, fit the frame, and thenattach the matrices with autopolymcrizingor light-activated resin. The comp lete ,L~ ­

scmbly must then, of cou rse, be returne dto the master cast for verifica tion .Tolerances for the relationship of eornpo­nents in the precision attachment partialdenture are much finer than for the con­ventional partia l, so the lise of magnifica­tion whenever possible is essential.

147

Advanced Removable Partia l Dentures

.\Iost of the extmcoronal attach ment s\x­n-ms are self-aligning \\'11('11 it com es 10 join­ing tlu- matrices to tilt' p atrices. The ('()IIl·

poncnts need only lx- fully seated Oil eachother and the resin applied. Some sys­tems-c-thc Roach , for exnmplc-c-have align­i n~ tools for the nuur tces thai are to be usedwith the dental surv(·yu r. Th esp systemsmust he attach ed on thr- bench.

For each of these systems, the decisionwlu-ther to solde r thr- ma trices to tlt(,fram ework o r to att ach them wi th resi nmust he made Oil an individual basis . \\i ti.till' space requirement be ing the bigg('s1factor. Both means work well an d, \\itl.can-, will not cause' proble ms.

The set-up and W.LX· llp of the partialdenture containing extmcoronal attach­nu-nts are generally 111 11 co mplicated exceptfor placing the den ture tooth that sits overthe uttuchment assembly Often, this Firsttooth will need to he hollowed out to amere shell. To ensure that the dentu re baseresin does no l show through the tooth, it\\ill be necessary to pack a small amount o f

tooth-colored resin, preferably heat -cluing.under the too th be fore the remainder ofthe denture base is packed. when spa('(' isat a premium, metal occlu sal surfaces arethe only way to prevent rap id wear ami as­soctatcd destruct ion of the attachment us­sl'lllbly. The cost of add ing a small onlay orone-halfcrown form to the partial is mini­mal comp ared to th« c-ost of repairing thl'attac hment part ial dent ure dO\\11 the road.

For any o r all of these syste ms , wln-nused in a Class I or II arch , primarily ill tln­mandible . an altered cast must be madeaftt·r the attachme nts have been joined totill' framework. A separa te appotn tnn-utwill often be requin-d to obtain th is im­pression and the following jaw relationrecords. because the ad dit ion of resin to

148

the matrices/paufccs requires ' K "<:'PSS to theretentive meshwork ill the same areas ,L>;would lit, used to join the altered east trays.With the attachme nts fully seated. the al­tcrcd eas t impression can he made wi thco nfklcuce since the support of both thehard and soft tissues has lx-en optimized.

Resili ent Attachm ents

A final classification of extrucoronal attach ­men ts n-umins to be discussed. The use ofresilient materials to line lite matrices ofsome of tile tu be-type uttacl mu-nts has al­ready lx-c-n uu-nttoned in p,L>;sinK Th eseco uld IJe classified as resilient attachments.but the te rm is ilion' apt to lx- rest ricted toa relatively recent development, be st Illus­nuted by the E HA and O-SO attachme ntsystems. Both of these systems we re deve l­oped to ullow for stress rd it~r and for sim­ple and rapid replacement 01" till' resilientcomponr-ut c. Both systems wear ou tquickly hut are so eas ily replaced that somepatients can do the job themselves.

Th e EHA syste m is simila r to the Cekaattachment already described. the di ffer.ence Ix'inp; that the pat ti\: i ll the ERA is aplastic man-rial tha t snaps into a matrix ringattac hed til the crown (F ig 10-31 ). The riugcomes as a castablc plastic pa lle rn. FOIlfdifferent levels of retention are uvallablcwith fOIlT slightly diffe rent plastic put rtces .A metal hOU Sing with intcnml retentivegnx)\'('s for the plastic Inse rts and exte rnalridges for n-sin retention is included withthe at taclmn-nt system. The pat r ices arecolor-coded . with tilt:" wh ite unit being themost !l('xihle and progressing th rough or­ange to him' to gray .LS the most rigid.Hcceut studies have Indicated that after ashort time , there is no clin ical diffe rencebetween the three co lored uni ts. Most situ-

Metal housing Resilient O-ring

Precisio n Attachments

Castable plastic stud

Fig 10-]2 Resilient stud attachment (0-50 ), extracoronat in crosssection.

atious willneed only the white pat rix. as thoamount of retention it gives co mbined withother frictional retentive eo mpo!ll'llls ofthe partial den tu re, is more than ad equate .A trephine bur that allows rapid removal ofthe worn patr ix is p rovided. Also providedis an insertion tool that carries tlw new pa­trix into the partial and force s it to place inthe housing. The entire ope ration takes lessthan a minute. A proce ssing patnx is also apart of the syste m. It allows sonu: spact" formovement of the patrix in the housing toen-an - stress relief, as it is slightly longerthan the colored units that are Installedafter p rocessing. The EHA has becomevery popular d ue to its ease o f replacementand the s l i ~h t amount of flexibiIity it a11O\\'s.

The o -SO attachment is actually classi­fle- das a stud attachm ent , with a pat rix th atlooks sOlTK'wllat like a doorknob and wi th arublx-r O -ring; mat rix. The O -rillg; comes, inits most rece nt form, wt th a meta l housingnot unlike that used wi th othe r syste ms(F ig; 10-32). The syste m also uses a pm­ccssing ring that is replaced hy a soft rub­he r ring; befo re being placed in the patient'smouth, "111l' rill~ is quite so ft and therefore

quickly worn , hut it can he easily replaced.The old riu g; call he p icked o ut wi th all ex­plorer o r small tweeze rs and the ne-w ri ll~

pushed into place with any small hhmt­ended instrumen t. The patrix comes as acastable plastic patte rn that l.'"J.1I be attachedas all cxtracoronal attach ment o r, in aslightly diffe n -nt form. as an ovenlentnrestud. Implant manufacturers p rovi de a situ ­ilar stud ami O-ring attachments that screwdlrectlj- into the flxture or onto the trans­mucosa] abutme nt. It is the most Ilexlble ofall the attachment systems and is thereforeof greatest use ill situations where toothsupport is minima].

For the mo st part , the metal hOllsill g;.~

for the nuurtcvs ofthe EllA, the O -SO , andother resilient systems "ill be attached tothe fnnucwork of the removable pa rtialdenture with resin. not soldered. Tlu-sematrices call he rela ted in the mou th o r Oilthe cast. In either case , a thin coat of n-sinmust be can-fully ap plied to the exte rnalsurface of the hOllsing and allowed to set inthe pressure IXlt before the hulk of r esin is

added . This step is made n(x1:'ssary hy thefine retentive groves and ridges 0 11 the ex-

149

•Advanced Removabl e Partia l Dentures

Surface to be etched

Slightly taperedmicrog roove pins

Fig 10-33 Inter nal view o f resin-bo nded pin attach ment withmicrogrooves ,

tcrual of the housing. The quality of thejoint between the housing and the partial isdepe ndent on the highest-quality resi n­metal interface. If a laborato ry-grade repairresin (such as Perm by Caulk/Dentsply) isto be used, remember to remove the fibers.The fibers tend to clump when the resin isadded using a brush. Once the resin hasfully cured, additional, fi bered resin isadded to complete the attachment and theunit is placed back into the pressure pot .Late r the hulk of the resin can he thinnedappropri ately 10 [it within the confines ofthe part ial without damaging the inte rface.Autopolymerizing tooth-colored resin canalso be used to reduce the risk of a show­thro ugh of the pink resin for those situa­tions in which space is limited and estheticdemands are great. All intern al traces ofresin must be removed , preferably unde rmagnificatton. after the processing unit isremoved from the housing and before theretentive patrix is snapped into place.

The resilient attachment systems workbest when thei r path of insertion/removal isrestri cted by the guiding planes p reparedon the abu tments and the well-fltttng guide

150

plates of the modern framework. \Vhen arestricted path of insertion exists, patientscannot jam the attach ment to place from avartetv of directions. They are limited tothe path dictated by the planes . Patientsmust be advised that if they wish to mini­mize the wear and replacement of the re­silient elements, they must place the at­tachment partial with their Hilgers only,never biting it to place. \\1ICn the resilientcomponent is forced to function only alongits intended axis, the wear is greatly re­duced , for both the EHA and the O -SO , aswell as for any othe r modern attachmentthat uses a resilient insert . The manufac­tur ers often show these attachments asbeing the only connection between the par­tial and the abu tment teet h, implying thatthey function as an adequate rest system inaddition to providing retention. It is myopinion that th is approach breaks the basicsof modern partial denture des ign and con­struct ton, and should therefore be ignored .

It has been implied that all cxtracoronalattachments are east as a part of abutmenterO\\11S. This is not strict ly t rue , as recentevents have demonstrated the high level of

SlICCl'SS of resin-bonded extmcoronal at­taclunent s (Fig 10-3:3). \\1lile it lIlay 1I0tappea r that an etch ed and bonded n-stora­tion would have sufficient retent ion to thetooth to resist the additiona l stress of an at ­tachment, when microgroove preparation0 11 the abutments is combined wi th ca re fulpatien t se-lection, the bonded attachment isa successful and conservative means of ob­taining the esthe tics of an attachment !'» "S­

tern. A review of the work of Scharer andMan ncllo will acrfllaint the reader with theparunu-tcrs of this therapy. III these casesespecially, the partial denture should not10:«(1only the attachments. Addit lonnl ubut­ments with positive rest p roparut lous . ei ­ther ill natural tooth struct ure, crowns, orbomk-d surfaces, will reduce the load 0 11

the bon ded at tach ment and shouldIncrease its length of se rvice . All the­extmco rouul attachments discussed in thischap ter are amenable to bonded restora­tion and han - been used Sll("("t'sslilll" oyerthe last 8 to 10 yl?ars.

There are a va riety of stud nttaclunentsthat c an he used for retention of the re­movuhle partial den ture even though the)are gcnerallj-intended for the overdcn turc.The stud attachments, placed either in theendodontically p repa red toot h or an im­plant , create potential prolih-ms for the

Precis ion Attachments

precision attachment part ial because thctrangulation is limited by the long axis or c-i­ther base. They are to be placed first amithe remnmdcr of the ~uiding plane/attach­ment surfaces uhgned with thei r long axis.If the ir ali6'llllll'nt causes the other {'(lIll IX)­

nents to he directed beyond a usable limit.the use of the root or implant for retentionshould he ret hought and these un its usedfor occlusal stops only. A recent, and as yetnot fully tested , s)"Ste m utilizing a ball thatcan swivel in a pressed fill ing offe rs thep romise of allO\ving a self-cente ring at tach­mcnt to ()\'l'rCOlI1 {) alignment probl ems.

A mastery or these few attachment sys­tems will cover I IH~ needs of most prostho­don tlsts as wel l as provide a basis for tileund erstanding of those systems to ( '( 11m '.

\\'hile the actual attachments can he ex­peeled to change and imp rove with time,the techniques for their use are standardand must he a part of the technical back­ground of clinician and technician alike.The pn"l'ision attachment, in combinationwith the othe r aspects of advanced part ialden ture co nstruct ion, offers ns the possi­bility of mal-dng prostheses that are e-s­

thetic, reten tive, strong, and problem free,and that are undetectable by and \\; 11 notcompromise the oral health of the ourpatients.

151

Advanced Removable Partial Den tures

Sources for Precision Attachments

152

Implants and RemovablePartial D entures

T ln- advent of endosscous iJ lIplants, hasdramatica lly changed our vk-w 01the

complete denture, single tooth replace ­mont, am i full-mouth fixed re sto rat ion. O ursuccesses ill these areas haw k-d to theconsideration of obtaining Implant suppo rtfor the removable partial dcntn n-. Theideal lise of on e or more Implants fur theremov..rblc partial is to eliminate the distalextension base, especially in the mandible,where chronic problems associated withthe loading of the eden tulous ridge haveplagued the profession. A second und moreco mplex indication for their lise is us a re­p1oK'(' 1I 1Cnl for critical abutmen t tee th. Allexample iswhere a mandibular canine SC IV­

ill~ a." a primp ab utmen t is lost, leaving alateral incisor as a terminal abutment. Inthe past, as describe d earlie r, om- Illigl ltha\'(' considered a hinged major connectorin this situation. A single implant placed illor Hear the canine position can provideboth vert ical support and. through the useof any of a number of attachment syslpms.n-tcnnou as wel l. The future would appearhrigh t for the usc of selected implants . pro-

\i ding critical suppo rt for part ial dcutun­patie nts and still kl'l'pillg the total co st oftreatment at a n -asonnblc level through theuse of the rem ovnhle partial dent ure as thep rime restoration . Th e well-planned lise ofall Isola ted implant in these sttuatfons doesnot preclude a late r. more comple-x treat ­me nt plan ut iliv:jll~ additional implants am ifixed restorations.

Class I and II Situations IThe ohvioll.s situation in which a single im­plant call make a major contribution to thesuccess of a removable part ial denture is illtho distal extension part ial de nture. Pntlcn tshave often lx-cn dissatisfied with our lu-stefforts, e ithe r with conventiona l or preci ­sion attucluncnt p artials, beca use of'chronlcsore-ness under the dista l extension base.Thi s is especially true in those situat ionswhere the 0Plxlsing arch contains a fullcomple ment of natural teeth or Fixed p artialdentures . \\1w lI a compl ete den ture is ill-

153

Advanced Removable Partial Dentures

Soft tissue level

oOccl usal view

Fig 11·1 Late ral view of im­plant abutm ent w ithout a centerscrew access (experimental).

volvcd, the potential load on the tissues is

gelll'rally reduced and there are fewer pa­tient complaints. Implants placed d istal tothe foramen, idl·ally ill the area of the sec­ond molar, would effect ively change theClass I or ITsituat ion to that of the Class Il l.Th e implant ru-ed not necessarily provtdon-tcn tion, since adequate retention is mos talways available fr om other abu nucnt s.

Unfortunately, lx-causc of loug-tennridpr resorption, finding sufficient bonein the d istal extension base area br-coun-sa major Impedime nt to this therapy.Xuuwrous stmlks have shown th at im­plant loss is proportional to the length ofthe implan ts used, with special concernfor the i -mm implant, which is presentlythe shortest uvailuhlc. These stud ies haveeval uated the impla nts for lateral snpportam i retention as wel l as for ver tical snp­porI. If the implants are used fo r vert ica lsuppor t only. the S Il('('('SS of the shorterimplants may wel l show bette r res ults .There are shorter implant.. that lIIay beIIsed in th ese situat ions . The\' arc in­tended for ext raoralmax illofacial usc andare i ll the 3- to -t -mm range. Th ey have110 1 yet been evaluated for this plllllose ,hut, again, when properly integra ted and

154

if not stressed laterally. they offer real po­tential. To ear the implant with a roundedab utmen t that would provide poin t con­tact Oil its must superior surface and no e l­eme nt of lateral con tacts at all wouldallow vcrt tcalloading with minim al lateralstress. The partial denture connect ion tothe abutment will nood to be desig ned toprovide the point contact alld to mainta in

this contact throughout tile life of the par­tial. A sliding point contact lx-tween theabutment und the part ial would also allowthe expansion and cent ractton of the man­tlihlf' d uring opening ami d osing wit hminimum lateral forces I)('i ng tran sm utedto the imp lant.

A problem arises with the use of anyabut uu-nt that utilizes a center screw to

cngage the implan t. Til l' cent er poi nt isthe desi red co ntact wit h the partial, and ifthat area hears the enti re load, disto rtionof the ce nte red screw head can be ex­peered. \\'i th the lise or a hexagonal con ­flgumtion at the base of 01 roun ded centercontour, the unit can be torqued with amatching torque wrench. Il'a\ing the con ­tel' of the hall stop for full co ntact (Fig11. 1). Th e hex is inte nded to lie at or j us tslightly above the soft tissue level.

Implant s and Removable Partia l Dentures

Precision attachmentModified border

Fig 11-2 Modification of ceo­ventional denture borders withpo st e rio r imp lant sup port o fClass I RPD.

Fig II · ) Po sterior extensionof o ne de nture too th beyondimplant support.

,I,,

/ '- -./ ------Conventional

border

Precision attachment

Flange outline

Rounded implantsupport coping

Extension

It is quite possible that future advancesin implant biomechanics will provide theprofession with alternative forms of im­planIs Ihat will he subpe riosteal rath er thanendosteal. Presently, a udntaturt zcd sub­perios teal implant, tentatively called an"on-plant," is being used experimentally inorthodoutlcs and is under conside ration forlise with removable partial dentures. If theload Oil the implant can he made exclu­sively vertical , sometluug of this t) lw {'O I II<1

be used in severely rcbsorlx-d mandi bles.eliminating or greatly red uci ng tile needfor grafting bone.

\\11i1e the idea l position for Class I ami11 Implant placem ent llIay be in the S{'C­

ond molar area , any position distal to the

terminal abutment where sufficient boneremains is acce ptable. There is no reasonfor the dentu re base, whe n supported bya ll implant , 10 extend to the traditiona lborders. In fad . once pmterior snpport isuvailublc, the design of the dent ure baseshou ld ht ~ altered to make its contours a.~

muc h like ' hose of a fixed restoration aspossible (Fig 11 -2). This wil l un-an thatthere will bo 110 advantage to extendingint o till' flo or of the month, or onto the ex­ternal oblique ridge . It may \\'£'11he possi­hlc to extend one occlusal unit posterior tothe area of implant abutment support sothat an implant placed in the seco nd pre­molar position would support at least afirst mola r (Fig 11-3).

ISS

Advanced Removable Partia l Dentures

As long as the implant abutment is notexpected to carry an attachment compo­nent, the angulation of the implant relativeto the remaining abutments is not impor ­tant. For those situations where some re­tentive attachment is required, the angula­tion is cri tical. '111e implant can he placedinthe long axis of the remaining abutments(parallel to the path of ins ert ion/removal),so that any attachment will draw wtth theremainder of the mouth, or the abut ment ,with its attachment component, must hecompleted first and the remainder of themouth prepared to accept that path . ThetYrc of restltent attachments that wouldmost often be used in th is situation (ERA,O-SO, or similar) do allow for a small diver­gence from the path without damage to theresilient eomponrml. Recent additions tothe available attachment systems, in partic­ular the Sphere Flex (fro m the Rhein 8:3Corp of Bologna, Italy, and available inNorth America from l'rcat Corp ), offerswivel ball attachments that screw dircctiv

into the implan t, allowing 8 degrees free­dom ofrotation. The retentive clement is anO-ling much like that or the o~so system.

Space may often be at a premium inthose situations for which an attach mentcomponen t is intended, espe cially if theimplant is placed quite posteriorly. A mea­suromcnt taken from the occlusal surfaceof the opposing tooth must show that spaceexists for the abu tment, the attachmentcomponents, sufficient resin to pick up theattachment, and for the denture tooth des­tined to complete pros thesis. Whe re spaceis minimal, the occlusal surfaces of the den ­ture tooth over the implant are prot ectedwith metal as in anv attachment situation, Ifthe implant is distal to the first molar, it isnot essential that a denture tooth be placedwhere spaee is lacking. Occlusion th rough

156

the first molar, when the base is well-sup­[JOlted posteriorly, will provide adeq uatemastication.

The implan t-pa rtial interrace can beconstructed in a number or ways. The pos­sihili tv or using a modified healing abut­ment as the stop for the distal extension iscertainly to he considered. A pot en tialproblem arises from the fact that the heal­ing abutment is not to be torqued down tothe same load as a t rausuruc osal abutment\\'ould be. This means that screw looseningof the healing abutment C:Ul he expectedand, indeed, that has been my experien ce.As long as the patient is aware of this possi­bility and inspects the healing abut ment pe­riodically, no damage is apt 10 occu r shouldthe abutment loosen . The modification ofabutments that can receive greater torqueshould solve this problem for most situa­tions, although at some increase in cost. Acustom casLing to the abutment or to theimplant can be made to conta in either anattachment component or the rounded oc­clusal stop. These can be made using thehexed UCI.A-type castable abutment or bymodifying anv of the hall abutments nor-

" "mallv used for ovcrdcnturcs . Contour mod-iflcations of these attachments would bedone on the working cast so that the angu­lation or the sides or the rounded occlusalstops would be in general alignment wtththe guiding planes planned for other abut­ments. This step will reduce the need furexcessive blockout on the partial.

The clinician must choose bctwccu mak­ing a custom metal casting to ride on thehall (rounded occlusal stop ) or to allow thatcontact to be in the resin of the denturebase. For the fonnor; implant analogueswill have to he p resent on the master castfor the partial denture casting. They maybe needed on the working cast for any fixed

•Implants and Removable Partial De ntures

Point contact

Finish line

Blackout

Res inretention

Fig 11 -4 Design of overcoping for implant stud attachment.

componen ts as well. On the maste r cast,the patrix (ic, the ball ) is blocked out so thatonly the center of the ball su rface will hecontacted; th is unit is duplicated in refrac­IOJY (Fig 11-4) . An ove rcasting is waxedwith retent ive heads or loops to lock thecasting into the denture base if the over­casting is to he retained with resin alone . Atan g extens ion, n llHling to the retenti ve

meshwork will also be required so that thecasting can be picked up from the mouthafter the framework is fitted. In situat ionswhere space is limited, the tang extensionscan he soldered to the retentive meshworkof the part ial den ture casting.

The anterior retentive componen ts oftrnplant-supported distal ext ension part ialdentures need not offer any stress relief asthey shou ld wtth the convent ional Class Iand II situat ions. Either mtmcoronal or ex­tracoronal attachments or conventionalclasping call be used effectively, since thesepartials arc now all "tooth't-supportcd .

The other major area of'tnte rest is that inwhtch the implant becomes a prime reten­tive abutment, as it would if a canine were

to he replaced by an implant. Tn these situ ­ations, we are going to be faced with deci­sions on the best way to integrate the im­plant into the support, stnhili tv, andrete ntion of the partial den ture. we willalso need to consider the esthet ic rep lace­ment of the missing tooth that would hefound over the implant in question .

Perhaps the easiest approach will alwayshe to place an attachment on the imp lant,eithe r connecting directly to the implant orthreaded onto the transnmcosal uhutm ent .Given sufficien t space , any stud -type at­tachment could he used along with theEHA- and O-SO-type systems . The attach­ment need only fit within the shape of thereplacement tooth and allow metal reten ­tive extensions from the framework thatwill provide dependable rete ntion for thedenture tooth and associated denture baseresin. When space is vel)' limited, as onemight fi nd in a severe Class II Div II case,it may he necessary to place a Single toothOil the implant and usc that unit us a con­ventional or attachment abutment. Wehave little experience in this area as yet,

157

Advanced Removable Partial Dentures

and cannot predict the prognosis of t )in~

this im plan t abutment to th e part ialthrough the implant crown.

\\1len using the implant crown as a eon­vcuticna l abutment too th , the partialFramework must 1)(' intimatelv in contactwith all remaining abutment teet h, naturalor crowned, so that I he teeth " ill lit' clfec ­lively splinted to the implant. Th e 1;I<:t thatthe implant crown will not change its posi­tion tn thc arc h while the remaining naturalte eth have the pOkntial to migrate shoul d11111 complica te tile (Iesign if tile part ial filsto our standards and is worn by th e pa tien tOil a daily basis. Should the pa rtial 110 1 heworn for any k'll~hy lX'riIXI, this disparityill the possible llli1!:ralioll of the abut men tscould result in a framework that 110 longerfullv spats.

Fo r these singlc im plant abut mentcrowns, the lise of an extracoronal at tach ­111 (;lIt to retain the parti al denture scctns ill­dicatcd. lnt rucoronal uttach monts willmostlikely 1I0t be po ssible because the Internalcontour of the crown is taken lip hy the im­plant components, The selection of tlu- at­tachmcnt to be added to the implant crownis driven by both till' design of the impl antand the needs of the partial denture. Sincethe implant crown. prope rly Integrated . willnot move, there "ill be some need to con­xidcr stress relief if till' partial in question isa Class 1. The potent iallever arm is all issuehe re as it would be for unv cantilever froma tunntnal implan t. Unfort unately, thoro isno specific body of knowledge to which torefer at this time to lu-lp us wit" our deci­sions Oil stress relief \\'e wtll have to draw0 11 our experience with other implant pros·theses as well .-..s conventional kuowl<'11ge orthe removable partial denture. For Class Isituations, in the mandible atleast. it wouldappear that if then' is no possibility of pos·

158

tenor implant support , tln-n tl.e more re­silient t!lt' attachm ent. tln, less tile possibledamage to the implant. l 1Jis would su~est

a hall attachme nt with an O-ring retentiveelement placed extracoroually as the bes tpossible option. Obviously; conven tion al

clasping with resilient wire forms " i ll alsooffer st ress reliefdependi ng 011 the amountof rolk-f built into t he casting,

Class III and IV Situations

\\'e would expect imp lant s ill Class lIT andIV sttuanons to IX' IIs('11 ax ovcrd en tureabutment s, usually \\itll some l)lJe of at­tuchnu-nt syste m for retentio n of the par­tial. \\1Il 'lI two or mon- implants ca ll hespl inted togd her with a har, a clip-ret ainedpartial offe rs a dependable option. Th e bar­dip assr-mhly can he used with any otherattuchnu-nt system, cou veutfonal daspil lgon other teet h , and with pn-ctslon milledcrowns 10 provide both lateral stability andrcu-ntlou . Since the paralle-lism of mult ipleimplants cannot be assured , the bar-d ipsystem allows any IIJU!t'R'uts in the ~old

cvltndr-rs to he blocked out in the housingand no! he contact ed hy the partial casting(F ig 11-5), The superior surface or the barcan a lways he used as a vertical stop for thepartial so th at the implant attachmentsneed take no wea r at all From the housing.

T he lack of vertical slJat'll for the implantattachment system will always he a potPIl.t ial source of prolJICIlIS. For th at masonalone, a d iagnostic \\" lxi ll~ ami set-lip is ('s·scntial. Th is procedure must contain anevaluation of th e implant attachmen tmechanism, be st accomplished by placingthe implant components 0 11 the diagnosticcast afte r a plllly matrix has been madefrom the diagnostic set ·llp so that the ac-

•

I

•Implants and Removable Partial Dentures

Cl ip Conventionallooth blackout

Fig 11 -5 Bla ckout of implant bar-clip fo r cast partial de ntu re frame­wo rk.

tual remaining space can be dearly identi­fied. This step will also allow th e clinicianto decide if metal occlusal surfaces on thedenture tee th w tll he required to protectthe attachment system, since the additionof these surfaces will he a factor in the finalcost of treatment.

\\'1Iile th e use of implants in conjunctionwith removab le parti al den t ures is in its in­fancy, the chances are excellent that newsystems and new uses for those systems will

enter our pract ices in the fu ture. As long asimplants are used in conjunct ion with th or­ough mouth preparat ion of soft and hardtissues , employ precisely fitt ing castings,and are cared for with regula r recall andappropriate maintenance, we can be confi­dent that they will improve the quality ofremovable prosthodontic therapy. To ex­pect them to be a solution fix all our prob­lem s wit hout th is level or careful adherenceto basic principles is foolha rdy.

159

Index

P'l~" uunrla-rs follo\\t>t l by "f' ,1,·­Ilo t" fh,'lJrl 's; numbers fiJl1ow('(1by "' " ,ll'lIOtl' tublcs

AAbutuu-ut s

for c h,s I fl I'D, 2.'3L 2J-25for c hs, II HPD, 27-29, 2Hffor Class III HPn, 32~1..1 . 3.1ffor Chss 1\ ' BPI) , .1-I--..1..=jddillt'l,l. 7-1)Tl'tlll in;' tIIl ' lll for f'lKlodolltieall)"

n,mpmtllis(",1. 9, 9f."...I,'t1io ll of. S. 9

,k l.:,'n ""u dip Tl1llattllwnt. 132.133f

A.k li!in · mouth pn'pardticmIllnl' \('l.IIIIf'lal contours ill. 47- 19bomk- dresiu co ntours in. 49--50contour apprnadll's in , 47-50contour height-und" n:u l de ptl.

n'1alic>mllip in, 39-·m , -III', !ia"'110 slie , 39--10, -101'guid ing:pl.un- ill, 39. ·lOffur ( )v l'rn ' p i ll g!OW ft'ftj"\1 1S, I:Wposit i"n ill g: dr-utun- teeth in.

-10-1 1snrv('Y"d c-ro wns in, ,31h34

Algi lla l< 'ill final impn'ssiml , 3..'5 , 3Mm ixillj.( o f. 4ill p Tt·lim inill)' und filia l irupr cs­

sions. 3. .jforprm i sioual n-sin HPD, 120

Al1oy-<u lIIl-.. lsile rcst orauou.IIml" r t''{h1ill~ RPDs, 99. 99f

Ann..' n -storatiou. of abutment1; ~ ·lh . 99

160

Aln-red c as t imp ressio llS, IOIII,I" -po lir tl'd miql U' I()r,

(iO.. 6 1, 6 11"fi,r intrac-orouul sc-miprcctsion

att.u-hun-utx, 14:3[uw relation records for, ()]'l,u' lIIala li],ular Class I and

c lass II IU' D s. ,j l{....,jH

lilah- ria l f .r. 59for pn-cision alladlln~llf .I,·n_

(lire . l iSre moval and trim min g o f. 60t ravro ns tmonou for. 59

AIt , , ~ 't I l'as1s . for mandihulur Ilis­1;11 , ·Xk IlSioll s. 74

Ama l,galll rr-storanoosp n 1);lratioll for occlusal R"SI

sc.~<ll s. 4 2.-......n. 4-1 fAnlc'rio r-posff'rior ha r, 10:\ lfal·I' lllf'nt co mpm ). 'llfs , pick-up

o f, 117- 11'"Attadlllw nt(s). See Preeisiou at­

t N,llIm'll f splt'm (s)

BHur att.uhnu-ut, without di p, L10Har-cltp att "dlTl lCIlt (s ,l, 12S-1.11Hlockont

witll 1,,<1/.\,, for clasp p lal'l' ll)" III,(Ill, es r

o f 1I 1111, 'n 'lIts. (-j(-j

",~n-W li,lil1g p lam· rr lalim lslJipill. 6.3. 65 f

wu\ n-lu-f p ads ill, 66BOIl.I.'tl llld all'tmtollrsdll~lI lnm n -st seat am i, 17. 4Sfinal im pn'ssioll fur, 47fi lli .slli ll~ aIMI , -..,lishing.. -I'>-J1:l

gllilling planes nn eas li ll~ ;lJld.4i . 4S

Illicn lj.,fTO" \'P p rqmTatio ll of"astillgs am i, 47, lkf

vs bonded resincontours, ·I IJ-."')(lwas ·np ,111l! sprniu g,lH, ,I i'll'

Bomh '(l n-sin oontours~uidi llg plane-s f'x , ·19rr-st st·"ts for; -19. ·19 f

Bml'illg arlJl. I6-17, 17fHn ~l. I I );llatal strap . 10, IOf

in c lass II BPI), 2HfHurl(·ws 1) 1)' Foil. fnr ,.tI(l", Il l\'­

N agt', 123

c('..a.sl H'uMn'able partia l l lt' u illn'

( HP O), conversion of ('\isling10 pro\is io nal re -si n BPI).119---12.1. 12()f

o b H<"Saxai lach m' -llf. 144- 1-1.'5.14-3f

C illg ilium rest. S. s fIilr IXlIld,"(l ll}("t<U ('OIl t. )! ITS, -17, ·1,,)p rqxlndio ll of, -1.'5, 4-')f

( ;ir('lun fl' ll ' Il(ial "h ;psr-ast, Hi f, 16-1 7• .12i ll r-lusp l'''lmir, fJ6. UBI"ill class J HPl>, 26 , 271"ill Class 11 BPD. 31ill Clas s IV Hrn, :3Or'"lg onlay rest wnh, 3 1, ,11fl"f'p l,I(\ ' m("ll l for frad llf. '<I , \Hsllh lr,-1d i \"f' mouth pn 'Il<lra lil lil

fnr, -I.'l, 4-3fwire (wm ngIJI), 17- 21. 1M. mf

( :Ia.sp arms. dnmi llg ill ll. ....igllIrdllsff'r, fi..I-65

( ;I,lSp fmd ure, cause, 9.3

•

Cbsp(s)adjllstlTl f'llt at ins ertio n, SSin Class I H.I'\), 26-27, 271"i ll Clasp II BPD , :3lf, :31-:32i ll Class III HPD, .14in Class IV HPJ), :\6design or , ],'>-22

circumferentialcast, 1.'5--17, lflf,17f, isr

d WllTnfpll'ntial (\',T()11g1It ) \\1W,

17-20illfraI11l1gl', 20- 22seler-tinu of, 1.'5

in ruandihulur Class I HI'D,26-27

,,,·i re , 72- 74Cl ass I removi\ hle partial dt'IlIIl W

(HI'I))

dcsi~ 1 slwciHes in , 22-27iIlJplants with, 15.3- E i-1

Class II re movable pa rtial den ­turc (i\PD)

design spe cifics in, 27-:l2implant s with, 153- 1.34

Class III rem ovable partial dell ­t u rf' (1\1']))

de sign sp pcifk s in, .12--,14Cbss IV Holllovablc partial dell -

turc (RPD )application of, 158de sign specifics in, :l4--;',,'iimplants wtth ]51)- 1.'59

har-dip assclIIhlv wtth 158.I.'5Df

verti cal space proble m in,158 - 1':;9

Composit e res torat ion , undercxisting HPDs, 9!-)

Connecto rsin class I HPI), 2.'5[, 2.'5---26in class II HPJ), 2\)[, 2\)~10

in c bss III HPI) , :j,1-:j4in c lass IV HPJ), 35r, J5-.:j6hing ed major, 107- lJOuumdihularmajor. 11, I 1fmaxilla ry majur, 10, torminor, 11- 12modificat ion sp aces for H1 issillg

anterior te-e-th, JOse-lection of, 9-12

(;OIlSClIt le tt er, 6Conxultutions, prcprosthctic, 5-fiContact spots. adj ustment of, 75Continuous (stru t) occlusal res t

splint

c-ross sect io n o f, ] osrpos itiw rpsts with. 106with te rm inal h'u idi ng planes,

103. 106 fw'axing of, ]()fi

Conversion, for too th lossm.mdibulur; aomuxillar; :jO-:31

Crowns. SI'I'lIl so Slln'pved crownunde-r existing HPJ), Ufl-lOlporcclaiu veneer, I()O- IOIprpp amtiOl I for iutrucoroual at -

tachmc-nts , 118- 119, 119flimier removable pa rt ial dell­

turos, 99-101

oDentnrr- has e

.uljustrnonts ar eas ill, AH--69insert ion o j', 81)

Denture teethadd ition to HPJ), 97-91:1. 91>feircumfpre lllia l clasp exit an d ,

!·n, S4fdiasl l'mas and, k.')

fhral \\~L,,-ing ami wasillg for try­in,A5

flaskill g of. 86hvpc-roor-luxiou adjustment.

1)4--1>.,)

p laePHIellt or, k2-K-'5resin flallge contour ami, k.'3, 8:3fre sin repair of. 9 '1HPD opposed by complete dell­

tore. 1).1 , 8.')HPI) opposed by natu ral teeth.

1)4---&'isl'(xl11l l molars in mamlilmbr

HI'J), k.'5selec-tion of singl,., 14split paeki llg of flask, /'i6tillting of, 86 -87

Ik signof ahutmc-ntx, 7-9of clasp ret ention, 15-22c bss I, 2:1-2 7c ia,s 11 , 27--32Class III , J2 -34Clae, 1\: J·t--Jfiof connectors, 9-12c-lements of, 7- 22path of insert ion/re mov al and ,

22-2.1of resin rcu-ntton. 12-1.3o f rests , 8-9

Index

Diagnosti c eastdrawing d"si6trl O il, :11>sn n ·p)in g, .18

Diast cmas , ill H.PD~ , 8.5Double r-mhrasnrc clasp, 16, 161'1) llp licatiollagar~ for, 67flask for; 67liquid-powder ratio for n~fnlc­

tory cast, 67

EEmbrasure clusp

ill Class \I HI'\) , 2S( 2S-2})re-pair 01; 97, 97fsubtractive 1ll00 1t!J preparation

for, 4.'5, 4fifEndodontic cousultatiou

prt-prosthc-tic, 6Ex t racorun..rl pre cis ion attach­

ment (s),14.1-1.31alt ered eas t for Class 1 or Class

II, ]41)Ceka Hevax , 144--14!), 14,')[EKA ove n lplltll w matrix, ] 471'1<:H.\ patJ-ixill. 146, 146fextension c-utback of ~ l1 pport

h XJt!J, 147lIader ba r, 144hingpd, ]43pin-tube, 143- 144 . 1441'pla stic- pattern placement lin-

goalto ridge cre st , 146, 1461'rosilir-nt , 148-1.3 1rigid, ]43---]4S!-\oilcl l, 143f, 14,'5---146splf-aligll llu'llt of, 148,';Pt-IIP mill WitS-llP of denture

J(Jr, 148,';oldering vs resin att achme-nt 01;

U8

Ffinal imp ression . s.,c IIlwJ Pick-up

imprl:'ssion; ]'nelilllillilly im­pwssilm

algillatp , 5.'5for bonded metal contours, 47lliagn ostie cast in, 3.3double-pour tedlllifjlW(or, 5.')......,')6silicone-type, ,),')for su rw w d crowns, ,'51tr illlilling of cast, ,'5t

F nllll('\"n rk dl:'sigllmodillc,ltions of. 124, 1241'

161

Advanced Removable Partial Den tures

FUlld ional fitof frame 10 rk-utun- It't>j1J. , 6--77o f fr.lI IM' to nuturnl tl't 'l h, 77n·t rufitting of Il'"" Is ill. 77mtation of fram.'\mrk in . ,6-77~tn·s.\ rehefiu, ,6

G( ;ui(l" platt'o\

us minor connectors, 12fo r positivp rests , 9, ~J f

C;,Jid illg planesfor bonded un-ta] contours. 47, 41';hu , 't'al <.l1J(l liTlh'llal ('xlt 'lISio ll of.

·12fill c la,<os 1 BPI>. 23--Z.'5. 2-tf. 25fill snh tmd in' lI KJllth pn"para­

rion. -11. -11 f, -1Z, -1Zf. -16

H11i1l1.!;....llIlajorO)lllK't"tOf)l. 10, - 110

double cas ting coustr uction of.lOS. 109f -

fr ontal view nf, Illi . [(~'if

I,illg" (Iesign for. Wiindicntio!lS for, lililprohli'Il IS with, IOH- l l 0rr-st preparatiolls li,l'. 1Oil- l09W'JI( '('f{'(l lahia l phil., ill. 107, 1081"

l-har clasp, 20f. 20--21ill Clasp II RPD. 3 1ch\.I. II 1Il'1'li lla. 32ill CUss I HI'D, 2("tI_Jllt-ba r rt'laliollship with, 21.

2JfI-hal' \\;1"\'" ehsp

for ci rClllufl'rl' ll lial cla-p r{" -

placement. H·I--!).'), 95fc lass II maxilla, 32ill chss IV HPJ) . :](i

Illlrm 'diah' h 'llJl)orary n-movuhlr-partial rh-ntun - ( 11 1']))

clasp urtns for. 12:J- 12·jl -bar \li re ch\ps ill , 12"3matr-rials for. 123prt' p'lratioll for. 121

Im plant-partial illkrh n ' . " IIl-st n ldion of, 1.51i--157

Implalltsill c lass I ;Uld c h ...~ I I HPDs.

1.5.1--I.'i':lahullllc ni CIll\\1ISOtl sill,.,-tt.. 1:;'~

ahlltmclll for. 154, 1.54f

162

allj.~lIlaliull of. J56erowu of as COIl\"t'lltimlal ,ll >11t­

IlK' ll t tooth, 15S1t ·11K'll of. l5-i.M·i-t"l'ilig fo r implant silld

attachment , 15, . l.:i' fIX~ illl)1l for. I ,)(j

pusl,' rior ex te nsion of 01'"dl'll t llr{' l)(",llIHI. 1.55, I,).')f

posh'rior support of Class I111'1), 154, L'5.'5f

as rt-tentive abunnout, lSisjHlr'(' ami . 1.'56stud-type attachments Oil , I,'>i

ill Ch,,\ III and 1\ ' situa tions.1,').3--1.59

Impn ·ssiulIs_~ Final im pn's­s io ll; l'i<'k-np impn'ssio ll ;1)....limiuarv illlpn~s ioll

Illd sal n -st, SfIlId _\;11n -st "...ats

pn -paration ufo44. 4--4ftndm-et n -tai ru-r; 2I'i--29IlIfr;(I'IlI1-\(' d asp!s}

Ii)r ( ;h,,~ I and Class II 1\1'1>.20contmuuhcuncn to. 22I-har. 201', 20-21L-ha r, 2 1, 2lf,IS rI'(la ir "':ISp . 9,i - W5, 951'T-har, 21h_JlI,-bar re lation slrip ill. 2 1fV-bar. 21

Iusc-r non, of dentnn- In...-. S.~911I1r.lt" nJIMl ,lltadlln ('1lt (s )

' . l<4iJllt llu lific.'<ll:ioI1fIK,12-1. 124f'·Il n pn1Mratioll for. I IS- 119p" i .\ioll, 133-13.')pn-paration o f stone I<)(,th O il (Ii­

a).,'l loslic cast. JIBS{·ulipn...-is jou, 131:>-- 14,)

Jawn-Iuttou n'(~ml (s )

uhen- dcnst impress ion >lII(I , (j lcentric n-lation in, 81--82l1 11 1('-il l{i sorcon lact in , S2

l ~dT-I ,,)..\t, Stlfae:...-llI..... . Ml

ill,li":ltio ll for. 79for m,L\t t'r (.'usn , 57mlL\illa~' \lil ll ('OIlC ami fK liStt'­

rior tleTllnre It'dll. 1)2. 1';2ffor pn...; sioll ,lttacluTI\'1l1 (Il'n­

tll" " 118

regislra ti" lllTJah-rials for. 79---1;U.sof

for HPJ) upp•.>M-d ~. l '()mpld"(k '1lhm', MJ--t)l

verfical d im. ' nSK)l1 o f oc...·lns i(MIin, Sif, 8 1--82

KKay-Sp(, kil. I,f)--,'j'

LI~lhorat<,r.' construction o f fra lll, '_

work '

hloekoHI ill . b')f. 6.'>--67. tiMeastiui-: ill , ,ndesign lrall sf"r from master 10

l1·frad '"Y cast. 6.')dt-sigll Irallsflor in. 64--fi.5dHplil'<lli(MI ill. 67dectrupolislling in , 71fill i ll~ a L\ting to mast e-r cast ,

71- 72inve st ing in. 70m.ucnuls for, 6.1-64]]1(>1,\1 nlti \hi ll ~ ill. 70---72phas(' ~ of. f~3 -pbstk patn-m-waxcd mi nor

(~ n ll u,,:tor junction in, 6S. !'iNfpo lisllill!4(.1 Illt:wl area. 72, 72f~]J nl i llg ill, 70 , 70fwaxillg ill. ('j..t;f. fi8--69. 68-70, (;!.;If

wi re (,lasps In. 72-74L-Ila r d ...\ p

in CIa.\S I HPJ), 26illdil'<lIi(M 1 for. 1 1. 21f

LiI I,l~lIai pia" 's, 'l~ mino r lUI IIII'C­tors . 12

wng-te rm maintenance. 9 1

M:\1airllt'l lam '(\ \)1:\1:1Jor (1HIIU't1r)r

m:llulill1 l1:lr. S('" Mundtbnlar11l<ljor connect o r

maxillary. Si'(' \Ia~i ll ary major''( )II1I(<(·tor

repair of. !m.\la lld iIJula r , lislal extens ions. S(,,(' -

oudaf)" hnpn-ssson fo r. 74Mandilmhtr major conllf'("for

in Cia\!> IV BPI> , ;).5dt~iWlof. Il .llf

M d-\ tn l'd..\ I. s.." also Alle n '(l ('<lsl

imp u'ssio llsd illil'J.1 U'Vil .....· of. 69-70

•

jaw re!a tion w cords lor; ,'57m axillary, ,36-57record has e construction [ O f ,

,37<;1), !":if;frcsurvcv or, 57

Maxillary majo r connectorht~ading ill mas ter cast, ,'56--:57for CIa~s I H. PJ) , 2,..'5[, 2..)~2fi

for Class IV HPJ) , 35f :1""'")-·..J hdcsigll of, 10, 1Of, \Ol f

:\Iaxillofa eial sllrgical consnltu-tion, pn-pmstln-tic.. 6

:\ktal occlllsal surface-Cla ss I restoration limn of DOfabricanou of'. S9-00silicone mold of, k9, S9L gOspn lc lead attac1ml cnts to, so, s9fwax patten! with retention

grooves in, 90, 901'Met al repairs

circu mferential clasp in. 9G. OOfembrasu re clasp in, 97 , ssrinfrallUlge clasp fOf, 94-95, g,jfof major connector fract ures, 91)mouth preparatiou fm: 9,'}ocdlls"l n"st repla(1~1TI('llt , 97, 971'pirk-up irnpn~ssiOlI for, 9:5-90protection of tissue from clasp,

9'1-95, 9,'5ff\.loulh propuranon

additiV(' , :m---40, 40f, 47-54for clasp H'pair, \),'5clinical , 41- 54{lia~'1 1ostic, 39- 11d iaj..,'1 lostic p rocedures in, 37po siti('niu g rcpl.ux-mont te-e-th,

40---4 1preprostlu-tio, 5-6suhtractive , :m, 41---47surve}i ng diagnostic cast, 3K

NXutritioual evaluation, pH'p ros-­

the-tic, ,5

o(kdllsal mlJ"st rnen ts, at insert ion,

Kfi.--..H~)

Occlusal rest, 8, xfreplacement of; 97, 97f

Occlusal rest sc-atxpreparation in amalgam rcstoru­

tiuns, 43---44, 14fpreparation 01', 42---43, 4,'3 1'

Onlay rest. in Clas s III BPD, 3 11'

Orthodont ic consult ation, pre -­p rosthe tic, 6

Orthodontic- H"sins, in irn rlH'lliakte-mporary resin BI'J), 12:3

OVlTt~)pilJg

ind ication for. 12.3vs (lVe rCH1\\1l, 127

()vt~rtX)pil l g((lVercrowl l restorationadditive mou th p reparation for,

126aunolunent to raised meshwork,

127dt~seri ptioll of, 12.'5diagll ostic wax-np for, 12(-jfunctions of, 127margin options in , 126 , 1271'mast e r impression for, 120, 1271'sp fll ing und castin g o r, 12('i---127subtractive 1II 01 1tll p n'paration

for, 126vital nlmtm.-nts with , 12.5- 126with and without occlusal con ­

tOUf:S , 127

pParall elism, of guiding: pl.uros,

24 f, 24--25Patien t evaluation, in ithil exa mi-­

wltioll,I - 2Periodontal cx.nninatiou. pre­

prosthetic, 6Perioprostheses . Sec Ovorco ping/

overcrown res torationPick-up die , with wire ret ention ,

117, 1171'Pick -up itnprc-ssiou, 9;)-94

for me-tal repairs, 95-~96I(Jf precision attachme-nt den­

tu re , 116-117, 1I7fPin-tube uttar-hmc-n t , U 3- 1'U ,

144fl'olvcthcr impression mate rial

for alte red cust impressions , ,')9

for provisional re sin IU'I) , 120l'outic(s J

reinforced acrvlic, 13. 1.'3f, 14fvcnoon-d llld~I , Ia-14, 1M

Porcelain velwering, anti sur-wyt'd crowns, ,).J--,')4

Posi tive restwith continuous (stI111) occ!usal

re st splin t, 106t1cfilU'lL Swith guide p lates, 9, ufse-le-ction and forms for, S, I'll'

Index

Pre-cision uttac-lnueut de-ntureclinical proccdnros for, 116-124conversion of existillg cast RPD

to provismnal resi n BP D,119- 12:3, 120 1'

c rown preparatiou for iutru-txJIOnal, 118-1 1D

diagm!-stic procodun-s for, 116esthet ic adva ntClgc 01; [ 1,'5- 116Iruuu-wurk dt:sigll modification

for, 124, 12-11'innncdiato temporary 12.3- 124p ick--up imp re ssion for; 1I6-1I7pick-up of attach me nt COlll p O -

m-nts ror, ] 17- 111)vs couvcntioual deuture, 11,'5

Precision attaohnn-nt sysil' rn(s)har-elip, 128- 133extral"o m rlal, I4.1-1.31intracoroual, 1:1:'.----- 1:lK

sClIlipn 'cis iOJ I, 1 :~K-----14.1

ovcreopiJIg(()vprcmwlJ, 125-----127Pn-liruinarv impwssion , Sce also

Filla) impn 'ssioJl; Ptok.up im ­pression

algiJlak ill, .'3 , "removal aml ins pe-ction of, 3---,'5sequence !()l1owillg removal, 4-5st(xl t ruv modtficauon in , 3

I'rovisiom:l rexiu re lllova hle par--tial dcnturr- (HI' ])), 1HJ- 123

conve-rted CCisI parti al denturefor, 120, 12lf

fmal wR\i ng: of, 120, 12 lffixed provisronnl. n-Inforccd,

122, 12NiJllpn'ssiou r nalenal ror, 120pn 'paration o r existing BY]) 1'01'

conversion, 120, 120 rwlining of fixed provisional,

122, 122fProximal rest Sf

RIta.sed mesh retention, ill Class r

HI' J) , 20Hl'lmsps, for ll 'lilJe imp ression, 102BtTall and muiutc-uuncr- pllas(o, 9 1Recall e-valuation. 103Recipro cation, with circuurk-rc-n-

tial cast clasp, 17Hefractorv cast

clini cal ~eview of 69-70dessication or. cthquid-pcwder rat io for, 67

163

Advanced Remo vable Partia l Dentu res

Helilleill chair \'!; \<tho r.llm'\", 101-102goal uf. 102. Ilt2f -Iil..oilt-o,Tl"'d mall -rial fOf, 101.';,.'clusa! ", ljllshlll.-nt and. 103

H,·line impn's.sitJl), pn'Il;Ir.llioll ofpartial de-nture I"L"I' aur], 102

Hl'll Klllllt m.st , S7, li7fHI'JMif cast, pom; II~, ~H

Hr-puirs. pick-up impn'.s.siolls ill,!H--!H, 95-Bfi

Hr-silieut 'IttachllU'lIt(S), 14S--131EHA svstc-m, 147r, 14S-149O -SO svstern. 14S- I·m. 1491'path o( inSl"rtiolJ fi,r, ISOJl'sill vs sold.,Tt'l1" lIadlll I('1I\ of.

149-150, 15(}I: 151stud . 149f, 151

R..s in J('IIIO\<l,hlt, pa rtial tlt'lIh ue( HPD ~. St'" Illlll it'liialc tem­porary BPI); Pn "'; siolla! R"Sin

HPDHesin repairs, \).-1

of denture I"L... · [rac'tun-, 9-1of (Iell tlln· tool". \)·1

Hcsiu re-tentionc lass II conve-rsion to ch% I,

;30, :301'ill Class I HPIl, 21ii ll Class II BI' Il. ;3(1. 301'ill Class III HPIl, 3-1ill Ch ss 1\ ' RP D . 36rai"l"tlllll'slt, 12-13. 13 1'wi llfon'l-tl aCf~ lic pontic. 13f.

13-14for singl<" toot h n ' plal'l 'UK'ut,

13f. 13-14venee redmetal pOlitiC, n-I ·t,

'"BI·sl o ra lioll.s . mn !,'r . '~ist i llg

HI' I)s, 9'Jlk sl(s )

dl lg.l1 l1ll1 , Sfor Class I BI' l) , 2:1-25. 241'for Clas s II BPI>. 27-29. 281'tll'('l"saI, SIXJ;<;i li\t',.s, .sf

HI'S\ 'W-ilt, ill Slll'u'}l"ti r'rowus, 52RI'St struts, as nunor comn-ct ors,

12Rl"ll 'n liull. a<.k lihnn to RPD, 9S ,

ssrROJdl attachment. 145 1', 1.15-146Rotation, resln(1inll in C ia..... II

RPD, 27 , 2 1'1

164

Hut 'lliolla l partial d.-ullin 'S, 1 lOr.110....113

;l1lll'l'io r compoucnt hefon> ro-Milm.lIO. l l lf

untr-rior Ilaoge in. 112. 113fCh~s 1\: 110, i u r. 113fIXlSi li'\' R's1 pll'paralions for, IIIp llljl'liion in to proximal under-

t-nl, I II - 112rl'l l 'rlli vp plllj('di()IIS ill. 110rulaljon n-vc-rs a] ill, 112-11:1ml alioual ekll ](,lIts. !Ill block-

0111, 1121'

sSilil" III' impression mall 'rial

for pn l\i sional resin HPI>. 12flSp1i nlill~. I05--Hr.

wttl. hin/!:!'1I11l.ajor nlllm'dor,107- 110

Static fit, Sl'ati llg p n x"t""-" fur, 76Sln's.srelief

alld clus ps fo r m;JlUlil.llla r cbssI HPD. 26-27

ill c b s" II BI' J) . 27, 27f, 2Ugllidi ll g plam~s for. 23--2·1, 241'with illlplall ls, L'57. 15~

SIII,lra t 'liYP mo uth pn'lhlml it)llr" r<'in 'lIltiferrlltial ('h~I'lS. 4!'i. 4,'5fclnucal, -' 1--47I...fon' ('TO\Sl l pwparalitnI, 5fl, .5<}I'Ilia","1lIlslic, 3\)fur r-mbrasun- da.,l's, 4.3, 4bffiliisiling and polis1lill~ of n '('On-

Inu ring:, 46gJlilli n~ planl~r("S1 wat JlIlld itm

ill, -1:3

gnidi ll~ planes i ll . 4 1. 4 1f. ·'2..J2l: 46

inxlnnncnts for, :~U

o(,d us;\l res t spa!.s ill . ·12 C Iz-.-t:3• fill (IW1U lpi n g/o vl·rt'f(JWIl, 12fi

n-rlur-fiou of hucca] aJ lll li llgllalslIr fm1's, 45--4G

n-srshi . 4.'3-43. 441'. 4.'5 1'St'IIlI ' IlI'(' ill. 39

Supe-r C l" e palienl n ·p:ti r. 901Sllr.I'\ H.I crown. 50- 51

l,m;" ining with partial tl.·llhlR'fr,IIlK"\\urk .')4

CUP:S;l1g l,(lIltOIiTS in. 51clll!l;1l.1 margin in . .'5.1-.'>4 . ,)..I f

flual bnpn-ssion for. .31gJli(Jiug planes in. 5 1 ~'52, 52fmaskr l'ast fo r, 5 1

JXln'('laiH \t'lII"t:'nng a lld (" 11-tours . .'),1-.).1

re-st pnlM T;ltiolis ill, 51n ·lt-u ti \(· contours in . 52, 5'3fsoft liSSIU' lII'lIIagement fur. ,-Ill

S\\;nglot:k. S(1' IIi;lged majo r (1KI ­

IU'(.i o rs

TT-Imr d 'ISp . 21Thnmpsou dll\\"l'L 1:'llJf, U9- I·IO,

1<lOfTironium, for framework, Cl4TiSSIll ' -!"L"I ' relation rq~ist ratit ll i .

for J(·]jm ' im pressio n, 102Tt. lth-fmTrIl' n-lauouslnp

l1lm'(.iillll of I<XJth contac t sur -fal'l'S in, 75

fli lKiil n",1 fit ill, 76-.....

pour C'.Lstill!!: fil prohl.:m anti . 71'istahl' fit in IIK IIII!l. 75-76

Toot h lu's. (1)11n'niun of C I,L\$ IIto ( :h ss I for. 3Of, ,10---:31

Treatment plan. written , 6Tre'd ll ll 'l il p],lI1I1in1-\, decision Il lak­

ill g 1<11'. 2

uC'-har (-!.LsI'. 2 1l :nde l'(·111". atljllsl llll'lIt at i llst'r­

non, /-is

v\"ital1illlU "lIoy, for fraJlIf·\m rk. (j.j

w\\·'l'si u~

e xle m al fini.s" liru- plal'l 'IllI'nlill, {i.')---6!J. 69f

pbslit' IMllI-m .s ill, 60S, 6Sf'tiS.S I It' stop for distal ('\ l! ·II.\ j " lI

Illl'shwork and, mJ\ Vin ' clasp( s)

atladlllH 'n( 10 {rame, 7:3, 741'positiou on frarn(·wOlk 73 . 7;~ f

n lli lid ami hah-round. 72- 7:3

zZilll' oxid.. 'Ilid .'ugellol ('1..1101').

ill n-wst ratioll ma tt-rials, 79 ,I-)ll, sol'