Immediate Implants:Their Current Status

Izchak BarzUay, DDS. MSHead of Ific Division of ProilbodonlicsMount Sinji HospitalAssociate in DenlklryUniversity of TorontoToronto, Ontario, Canuda

Immediate implants are implants placed into a preparedextraction socket following tooth removal- Short-term animaland human studies have shown these implants to becomparable to implants placed into healed bone. Theadvantages of the procedure include fewer surgical sessions,elimination of the waiting period for socket healing,shortened edentulous time period, reduced overall cost, aswell as preservation of bone height and width. Althoughimmediate implantation is more demanding both surgicallyand prosthetically compared to the conventional placementtechnique, the advantages make it very appealing to patientswho are in need of both extractions and implant therapy,Int I Prosttiodont 1993;6:169-175.

W ith the introduction of "osseointegrationtechnology" to North America at the 1982

Toronto Conference, prosthodonfic treatment ofpatients was to change significantly. It became pos-sible to anchor prostheses firmly fo osseointe-grated implants and significantiy improve comfortfor those who for so many years were "sentenced"to wearing removable prostheses- Original studiesreported high success rates related to implantsplaced in the anterior symphysis of the mandible ofedentulous patients,'- It is based on these successrates that the implant procedure became morecommon in restoration of the maxillae and thenused for the partially edentulous patient and incraniofacial reconstruction. With experience, de-mands of placing restorations for the partially eden-tulous patient in less than ideal locations promptedthe development of newer surgical devices andtechniques (sinus and ridge graffing, local bonegraffing at individual implant sites) to assist in im-

Rvprint requests: Dr Izchak Barzilay, 2300 Yonge Street, Suite 905.

Box 2.334, Toronto, Ontario, Canada M4P1E4.

Presented at the University of Toronto Implant Symposium, "The

Impact of Osseointegration on the Treatment of the Prosthodon-

tic Patient,- November 12-13, 1992.

plant placement. New prosthetic components thatwouldallowfor prosthetic correction of angulationand esthetic difficulties were developed.

In situations where teeth required extraction,original protocol suggested a 6- to 12-month waitfor healing of fhe site before implant placement'-^to allow the complete ossification of the extractionsocket,' Placemeni of an impiant directly into aprepared extraction socket at the time of extractionhas severai advantages that have the potential toimprove patient acceptance of the procedure:

1, Elimination of the waiting period for socketossification

2, Fewer surgical sessions required3, Shortened edentulous time period4, Reduced overall cost5, Preservation of aiveoiar bone heighf and width

allowing for optimal placement in relation toimplant length, width, and angulation

Literature Review

Several investigators reported placing implantsdirectly into extraction sockets before the NorthAmerican osseointegration era,"'- These studiesgenerally reported poor success rates with soft tis-sue noted at the interface.

ne6. Number 2,1993 169 The International Journal of Prosthodortlcs

ediate Implanl Status Barzilay

Aluminum oxide intraosseous implants have beenplaced into extraction sockets of rhesus monkeysand baboons showing low "survival rates" ofsmooth and horizontal fin implants, respectively." "Human studies have shown poor success rates at 5years (57%)'' and at 8 years (23%!.'" The Tübingenimplant has been placed into extraction siles as wellas healed bone of human subjects with a high de-gree of success.""-" Long-term controlled animaland human studies using occlusally loaded Tü-bingen implants (placed into fresh extraction sock-etsl have yet to be reported.

Research showing that hydroxyapatite (HA) pro-duces bony ankylosis attachment when placed intoextraction sockets-' has led to its evaluation in im-mediate implantation. Fiydroxyapatite implants,designed to be loaded with a crown, were placedinto extraction sockets and showed immobile fixa-tion; however, failure occurred because of poorstrcngtb of the material, implant fractures," as wellas cement breakdown between tbe titanium postand tbe HA.'' Immediate implantation of HAplasma-sprayed implants have been shown to inte-grate with a great degree of success." -'

Farlier research using animal models to evaluateunloaded titanium implants in extraction socketsshowed high degrees of bone at the implant inter-face."' Barzilay et al-'*" compared pure titaniumimplants placed into extraction sockets of monkeyswith implants placed into healed bone. After a load-ing period of 7 months, clinical, radiographie, andhistoiogic data indicated no significant differencebetween immediate and conventional implants.

Altbough not evaluating implants placed into ex-traction sockets, investigators bave reported higbsuccess rates with titanium implants placed at thetime of extraction following radical alveolectomiesor alveoplasty.""

There have been many recent reports of immedi-ate implants witb the techniques of guided tissueregeneration. The technique appears useful in situ-ations of dehiscence and fenestration as well aswhen gaps are present between prepared bone andthe implant. Recent research evaluating tissue re-generative procedures using membranes aroundtitanium implants has shown enhanced bone for-mation at extraction sites when dehiscences werepresent." Other studies have shown improvedbone fill around titanium implants when mem-branes were used versus when they were notused."*'^ Clinical reports have documented thistechnique to be useful in the healing of immediateimplants."'"™

Recent research into the use of bone augmenta-tion materials and enhancing agents to increase

bone healing have suggested their usefulness itithe immediate implantation procedure.""'^ Thesematerials have been used with and without barri-ers. More researcb is needed before these materi-als can be used routinely in clinical practice.

While a review of the literature indicates a greatinterest in and promise for immediate implant treat-ment, much of the published information is basedon short-term data. One must still consider this typeof treatment new and not conclusively supported bylong-term controlled clinical studies. If the proce-dure is to be undertaken, it can only be done withpatient acknowledgment that placing an implantinto an extraction socket at the time of extraction is asurgical "art" and not implant science.

Clinical Requirementsfor Immediate Implantation

As with all implant treatment, good initial diagno-sis and treatment planning is essential. For theimmediate implant patient this includes the stand-ard procedures for conventional implant place-ment with special attention being given to:

1. The tooth that is to be extracted and surround-ing structures

2. Surgical difficulties3. Possible prosthodontic complications

The ideal scenario for an immediate implant in-volves an atraumatic extraction, stabilization of theimplant witbin the confines of the prepared extrac-tion socket so that it has maximal contact withfreshly prepared bone and is in proper angulation,primary closure of the surgical flap, uneventfulhealing, and final restoration of the implant with afunctioning prosthesis.

Evaluation of the Tooth and Surrounding Structures

In planning for an immediate implant procedure,it is vital that one considers the tooth that is to beextracted for its general dental health, root anat-omy, and root orientation. The published animalstudies generally evaluated extracted teeth free ofsigns of inflammation. Clinically, this may presentas an unrestorable tooth with little or no activeperiodontal disease. It is important to consider thatonce the tooth is extracted, the implant site mustbe free of pathosis. This is best achieved by properpatient selection and waiting for the extractionsocket to heal if disease is present in the area. Teethwith periapicai pathosis or active periodontal dis-ease are not prime candidates for immediate im-

The Inlernational fouinal of Prosthodontics 170 Volume 6, Number 2,1993

iiediate Implani Status

plants. Whereas the presence of caries in itself isnot a contraindication, its presence may make ex-traction of the tooth more difficult and therebynecessitate bone removal during extraction. Thisloss of bone would lead to an overall reduction ofinitial support for the implant.

An assessment of the root orientation must bemade, since this has a direct bearing on the angula-tion of the implant. Maxillary incisors and caninesare curvilinear in shape and as such the long axis ofthe root and the long axis of the crown are notparallel. Placement of the implant along the longaxis of the extraction socket (long axis of the root]in these situations may result in buccally angulatedimplants. An assessment of the root's shape(round, ribbon-shaped, etc) must be made, since ithas a direct bearing on both the type of implant-bone interface that can be expected once the im-plant is placed as well as the angulation of theimplant.

Since there are a limited number of implantdiameters available (most sizes being 3.75 and 4.0mm] it is reasonable to assume that spaces existbetween the implant and the prepared bone sitebecause of the shape of the extraction socket. Theimplant-bone interface can be classified as type !,l l ,o r l l l (Figi),

Type I Interface. Ideally, one would prefer to seean implant with freshly prepared bone along itscomplete periphery (type I). This can be accom-plished when the root is smaller than the implantand is often seen when small teeth are extracted orwhen the teeth that are extracted have had peri-odontal disease and the remaining socket size isminimal. The type I interface can be created byplacing the implant deep into the socket so as toengage only the apical portion of the socket and theprepared bone beyond the apex. In these situa-tions, once the site is prepared the implant will bein contact with freshly prepared bone along itscomplete periphery. The type I interface can alsobe created when an alveolectomy is performed,thereby allowing the implant to be placed into basalrather than alveolar bone. Unfortunately, if theimplant is forced into a deeper position, it mayencroach on other structures (nerves, major bloodvessels), be esthetically compromised, or have in-creased cantilever potential. The alveolectomy alsoreduces the potential implant length and thereforeit may be preferable to have immediate implantsstabilized within the confines of the socket at amore ideal occlusal height and then use guidedtissue regenerative procedures to fill the bone-implant void.

Type II and III Interfaces. Because of the different

Type i Type i Type I

Type I Type I i Type I

I Coronal .' ;

k'h Apical \.J

Fig 1 Classification of the impiant-bone interface.

Fig 2 Radiograph of a maxiliary rightcentrai incisor immediate implant af fhefime of insertion. Note ffie gap betweenfhe impiant and the prepared bone site affhe coronal end of the implant.

shapes and sizes of roots there is a greater likeli-hood that when dealing with immediate implants aspace will be present between the implant and theprepared socket. In the type II situation a space ispresent at the coronal aspect of the implant, whilethe apical portion of the implant is secured infreshly prepared bone (Fig 2). A type Ml situationexists when a space is present along the lateralborder of the implant. This may be the reason thatthe immediate implantation procedure was slow todevelop, since this gap may have initially con-cerned researchers as a possible mode for failure.

"TO}ume6, Number 2,1993 171 The International lournal of Frostliodontics

Immediate Implant Status Barzilay

Fig 3 Cross section ol an immediate implant piaced info thepalatal root socket ol a maxiiiary molar ol )W tascicuisris. Densebone of the paiafai cortex is supporting the paiatai side (right) ofthe impiant, whiie the buccai side (left) has only a thin iayer ofdense iammeiar bone at the interface with minimai physicalsupport. An impianf extending from buccai to paialai cortexwouid be supported by more corticai bone for overail betterphysical support.

Fig 4 Histologie section of the immediate maxiiiary moiar in Fig3. Thick, dense iameilar bone is present on fhe paiatai aspecf(righf), whiie only a very fhin nm ol iameilar bone is present onfhe buccai aspect ¡iett). The buccai-side interface is supportedby bone marrow. (Modified Masson-Goldner tnchrome sfain,original magnification -25)

Fig 5a Pure fifanium screw-shaped implanl has been posi-tioned within the prepared root socket of a maxiiiary firsf premo-lar The impiant engages bone in fhe apicai region of fhe socketand aiong the buccal socket wail but is not m contact with bonealong most of its palatal surface ¡good exampie of a type lilinterface). The site was augmented with freeïe-dried decalcifiedbone and a nonresorbable membrane. ¡Courtesy of Dr M. Arlin,Weston, Ontario.)

Fig 5b At Ihe lime ot uncovery, bone can be seen fiiltng thevoid that was present af the time of impianf piacement. (Cour-tesy ot Dr M. Ariin, Weston, Ontario.)

Surgical Difficulties

Surgical complications encountered with imme-diate implantation can be associated with severalfactors:

1. Complicated extractions2. Perforation of the cortical plate3. Socket anatomy that precludes ideal implant

placement4. Close proximity to adjacent teeth, sockets or

implants5. Difficulties associated with barrier iechniques6. Problems associated with flap closure

Complicated extractions lessen the amount of alve-olar bone available for implant support. Once thetooth is extracted, the socket must be closely evalu-ated for the most ideal location to secure the im-plant. Ideally, an implant placement guide shouldbe used to orient the implant surgeon as to theproposed placement of the clinical crown. The im-plant should be placed so that its coronal surface isapproximately 3 to 4 mm apical to ihe cemento-enamel junction of the adjacent teeth, and thescrew access should exit through the cingulum orthe central groove of the final crown. While keep-ing these factors in mind, the implant surgeon mustplace the implantwithin the confines of the socket

The International loumal of Proithodontii 172 6, Nurrber2,1993

:ilay ediate Implant Stalus

and maximize contact between prepared bone andthe implant. The implant should be placed so that itcontacts cortical plate, wherever possible, to im-prove stability. This is difficult because a superiorcortical plate is unavailable (as a result of extrac-tion). The inferior, buccal, lingual, or palatal cor-tices should be engaged if possible. This is mostimportant in areas of poor bone quality (posteriormaxillae and mandible) (Figs 3 and 4).'" When anideal bone-implant interface (type II cannot beachieved, it becomes necessary to use guided tis-sue regenerative procedures to augment areas ofthe interface that are not in contact with bone (Figs5a, 5b, and 61. However, using this techniquemakes it difficult to approximate the edges of theflap because of the increased bulk of material un-der the flap. Although it may not always be neces-sary to approximate the edges of the flap, it isdesirable.

Ideally, the flap should be approximated to ailowfor primary healing of the surgical site. When deal-ing with conventionally placed implants this is not aproblem, because intact tissue was originally in-cised to raise the flap. An immediate implant doesnot have the tissue to close as a result of the extrac-tion. The flap edges can be approximated by releas-ing the periosteum, creating a sliding pedicle flap,or interdigitating the papillae to close the surgicalsite. When placing the implant into the extractionsocket, it should be subtnerged below the level ofthe surrounding bone. In such instances, primaryclosure of the flap may preclude the guided tissueregenerative procedure.™

Prosthodontic Complications

Prosthodontic complications associated with theimmediate implant procedure can be encounteredimmediately after the surgical implant placement.These complications include:

1- Reduced vestibular depth2. Angulation problems3. Deep or shallow implant placement within the

socket

8y approximating the flap edges, a loss of vestib-ular depth may occur and make reinsertion of thepatient's interim prosthesis difficult. The dentureborder must be adequately reduced, and a softliner is placed to minimize pressure on the dis-placed vestibule.

The most common problem faced by this authoris that of poor implant angulafion (Fig 7). Most ofthese problems are easily managed with "angula-

Fig 6 Radiograph of maxillary right cen-trai incisor immediate impiant shown inFig 2 after guided tissue regeneration anda 6-month heaiing period. Radiographicevidence of bone fill can be seen in thecoronal portion of the implanl.

Fig 7 Immediate impiant piaced into a maxiliary premolar siteshows severe buccal angulation.

tion abutments" that reorient the screw access ofthe crown. Angulation problems can also be man-aged using cementable components.

A surgical tendency fo place the implant deepwithin the socket (to engage more bone) can leadto prosthetic difficulties in restoration as well as inpatient maintenance of a prosthesis. Shallow place-ment makes esthetic restoration difficult if a mini-mal amount of gingival tissue is present. Compo-nents bringing the prosthesis to a level close to theimplant body itself help with this type of problem.

5, Number2,1993 173 The International loiirnal of Proithodontic!

Immediate Implant Stain; •il ay

Conclusion

Short-term research (animal and human studies)has shown that immediate implants are comparableto implants placed using the conventional tech-nique. The procedure is more demanding bothsurgically and prosthodontically but provides sig-nificanf advantages for the patient. Long-term stud-ies are needed to conclusively prove the usefulnessof this procedure.

References

1, Adell R, Lekholm U, Rockier B, Branemark P-l, A 15-yearstudy o¡ osíeointegrated implants m the treatment ot theedentulous jaw, Int | Oral Surg 1981,-6:387-416,

2, Adell R, Eriksson B, Lekholm U, Branemark P-l, lemt T, Along-term follow-up study of osseointegrated implants in thetreatment of totally edentulous iaws, Int 1 Oral MaxillofacImplants 1990:5:347-359,

3, Ohrnell LO, Hirsch |M, Ericsson 1, Branemark P-l. Singletooth rehabilitation using osseointegration. A modified sur-gical and prosthodontic approach. Quintessence Int 1968;19:871-877,

4, Branemark P-l. Personal communication, 1986.5, Anneroth C, Hedstrom KG, Kjellman O, Kondell PA.

Norderam A, Endosseous litanium implants in extractionsockets —An experimental study in monkeys. Int I Oral Surg1985;14:50-54,

6, Shulman LB, Surgical considerations in implant dentistry, JDent Educ 1988;52:712-720,

7, Sarnachiaro O, Cargentini LC, Biological tissue reaction loimmediate post extraction blade implants, Implantol 1979:1:44-51,

8, Weiss MB, Rostoker W, Development of a new endosseousdental impiant. Part 1: Animal studies, | Prosthet Dent1981;46:646-651,

9, Hodosh M. Povar M, Shklar G. The porous vitreous carbonpolymethacrylate replica implant. Continuing studies. | Pros-thet Dent 1979;42:557-565,

10, Karagianes MT, Westerman RE, Hamilton Al, Adams HF. WillsRC, Investigation of long-term performance of porous metaldental implants in nonhuman primates, | Oral Implantol1982,10:189-208.

11, Stanley HR, Hench L, Going R, Bennett C, Chellemi S|, KingC, et al. Implantation ol natural tooth form bioglasses inbaboons, ) Oral Implantol 1976/77:1:34-47,

12, Stanley HR, Hench LL, Bennett CC, Chellemi S], King C¡,Going RE, et al. The implantation oí natural tooth formbioglass in baboons - Long-term results, J Oral Implantol1981;2:26-31,

13, Brose MO, Rieger MR. Driskell TD, Multicrystalline alumi-num oxide tooth impiants in rhesus monkeys, ] Oral Implan-toM987;13:204,

14, Brose MO, Rieger MR. Dowries R|, Hassler CR. Eight-yearstudy ot alumina tooth implants in baboons, | Oral Implantol1987;13:409-424.

15, Brose MO, Reiger MR, Avers R|, Hassler CR, Eight-year analy-sis of alumina dental root implants in human subjects, J OralImplantol 1988:14:9-23,

16, Brose MO, Avers Rj, Rieger MR, Duckworth |E, Submergedalumina dental root implants in humans — Five-year evalua-tion, | Prostbet Dent 1989;61:594-601,

17, Schulte W, The intra-osseojs AI,O¡ (Ffialit'l Tuebingen im-

plant. Developmental status after 8 years (I), QuintessenceInt 1964:15:9-26,

18, Ouayle AA, Cawood |, Howell RA, Eldridge D), Smith CA,The immediate or delayed replacement ot teeth by permuco-sal intra-osseous implants: the Tübingen implant system.Part 1, Implant design, rationale for use and pre-operativeassessment, Br Dent 11989:166:365-370,

19, Quayle AA, Cawood ), Smith GA, Eldridge D], Howell RA,The immediate or delayed replacement of teeth by permucc-sal intra-osseous implants: The Tubingen implant systern.Part 1: Surgical and restorative techniques. Br Dent J1989:166:403-410,

20, Zetterquist L, Anneroth G, Nordenram A: Tissue integrationof AljOj-ceramic dental implants: An experimental study inmonkeys, Int | Oral Maxillofac Implants 1991;6:285-293,

21, Denissen HW, deCroot K, Immediate dental root implantsfrom synthetic dense calcium hydroüylapatite, ] ProsthetDent 1979; 42:551-556,

22, de Putter C, de Lange CL, de Groot K, Permucosal oralimplants ol dense h yd roïyl apatite: Fixation in alveolar bone.In: van Steenberghe D led). Tissue Integration in Oral andMaiillo-lacial Reconstruction (proceedings of an interna-tional congress. May 1985. Brussels!, Amsterdam: ExcerptaMedica, 1986.

23, Denissen HW, Kalk W, Velhduis AAH, van den Hooff A,Eleven-year study of hydroxyapatite implants, | Prosthet Dent1989;61:706-712.

24, Block MS, Kent |N. Placement of implants in extraction sites— Four-year experiences. J Dent Res 1991;701 special is-sue) t60.

25, Block MS, Kent |N. Placement of endosseous implants intoextraction sites, I Oral Maxillotac Surg 1991;49:1269-1276,

26, Vukna RA. Clinical comparison of hydronyapatite-coated tita-nium dental implants placed in fresh extraction sockets andhealed sites, ) Periodontol i991;62:468-472,

27, Colee TS, Krauser ]T, Long-term retrospective studies onhydroxyapatite coated endosteal and subperiosteai implants,DenI Clin North Am 1992:36:39-65,

28, WoolfeSN,KenneyEB, KeyeG, Taylor D, O'Brien M, Effect ofimplantation of titanium implants into fresh extraction sock-ets. I Dent Res 1989;68lspecial issue):762,

29, Bariilay I, Craser CN, Iranpour B, Natiella |, Proskin H,Histologie and clinical assessment of implants placed intoextraction sockets. | Dent Res 1990;69lspedal issue):1452,

30, Barzilay I: Immediate Implantation of Pure Titanium Im-plants Into Fresh Extraction Sockets of M Fascicularis (Mas-ter's thesis], Rochester, NV: University of Rochester, 1991,

31, Krump |L, Barnett BC, The immediate implant: A treatmentalternative, int | Oral Maxillotac Implants 1991;6:19-23.

32, Tolman DE, Keller EE. Endosseous implant placement imme-diately following dental extraction and alveoloplasty: Prelim-inary report with 6-year follow-up. Int I Oral MasillofacImplants 1991:6:24-28,

33, Becker W, Becker BE, Ochsenbein C, Handelsman M,Albrektsson T, Cellete R. The use of guided tissue regen-eration for impiants placed in immediate extraction sockets.In: Laney WR, Tolman DE leds). Tissue Integration in Oral,Orthopedic, and Maxillofacial Reconstruction, Chicago:Quintessence, 1992:200-202,

34, Warrer K, Codtfredsen K, Karring T, iH j o rt ing-Han sen E.Guided bone regeneration around dental implants insertedinto extraction sockets. I Dent Res 1991;70(special is-sue] :654,

35, Jovanovic SA, Spiekcrmann H, Richter EJ, Kenney EB, Re-entry measurements after guided tissue regenerationaround titanium denfal implants, | Dent Res 1991 ;70(specialissue):658.

The Internationa ot Prosthodonlit 174 e, Number2,1993

nediatc Implanl Status

36. Lazïara R|. Immediale implanf placement info exfractionsockets: Surgical and resforative advantages, inf | PenodonfResf Dent 1989:9:333-343.

37. Nyman S, Lange NP, Buser D, Bragger U. Bone regenerationadjacent to t i tanium dental implants using guided tissueregeneration: A report of two cases, inf ) Oral MaxillofacImplants 1990;5:9-14.

38. Ross SE. Strauss T, Crossetti HW, Gargiulo AW. The immedi-afe placement of an endosseous implanf into an exfractionwound: A clinical case report using fhe RosTR system. Inl |Periodont Rest Dent 1989;9:35-41.

39. Becker W. Becker BE. Guided lissue regeneration lor im-plants placed into extraction sockets and for implanf dehis-cences: Surgical techniques and case reports. Inf | PeriodontRestDent1990;10:377-391.

40. Todescan R, Pilliar RM, Melcher AH. A small animal model forinvesfigafing endosseous dental implants: Effect of graltmaterials on healing of endosseous, porous-surfaced im-plants placed in a fresh estracfion socket. Inf | Oral Maxillo-fac Implan Is 1987; 2:217-223.

41. Armstrong R, Chang R, deLeon £, Rao P, Kincaid S, Chu C.Osteoinduction in titanium and ceramic implants treatedwifh bone extracts. | Dent Res 19B9;6B|special issue):1327.

42. labro M, Sotiriou F, McLey L, Strates B. Osteogenesis ¡nimpiants of bone maf rices and bone morphcgenetic protein.I Denf Res 1991 ;7Ci|speciai issue) :650.

Literature Abstricts.

Marginal Adaptation of Castings Made With Dual-Archand Custom Trays

The dual-arch impression technique, which incorporates fhe maxillary and mandibular impression anda jaw relation record into one procedure, has gained wide popularity. The purpose of this study was tocompare the marginal fit of castings made with custom acrylic resin trays and castings made with mclalor plastic dual-arch impression trays. Standard clinical and laboratory procedures were used to make36 gold castings, 12 castings wifh each type of tray, for a metai typodont die. Marginal openings of thecastings were determined on the metal die with a measuring microscope at six precisely markedlocations on the die. Mean marginal openings were between 25 and 28 fim in all test groups. Therewere no significant differences in marginal opening based on Iray type or location of measurement on themefal die. The results of fhis sfudy supporf and sfrengfhen the findings of previous studies which usedImear measurements to compare the accuracy of the impression techniques. The authors conclude thatthe limitations of the dual-arch impression technique are related to fhe development of occlusion ratherthan the accuracy of the dies.

Divis R, Schwarti R, Hilton T. Am j Dent 1992;5(S):253-254. References: n . Reprinis: Or Richard Schwartz,Department of General Practice, Universily of Texas Health Science Center at San Antonio, 7703 Floyd Curl Dr. SanAntonio, TX 78284-7914.— ßichardR. íeah, I'. DDS. MEd, MS. Department of Prosttiodontics, The Universily ofTexas Health Science Center al Ssn Amonio. San Antonio. Texas

Microleakage — Full Crowns and the Dental Pulp

The purpose of this study was to fest fhree crown margin preparations to determine whether marginpreparation affects microleakage. Thirty freshly extracted molar teeth, all noncarious or wifh smalirestorations, were mounted in acrylic resin blocks and prepared with a full shoulder, a chamfer, or ashouider and a bevel. All crowns were cemented with zinc phosphate cemenf. All teefh were cycled100 times between 4°C and 60°C water baths containing 0.05% crystal violet dye. lotal immersion timewas 100 minutes. Tbe crowned teetb were then embedded in clear autopolymerizing acrylic resin andsectioned buccolingually into three equally thick sections. All crowns leaked regardless of the type ofcrown margin preparation. The leakage pattern was fhe same and the leakage followed the denfinaltubules directly into the pulp in every case. Since this study demonstrated that there is leakage in everytooth regardless of which crown margin preparation is used, dentists must be aware of the possibility ofsubsequent microhiologic damage to the pulp through the dentinai tuhules. The authors conclude thatmicroleakage could be a cause of pulpal inflammation, and even pulpal death, under complete crowns.

Goldman M, Laosonrhorn P, White HR. / Endodon 1992; 18(10):473-.475. References: 20. Reprints; Dr Meli/in Coldrran,Department of Endodontics, Tufts University School of Dental Medicine, 1 Kneeland St, Boston, MA 02111. —Richard R. Seais, ¡i, DOS, MEd, MS, DepartmenI ot Prosthodontics, Ths Universily of Tetas Health Science Center atSan Antonio, San Antonio. Texas

Volume 6, Number 2,1993 175 The International lournal of Prosthodortics