Impressioning Compendium - A guideline for excellent ...multimedia.3m.com/mws/media/517089O/espertise-impressioning... · A guideline for excellent impressions in theory ... A guideline

In collaboration with Prof. Dr. med. dent. Bernd Wöstmann Prof. John M. Powers, Ph.D.

Impressioning Compendium

Espertise™

A guideline for excellent impressions in theory and practice

A guideline for excellent impressions in theory and practice

guideline

Espertise™

2 |

Preface

Astheworldwidemarketleaderinimpressioning,3MESPEaspirestobethepartnerofchoiceforprecisionimpressionsinpracticeandteachingestablishments.Ourgoalistoleverageourexpertiseininnovativematerials,technology,andmanufacturingtoprovideourcustomerswiththehighestperformingimpressioningsystemsandworkflowonthemarket.Wehavereceivedaresounding,positiveresponsetothefirstandsecondeditionsof“PrecisionImpressions–AGuidelineforTheoryandPractice”fromdentistsaroundtheworld.Thisconfirmstheimportanceofourprocess-orientedapproachanddemonstratesourcommitmenttocontinuallydelivercustomer-valuedsolutions.

Overthepastnineyears,thousandsofdentistsandtheirteamshavebeenworkingwithourhandbook.Inaddition,manyuniversitiesandtrainingcentresutilisetheguidelinesforprecisionimpressiontakingasabenchmark.Manyofthedentistsespeciallyvaluetheclearandconcisestep-wiseprocedures,aswellasthesupportivefunctionforvocationaltrainingandfurthereducationinpractice.Thisthirdeditionputsevenstrongerfocusontheprocedureofimpressiontakingsincethisisthemostimportantstepforultimatelyproducinghigh-qualityaestheticresto-rations.Theimprovementsachievedthroughmaterialscienceanddentalprocedures,aswellasimportantchangesintheworkflow,promptedustoupdatealmostallthechapters.

3MESPEfeelsverymuchindebtedtoProf.Dr.med.dent.Wöstmann,oneoftheauthorsofthefirstandsecondeditions,forhiscompetent,clinicalandprocess-orientedview.Chapters1,2,4and6–11verymuchbenefitfromhisoutstandingclinicalexpertise.3MESPEwishesalsotothankDr.Powerswhoinchapter3linksthechemistryofimpressioningmaterialstotheirclinicallyrelevantpropertiesinanintelligibleanduser-friendlyway.

3MESPEcomplementstheirworkwithourlongstandingexpertiseinimpressionmaterialmixingtechnologyinchapter5.

Wehopethatyoufindthechangesmadetothelatesteditionwillhelpyoutofurtherimprovethequalityofyourimpressionsandtherestorationsyouproduceinpracticeortraining.

Dr.AlfredViehbeck3MESPEGlobalTechnicalDirectorSt.Paul,MN,USAandSeefeld,GermanyMay2008

Biographical sketch

BerndWöstmann,Prof.Dr.med.dent.Dr.WöstmanngraduatedfromtheUniversityofMünster,Germanyin1985.From1986to1992hewasassistantdoctorandfrom1993to1995assistantmedicaldirectoroftheDepartmentofProsthodonticsoftheWestphalianWilhelms-University,Münster,Germany.In1995hewasappointedassistantprofessorandin1998professorattheJustus-Liebig-UniversityinGiessen,Germany,whereheiscurrentlyholdingalifetimeprofessorshipforClinicalDentalMaterialsSci-encesandGerodontology.Hismainareasofinterestaredentalelastomersandrelatedaspectsofmaterialscience,especiallyimpressiontakingindentistry.Heisalsoworkingingerodontologyandimplantology.Dr.WöstmannisamemberofseveralscientificorganisationsincludingtheIADRandalsoseveralDIN-ISOworkinggroups.HeiscurrentlyPresident-electoftheEuropeanCollegeofGerodontology(ECG)andsecondvicepresidentoftheHeadAssociationoftheGermanGeriatricScientificSocieties(DVGG).Dr.Wöstmannistheauthorofmorethan200scientificarti-cles,abstracts,books,andchapters.Heservesontheeditorialboardsofmanydentaljournalsandhasgivenmorethan400scientificandprofessionalpresentationsandlectures.Dr.WöstmannhasbeenawardedtheFriedrich-Hartmut-DostAwardin1999forexcellenteducationindentistryandco-authoredseveralpresentationsthathavebeenawardedbytheGermanProsthodonticSociety(DGZPW),theGermanGeriatricSociety(DGG)andtheAustrianGeriatricSociety.

Dental Consultants, Inc. (THE DENTAL ADVISOR) 3110 W. Liberty Ann Arbor, MI 48103 Phone: 734-665-2020 (x113) Fax: 734-665-1648 E-mail: [email protected] www.dentaladvisor.com

JohnM.Powers,Ph.D.Dr.PowersgraduatedfromtheUniversityofMichiganwithaB.S.inchemistryin1967andaPh.D.indentalmaterialsandmechanicalengineeringin1972.HeisseniorvicepresidentofDentalConsultants,Inc.,andeditorofTheDentalAdvisor,adentalnewsletter.HeisalsoProfessorofOralBiomaterials,DepartmentofRestorativeDentistryandBiomaterials,andSeniorScientistoftheHoustonBiomaterialsResearchCenterattheUniversityofTexasDentalBranchatHouston.HeisalsoamemberofthefacultyofGraduateSchoolofBiomedicalSciencesandAdjunctPro-fessorattheUniversityofMichiganSchoolofDentistry,UniversityofRegensburgandtheLudwig-Maximilians-UniversityMunich.Heisactiveintheappliedandbasicresearchofbondingtodentalsubstrates,colourandopticalpropertiesofaestheticmaterials,andphysicalandmechanicalpropertiesofdentalcements,compositesandotherrestorativematerials.Dr.PowersiscurrentlytheCounciloroftheDMG/IADRandChairofANSI/ADAWorkingGroupsonwaxesandcements.Dr.Powersistheauthorofmorethan875scientificarticles,abstracts,books,andchapters.Heisco-authorofthetextbook,DentalMaterials–PropertiesandManipulation,andco-editorofCraig’sRestorativeDentalMaterials.Heservesontheeditorialboardsofmanydentaljournals.HehasgivennumerousscientificandprofessionalpresentationsintheUnitedStates,Europe,Asia,MexicoandSouthAmerica.

Prof. Dr. med. dent. Bernd Wöstmann Department of Prosthodontics – Dental Clinic Justus-Liebig-University Giessen Schlangenzahl 14 35392 Giessen Germany Phone: +49 641 99-46 143 /-46 150 Fax: +49 641 99-46 139 E-mail: [email protected].

uni-giessen.de

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Contents | 5

Aguidelineforexcellentimpressionsintheoryandpractice

Preface 2

Biographical sketch 3

1. Clinical importance of the precision impression 61.1. Introduction 61.2. Reasonsfordiscrepancybetweenlaboratoryresultsandprecisioninclinicalsituations 81.3. Improvementofresultsbystandardisation 81.4. Standardisationinthedailyroutine–dentalpracticeanddentallaboratory 9

2. Clinical parameters influencing impression taking 102.1. Periodontalstatusandoralhygiene 102.2. Waitingperiodbetweenpreparationandimpression 102.3. Preparationoftheoperativefield 112.4. Anaesthesia 122.5. Choiceoftrayandspecificimpressiontechniques 122.6. Removaloftheimpressionfromthemouth 13

3. Properties of today’s impression materials 143.1. Historyofprecisionimpressions 143.2. Additioncuringprecisionimpressionmaterials 153.3. Condensationcuringelastomers 183.4. Impressionmaterialsforpreliminaryimpressions 193.5. Materialincompatibilitiesandimpressiondisposal 203.6. OverviewofmaterialtypesandconsistenciesaccordingtoISO4823:2000 21

4. Impression trays 224.1. Choiceoftray 224.2. Stocktraysforfullarchimpressions 224.3. Stocktrayswithoptimisedfit 244.4. Customtrays 244.5. Dual-archtrays 264.6. Trayadhesive 26

5. Mixing of impression materials 275.1. Hand-mixingofimpressionmaterials 275.2. Handdispensersystem 295.3. Automaticmixingsystem 30

6. Impression techniques 336.1. 1-stepimpressiontechniques 336.2. 2-stepimpressiontechniques 346.3. Takingtheimpression 36

7. Indications 387.1. Orthodonticsplints 387.2. Veneers 387.3. Adhesivebridges 397.4. Inlaysandpartialcrowns 397.5. Singlecrowns 407.6. Bridges 407.7. Combinationdentures 417.8. Implants 427.9. Summaryindicationsandtechniques 43

8. Disinfection 44

9. Storage of the impression and transport to the dental lab 45

10. Fabrication of the stone model 4610.1. Standardisationofthemodelfabrication 4610.2. Modelsystems 4610.3. Timingofthemodelfabrication 47

11. Conclusion 48

12. Impression taking in the clinical workflow – Overview 49

13. Literature 50

14. Glossary 53

15. Overview 3M ESPE impression materials 54

6 | Precisionimpressions

1. Clinical importance of the precision impression (B.Wöstmann)

1.1. IntroductionRestorationswhichfitexactlyandcanbeinsertedwithoutanyfurthercorrectionsarehighonthelistofeverydentist.Exactfittingrestorationsdonotonlyfacilitatemoreefficientandfasterwork-ing,theyalsoaidperiodontalprophylaxis.Furthermore,today’saestheticallysuperiorrestorationsdorequireexactfitting.Afullceramiccrownsurroundedbychronicgingivitiswithitscharacteristicdiscolourationcausedbyawidelyprotrudingcrownmarginistotallyunacceptable.Theimpressionisanimportantstepintheprocedureofobtainingaperfectrestoration.Itistheaimoftheimpressiontoproduceadimensionallystable“negative”whichcanserveasthecastmouldforamodel.Duetothefactthatindirectrestorationsareclassicallyproducedinthedentallaboratory,itisinevitablethatanoptimalprecisefitofthelaboratory-madeapplianceisonlygivenifthemodelexactlymatchestheoriginalsituation.DespiterapidtechnicalprogressinthefieldofCAD/CAMsystems,theimpressionremainsimmenselyimportanttoprostheticdentistry.Atleastinthenearfuture,theimpressionwillcontinueitsvitalroletransportinginformationfromthedentisttothedentallab.MostCAD/CAMsystemsavailabletodaystartfromthemodeland,thus,alsorequireprimarilyanimpression.Despitemanyefforts,theconventionalimpressionprocesshasnotyetbeenreplacedbymoremodernreproductionprocedures–suchas“photo-graphic”impressionwiththehelpofanintra-oralscan,e.g.withtheCEREC(SironaDentalSystems).However,3D-imagingprocedureswillincreasinglybeused(e.g.3MESPELava™Chair-sideOralScannerC.O.S.)inthefuture.Theseinnovationsarequitepromising.However,especiallyfordeepsubgingivalareasandareasdifficulttoaccess,theconventionalimpressionremainsanecessaryandindispensableprocedurestepindentaltreatment.

Current trends in digital impressioningOverthelast100years,elastomericimpressionmaterialswerecontinuouslydevelopedandoptimizedforimprovedprecision,patientcomfortandeaseofuse.Modernmaterialsarerobust,precise,fast,hydrophilic,andcanbeautomaticallymixed–butstillthepatientneedstokeepafilledimpressiontrayinthemouthforsomeverylongminutes,andexternalfactors,e.g.temperature,canimpactthefinalresult.

Thus,digitalapproachesweremadetocircumventtheseproblems.Thefirstopticalimpressioningsystemwasmarketedinthe1980saspartoftheCERECsystem(SironaDentalSystems).TheLava™ChairsideOralScannerC.O.S.(3MESPE)uses3D-in-MotionTechnology.Thistechnique,incontrasttoknown“pointandclick”systems,capturescontinuous3Dvideoimagesanddisplaystheseimagesinrealtimeonatouchscreenmonitor.Thesedigitalimpressionswillbesenttothedentallabwhereatechnicianwilldigitallycutandmarkthemargin.Modelsforthelabtechnicianwillbemadewithdigitalprecisionusingstereo-lithography.Whilemodelfabricationstillisanecessaryworkstep,itmightbecomelessimportantinthefuture.3MESPEalreadymanufacturesLava™ZirconiacopingswithCAD/CAMtechnology.Inthefuturethesecopingscouldbemilledbasedonadigitalimpression.

Precisionimpressions | 7

Marginal accuracy: what is necessary and what is possible?Duetonumerousmaterial-relatedaspects,anidenticalreplicationoftheoriginalsituationisnotpossiblewiththematerialsandmethodsusedintoday‘sdentistry.Infact,impressioningisaconstanttightropewalkbetweenluminathateithercameouttoosmallortoolarge,andthus,betweenoversizedorundersizedmodelabutments.Theequivalentisinthelumenofacrown,whichiseithertoolargeortoosmall.Crownsthataretoolargehaveintolerablemarginalgapsandiftoosmall,crownsdonotreachthepreparationmargin.

Thebiologicaltoleranceformarginaldiscrepanciesisalmostunknown,althoughboththecorrela-tionbetweenmarginalaccuracyandperiodontaldamage1;2,andtheappearanceofsecondarycariesinthecaseofinaccuratefit3hasbeenproven.

Themarginofarestorationisthecriticalpoint,sinceinadequaterestorationmarginscanhardlybecorrectedafterwards.Occlusalinterferencesaswellasinaccuratefitaroundtheapproximalcon-tactscanbecorrectedmucheasier–independentofwhethertheseareclassicalmetalrestorationsorCAD/CAM-producedzirconiumoxideframeworks.Thus,thereproductionofthepreparationmargininanimpressionisanecessaryrequirementinordertoachievegoodmarginalquality.Invitro,themarginalprecisionofadentalrestorationisapprox.50µmonaverage4–6.However,thislevelofprecisioncanrarelybemetclinically.Thisdivergenceappliesmainlytorestorationswithsubgingivalorparagingivalmarginareas.Ifthecrownmarginiscompletelysupragingival,itispossibletoobtainaccuracieswhicharequitecomparablewiththeresultsfromlabtests.Thishasbeenimpressivelyproveninseveralstudies7–12.

Whatarethereasonsfortheconsiderablediscrepancybetweenthetechnicalpossibilitiesoftherespectivematerialsandtheclinicalresults?Thesemainlyrelatetotheclinicalfactorsencounteredduringthetreatmentofthepatient.Otherwise,similarresultsasinlabtestswouldbeachieved.Thus,factorsrelatedtoclinicalprocedurehaveasignificantinfluenceonthefittingaccuracyandwillbedescribedinthenextchapter.

Preparation

‚

Impression‚

Fabrication of the models

‚ ‚

Scanning

‚

Milling

‚

Sintering

‚

Veneering

‚

Seating in the mouth

Casting

‚

Manual finishing

‚

Veneering

‚

Seating in the mouth

Fig. 1: Today’s typical workflow for metal restorations (left) and for CAD/CAM-manufactured restorations in the lab (right).

8 | Precisionimpressions

1.2. Reasonsfordiscrepancybetweenlaboratoryresultsandprecisioninclinicalsituations

ThepreparationofafixeddentalrestorationwiththehelpofprecisionimpressionmaterialsrequiresseveraltreatmentandlaboratorystepsindependentofwhetheraconventionalorCAD/CAMtechniqueischosen.Thesamesourcesofpotentialerrorapplytoallfixedrestorations.Wewillusetheexampleofacrownforexplanation.

Thelumenofacrownhastobealittlebitlargerthantheoriginalabutmentsothattherestorationcanbecemented,soitisdesirabletoachieveaslightenlargementofthecrownlumeninthecourseoftheworkflowfromimpressiontocrown.However,duetomaterial-relatedreasons(likeshrinkageofcastgypsumorimpressionmaterial)thisisnotpossible.Usually,theknowndimensionalerrorsoftheimpressionarecompensatedbytheexperienceddentallabbyapplyingspacersorchangingthesettingexpansionoftheembeddingmaterialtoachievewell-fittingrestorations.

1.3. ImprovementofresultsbystandardisationToachievereproducibleresultswithregardtoaccuratelyfitting,fixedrestorationsonemuststandardisetheprocessfromthepreparationofthetoothtotheseatingofthefinalrestoration13.Fig.2shows–inasimplifiedmanner–thatthedimensionoftheabutment,asitisreproducedintheimpression,approximatelycorrespondstoanormaldistribution(Gaussiandistribution).Itswidthdependsontheconsistencyorrathertheinconsistencyoftheinitialconditionslikeimpres-siontechnique,traychoice,temperature,etc.Indailypracticeitisscarcelypossibletoevaluatetheactualdimensionofthereproducedabutmentintheimpression,sincesuchdiscrepanciesarerarelyobvioustothenakedeye.

Thesubsequentworkstepsinthelab(fabricationofthemodel,carving,embedding,casting)inprinciplefollowthesamescheme.Thedifferenceisthatthepositionofthecurvemaximumnolongercorrespondstotheoriginaltoothbuttothepositiondeliveredintheimpression(e.g.positionsa,borc,Fig.2).

Atthispointtheproblemisclear:witheachfurtherworkstepthespreadingoftheresultsbecomeslarger.Itcanneverbecomesmaller(Fig.2redcurvebelow).

Thus,itisawidespreadfallacythatthedeviationsresultingfrominsufficientstandardisation“levelout”ontheirown22.

Precisionimpressions | 9

Thestatisticalspreadofresultscanbereducedbystandardisedprocedures,goodcommunicationbetweentechniciananddentist,theuseofmodern,high-qualityimpressionmaterials(withcon-stantandreproduciblepropertiesinallproductionbatches)andcorrectandreproduciblehandlingofthesematerials,especiallythroughautomaticmixing14.

1.4. Standardisationinthedailyroutine–dentalpracticeanddentallaboratory

Indailyclinicalpractice,thestatisticalspreadcanbereducedespeciallybystandardisingpro-cesses.Thisstartswiththeplanningofthetreatmentandendswiththeshipmentconditionsusedtosendtheimpressiontothelab.Furthermore,itisessentialtoco-ordinatetheworkstepsinthedentalpracticeandthelab.Itisveryimportantforthedentallabtoknowthegeneralconditionsoftheimpressiontocompensatethesystem-relatederrorsbysuitablemeasures.Inprinciple,theproceduresinpracticeandlabwouldrequireaprocessmanagementasknownfromindustrialfabricationandanintensivecom-municationbetweendentistanddentaltechnician.Onlyifhe/sheknowswhichimpressiontech-niqueandmaterialwereused,canthedentaltechnicianeffectivelyco-ordinatethematerialchainandfinallyproduceanaccuratelyfittingrestoration.

Dental practice

D ent al lab

InformationExchange

Fig. 2: Schematic of the spreading of results along a multi-step workflow.

2. Clinical parameters influencing impression taking (B.Wöstmann)

Systematicstandardisationcanreducethenumberofretakesandcorrections.Additionally,thefinalsuccessofanimpressionisstronglyinfluencedbytheclinicalsituationandisindividualforeachpatient.

2.1. PeriodontalstatusandoralhygieneTheperiodontalandoralhygienestatusofthepatientsignificantlyinfluencetheresultofanimpression,sinceinflamedperiodontiumaroundadiseasedtoothshowsincreasedbleedingten-dency.Asperiodontaldiseaseandsulcusbleedingareinextricablyconnectedtotheoralhygienebehaviourofthepatient,itisveryimportanttoachievegoodoralhygienecircumstancesbeforetheprosthetictherapy,especiallywithregardtotheimpression.Theworsetheindividualhygienecircumstances,themorefailuresmustbeexpected.Thus,theviciouscircleasdisplayedinFig.3isinevitable70;71.

Fig. 3: Insufficient periodontal circumstances and possible after-effects.

2.2.WaitingperiodbetweenpreparationandimpressionThewaitingperiodbetweenpreparationandimpressionisanextremelyimportantparameterforthesuccessoftheimpressionandhasbeenwidelydisregardedtodate.Inparticular,wheneveraninjurytothemarginalperiodontiumhasoccurredduringpreparation,theperiodontiumshouldbeallowedtohealcompletelybeforetheimpressionistaken(aboutoneweek,ifitisnotpossibletoeffectivelydrythesulcus).Thisgreatlyreducestheriskoffailurefortheimpression15;16.Thegreatestinaccuracycanbeexpectedwhentheimpressionistakenonthedayfollowingthetoothpreparation.Positioningofthecordinevitablycausestraumatothegranulationtissuewhichhasformed,involvingbleedingwhichisgenerallydifficulttoarrest25.

Lessfailurescanbeexpected–evenwithfullysupragingivalpreparations–whentheimpressiondoesnotimmediatelyfollowpreparation15;16.

10 | Clinicalparameters

Inflamed periodontium

+ caries

Necessity of restoration

Preparation margin not completely

reproduced Bleeding at impression

Loss of tooth

Bad oral hygiene

Difficult cleaning Irritation of

periodontium

Ill-fitting restoration

Clinicalparameters | 11

2.3.PreparationoftheoperativefieldRetraction Anessentialrequirementforasuccessfulimpressionistheaccuratereproductionofthepreparedteeth.Onlythencanthepreparationmarginbedefinedunequivocallyonthestonemodel.Youcanonlyreproducewhatisaccessible.Withsupragingivallylocatedpreparationskeepingtheareatobeimpressioneddryandaccessibleisusuallyquiteeasy8;17.However,ifatoothiscrownedtopreserveit,itisoftendeeplydestroyedandthepreparationmarginisfullyoratleastpartlysubgingival.Ifthetoothshouldserveasabridgeabutmentitisthequestionofsufficientretentionofthebridgewhichforcesaparagingivalorsubgingivalpreparation.

Ifthepreparationmarginisnotaccessibleitcaneitherbecomesupragingivalbysurgicaltreatmentand/or–preferably–thesulcuscantemporarilybeextendedwitharetractionmaterial.

Haemostaticpropertiesoftheretractionmaterialarenotrequiredwhenhealthyperiodontalcondi-tionshavebeenachievedwithgoodoralhygieneandsubsequenttissuemanagement.However,sometimesitisnecessarytoworkwithpre-impregnatedretractioncordsdespitetheuseoflocalanaestheticcontainingavasoconstrictor(warning:cardio-vascularriskpatients).Pre-impregnatedretractioncordsoraddedretractionliquids–especiallybasedonmetalsalts–caninteractwithimpressionmaterialsandpreventtheirsettingprocess18;19.

Theaimofaretractionistoclearlydisplaythepreparationwhilecausingtheleasttraumapossibletothetissue.Mainly,singleanddoublecordretractiontechniquesareuseddependingontheimpressionsite.Inthedoublecordtechnique,atfirstathincordisplacedonthebottomofthesulcus,athickercordontopofittakescareoftheactualtissuedisplacement.Inbothretractiontechniquesthecordplacedlastisremovedshortlybeforetheimpressionistaken.

Analreadyopensulcuscanbedriedefficientlybyusingpastes,e.g.Expasyl™(PierreRoland)72.

Forsingleteeththeuseofretractionsleeves(e.g.Peridenta)toopenthesulcusisanalternativetoretractioncords.

Testing the compatibility of impression materials

and retraction agents is easy: A retraction cord is soaked with the astringent to be tested, slightly dabbed and coated with the light-bodied impression material which is selected to be used later. As a control use another cord soaked with saliva or salt solution. After setting of the impression material the cords must stick tightly and it should not be possible to remove them from the impression mate-rial. If they can be removed easily and if there is even some unset impression material on the cords, the materials are NOT compatible.

Youcanonlyreproducewhatisaccessible.

Fig. 5: Retraction cord in situ.Fig. 4: One cord technique (left), two cord technique (right) for retraction.

Cleaning the prepared toothBeforetheimpressioncanbemade,agentsthatmighthavebeenusedforcleaningordisinfectingthecavity(e.g.hydrogenperoxide)mustbethoroughlyrinsedofffromthepreparationwithwaterspray.Residuesofthesematerialscanpreventcompletesettingoftheimpressionmaterial.VPS(A-silicone)andpolyethermaterials,forexample,canreactwithremaininghydrogenperoxide,VPSmaygeneratefoamandthuspreventanaccuratereproductionofthepreparationmargin.Also,unsetresiduesofmethacrylatecompositescaninterruptthesettingprocessand,thus,havetoberemovedcarefullywithalcoholandthenwithwater(see“Materialincompatibilities”,chapter3.5.).Subsequently,thetoothisdriedwithagentleairstream.

Fig. 7: Thorough rinsing and drying of the tooth using water spray and air.

2.4. AnaesthesiaImpressionswhicharetakenunderlocalanaesthesiaareoftenmoresuccessfulthanthosetakenwithout15;16.Withoutanaesthesiaitisalmostinevitablethatthepatienthastoendurepainduringtheimpressionprocedure;especiallyduringthepositioningoftheretractioncordsandthedryingofthepreparedabutments.Thereactionofthepatienttopainoftenleadstoinappropriatelyplacedretractioncordsorinsufficientlydriedteeth.Ifthishappens,theresultisarelativelybadimpression.Furthermore,mostanaestheticscontainvasoconstrictorswhichcauseanaemicconditionsaroundtheanaesthetisedarea,counteractsulcusbleedingand,thus,favourapositiveimpressioningresult.

2.5.ChoiceoftrayandspecificimpressiontechniquesBoththeselectionoftheproperimpressiontrayforthespecificindicationandtechniqueaswellasthechoiceoftheimpressiontechniqueappropriatefortheindicationhavesignificantinfluenceonthefinalsuccess.Thatiswhywehavededicatedthemafullchaptereach(chapters4and6).

Fig. 6: Drying of the sulcus with retrac-tion paste.

12 | Clinicalparameters

2.6.RemovaloftheimpressionfromthemouthEvenwithaseeminglyuncomplicatedtasksuchastheremovaloftheimpressionfromthemouth,somebasicshavetobeobservedtoavoidpermanentdeformationoftheimpressionmaterial.Sincethetoothaxesonbothsidesarenotparallelbuteitherconverge(lowerjaw)ordiverge(upperjaw),thepreferredremovaltechniqueespeciallywhenusingfullarchtraysdependsonthelocalisationandnumberofpreparedteeth.Permanentdeformationoftheimpressionatthepreparedtoothcanonlybeavoidediftheimpressionisremovedexactlyinthedirectionofthetoothaxisof the prepared tooth.Withpreparationsinthelowerjawposteriorareathiscanbeachievedbestiftheimpressionisloosenedatthesideofthepreparedteethsothatitrotatesaroundasupportinthecontra-lateralvestibulum(Fig.8).Impressionsofpreparedteethintheupperarchposteriorarea,however,arepreferablyfirstloosenedattheoppositeside(Fig.8).Inthecaseoffrontteeththeprimarylooseningoftheimpressionshouldbedorsallyonbothsides.Ifthisnotobserved,theimpressionmaterialcanbecompressedconsiderably,whichresultsindeformationofthematerial.Ifanimpressionwithpreparationsonbothsidesofthejawhastobetaken,deformationoftheimpressionmaterialaroundthepreparationsisinevitable.Insuchsituationscarefullychoosetheimpressiontrayandtakecarethatthetrayislargeenougharoundtheundercutareas(see“Impressiontrays”,chapter4).

Especiallyforhighprecisionimpressionsavacuumbetweentheteethandimpressionmaterialdevelopsduringmaterialsettingwhichcomplicatestheremovalofthetray.Inordertodisruptthisvacuum,openthetightsealbymobilisingtheoralmucosawithanin-rotatingmovementoftheforefingeratasuitableplace.Additionalapplicationofcompressedaircanbehelpful(seeFig.9).

Clinicalparameters | 13

Removealongaxisofpreparedtooth.

Fig. 8: Optimum removal of impression tray: for upper jaw loosen tray on opposing side, for lower jaw, loosen tray on prep side.

Fig. 9: Use of finger and air stream to loosen impression.

3. Properties of today’s impression materials (J.M.Powers)

3.1. HistoryofprecisionimpressionsTheintroductionofreversiblehydrocolloidsinthemid-1930sheraldedanewageintheimpressionsector.Forthefirsttimetheimpressionofundercutsbecamepossible.Withtheappearanceofpolysulfidesatthebeginningofthe1950s,anelastomericimpressionmaterialwasusedinden-tistryforthefirsttime.Around55yearsagotheworldofdentistrysawtheintroductionofacate-goryofmaterials–theC-typesilicones(condensation-cured)–which,likeanothercondensation-curedclassofmaterials,thepolysulfides,werenotoriginallyintendedfororalapplications.

Thegreatdisadvantageoftheseproductsstillremains:shrinkageintrinsictothesystem–beitduetotheevaporationofwaterwiththehydrocolloidsoroflow-molecularside-productsinthecaseofthecondensationcuredelastomers20;21.

In1965,3MESPEpolyetherswereintroducedtothemarket(Fig.11).Polyetherisahydrophilicimpressionmaterialcuredbycationicring-openingpolymerization,whichisfarsuperiortothehydrocolloidsandC-typematerials.Ithashighmechanicalproperties,goodelasticrecoveryandissubjecttovirtuallynoshrinkage.Themainadvantagesincludehydrophilicity,uniqueflowandsettingbehaviour.Sincetheimpressionmaterialisinclosecontactwithwetsoftandhardtissue,hydrophilicityisonemajorfeatureofamodernprecisionimpressionmaterial.Hydrophilicityisdefinedasanaffinityforwater(Fig.10).

Tenyearslater,siliconesintheirenhancedform,theaddition-curedsilicones(vinylpolysiloxanes)wereintroducedasimpressionmaterials.However,theyarehydrophobicbytheirmolecularchemistry(hydrophobic=repelsordoesnotabsorbwater,theoppositeofhydrophilic).Ithasbeenpossibletoreducethelevelofhydrophobicitybytheadditionofsoap-likemolecules(surfactants).Theseincreasethehydrophilicityofthematerial,especiallyinthesetstage22–24.Setvinylpolysiloxaneshaveveryhighdimensionalstabilityovertimeandtemperature,eveninamoistenvironment.Theyareknownfortheirsuperiorelasticrecovery.SomeofthemostrecentmaterialslikeImprint™3/Express™2VPSImpressionMaterials(3MESPE)havebeenimprovedwithregardtotheclinicalproblemoftearing.

14 | Properties

Fig. 10: On hydrophilic material water can spread easily (left) whereas its contact surface is minimised to hydrophobic material (right).

1975VinylPolysiloxanes

2006 Imprint™3,Express™22000/

2005 Impregum™Soft/Quick

1965 CationicRing-OpeningPolyether( Impregum™)

Withthelaunchof3MESPEImpregum™Soft/DuoSoft™PolyetherImpressionMaterials,newpolyether-basedimpressionmaterialsbecameavailable,combiningallthepositivecharacteristicsofpolyetherwithsimplerhandlingbothchairsideandinthelaboratory.Themostrecentlyintroducedfast-settingImpregumSoft/DuoSoftQuickPolyetherImpressionMaterialwhichisrecommendedforonetotwounitsoffersmorepatientcomfortandsaveschairtime.

3.2.AdditioncuringprecisionimpressionmaterialsVinyl polysiloxanes (VPS, addition silicones, A-silicones)Vinylpolysiloxaneexploitstheprincipleof“additionreactioncuring”.Asopposedtocondensationcuringmaterialsthatexperienceshrinkageasaresultofevaporationofby-products,vinylpolysi-loxaneremainsdimensionallystable.Withvinylpolysiloxane,differentpre-polymericsilicon-functionalisedhydrocarbonchains(hydro-gensiloxane,vinylsiloxane)andaplatinumcatalystareinvolvedinthereaction.Theadditionofhydrogensiloxane(-O-Si-H)tovinylsiloxane(CH2=CH-Si-O)iscalledahydrosylationreaction.Asaresultofthisreactionthevinylpolysiloxaneisformedattheplatinumcatalyst23;25;26.Theplatinumcatalystisaplatinumcompoundwhich,startingfromH2PtCl6,isadjustedthroughreductionandservesasamolecular“dockingstation”forthetworeactingpartners,whichleavetheplatinumcompoundoncetheyarelinkedtoeachother(seeFig.12).

Vinylpolysiloxaneimpressionmaterialsarehydrophobicbytheirchemicalnature–theyaremoreorlessapolarhydrocarbonchains–andcanbemadehydrophilicusingsuitablemolecules.How-ever,thesearealwaysextrinsicmolecules;atrueintrinsichydrophilicity,asinthecaseofthepolarpolyethermolecules,cannotbeestablishedforthesemolecules.Somedegreeofhydrophili-citycanbeachievedafteracertainperiodoftimebytheuseofsurfactants.Surfactantscontainahydrophobicpart,whichensuresmiscibilityintheformulationandahydrophilicpartwhichisresponsibleforimprovedwetting.

Toconverttheliquidsiloxaneparentcompoundsintoapaste,inorganicfillersareadded.Thethixotropicpropertiesofthevinylpolysiloxanecanbecontrolledusingappropriatefillers.Thecoloursofthematerialsareadjustedthroughtheadditionofdyesandpigments.

Properties | 15

Fig. 11: History of precision impression materials.

1925ReversibleHydrocolloids

1950CondensationCuringElastomers

2003 CondensationPolyether

1955 CondensationSilicone

1950 Polysulfide

CH3 – CH – RI – O – CH – (CH2)n – O m – CH – (CH2)n – O – RI – HC – CH3

R R

R" R"

Recentvinylpolysiloxanes,suchas3MESPEImprint™3/Express™2VPSImpressionMaterialcontaintailor-madecrosslinkers.Thematerialsaredesignedforhightensilestrength,resultinginhightear-resistanceandhighelasticrecovery.

A-siliconeshavealmostnolimitswithregardtodisinfectionandarecompatiblewithmostmodelmaterials27.

Polyethers cured via ring-opening polymerisationThepolyethercontainedinthebasepaste,whichisalreadyalongerchainpolyether(macromono-mer),isatailor-madecopolymerofethyleneoxideandbutyleneoxideunits(Fig.13).Theendsofthemacromolecularchainareconvertedintoreactiverings,whichformintothecross-linkedfinalproduct(Figs.13,14)undertheinfluenceofthecationicinitiatorofthecatalystpaste.

16 | Properties

Popularbrands:• Imprint™3VPS

ImpressionMaterial(3MESPE)

•Express™2VPSImpressionMaterial(3MESPE)

•Aquasil™Ultra(DentsplyCaulk)

•Affinis™(Coltene/Whaledent)

•Honigum™(DMG)

Fig. 13: Polyether macromonomer – the chains are terminated by the highly reactive ring groups (marked with an R).

CH3

H – Si – CH3

O

CH3 – Si – H

O

H – Si – CH2

CH3

O – Si – CH = CH2

O – Si – CH = CH2

CH3

CH3

+

platinumcatalyst

+

platinumcatalyst

CH3

CH2 = CH – Si – O

CH3

platinumcatalyst

+

CH3

CH3

O – Si – CH2 – CH2 – Si – CH3

O – Si – CH2 – CH2 – Si – CH3

CH3

CH3

O

CH3 – Si – CH2 – CH2 – Si – O

O CH3

CH3

Fig. 12: Polymerisation mechanism for vinyl polysiloxane.

Thereactiveringofthepolyethercopolymer(basicpolyethermolecule)isopenedbyacationicstarter(Fig.14)andcanthen,asacationitself,attackandopenotherrings,creatingasnowballeffect.Wheneveraringisopened,theopeningcationicstarterremainsattachedtotheformerring,thuslengtheningthechain23.Thisuniquesettingmechanismcauses“snapset”behaviour,whichreferstotherapidtransitionfromtheworkingtothesettingstage28(Fig.15).

Properties | 17

Popularbrands:• Impregum™Poly-

etherImpressionMaterial(3MESPE)

•Permadyne™Poly-etherImpressionMaterial(3MESPE)

Working Time

Viscosity

Time

Setting Time

Polyether

A-Silicone

Fig. 15: Snap-set behaviour of 3M ESPE Polyether Impression Materials.

Source: 3M ESPE

Theactualpolyethermacromonomer(Fig.13)consistsofalongchainofalternatingoxygenatomsandalkylgroups(O-[CH2]n).Thehighlevelofhydrophilicityofthepolyetheritselfisduetothelargenumberofoxygenmoleculesinthelongchainandthelargepolaritydifferencebetweenoxygenandcarbon(orhydrogen).Inotherwords,uponcontactwithmoisturethehydrophiliccharacteristicswillimmediatelybecomeevident.

Nexttoaddition-curedsilicones,polyethermaterialsarethemostimportantproductsinthesectorofhigh-precisionimpressionmaterials.Thenaturalhydrophilicityofpolyethers–duetotheiruniquemolecularstructure,formulationandchemicalsettingreaction–iswell-suitedforaper-manentlymoistenvironmentsuchasthemouth.Thischaracteristicisparticularlyusefulwhentakingimpressionsofgingivalareasorinthesulcus,suchassubgingivalpreparations29.

Thankstoitshydrophilicmacromonomers,polyetherofferspreciseflowbehaviour,whichalsoexplainsthestronginitialadhesionofthepolyetherimpressionuponremoval.Triglyceridesareresponsibleforthesespecialflowcharacteristics,whichensureoptimalwettingofthepreparationsurfaceaftersyringingaroundthepreparations.Inorganicfillersproducethehighrigidityoftheimpressionandcontributetodimensionalstabilityfollowingremovalofthesetpolyethermaterial.

Giventheidenticalchemicalbasis,allthreeconsistenciesof3MESPEpolyetherimpressionmaterialscanbefreelycombinedwitheachother,e.g.fortakingedentulousimpressions.Achemicalbondaftercuringisguaranteed.

Fig. 14: Polymerisation process during setting of polyether.

Pol

yeth

er

Pol

yeth

er

Pol

yeth

er

Pol

yeth

er

Cationic Starter Reactive Ring (= R)

Popularbrands:•AccuLoid™

• Identic™(DuxDental)

3.3.CondensationcuringelastomersPolysulfides (Thiokols)Cross-linkingofpolysulfidesisbroughtaboutbyapolycondensationreactioninwhichwateristhereactionproduct.Somepolysulfidesmaybecategorisedastoxicsubstances,primarilyduetotheheavymetal(esp.lead)oxidescontainedinthereactorpaste30.

Comparedtopolyethersandsilicones,polysulfidesdonothaveagoodelasticrecovery.Aftertheclinicallyrecognisablehardeningthecrosslinkingcontinues.Duringthisongoingcuringreactiontheelasticityandelasticrecoveryincreaseconsiderably.Therefore,polysulfideimpressionsshouldbeleftforatleastanother5minutesinthemouth–beyondtheclinicallyrecognisablesetting31.Today,polysulfidesdonotplayanimportantroleinthemarket23;25,butarestillinuseforsomeindications32.

Condensation siliconesThebasecomponentofthecondensationsiliconecategoryconsistsofoleaginouspolydimethylsiloxanewithhydroxyl-terminatedgroupsandfillerssuchasdiatomite,TiO2andZnO.Thebasecomponentcontainstetrafunctionalalkoxysilaneswhich,inthepresenceofacatalystsuchasdibutyltindilaurateorzincoctoate,willreactwiththehydroxylgroups,splittingoffacondensate(usuallyalcohol)andcausecross-linking.Aftercuring,subsequentandinevitableevaporationofthealcoholresultsinshrinkageofthematerial.Afurtherproblemcommonlyencounteredisthedifficultyofobtainingthecorrectproportionsoftheindividualcomponentswhenhand-mixingcondensationsiliconeimpressionmaterials.WiththestandarddispensingofC-typesilicones,adeviationof+/–25percentfromthesetpointcanbeexpected.Thismaycausetheworkingandsettingtimeofthematerialtovary,thusindirectlyaffectingthequalityoftheimpression23–25.

C-siliconesarecompatiblewithmostmodelmaterials.However,allergicreactionstothecatalystpastehavebeenreported.Therefore,skincontactduringmixingshouldbeavoided.

Condensation polyethersThereisonlyonecondensationpolyetherimpressionmaterialonthemarkettoday.Itsbasecomponentcontainsapolypropyleneglycolthatisfunctionalisedwithalkoxysilaneendgroups.Cross-linkingisachievedbythetransformationofalkoxysilaneendgroupswhileethanolisreleased.Thecatalystcomponentcontainsacidandwaterthatareneededforthecuringreaction33.

Reversible hydrocolloidsThemainconstituentofhydrocolloidsiswater,whichsetstogetherwithagar-agar,along-chaingalactosepolysaccharide.Thisproducesagelatinousmassthatissolidatroomtemperature.Ifthemassisheated,asol-geltransitionoccurs,andthematerialbecomesliquid.Asthisprocessisreversible,thematerialsolidifiesagainaftercooling.Bothsolidificationandliquefactiontempera-turesdependon,amongotherfactors,thepurityoftheagarandtheadditionofothersubstances.Talcum,limeandboraxareaddedtohydrocolloids,affectingtheirflowability.

Whenproperlyhandled,hydrocolloidsofferahighlevelofaccuracy.Thisiscomparableto,althoughnotsurpassedby,otherelastomericimpressionmaterials.Ontheotherhand,thehandlingwhentakingahydrocolloidimpressionissometimescumbersome.Wideruseisadditionallydiscouraged

Popularbrands:•Permalastic™

(SDS/Kerr)

Popularbrands:•Optosil/Xantopren

(HeraeusKulzer) •Speedex(Coltène

Whaledent)

Popularbrands:•P2®Impression

Polyether(HeraeusKulzer)

18 | Properties

bylimitedshelflifeandinsufficienttear-resistance.Asaresult,theuseofhydrocolloidshasdwindledtoasmallnumberofusersovertheyears,andagarimpressionmaterialsarebynomeansasimportantastheyusedtobebeforetheintroductionofpolyetherandvinylpolysiloxane23;25.Hydrocolloidimpressionsneedtobecastimmediately(within20minutes).

3.4. ImpressionmaterialsforpreliminaryimpressionsForthefabricationofaprostheticrestorationamodeloftheopposingarchisnecessary,asthereisnootherwaytoensureacorrectocclusion.Itisimportantthereforethatmaterialsusedforpreliminaryimpressionsarediscussed:

Alginates – irreversible hydrocolloidsAlginatesareirreversibleelasticimpressionmaterials.Thebasicsubstanceofalginatesisalginicacid,apolyglycosideofD-mannuronicandL-gulonicacidwhichitselfisnotsolubleinwater.Usualalginatepowderscontain,besidesfillers,sodiumorpotassiumalginate,calciumsulphateasareagentandsodiumorpotassiumphosphateasaretarder.Alginatesareusuallymixedbyhand.Withtheavailablemixingdevices–dependingonthetypeofdevice–thematerialpropertiescanonlybeslightlyimproved.

Alginateimpressionsshouldbecastwithin15–30minutes,sinceduringfurtherstoragetheimpressioninevitablyshrinksduetosyneresisandevaporationofwaterfromthealginategel.Additionally,alginateimpressionscannotbestored,showalowtear-resistance22andtheelasticrecoveryafterdeformationisnotasgoodaswithprecisionimpressionmaterials34.Theuseofsuchanimpressionforthepreparationoftemporaryrestorationsislimitedsinceitcannotbestoredoveraprolongedperiodoftime.Althoughthehandlingofalginatesaswellastheirmaterialpropertiesarealtogethernotveryefficient,theirlowtear-resistanceoffersadvantagesinsomesituations,i.e.whentakinganimpressionofaperiodontallyaffectedtoothoroverfixedorthodonticapplianceswhichcannotbereproducedwithtear-resistantmaterialssincetheimpressioncouldnotberemovedfromthemouth.

Alginate replacement materialsToavoidthedescribeddisadvantagesofalginates,so-calledalginatereplacementmaterials(e.g.Position™Penta™VPSAlginateReplacement,3MESPE)weredeveloped.Sincetheyareprocessedwithautomaticmixingsystems(e.g.Pentamix™3AutomaticMixingUnit,3MESPE,seechapter5.3.),mixingandprocessingerrorscanalmostbeexcluded.Alginatereplacementmaterialsarecost-effectiveVPSmaterialswhich,asotherVPSmaterials,haveahighdimensionalstability.Whenusedwithprefabricatedsingle-useimpressiontrays(Position™Tray,3MESPE)(seechapter4),alginatereplacementmaterialsquicklyandefficientlyprovidepreliminaryimpressions.

Popularbrands:•Palgat™Plus/Quick

AlginateImpressionMaterial(3MESPE)

Properties | 19

Especiallyforthefabricationoftemporaryrestorations,theuseofalginatereplacementmaterialsincombinationwithsuchtraysoffersseveraladvantages:theirsmoothsiliconesurfacefacilitatesthetrimmingoftemporaryrestorationsconsiderably;duetotheunlimitedshelflifeoftheimpression,temporariescanberenewedlaterwithoutproblems.Nofurtherimpressionshavetobemade.Thepreparationofthetray(adhesive,customisationetc.)aswellasitscleaningandsterilisationisnotnecessary.

3.5.MaterialincompatibilitiesandimpressiondisposalGeneral incompatibilitiesMetalsaltswhicharecontainedinmanyastringentsusedforhaemostasiscaninhibitthesettingofimpressionmaterials.Theresultis–atleastpartly–aninsufficientsettingofthematerialespeciallyinthecriticalsulcusregion(seealsochapter2.3.).Generally,onlymaterialsofthesamematerialclassshouldbeusedtogether(seee.g.chapter4.2.1.Customisationofstocktraysorchapter6.1.1-stepimpressiontechniques).All3MESPEpolyethers(cationicring-openingpolymerisation,chapter3.2.)canbecombinedwitheachother,yet,notwithothermaterialclasses.Ifamethacrylatecompositematerialhasbeenusedforabutmentcompletionorcorebuild-up,oratemporaryrestorationofmethacrylatesorcompositeswasproducedbeforetheimpression,theresultingsmearlayerhastoberemovedwithalcoholandcottonpellet,otherwisetheimpressionmaterialwillnotsetatthecontactareas.Grindingandpolishingisnotenoughinthiscase.Therefore,theimpressionareashouldalwaysbethoroughlycleanedanddriedbeforetheimpres-sionistaken(chapter2.3.).Whenworkingwithhand-mixVPSputtymaterialsithastobeobservedthatthecontentsoftheglovescannegativelyinfluencethesettingbehaviouroftheimpressionmaterials(chapter5.1.).

DisposalImpressionmaterialscanbedisposedofinthehouseholdwaste,speciallocalregulationsmightapply.Withregardtowastepreventionthematerialsfilledinfoilbagsandusedinautomaticmixingdevicesareespeciallyenvironmentallyfriendly,sincetheycanbeexactlydosedandonlylittlepackagingwasteisgenerated.

Popularbrands:•Position™VPS

AlginateReplace-ment(3MESPE)

•AlgiNot(Kerr)

Warning:Incompatibilitiesmayariseduring–Retraction( 2.9.)

–Traycustomisation( 4.2.)

–Puttywashtechnique( 6.1.)

–Aftercorebuild-uporfabricationoftemporaries

20 | Properties

3.6.OverviewofmaterialtypesandconsistenciesaccordingtoISO4823:2000

Fig. 16: Material types and consistencies according to ISO 4823:2000. Materials are classified according to the disc diameter they achieve in the ISO test 4823:2000; 9.2. The larger the disc, the thinner the material, i.e. the lower the consistency of the impression material.

Type0 Puttyconsistency

Alternativeterminology:

Kneadablematerial/puttyUse(technique):

Traymaterial(1-step,2-step)

Type 0<= 35 mm

Type1 Heavy-bodiedconsistency


Heavy-body/trayUse(technique):

Traymaterial(1-step,2-step)

Type 1<= 35 mm

Type2 Medium-bodiedconsistency


Mediumbody,mediumviscosity,regularbodyUse(technique):

Tray/syringematerial(1-step,monophase)

Type 231 – 41 mm

Type3 Light-bodiedconsistency


Lightbody/wash/lightviscosityUse(technique):

Syringematerial(1-step,2-step)

Type 3>=36 mm

Properties | 21

4. Impression trays (B.Wöstmann)

4.1. ChoiceoftrayUnlessyoutakeanimpressionofanedentuloussituation,younormallyhavetocopewithunder-cuts.Theseundercutsareeitherinthenaturalshapeoftheunpreparedteethorresultfromtheopposinginclinationofthetoothaxes.Mostofthetimeeventhealveolarridgeshowsundercuts.Inallcasestheimpressionisinevitablycompressedduringremovalfromthemouth.Elastomericimpressionmaterialscanbedeformedbothelastically–whichisreversible–andplastically,irreversibly.Socaremustbetakennottocompressthematerialssomuchthattheyundergoplasticdeformation.Materialcompressioncanbecontrolledbysufficientspacebetweenteethandimpressiontraywall.AruleofthumbistocompressVPSandpolyethermaterialsbyno more than 1/3 oftheiroriginallengthorthickness.Fortrayselectionthatmeansthataroundundercuts,thedistanceofthetoothtothetraywallneedstobeatleasttwicethedepthoftheundercut(Fig.17).

4.2.StocktraysforfullarchimpressionsMetalstocktrayswhichcompletelycoverthetoothrowdistallyshouldbethepreferredchoice.Ifthisisnotpossibleadorsaldamcanbeproducedindividually(seechapter4.2.“Customisationofstocktrays”).Forpolyetherstheuseofnon-perforatedtraysisrecommended.VPSputtymaterialscanbeappliedinperforatedtrayssincetheperforationincreasestheretentionofthematerialsinthetray.Usingputtymaterialsinasimpleplastictray(stocktrayorcustom-madetray)cancauseprob-lemsasthetraymaybedeformedwheninsertingtheimpression.Theimpressionmaterialthensetsinthispositionandisuncontrollablydeformedaftermouthremovalduetotheelasticrecov-eryofthetray.Ifacustomtrayoraplasticstocktrayisused,heavy-orregular-bodiedconsist-enciesshouldbechosenfortheimpression(seealsoFig.16,chapter3.6.).

22 | Impressiontrays

Fig. 17: Silicones and polyethers require twice the undercut depth as a distance to the tray wall (3-fold depth of the undercut from tooth to tray in total).

Customisation of stock traysIfthereisnoadequatelyfittingimpressiontrayavailable,itispossibletocustomiseaserialtray.Customisationcanbedonewithacompositetraymaterial,shellacoraputtyimpressionmaterial.Especiallyifthetrayhastobeprolonged,astablecompositetraymaterialispreferable.Ingen-eral,thedammingmaterialusedneedstobecompatiblewiththeimpressionmaterial.If,e.g.anaddition-curedsilicone(VPS)isusedforimpressioning,C-siliconesshouldnotbeusedfordamming,sincethecatalystoftheC-siliconesinhibitsthesettingreactionoftheVPSmaterial.Dorsaldamming(Fig.18a–d)helpsthedentisttofindanexact,reproduciblepositionoftheimpressiontrayinthedistalareaandincreasesthepatient’scomfortsinceitpreventstheimpressionmaterialfromflowingdownthethroat.Occlusalstops(Fig.18c,d)avoidthecontactofthetrayandtheocclusalsurface,especiallyduringpressurelessimpressions(e.g.withpolyethers)orwhenusinglow-viscousmaterials.Occlusalstopsaremainlyappliedwithcompositetraymaterialintheincisalareaand/ormolarareaatplacesdistantfromthepreparation.Additionally,theapplicationofasupportinthepalatearea,forexamplewithaVPSputtymaterialispossible(Fig.18c,d).Thisiscustomisedtothepatienti.e.byquickinsertionandremovalofthetraywithafastsettingputtymaterial.Theoptimisedfitofcustomisedtraysreducestheappearanceofflowdefects(seealsochapter6.1.).

Impressiontrays | 23

Fig. 18a: Application of dorsal stops. Fig. 18b: Try-in and reduction with scalpel if necessary.

Fig. 18c: Palate (putty material, customised to the patient) and occlusal stops added, application of the tray adhesive followed by drying for at least 5 minutes.

Fig. 18d: Example for a customised tray with palate and occlusal stops, dorsal damming and applied adhesive.

4.3.StocktrayswithoptimisedfitWhilechoosingatrayforimpressionsoftheupperjawisusuallyquiteeasy,youmightencounterproblemswithafully-toothedlowerjaw.Mostlowerjawserialtraysavailableinthedentalmarketareeitherwideenoughbutthendorsallytooshortor,iftheyarelongenough,theyaretoowide35;36.Thus,theuseofimpressiontrayswhichhavebeenespeciallydevelopedfortheimpres-sionoffully-toothedlowerjawsisadvantageous*.

ForpreliminaryimpressionsPosition™Trays(3MESPE)canbeusedalternatively(Fig.19).Asthistraysetwasdevelopedfromananalysisofjawshapesofover1,500testsubjectsinEuropeandtheU.S.,itisusuallypossibletofindamatchingtray35.Thetrayiscoatedwitharetentivefabricwhichensuresadhesionoftheimpressionmaterialtothetrayanditmakesatrayadhesiveredundant.

Forprecisionimpressions,autoclavablecarbonfibretrays**canbeusedasanalternativetometalstocktrays.Thesetraysarealmostasstableassteeltrays.

4.4. CustomtraysRequirementsAcustomtrayisintendedtocreateoptimumflowtotheteethandanevenlythicklayeroftheimpressionmaterialinallareasoftheimpression.Thus,theabsolutevalueoftheinevitabledimensionalchangeoftheimpressionremainslow37;38.Thisidealcanonlyberealisediftheareaofwhichtheimpressionshouldbetakenisfreeofundercuts.Ifthereareundercutstheirthreefolddepthneedstobeblockedoutonthegypsummodelbeforethetrayismade.Thisavoidsexcessivecompressionoftheimpressionmaterial39andfacilitateseasyremovalfromthemouth–analogoustothestocktray.Themainindicationforcustomtraysistheedentulousorpartiallytoothedjaw.Alsoforspecialimpressionsituations(e.g.above-averagesmallorlargejaws,exceptionalabutmentpositions,implants)thefabricationofacustomtrayisnecessary.

Customtraysrequirecarefulfabrication.Todaymainlylight-curedtraymaterialsareused,sincetheyaresufficientlyrigidanddimensionallystable42;43.Thermoplasticmaterials(e.g.shellac)arehighlydeformableand,thus,onlyconditionallysuitableforthefabricationofcustom-madetrays40;41.Autopolymerisingmaterialsaresubjecttobothpro-longedpolymerisationshrinkageandtendtoexpandduetowatersorption.


* Aesculap, Tuttlingen, Germany

** Clan BV, Eindhoven, Netherlands

Fig. 19: Position™ Tray (3M ESPE).

FabricationForthefabricationofacustomtrayastudymodelisneeded.Drawtheprospectivetraymarginsontothemodel(Fig.20a).Then,theundercutsareblockedoutsufficiently(seechapter4.1).Itcanbeusefultoanalysethedepthoftheundercutswithameasurementdevice.Subsequently,theteetharecoveredwithwaxplatesuptothelatertraymargins(2stackedwaxplates➔resultinglayerthicknessapprox.2.5–3mm(Fig.20b)).Ifnomodernlight-curingbuttraditionalautopoly-merisingresinsareused(“coldpolymer”),thewaxshouldbecoveredwithathintinoraluminiumfoiltoprotectitfromthepolymerisationheat.Afterthat,thesoftplasticplateisadaptedtothemodel(Fig.20c).Takecarethattheplateisnotthinnedoutbystretchingittoostrongly,whichwouldresultinareducedstiffnessofthetray.Then,thetraymaterialiscured.Toimproveitsstabilityitisrecommendedtoadaptanotherplasticplate(doublethickness➔8-foldflexuralstrength).Finallyatrayhandlecanbeattachedbypolymerisation,ifdesired.Beforeusingthetray,theinsideshouldberoughenedtoimprovetheeffectofthetrayadhesive44.

Impressiontrays | 25

Fig. 20a: Marking of prospective tray margins. Fig. 20b: Covering of teeth with wax plates. The wax layer thickness defines the space available for the impression material later on.

Fig. 20c: Adaptation of resin plates here with spacers for an open tray implant impression.

Fig. 20d: Cross-section of well fitting custom tray with optimised impression material layer thickness.

Fig. 20e: Custom tray for an open implant impression, with occlusal stops.


4.5.Dual-archtraysEspeciallyforsingle-toothrestorations,thetimeneededfortheactualprecisionimpressionofthepreparedtooth,anadditionalimpressionoftheopposingjawandthebiteregistrationisinaveryunfavourablerelationtotheremainingtimerequiredforthetreatment.Inordertoworkmoreefficientlyinthissituation,dual-archimpressiontraysareoffered.Thespecialtyofthisimpressiontechniqueisthata(partial)impressionofthetoothedupperandlowerjawsaswellasabiteregistrationaretakensimultaneously.Todoso,theimpressionsupport/trayisdesignedinsuchawaythatthepatientcanclosethejawinalmostmaximumintercuspitationwhiletheimpressionistaken.TheimpressiontrayismostlyU-shaped.Inbetweenthearms,thereisusuallyafinemetalorplasticnetwhichseparatesthetoothrowsoftheupperandlowerarchduringimpressioning(Fig.21).Ifthepatientbites,theloopofthe“U”liesdistaloftheterminalteeth.

Thesetraysonlyallowfor1-stepimpressiontechniqueswithtraymaterialshavingsufficientflowability(seechapter6.1.).Sincecorrectocclusalrelationshavetobeensured,theimpressionofmorethanonepreparedtoothorofterminalteethshouldbeavoidedwithdual-archtrays.Inordertogivetheimpressionsufficientstabilityfortheproductionofthestonemodel,itisimportanttouseanimpressionmaterialwhichhasahighshorehardnessaftersetting45.Withcorrectindicationanduse,impressionsindual-archtraysproduceaccuracieswhichdonotdifferoronlyslightlydifferfromthatachievedwithconventionalimpressiontraysundercomparableconditions46.

4.6. TrayadhesiveTheuseofatrayadhesiveimprovesthereliableadhesionoftheimpressionmaterialtotheimpressiontrayand,thus,isanessentialfactorforthestandardisationofthegoodimpressionresult.Allimpressiontraysshouldbecoatedwithathinlayerofasuitableadhesivebeforeuse.Theusedadhesivehastomatchtherespectiveimpressionmaterialtypetoensureadhesion.Forthesamereasonthedryingtimerecommendedbythemanufacturershouldbeobserved.

Whenusing3MESPEPosition™Traysnoadhesiveisnecessary,sincetheretentionfabricprocuresadhesiontotheimpressionmaterial.

Sufficientdryingtimesimplifiescleaningthetraylater.

Popularbrands:•TripleTray®

(PremierDental)

Fig. 21: Dual-arch tray (posterior).

Available3MESPEproducts:

• Impregum™FPoly-etherImpressionMaterial

•Permadyne™Poly-etherImpressionMaterial

•Ramitec™PolyetherBiteRegistrationMaterial

5. Mixing of impression materials (3MESPE)

Theimportanceofastandardisedworkflowhasbeendiscussedinchapters1.3.and1.4.Modernimpressionmaterialsarehigh-techproductswithasophisticatedchemistrywhichareproducedbythemanufacturerwithintighttolerancelimits.Allimpressionmaterialshavetobemixedfromatleasttwocomponents(usuallynamedbaseandcatalystpaste)beforeuse.Onlyahomogeneous,void-freemixingwithacorrectmixingratioofthecomponentsallowsaperfectprecisionimpressionwhichexploitsallqualitiesofmodernimpressionmaterials.

Themajorityofimpressionsworldwidearestillperformedwithhand-mixedmaterials,althoughautomixedsystemsbasedonhanddispenserswithdual-barrelcartridgeshavebeenavailablesince1983(Express™,3MESPE)andautomaticmixingsystemsforfoilbagssince1993(Pentamix™AutomaticMixingUnit,3MESPE).Meanwhileallcommonimpressionconsistencies,includingtheespeciallyhigh-viscousputtymaterialcanbemixedautomatically,homogeneouslyandvoid-free,usingthePentamix™System.

Today’smostcommonmixingproceduresare:

5.1. Hand-mixingofimpressionmaterialsForpastetypematerials(type1–3),dispenseequallengthstrandsofbaseandcatalystpastenexttoeachotheronamixingpad(Fig.22a).Ifusingapolyether(e.g.from3MESPE),dispensingtoomuchortoolittleofthecatalystwillhavenoeffectontheworkingtime,butwillimpairthequalityoftheimpression.TheworkingtimeofpolyethercanbeprolongedforuptooneminutewithPolyetherRetarderforcomplexcases.Thisisanextremelyusefulpropertyespeciallyforfunctionalimpressions.

Useaspatulatomixthestrandsofpastetoformahomogeneousmassuntilevencolourresults(Fig.22b).Repeatedspreadingoverthemixingpadandthenpickingupwiththespatulawillproduceahomogeneousmixture.Themixingprocessshouldnottakelongerthan45seconds(Fig.22c–e).Undernocircumstancesshouldthepastesbemixedusingstirringmovements.

Fig. 22a: Dispensing of correct ratio of base and catalyst pastes. Fig. 22b: Hand-mixing of polyether impression material.

Mixingimpressionmaterials | 27

Available3MESPEproducts:

•Express™STDPutty •Express™2

PuttySoftVPSImpressionMaterial

•Express™2PuttyQuickVPSImpressionMaterial

Formixingofputtymaterials,measureequalvolumesofputtybaseandcatalystusingthecolour-codedputtyspoons.Mixthebaseandcatalystwiththefingertipsuntilahomogeneouscolourisachieved.Themixingprocessshouldnottakelongerthan30seconds.

Theputtymaterialsshouldnotbemixedwithlatexgloves,sincecomponentsofthelatexrubbercaninterferewiththepolymerisationreactionoftheimpressionmaterial.Ifpossibleuseglovesmadeofothermaterials,e.g.nitrile.

Fig. 22c – e: Hand-mixing of polyether impression material.

Fig. 22d Fig. 22e

Fortype2or3materialsuseafillingdevice(red)tofacilitatefillingofthesyringe(Fig.22f–h).Duetoincreasedviscosity,thepolyetherpastescannotbesqueezedfromthetubeattempera-turesbelow16°C/61°F.Whenreturnedtoroomtemperaturetheybecomeworkableagainwithnolossofquality.

28 | Mixingimpressionmaterials

Fig. 22f: Filling of hand-mixed impression material into syringe for intra-oral application.

Fig. 22g Fig. 22h


5.2.HanddispensersystemAutomixsystemswithhanddispensersanddual-barrelcartridgeshavebeenusedsince1983(Express™,3MESPE).Thesesystemshavebeendevelopedcontinuouslyandtodayarethestandardforlight-bodiedsyringingmaterials.Evenmanymonophasematerialsortraymaterialsforthe1-steptechniqueareofferedinthisapplication(e.g.3MESPEGarant™System).Suchsystemsusuallyconsistofa50mldouble-barrelcartridgefilledwithbaseandcatalystpaste,thecorre-spondingmixingtips,applicationtipsandhanddispensers.Themixingprincipleisarepeatedseparationandblendingofpastestrandsintheso-calledstaticmixingtips.Withanincreasednumberofstrandseparations(numberofmixingelements)inthemixingtip,thequalityofthemixincreases,butalsotheextrusionforce.Thisundesiredeffectcanbeovercomebyenlargingthediameterofthemixingtip.However,thehighertheconsistencyofthematerialstobemixedthemoredifficultitistocombineontheonehandacceptableextrusionforcesandsimultaneouslygoodmixingqualitywithanacceptableamountofwastematerialinthemixerontheotherhand.Thus,thesesystemshaveanuppercon-sistencylimitwithrespecttotraymaterialsandareunsuitableforputtymaterials.

For3MESPEimpressionmaterials,usetheGarant™Dispenser1:1/2:1.Inordertoensureoptimalmixing,itishighlyimportanttousethecorrectcolour-codedmixingtipsandintra-oraltipsforeachmaterial(Fig.23).

Insertthecartridgewiththeimpressionmaterialintothedispenser.Beforeapplyingthetip,checkthatthetwocartridgeopeningsarenotclogged,andbleedthecartridgeuntilthebaseandcatalystpasteareevenlyextruded.AttachtheGarant™MixingTip,andifnecessary,theintra-oraltipforsyringing.

210 x 297 mm - Seite 1 - 163/0/571/51-54+F 11/07 - BLAU • GELB • GRÜN • SCHWARZ - 4-Farb-Satz nach Euroskala - 07-0435 (sr)

Dispenser 4:1/10:1

1:1/2:1

4:1/10:1

3M ESPEVPS/Vinyl Polysiloxane

Wash Impression Materials – ISO 4823 Type 3

3M ESPEImpregum™ and Permadyne™ (Polyether)

Wash Impression Materials – ISO 4823 Type 3

3M ESPEVPS/Vinyl Polysiloxane

Heavy Body + Monophase Impression Materials –ISO 4823 Type 1+2

and Bite Registration Materials

3M ESPEProtemp™ Temporization Material

4400

0727

808/

03 (N

ovem

ber 2

007)

Garant™

Dispenser 1:1/2:1

EPSE M3GA EPSE M3stcudorP latneDstcudorP latneD

D-82229 Seefeld - Germany St. Paul, MN 55144-1000

3M, ESPE, Garant, Impregum, Permadyne and Protemp are trademarks of 3M or 3M ESPE AG.© 3M 2007. All rights reserved.

Caution: U.S. Federal Law restricts this device to sale by or on the orderof a dental professional.

Fig. 23: 3M ESPE Garant™ Dispenser, Mixing Tip and Intra-oral Tip.

Makesurethatbasepasteandcatalystpastearemixedcompletelyandareextrudedinuniformcolour.Alternativelythe3MESPEPenta™ElastomerSyringecanbefilleddirectlyfromthemixingtip,whichmightgiveaneasierhandlingwhilesyringing.

Theusedmixingtipshouldbekeptonthematerialcartridgeasaseal.

5.3.AutomaticmixingsystemExactdispensingandthorough,homogeneousmixingofthematerialsarefundamentalrequire-mentsforsuccessfulprecisionimpressions.That’swhy3MESPEdevelopedthefully-automaticPentamix™AutomaticMixingUnitwhichenteredfull-scaleproductionattheendof1993.ThenamePentamixisderivedfromtheGreekwordforfive(penta),reflectingthemixratioofbasepastetocatalystpaste,namely5:1.Meanwhileinitsthirdgeneration,thissystemhashelpedtostandardiseclinicalworkflows,eliminatingthestrainanduncertaintyofhand-mixedmaterialsformanypractices.ThePentamix™3AutomaticMixingUnitdeliversacompletelyhomogeneousandvoid-freemixforhighlyaccurateimpressionsandperfectlyfittingrestorations.

Directfillingoftraysandsyringesfromtheautomaticmixingunitishygienic,andoverall,lesstimeisspentcleaninganddisinfectinggunsandcartridges.Theriskofcross-contaminationisreduced.

ClinicaltimingwiththePentamixmixingunitisreliableandreproducible.Twomainadvantagesofmachinemixingbecomeclearerthefasterthepastecanbeextruded:•Shortertrayfillingtimeleavesmoreworkingtimefortheactualimpression.•Shortertrayfillingtimegivesmoretimetotheassistantforchairsidehelp.


First*

1983 1993 1999 2004 2008

Jars/tubes Cartridges Penta™ Cartridges Pentamix™ 3 Metal Reinforced

Cartridges

Penta™ Metal Reinforced Cartridges

Handmix Garant™ DispenserPentamix™ Automatic

Mixing UnitPentamix™ 2 Automatic

Mixing UnitPentamix™ 3 Automatic

Mixing Unit

New!

New!

* 3M ESPE was the first manufacturer to introduce automix dispensing in both the Garant™ Dispenser and the Pentamix™ Automatic Mixing Unit.

Fig. 24: Important milestones

Mixing principleThePentamix™Systemisbasedondynamicmixing,i.e.themixingspiralinthemixingtipisdrivenbyaseparatemotorviaashaft.Therotationofthemixingspiralinconjunctionwiththeextrusiongeneratesaturbulentflowwithinthematerialwhichresultsincompletemixing.Incomparisontostaticmixingsystemsorhand-mixingthequalityofmixismuchmorehomo-geneous68,69.

Anotheradvantageofthedynamicmixingprincipleisthatitalsoallowshighlyviscousmaterialssuchastype0puttiestobemixedautomatically.

Pentamix™ System and componentsThecoreofthePentamixsystemisthePentamix™AutomaticMixingUnit,whichpermitsmorerelaxedandcost-effectivework.Overtime,systemcomponentswereimprovedtoenhancetherobustnessandreliabilityofthesystem.

Penta™ Mixing Tips – RedThePentaMixingTipenablesanefficientmixingprocessbyoptimisedinnergeometrywhichsignificantlyreducestheflowresistance.

PentaMatic™ AutoOpen System Foil BagsThePentafoilbagsrequirenoseparateactivationandarecolour-coded.APenta™AuthentificationLabelensuresgenuine3MESPEquality.

Penta™ CartridgesPentacartridgesarereinforcedwithsteelinnertubesandarelesssensitivetofatiguethantheoriginalplasticcartridges.


Fig 28: Pentamix™ 3 Automatic Mixing Unit.

Fig. 25: Example of an impression taken with hand-mixed impression material. If such voids occur in the area of the occlusal surface or the prepared abutment teeth, the result may be inaccuracies which jeopardise the success of the work.

Fig. 26: Example of an impression with Pentamix™ mixing: abolutely void-free, homogeneous impression.

Fig. 27: Superior mixing quality of Express™ 2 Penta™ Putty with the Pentamix

™ Mixing Unit (left) compared with a putty mixed by hand (right, Express™ STD Putty).

Fig. 29: Penta™ Mixing Tips Red.

Mixing with the Pentamix™ System InsertthePenta™FoilBagintothecorrespondingPenta™Cartridge(Fig.32a).PlacethecartridgeintothePentamixSystem(Fig.32b)andattacharedPentamixingtip.Pushandholdthestartbutton.Whenstartinganewpairoffoilbags,itmighttake10–15secondsforbothfoilbagstoopenautomatically.Extrudealittlematerialuntilitscolourisconsistent(Fig.32c).DispensethematerialintothetrayandthePentaelastomeresyringe(Fig.32d,e).Leavetheusedmixingtipattachedtothefoilbagsfortightsealing.Alwaysstorefilledcartridgeshorizontallyorwiththemixingtippointingdown(Fig.32f).


Fig. 30: Penta™ Foilbags with Penta™ Authentication Label.

Fig. 31: Steel-reinforced Penta™ Cartridges with new colour coding.

Automatic mixing and dispensing of impression materials with the Pentamix™ 3 Automatic Mixing Unit

Allavailable3MESPEimpressionmaterialsforautomaticmixinganddispensingwiththePentamix™Systemarelistedinaseparateoverview. Thisoverviewcomprisesmaterialscoveringallindicationsandtechniquesforprecisionimpressions,includingputtytypeconsistencies,occlusalregistrationandalginatereplacementmaterials.

Fig. 32a: Insertion of Penta™ Foil Bags into matching, unlocked Penta™ Cartridge.

Fig. 32b: Insertion of cartridge into the unit parallel to the unit opening.

Fig. 32c: Material extrusion until mix is homogeneous.

Fig. 32d: Direct filling of impression tray. Fig. 32e: Direct filling of syringe. Fig. 32f: Correct storage of cartridges with partially used foil bags.

6. Impression techniques (B.Wöstmann)

6.1. 1-stepimpressiontechniques1-step putty/wash, sandwich, single-stage two-phase, 1-step heavy body/light body techniqueInthe1-stepputty/washtechniqueaputtyorputty“soft”materialisusedasatraymaterialincombinationwithalight-bodiedmaterial(type3or2,seechapter3.6.).Ifthepreparedtoothissyringedwiththelight-bodiedmaterial,theterm1-stepputty/washtechniqueisusedasopposedtothesandwichtechniquewherethelight-bodiedmaterialisappliedasasecondlayer(“sand-wich”)ontheputtytraymaterial47.The1-steptechniqueallowsverygoodreproductionofepi-andsupragingivalareaswhicharestateoftheartintoday‘saesthetic,minimallyinvasiveapproachtodentistry.Thereproductionofareasdeepinthesulcuscanbedifficultsinceoftenonlylowinsertionpressurecanbeappliedtopushthematerialintothesulcusand,thus,impresssubgingivalareasofthetooth9;48;.Sometimesflowdefects,pullsanddragsaroundtheundercutsoftheimpressedtootharevisible.Theyalwaysrunparalleltotheinsertiondirectionofthetray.Theseflowdefectscanappearifthetraymaterialslidesoveranedgeduringinsertionandthentheimpressionmaterialisnotabletocompletelyfilltheundercutlyingbehind.Thiscanbeavoided–forinstance–byapplyingsufficientpressureusingthe2-stepimpressiontechnique.Alternativelytheproblemcanbesolvedbyusingatraywhichisbettersuitedfortheanatomicalshapeofthejaworacustomisedtray(seechapters4.2.–4.4.).Anotheralternativeistheuseofalightbodymaterialwithverygoodflowproperties.

Impressiontechniques | 33

Fig. 33: Pulls or drags in the impression appear if the tray material slides over a protruding shape and fails to fill the undercut lying behind. The pulls/drags always run parallel to the insertion direction.

Ingeneral,insertingtheimpressiontray

veryslowly(take5secondstime)helpstoreduceflowdefects.

Heavy body/light body techniqueTheheavybody/wash(orheavybody/lightbody)techniqueis–likethesandwichorputty/washtechnique–asingle-stage,two-phaseimpressiontechnique.Asopposedtothetwotechniquesdescribedpreviously,inthistechniqueahigh-viscousmaterial(heavy-bodied,type1,seechapter3.6.)andnotakneadablematerial(putty,type0,seechapter3.6.)isused.Sometimesalsoamediumconsistency(type2,seechapter3.6.)isusedasatraymaterial.Theuseofacustomorcustomisedtrayoranothertraywithoptimisedfitisadvantageoustosupportthematerialflowintosmallgapsandtoavoidflowdefects.Withalltwo-phaseimpressiontechniquesonlymaterialsofthesamematerialclasscanbecom-binedsincetheimpressionmaterialwouldnotsetotherwise.

Monophase techniqueInthemonophasetechnique,atype2(seechapter3.6.)materialconsistencyisusedasatraymaterialandforsyringingtheabutments.Sincestocktraysusuallycreatelesspressureuponinsertion,themonophasetechniqueisbestsuitedforusewithacustomisedtrayoranothertraywithoptimisedfitandanimpressionmaterialwithexcellentflowproperties.WithcustomtraysandanautomaticallymixedpolyetherorVPSmaterialextremelypreciseimpressionscanbeachieved25;49.

Hydrocolloid impressionAhydrocolloidimpressionisalsoa1-stepimpressionprocedure.Insteadofsiliconesorpoly-ethersareversiblethermoplastichydrocolloidisused.ThehydrocolloidtechniqueachievesresultswhicharecomparabletoVPSandpolyethermaterialswithregardtoaccuracy.However,itisnotthateasytoexactlyreproducesubgingivalareas50;51.Thisimpressiontechniqueinparticularshowstheimportanceofahighlystandardisedworkflowinthedentalpracticeforgoodandreproducibleresults.If,forexample,thematerialisonlyalittletoocold,itcannotbeapplied.Aslightlytoowarmmaterial,however,canbeperceivedbythepatientasratheruncomfortableorevencauseburns,whichalsoaffectsthequalityoftheimpression.

6.2.2-stepimpressiontechniques2-step putty/wash techniqueInthe2-stepputty/washtechniquewithsiliconesafirstimpressiontakenafterpreparationis“corrected“withamoreflowablematerial.Theinitialimpressionistakenwithaserialtrayandaputty(type0,seechapter3.6.)orheavybody(type1,seechapter3.6.)consistency.Thencarefulremovalofallundercutsandinterproximalseptaisessentialforthesuccessoftheimpression.Ifundercutsarenotremoved,displacementofthefirstimpressionmaterialwilloccurthroughthepressureoftheflowablematerialduringthesecondimpressionstepand,thus,errorsintheimpressionareinevitable.

Fig.34showsacarvedfirstimpression.Allinterferingareashavebeencutwithascalpeltoenableeasyre-insertion.Alsochannelsarecarvedinordertoallowexcesswashmaterialtobedisplaced.Otherwisedeformationswilloccurwhichresultinill-fittingrestorations,e.g.tootightcrowns.Theimpressionhastobecleanedwithplentyofwater(oralcohol)andairtoremoveexcessiveordetacheddebris.Duringthisprocedure,salivahastoberemovedcompletelyfromtheimpressionwhichthenmustbedriedthoroughly,otherwisetheadhesionofthewashmaterialtothefirstmaterialcanbeinterrupted.

34 | Impressiontechniques

Fig. 34: Properly carved initial impression (Express™ 2 Penta™ Putty) for the the 2-step putty/wash technique. Since the impression is carved for the use of Express™ 2 Ultra-Light Body which forms very thin layers, the impression was not carved extensively.

Carvingof2-stepimpressions:

•Donotcutatthepreparedsurfaces.

•Carvinginstrumentshouldbesharp,other-wiseimpressionmaterialmighttearoffpartly,e.g.aroundthegingivalsepta,whichwouldreproducelaterinthewashmaterialataran-domposition.Further-more,theputtymaterialcoulddetachfromthetrayunnoticedandcausedeformation.

Eveniftheimpressionhasbeencarefullycarvedtheteetharereproducedslightlytoosmallduetothedistortionofthetraymaterial,whichcannotbecompletelyavoidedduetothematerials’inherentflexibility52–54.Thiscanbecompensatedforbythedentaltechnician,e.g.byapplyinganadditionallayerofspacer.

Alternatively,theinitialimpressioncanbetakenbeforethepreparationoftheteeth.Inthiscasetherewillbealargegapatthepreparedtoothinthesecondimpression,sothatthereisnocon-gestionofthesecondmaterial.Ifthatimpressioniscarvedcarefully,displacementeffectscanbeavoidedalmostcompletely.Anotheralternativeistheso-calledfoiltechnique(e.g.Plicafol).Here,ahighlyelastic,approxi-mately0.2mmthickplasticfoilisputoverthetrayfilledwithputtymaterialandthentheinitialimpressionistaken(Fig.35).Thenecessarycarvingoftheimpressioncanthusbeconsiderablyreduced,however,somewhatmorelight-bodiedmaterialisspent.

The2-stepimpressiontechniqueslowsdowntheprocedureinthedentalsurgerysincetheimpressioniscarriedoutintwosteps.Errorswhichoftenoccurwiththe1-stepimpressionduetonon-timelysupplyandsettingofthetraymaterialontheonehand,andsyringematerialontheotherhand,canbeminimised.Thedisadvantageofthe2-stepimpressiontechniqueisthatitismoretime-consumingthan1-stepimpressionprocedures.The2-stepimpressiontechniqueisnotrecommendedwith3MESPEpolyethermaterials.


Fig. 35: Initial impression (Express™ 2 Penta™ Putty) using the foil technique.

6.3.TakingtheimpressionSyringing the preparationImmediatelybeforesyringingtheteeth,retractioncordsareremovedandtheteetharelightlydriedwithair.Ifretractionsolutionshavebeenused,thesulcusshouldbecarefullyrinsedanddriedtoavoidsettingproblems.Whenusingthetwo-cordtechnique,rinsecarefullybeforetakingtheimpressionandtakecarethatthecordremaininginthesulcusdoesnotcontainanymoreretractionagents.Thetipoftheapplicationsyringewiththeimpressionmaterialisplacedinthesulcus.Then,start-inginthesulcus,thepreparationissyringedwithoutinterruptionwithplentyofmaterial.Theabutmentisusedasaguidingsupport.Thesyringetipshouldalwaysremainwithinthematerialtoavoidairinclusionsand,thus,possiblevoidsintheimpression(Fig.36).

Insertion of the impression trayWheninsertingthefilledtrayintothemouth,atfirstonlyoneendofthetrayisinserted(Fig.37a).Then,theothercheekispulledbackandthetrayiscompletelyinserted(Fig.37b)andpositionedintothemouthwitharotatingmovementwithoutgettingintocontactwiththearchfromwhichtheimpressionhastobetaken.

36 | Impressiontechniques

Fig. 37a: Pulling back the opposite cheek and inserting the tray at side… Fig. 37b: … with a rotating movement.

Fig. 37c: If necessary at the end of tray insertion, the cheek can also be pulled back with mirrors on the other side.

Fig. 37d: Adaptation of the lip to the tray margin to reproduce the area of the gingivobuccal fold correctly.

Fig. 36: Syringing of the prepared tooth.

Trayinsertion:avoidcontactofteeth

andtray,e.g.useocclusalstops(seechapter4.2.)ifnecessaryandchoosetraysizecarefully(seechapter4.1.).

Ifnecessary,thecheekcanalsobepulledbackwithmirrorsasshown(Fig.37c).Slowly,thetrayisadaptedinthedirectionofthepreparationandheldinthesamepositionwithoutpressurebythesamepersonuntilthematerialisset.

Setting process of the impression materialWhentakinganimpressionoftheupperjawyoucaneasilyfindsupportonthechinorcheekboneofthepatient(Fig.38).Thispreventsblurringoftheimpressionandthemovementsofthepatientcanbefollowed.Withimpressionsofthelowerjawitisrecommendedtosupportthetrayonthemandibula.Also,thepatientsshouldclosetheirmouthasmuchaspossibletoavoiddeformationofthemandibulaand,thus,errorsintheimpression.

Pleasenotethattheworkingtimestatedinthemanufacturers’instructionsforuse(accordingtoISO4823)mostlyrelatetoroomtemperature.Somemanufacturers(e.g.3MESPE)additionallylistaclinicallyrelevantworkingtime(e.g.atmouthtemperature),asduetothehighertempera-turesinsidethemouthofthepatientthematerialusedforsyringingthepreparedteethsetsfaster.Inanoptimisedworkflow,syringingtheteethandfillingthetrayshouldbecoordinatedsothatbothproceduresarefinishedsimultaneously.


Fig. 38: Extra-oral finger support on the zygomatic bone and intra-orally on both sides on the distal sections of the impression tray.

38 | Indications

7. Indications (B.Wöstmann)

Impressionsofunpreparedtoothstructuree.g.forastudymodelorthefabricationofanorthodonticsplintisnotsubjecttoasmanyconsiderationsasatrueprecisionimpressionforalaboratory-maderestoration.

7.1. OrthodonticsplintsAnimpressionforthefabricationofclearaligners(e.g.Invisalign®)hastoreproducethetootharchcompletelyandprecisely.Theimpressiontrayshouldbechosenlargeenoughandbefilledwelltocompletelycapturetheterminalmolars.Sincenosubgingivaldetailshavetobereproduced,a1-stepimpressiontechniquelikethesandwichtechniquewithaheavy-bodiedtraymaterial(nottype0)isthemostefficientvariantinthiscase.

Theimpressionofpreparedtoothstructurerequiresadifferentiated,indication-dependentprocedure.Thechoiceofasuitableimpressiontechniqueandimpressionmaterialforaspecialindicationhasanessentialinfluenceonthequalityofthefinalrestoration.Dependingontheclinicalsituationthedifferentimpressiontechniqueshaveadvantagesanddisadvantages.

7.2. VeneersThefabricationofveneersrequiresutmostprecisionoftheimpressionotherwiseavisiblecementgapcouldaffectthefinalaestheticresult.Usuallythepreparationmarginislocatedsupragingivally,deeplysubgingivalpreparationsshouldoccurveryrarely.Inthesecases,single-stepimpressiontechniquesarepreferred.

Fig. 40: Impression for a porcelain veneer with Permadyne™ Polyether Impression Material (3M ESPE). (Courtesy of Dr. Zafiriadis, Zurich, Switzerland)

Fig. 39: 1-step heavy body/light body impression for aligner fabrication using Imprint™ 3 Heavy Body (3M ESPE) and Imprint™ 3 Regular Body VPS Impression Material (3M ESPE).

7.4. InlaysandpartialcrownsPartialcrownpreparationsandinlaycavitiesarethemostdifficulttoreproducesincetheymostlyhaveacomplicatedgeometricalshape.Therefore,1-stepimpressiontechniqueswithanaddition-curedsiliconeor3MESPEPolyetherImpressionMaterialshouldbepreferred.Especiallyforsinglerestorationsthedual-archimpressiontechniqueisanefficientandfastalternative.Duetoitsimminentdisplacementeffectsthe2-stepputty/washtechniqueisonlyrecommendedwithlimi-tations.Carefulcarvingistime-consumingandoftenimpossiblewhenundercutsaredirectlylocatedatthepreparedtooth.

Indications | 39

Fig: 41: 1-step heavy body/light body impression for an adhesive bridge using Permadyne™ Polyether Impression Material (3M ESPE).

Fig. 42: 1-step heavy body/light body impression for an inlay restoration using Express™ 2 Penta™ H Quick and Express™ 2 Light Body Standard Quick VPS Impression Material (3M ESPE).

7.3. AdhesivebridgesUsually,preparationmarginsforadhesivebridgesaresupragingivalandvisible,sotheimpressionshouldbeuncomplicatedfromthataspect.Inordertoachieveoptimumfit,itisrecommendedtotaketheimpressionusingthemonophasetechnique.However,the1-stepheavybody/lightbodyorsandwichtechniquecanalsobeusedifthetraycomponentisnottooviscous(e.g.useImpregum™Penta™HDuoSoft™PolyetherImpressionMaterial,3MESPE).

7.5. SinglecrownsFortakinganimpressionofapreparedcrownabutmentespeciallywithdeepsubgingivalprepa-rationmargins,the2-stepputty/washtechniqueissuitable.Thepressureduringthesecondimpressionreliablypushesthelight-bodiedimpressionmaterialintothesulcus.Whenusing1-stepimpressiontechniques,flowdefectscanhappenmoreoften,especiallywithaputty/washimpressioninastocktray.Thiscanbeavoidedbyusingthe1-stepimpressiontechniquewithaheavy-bodiedormonophasematerialforthetrayinsteadofaputtymaterial.Theuseofatraywithoptimisedfit(e.g.Border-Lock®)oracustomtrayisalsorecommended.Alternatively,thedual-archimpressiontechniquecouldbeusedifappliedcarefully.

7.6. BridgesFromanimpressionperspectivethereishardlyanydifferencebetweentheabutmentsforabridgeandasinglecrown.Themoreabutmentteethandthedeeperthepreparationmargins,themoredifficultitistouseasingle-stepimpressiontechnique.Chooseeitherthe2-stepputty/washora1-stepimpressiontechnique(monophaseorheavybody/lightbodytechnique),preferablyincombinationwithacustomorcustomisedtray.Forsmallbridges(3-unit)thedual-archimpressiontechniquecanbeanalternative;forlargerunitsthistechniqueisnotsuitable.

40 | Indications

Fig. 43: 1-step heavy body/light body impression for a single crown restoration using Express™ 2 Penta™ H Quick and Express™ 2 Light Body Flow Quick VPS Impression Material (3M ESPE).

Fig. 44: 1-step heavy body/light body impression for a single crown restoration using Impregum™ Penta™ H DuoSoft™ Quick (3M ESPE) and Impregum™ L DuoSoft™ Quick Polyether Impression Material (3M ESPE).

Fig. 45: 2-step putty/wash impression for a 3-unit bridge using Express™ 2 Penta™ Putty and Express™ 2 Ultra-Light Body VPS Impression Material (3M ESPE).

Indications | 41

Fig. 46: Monophase impression with fixed primary copings using Impregum™ Penta™ Polyether Impression Material (3M ESPE). (Courtesy of Dr. P. Chlum, Saalburg, Germany)

7.7. CombinationdenturesForthefabricationofcombinationdentures,twodifferentimpressionproblemshavetobesolved.Ontheonehand,abutmentteethhavetobereproducedand,ontheotherhand,mucogingivalareasandtheirrelationtotheteethhavetobereproduced.Forthereproductionoftheabutmentteeththesameguidelinesapplyasfortheimpressionofcrownsandbridges.Afterfabricationandseatingoftheprimarycopings,theimpressioniscarriedoutwithacustom-madetray.Here,theuseofpolyethermaterialsisadvantageous,sincetheyfavoursafefixationoftheprimarycopingsinthetotalimpressionduetotheirhighadhesion.Secondly,functionalmarginaladapta-tionispossiblesincethepatientcanmakefunctionalmovementsduringthesettingphaseoftheimpressionmaterial,and,thus,themobileareasofthemucosacanbereproducedintheirmaximumextension.(Ifapolyetherisusedforthefunctionalimpressionofatoothlessjaw,itcanbeadvantageoustousethePolyetherRetardertoprolongandadjusttheworkingtimeoptimallytotheclinicalrequire-ments).Alternatively,thesecondaryframecanbefabricatedontheprimarilyproducedstudymodelifitcontainsallthenecessaryinformation.

42 | Indications

Fig. 47: Open custom tray. Fig. 48: 1-step heavy body/light body impression for implant- supported restorations and multiple crowns with Permadyne™ Polyether Impression Material (3M ESPE). (Courtesy of Dr. S. Gracis, Milan, Italy)

Transfer technique for implant position

Impression technique Impression material

Tray Technique

Individuallygroundcorebuildup Closed Allimpressiontechniques PolyetherorVPS

Transfercapswhichremainintheimpression(abutmentlevel)

Closed1-stepimpressiontechniqueincustomisedorstocktray

Polyether

Screwed-inimpressionpostswhichremainintheimpression(implantlevel)

Open1-stepimpressiontechniqueinopencustomisedorcustomtray

Polyether

Screwed-inimpressionpostswhichwillberepositioned*intheimpression(implantlevel)

Open1-stepimpressiontechniqueinopencustomtray

VPS

*Repositioninggenerallyislessexact58andthusnotrecommended.

7.8. ImplantsWhentakinganimpressionforimplantsupporteddenturesadditionalaspectsneedtobeconsidered.

Sinceimplantsystemsworkwithprefabricatedprecisionparts,itisnolongernecessarytoexactlyreproducetheimplantsurfaceandmarginasneededwithapreparationonthenaturaltooth.However,implantsareosseo-integratedandcomparedtonaturalteethdonothavetheslightestmobility.Thus,itiscrucialtocapturetheexactthree-dimensionalimplantpositionsandtheirrelationtoeachother,aswellastoensuretheflawlesstransmissionofthatinformationtothecast55–57.Asoposedtoimplants,aconventionalbridgecanstillbeplacedinsituifthedistanceoftheabutmentsonthemodelslightlydeviatesfromtheactualpositionoftheteeth,sincetheperiodontiumenablesthesingletoothtomoveabout30–50µm.Theimpressionconditionsforimplantsdifferfundamentallydependingontheclinicalsituation,thechosenimplanttypeandthecorrespondingtransfertechniquefortheimplantposition(seetable1foroverview).

Table 1: Choice of impression technique and material depending on transfer technique and implant system.

Indications| 43

7.9. Summaryindicationsandtechniques

Indication

Preparation margin

Impression technique

Impression tray

Recommended available 3M ESPE impression materials

Iso

or s

upra

ging

ival

subg

ingi

val

Impressions without preparation (splints etc.)

– –

MonophaseStocktrayorPositiontray

Impregum™Penta™Soft(Quick)Position™Penta™(preliminary)

1-step StocktrayExpress™2Penta™H(Quick)andExpress™2LightBodyStandard(Quick)

Inlay, veneer, adhesive bridge

x –

MonophaseCustomisedorcustomtray

Impregum™Penta™Soft

1-stepStockorcustomisedtray

Express™2Penta™H(Quick)andExpress™2LightBodyStandard(Quick)

Onlay, partial crown

x x

MonophaseCustomisedorcustomtray

Impregum™Penta™Soft


Express™2Penta™H(Quick)and Express™2LightBodyStandard(Quick)

Crown x (x)

1-stepCustomisedorcustomtray

Express™2Penta™H(Quick)andExpress™2LightBodyStandard(Quick)orImpregum™Penta™DuoSoft™


Express™2Penta™PuttyandExpress™2RegularBody

Bridge x x

1-stepCustomisedorcustomtray

Express™2Penta™H(Quick)andExpress™2LightBodyStandard(Quick)orImpregum™Penta™DuoSoft™


Express™2Penta™PuttyandExpress™2RegularBody

Combination denture

x x

Primaryimpression1-step

Customisedorcustomtray

Express™2Penta™H(Quick)andExpress™2LightBodyStandard(Quick)orImpregum™Penta™SoftDuoSoft™

Secondary/fixationimpres-sionsingle-stage/partlyfunctional

CustomtrayImpregum™,Permadyne™(withoptionaluseofPolyetherRetarder)

Table 2: Impression techniques for different clinical situations.

Fig: 51: Impression material specimens contaminated with human saliva carry a multitude of potentially pathogenic microorganisms despite thorough rinsing with water.

Fig: 52: Impresept™ Immersion Disinfectant (3M ESPE) effectively kills microorganisms. After incubation on blood agar no colony-forming units can be detected.

8. Disinfection (B.Wöstmann)

Infectioncontrolisoneofthemostessentialtasksinthedentalpractice.Impressionsaremajorcarriersofbacteriaandvirusessincetheyarecontaminatedwithsalivaandoftenwithblood.Disinfectionensurestheinterruptionoftheinfectionchainbetweendentalpracticeandlaboratoryandprotectsthedentaltechnician.Soeachimpressionshouldbedisinfectedroutinelybeforeforwardingittothedentallabtopreventcontamination.

Impressionsshouldbedisinfectedassoonastheyareremovedfromthemouth.Eachdelaycancauseanincreaseinthenumberofmicroorganisms.Eachimpressionshouldbecarefullyrinsedunderrunningwaterbeforedisinfection,otherwisethebacteriaandviruseswhichshouldbedestroyedcanbeprotectedbysalivaorbloodproteinsandthedisinfectionsolutioncannotreliablydestroythegermsinthestatedimmersiontime.

Disinfectionaimsatreducingthenumberofgermsbyatleastafactorof105.Thus,inmostcasesspraydisinfectionisnotenoughascompletesurfacewettingcannotbeensured.Completeimmersionindisinfectantguaranteessufficientdisinfection59.Theimmersionbathshouldbeinasealablecontainertoavoidevaporationofthedisinfectionagentand,thus,enrichmentintheair.

Onlyusedisinfectantswhichhavebeenespeciallydevelopedandreleasedforimpressionmaterials(e.g.basedonaldehydeorperaceticacid:alcoholasdisinfectantisnotsufficientforsomegerms).Makesurethatthedisinfectantiscompatiblewiththeimpressionmaterialaswellaswiththestoneusedformodelfabrication60;61.Disinfectionsolutionsbasedonalcohol(insteadofwater)asasolventmaycauseswellingoftheimpressionsand,thus,ill-fittingrestorations.

Water-basedimpressionmaterialslikealginatesandhydrocolloidsarepronetoswellingandshouldthereforeremaininthedisinfectionbathforasshortatimeaspossible.Polyether,poly-sulfidesandsilicones,especiallyaddition-curedmaterialsarelesssensitive.Impresept™ImmersionDisinfectant(3MESPE)hasashortimmersiontimeandissuitableforallmaterials.Afterdisinfectiontheimpressionshouldberinsedagainunderrunningwateranddried.

Furthermore,pleasefollowtherecommendationsoftherespectiveassociationsforhygieneandoccupationalhealthandsafetyaswellasthemanufacturers’instructions62.

44 | Disinfection

Fig: 49: Immerse the impression trays completely. Action time 10 minutes (Impresept™, 3M ESPE).

Fig: 50: Let the impression drain in the basket after the immersion time and rinse with water. Exchange solution after one week.

Popularbrands:• Impresept™

(3MESPE)

9. Storage of the impression and transport to the dental lab (B.Wöstmann)

Onthewayfromthepracticetothedentallabtheimpressionisbestcarriedinacontainer,securelyfixedinfoam.Inappropriatetransportandstorageconditionscanleadtofurtherchangesindimension63,e.g.byoverheatingorabsorptionorreleaseofmoisture.Alginatesandhydrocolloidsshouldbecastimmediately(usuallyinthedentalpractice).Iftransportisinevitable,theimpressionshouldbestoredinhygrophororalternativelyinaresealableplasticbagtogetherwithamoist(notwet)papertowel.C-siliconeorpolysulfideimpressionsshouldbecastassoonaspossibleaswell,sincetheyarenotdimensionallystable.Polyetherimpressionsmustbesentseparatelyfromalginateimpressionsandshouldbetrans-portedandstoreddry,coldandprotectedfromdirectsunlight.Undertheseconditionstheycanbekeptforuptotwoweeks.VPSmaterialshavethemostfavourablematerialpropertiesforstorage.However,theyshouldalsobekeptandtransporteddryandnotaboveroomtemperature.Inanycasepleasefollowthemanufacturers’instructionsforuse.

Storage | 45

10. Fabrication of the stone model (B.Wöstmann)

Impressionsandmodelsarecloselyconnected.Basically,thesuccessfullyfabricatedmodelisthecompletionofthetreatmentstep“impression”.

10.1.StandardisationofthemodelfabricationEspeciallywhenusingVPSmaterials,thethermalcontractionofthematerialwhencoolingdownfrommouthtoroomtemperatureshouldnotbeunderestimated,sincetheextentofthiscontractioniscomparablyhigh64.Heatingtheimpressiontomouthtemperaturebeforepouring,however,isnotusefulsincethisprocessisneverreproducibleand,thus,cannotbestandardised.Forconse-quentstandardisationoftheprocessitismuchmorebenefitialtocompensateforthedimensionalerrorwithtargeteddentaltechnicalmethods.Thedentaltechnicianadjustsprocessesinresponsetoimpressionmaterial,trayandinformationreceivedfromthedentist(e.g.useofspacer,embed-dingmass,gypsumexpansion,controlofthemillingmachine,etc.)andcarriesoutcastingoftheimpressionunderconstantconditions(roomtemperature,watertemperatureetc.).

Resin-basedmodelmaterials,(e.g.epoxyresins)areusedlessfrequently.Someofthesematerialsarenotdirectlycompatiblewith3MESPEpolyetherimpressionmaterialsandcanonlybeusedwithaseparatorwhichcompletelysealsthesurface.Silverplatingof3MESPEpolyetherimpressionsinthegalvanisationbathispossible,butcopperplatingisnotpossibleforchemicalreasons.

10.2. ModelsystemsThesectionedmodelisstilloneofthemostusedmodelsystems.Inordertoworkonthemodelaremovalofthestonetissueisusuallynecessaryaroundthepreparationmargin.However,thesegypsumparts,oftenregardedassuperfluous,reproducethesofttissues.Inmostcasestheyfacilitateacorrectshapingofthecrown,sinceithastocorrectlyfittothepreparedtoothaswellasharmonisewiththeperiodontaltissue.Ifnecessary,aremovabletissue(gingivamask)hastobeprepared.Alternatively,modelsystemswithprefabricatedbasesorbasemouldscanbeused.

Theproblemwiththesesystemsis,however,thatthegypsumarchesexpandduringsettingand,thus,areputunderstressbeingfixedtothestablebase.Thesestressesarereleasedafterremovalfromthebaseplate,whichmightleadtodifficultiesincorrectlyrepositioningthetootharchlater.Theteethhavetobepinned,thensectionedintosmallsegmentseachofwhichcanberepositionedexactly.Still,highlyprecisemodelscanbefabricatedifthistechniqueisskilfullyused65–67.Modelsystemswithafinelydetailedbaseplateshouldbeavoidedsincecompleterepositioninginverticaldimensionissometimesdifficultorimpossible.

46 | Stonemodel

Fig: 53: Sectioned stone model.

10.3. TimingofthemodelfabricationCastBeforepouringthemastercasttheimpressionshouldbetrimmed.Theexcessimpressionmate-rialwhichdoesnotcontainanyinformationforthefabricationofthemastercastisremoved.Sinceeachimpressionisdeformeduponmouthremoval,theimpressionmaterialneedstimeforelasticrecoverybeforemodelfabrication.Usually,theminimumtimerequiredvariesbetween30minutesto2hours.All3MESPEpolyetherscanbecastafter30minutes.

Themanufacturers’instructionsmustalwaysbefollowed.EspeciallywithVPSimpressions,voidsinthestonemodelmaybearesultofcastingtooearly–reflectingacontinuingpolymerisationreactionduringwhichhydrogengasisreleased.Furthermore,thecastshouldberemovedfromthemouldonlyafterthetimestatedbythemanu-facturer.Carefulremovalofthearchisessential.Ifnecessary,itcanbecarefullyloosenedatthemarginwithaknife(thisiscomparabletobreakingthevacuumwhenlooseninganimpressioninthepatient’smouth,seechapter2.6.)thenremovetheimpressioninaflowingmovementtowardsthefrontteeth.Ifimpressionmaterialswithahighfinalhardnessareused,theimpressiontraycanberemovedfirst,ifpossible.Then,theflexibleimpressionmaterialcanbepulledoffthecastmucheasier.Alternatively,thetray(e.g.ofa3MESPEpolyetherimpression)canbewarmed,e.g.ontheradia-tor–butnotinahotwaterbath.Donotexceedamaximumtemperatureof40–45°C.Iftheimpressionneedstobecastasecondtime,itmustbegiventimetorecoverfromdeformationuponremovalofthefirstcast.

BaseThemodelbaseshouldbeofatypeIVorVstoneoraspecialbasestonewithalowexpansioncoefficienttokeepexpansionand,thus,errorsaslowaspossible.SuchspecialbasestoneshavealowerhardnessthantypeIVstone,buthavethesameorbetter(i.e.less)expansionbehaviour.TheusualtypeIIIstoneisobsolete.Itleadstoconsiderabledimensionalchangesofthemodel.Thehighlyexpandingstoneevenfurtherexpandsthefinishedtootharchfixedtoit.Themodelbaseisideallyimmediatelypreparedafterremovalofthecastarchorupto24hourslater.Ifthemodelbaseispreparedimmediatelythetootharchisnotsectionedimmediately,sincebaseandarchundergothesameexpansionbehaviour.Afterfabricationandfinalsettingofthemodelbase,thetootharchhastobetrimmedoffthebase.Otherwisethearchisunderstresswhichmightcausecracksandtears.Hardenedstoneishygroscopic.Ittakesupmoisturefromtheairandshouldbestoreddrytoavoidsurfaceanddimensionalchanges.

Stonemodel | 47

Fig: 54: Courtesy of J. H. Bellmann, MDT, Rastede, Germany.

11. Conclusion (B.Wöstmann)

Whatfurtherdevelopmentscanbeexpectedintheareaofimpressioning?High-techproceduresconnectedtoopticalimpressioningwillbeimprovedmoreandmore.This,however,doesnotsolvethebasicclinicalproblems.Allavailableimpressionmethodsallowonlyforthereproductionofaccessibleareas,irrespectiveoftheuseofanelastomericimpressionmaterialorascannerasreproductionmedia.

Accessible,visibleareascanbereproducedwithoutmanyproblems,andthesubsequentworkandmaterialflowissufficientlyexacttoachievegoodrestorations.Basically,today‘simpressionmaterialsandmethodsdeliverexcellentresults.Inordertotakeadvantageoftheirfullcapabilitiesitisessentialtorespecttheclinicalandprocess-relevant parametersdiscussedinthisdocument.Theyareoftenunderestimatedbutarethekeytoachievingresultscorrespondingtothehighlevelsofmaterialsciencebehindtodaysimpressionmaterials.

Followingastructuredprocedureduringimpressioninginconjunctionwithgoodcommunicationandcooperationwiththedentaltechnician(and,ofcourse,avoidingconsequentlyclinicalsourcesoferror)youcanproducerestorationswhichfullfilthehighestbiologicalaswellasaestheticrequirements.

48 | Conclusion

Clinicalworkflow | 49

12. Impression taking in the clinical workflow – Overview

Ifatoothisrestoredwithasupragingivalorminimallyinvasiverestorationsuchasaninlay,abutmentpreparationandprecisionimpressionusuallytakeplaceduringthesameappointment.Inthesecasesthetemporaryrestorationisfabricatedafterimpressiontaking.

Preparatory phasePlanning of restoration

Establishing healthy periodontal conditions

Preparation appointment

Impression of opposing arch | Bite registration

Anaesthesia | Tooth preparation | Fabrication of temporary

Precision impression taking

Selection of impression technique Impression material, technique Shape of tray for best impression result and patient comfort

Removal of temporaryClean abutment tooth

Tissue management Retraction and/or hemostasis

Preparation of impression* Tray: customisation, application of adhesive Prepare wash material, e.g. special application syringe Fill the tray

Impression* Syringe wash material avoid inclusion of air Seat tray slowly and hold in place steadily

with stable support for your hands Remove impression

Cleaning of impression Water rinse, disinfection, water rinse

Possible interference of

methacyclate composite

material or cleaning agents

Possible interference

of astringents with

impression material setting

Lower jaw: prepared side first

Upper jaw: opposing side first

Let dry thoroughly (≥ 5 min)

Front: distally first

Restoration seating appointment

Fabrication of restoration in the dental laboratory

* needs to be performed once for tray material and once for wash material only if 2-step technique is applied

Diagnosisincl. medical history

Send impression to the laboratoryInformation on material, time and date

Provide correct trans-

portation conditions

Fig. 55: Treatment procedure for (subgingival) crown and bridge impressions.

13. Literature

References

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2. MüllerN,PröschelP.Kronenrand und parodontale Reaktion Ergebnisse einer histopathologischen Studie an 368 Sektionspräparaten. DtschZahnärztlZ1994;49:30-36.

3. TurnerCH.A retrospective study of the fit of jacket crowns placed around gold posts and cores, and the associated gingival health. JOralRehabil1982;9:427-434.

4. TjanAH,LiT,LoganGI,BaumL.Marginal accuracy of complete crowns made from alternative casting alloys. JProsthetDent1991;66:157-164.

5. TinschertJ,NattG,MautschW,SpiekermannH,AnusaviceKJ.Marginal fit of alumina- and zirconia-based fixed partial dentures produced by a CAD/CAM system. OperDent2001;26:367-374.

6. GelbardS,AoskarY,ZalkindM,SternN.Effect of impression materials and techniques on the marginal fit of metal castings. JProsthetDent1994;71:1-6.

7. WöstmannB,KraftA,FergerP.Accuracy of impressions attainable in vivo. JDentRes1998;77:798.8. KernM,SchallerHG,StrubJR.Marginal Fit of Restaurations Before and After Cementation.

IntJProsthodont1993;6:585-591.9. WöstmannB,BlösserT,GouentenoudisM,BalkenholM,FergerP.Influence of margin design on the fit of

high-precious alloy restorations in patients. JDent2005;33:611-618.10. DiedrichP,ErpensteinH.Rasterelektronenmikroskopische Randspaltanalyse von in vivo eingegliederten

Stufenkronen und Inlays. SchweizMonatsschrZahnmed1985;95:575-586.11. WolfBH,WalterMH,BoeningKW,SchmidtAE.Margin quality of titanium and high-gold inlays and onlays – a

clinical study. DentMater1998;14:370-374.12. BoeningKW,WolfBH,SchmidtAE,KastnerK,WalterMH.Clinical fit of Procera AllCeram crowns.

JProsthetDent2000;84:419-424.13. MeinersH.Prophylaxe und Werkstoffkunde. ZahnärztlWelt1985;94:792-798.14. PospiechP,WildenhainM.Zur Frage der Mischbarkeit von Polyetherabformstoffen – ein Vergleich zwischen

Hand und dynamischer Mischung. DentalSpiegel1998.15. Wöstmann,B.Clinical parameters of impression techniques in dentistry.

ZStomatol93,531-532.1996.16. WöstmannB.Klinische Bestimmungsvariablen bei der Abformung präparierter Zähne.

ZStomatol1996;93:51-57.17. KernM,SchallerHG,StrubJR.Randschluß von Konuskronen vor und nach der Zementierung.

QuintessZahnärztlLit1994;45:37-48.18. KimotoK,TanakaK,ToyodaM,OchiaiKT.Indirect latex glove contamination and its inhibitory effect on

vinyl polysiloxane polymerization. JProsthetDent2005;93:433-438.19. RodriguesFilhoLE,MuenchA,FrancciC,LuebkeAK,TrainaAA.The influence of handling on the elasticity

of addition silicone putties. PesquiOdontolBras2003;17:254-260.20. ClancyJM,ScandrettFR,EttingerRL.Long-term dimensional stability of three current elastomers.

JOralRehabil1983;10:325-333.21. LinCC,DoneganSJ,DhuruVB.Accuracy of impression materials for complete-arch fixed partial dentures.

JProsthetDent1988;59:288-291.22. MeinersH,LehmannKM.Klinische Materialkunde für Zahnärzte. München–Wien:CarlHanser,1998.23. AnusaviceKJ.Phillips‘ Science of Dental Materials. 11ed.Philadelphia:W.B.Saunders,2003.24. EichnerK,KappertHF.Zahnärztliche Wertkstoffe und ihre Verarbeitung. 6ed.Heidelberg:Hüthig,1996.25. WöstmannB.Zum gegenwärtigen Stand der Abformung in der Zahnheilkunde. Berlin:Quintessenz,1998.26. WöstmannB.Accuracy of impressions obtained with the Pentamix automixing system.

JDentRes1997;76:139.27. GerrowJD,SchneiderRL.A comparison of the compatibility of elastomeric impression materials, type IV

dental stones, and liquid media. JProsthetDent1987;57:292-298.28. PowersJM,SakaguchiRL.Impression materials. Craig‘s restorative dental materials.

ElsevierMosby,2006:294-95.29. HembreeJH,Jr.,AndrewsJT.Accuracy of a polyether impression material.

ArkDentJ1976;47:10-11.30. SpranleyTJ,GettlemanL,ZimmermanKL.Acute tissue irritation of polysulfide rubber impression materials.

JDentRes1983;62:548-551.31. NayyarA,TomlinsCD,FairhurstCW,OkabeT.Comparison of some properties of polyether and polysulfide

materials. JProsthetDent1979;42:163-167.32. PetrieCS,WalkerMP,WilliamsK.A survey of U.S. prosthodontists and dental schools on the current materials

and methods for final impressions for complete denture prosthodontics. JProsthodont2005;14:253-262.

50 | Literature

33. KanehiraM,FingerWJ,EndoT.Volatilization of components from and water absorption of polyether impressions.JDent2006;34:134-138.

34. KandelmanD,MeyerJM,LamontagneP,NallyJN.Etudes comperative de 3 hydrocoillides irreversibles. SchweizMonatsschrZahnheilkd1978;88:134-152.

35. WöstmannB,LammertU,FP.Analysis of fit of stock trays for dentate jaws. JDentRes2002;81:A-60.

36. WöstmannB.Entwicklung neuer Abformlöffel für vollbezahnte Unterkiefer. DentMagazin1991;62-66.

37. BombergTJ,HatchRA,HoffmannWJ.Impression material thickness in stock and custom trays. JProsthetDent1985;54:170-173.

38. WirzJ.Materialien für individuelle Abformlöffel. DtschZahnärztlZ1982;92:207-211.39. MarxkorsR.Abformung bezahnter Kiefer mit individuellen Löffeln.

ZahnärztlWelt1978;87:682-684.40. ThongthammachatS,MooreBK,BarcoMT,HovijitraS,BrownDT,AndresCJ.Dimensional accuracy of dental

casts: influence of tray material, impression material, and time. JProsthodont2002;11:98-108.41. WirzJ,SchmidliF.Individuelle Abformlöffel. SchweizMonatsschrZahnmed1987;97:1417-142.42. MillsteinP,MayaA,SeguraC.Determining the accuracy of stock and custom tray impression/casts.

JOralRehabil1998;25:645-648.43. MartinezLJ,vonFraunhoferJA.The effects of custom tray material on the accuracy of master casts.

JProsthodont1998;7:106-110.44. AbdullahMA,TalicYF.The effect of custom tray material type and fabrication technique on tensile bond

strength of impression material adhesive systems. JOralRehabil2003;30:312-317.45. CeyhanJA,JohnsonGH,LepeX.The effect of tray selection, viscosity of impression material, and sequence

of pour on the accuracy of dies made from dual-arch impressions. JProsthetDent2003;90:143-149.46. CeyhanJA,JohnsonGH,LepeX,PhillipsKM.A clinical study comparing the three-dimensional accuracy

of a working die generated from two dual-arch trays and a complete-arch custom tray. JProsthetDent2003;90:228-234.

47. WirzJ,JägerK,SchmidtliF.Abformungen in der zahnärztlichen Praxis. Stuttgart:GustavFischer,1993.

48. KraftA,WöstmannB,FergerP.Marginal fit of crowns resulting from different impression materials and techniques. JDentRes2001;80:245.

49. WöstmannB,HöingM,FergerP.Vergleich von hand- und maschinengemischten Abformmassen (Pentamix-System). DtschZahnärztlZ1998;53:753-756.

50. NicholsC,WoelfelJB.Improving reversible hydrocolloid impressions of subgingival areas. JProsthetDent1987;57:11-14.

51. DeMourguesF,LloryH.Déflection et régéneration gingivale après électrotpmie. RevmenssuisseOdonto-stomat1979;89:1271-127.

52. OmarR,AbdullahMA,SherfudhinH.Influence on dimensional accuracy of volume of wash material intro-duced into pre-spaced putty/wash impressions. EurJProsthodontRestorDent2003;11:149-155.

53. LehmannKM,HartmannF.Untersuchungen zur Genauigkeit von Doppelabformungen. Quintessenz33,985–987.

54. LehmannKM,ZackeW.Untersuchungen zur okklusalen Schichtdicke des Korrekturmaterials bei der Korrekturabformung. DtschZahnärztlZ1983;38:220-222.

55. LorenzoniM,PertlC,PenknerK,PolanskyR,SedajB,WegscheiderWA.Comparison of the transfer precision of three different impression materials in combination with transfer caps for the Frialit-2 system. JOralRehabil2000;27:629-638.

56. KohaviD.A combined impression technique for a partial implant-supported fixed-detachable restoration. QuintessenceInt1997;28:177-181.

57. GiordanoR.Issues in handling impression materials. GenDent2000;48:646-648.58. WöstmannB,HassfurthU,BalkenholM,FergerP.Influence of Impression Technique and Material on the

Transfer Accuracy of the Implant Position onto the Working Cast. JDentRes2003;82:3060.59. BorneffM,BehnekeN,HartmetzG,SiebertG.Praxisnahe Untersuchung zur Desinfektion von Abformmateri-

alien auf der Basis eines standardisierten Modellversuches. DtschZahnärztlZ1983;38:234-237.60. HutchingsML,VandewalleKS,SchwartzRS,CharltonDG.Immersion disinfection of irreversible hydrocolloid

impressions in pH-adjusted sodium hypochlorite. Part 2: Effect on gypsum casts. IntJProsthodont1996;9:223-229.

61. AbdelazizKM,CombeEC,HodgesJS.The effect of disinfectants on the properties of dental gypsum, part 2: surface properties. JProsthodont2002;11:234-240.

Literature | 51

62. JaggerDC,VowlesRW,McNallyL,DavisF,O‘SullivanDJ.The effect of a range of disinfectants on the dimen-sional accuracy and stability of some impression materials.EurJProsthodontRestorDent2007;15:23-28.

63. WirzJ.Klinische Material- und Werkstoffkunde. Berlin:Quintessenz,1993.64. BrownD.An Update on Elastomeric Impression Materials. BrDentJ1981;150:35-40.65. AramouniP,MillsteinP.A comparison of the accuracy of two removable die systems with intact working casts.

IntJProsthodont1993;6:533-539.66. LehmannKM,WengelerU.Untersuchungen zur Genauigkeit verschiedener zahntechnischer Modellsysteme.

DentLabor1985;33:613-617.67. ReiberT,DertingerK.Zur Präzision von Präparationsmodellen nach der Sägeschnittmethode.

ZahnärztlPrax1988;39:257-263.68. GramannJ.andHartungM.:AADR2006Orlando,AbstractNo1297;„Mixing quality of static and dynamic

mixers for impression materials“ http://iadr.confex.com/iadr/2006Orld/techprogram/abstract_74418.htm.69. P.Pospiech,M.Wildenhain.Zur Frage der Anmischung von Polyetherabformstoffen – Ein Vergleich zwischen

Hand- und dynamischer Mischung. DentalSpiegel5/98.

70. MüllerN,PröschelP.Kronenrand und parodontale Reaktion. DtschZahnärztlZ1994;49:30-36.71. PadburyJrA,EberR,WangH-L.Interactions between the gingiva and the margin of restorations.

JClinPeriodontol2003;30:379–385.72. WöstmannB,HaderleinD,BalkenholM,FergerP.Influence of Different Retraction Techniques

on the Sulcus Exudate Flow. JDentRes2004;83:A-4087.

52 | Literature

14. Glossary

Glossary | 53

A

Abutmentlevel 42

Addition-curedsilicones(vinylpolysiloxanes) 14,17,23,44

Additionsilicones 15

Alginate 19,46

Alginatereplacement 19

Aligners 38

Anaesthesia 12

A-silicones 12,15

Automaticmixingsystems 9,19,20,27

B

Blurring 37

C

Communication 9

Condensationpolyether 15,18

D

Dorsaldamming 23

Doublecordretractiontechnique 11

Drags 33

Dual-archimpression 26,39,40

Dynamicmixing 31

E

Elasticrecovery 14,16,18,19,22,47

Epoxyresins 46

Extrusionforces 29

F

Flowdefects 23,33,40

Foiltechnique 35

Functionalimpression 27,41

G

Garant™ 29

H

Haemostatic 11

Heavybody 21,33,34

Heavybody/wash(orheavybody/lightbody)technique 33

Hydrogenperoxide 12

Hydrophilicity 14,15,17

Hydrophobic 14,15

Hydrophobicity 14

Hydrosylationreaction 15

I

Implantlevel 42

Infectioncontrol 44

Insertion 33,36

Intrinsichydrophilicity 15

Irreversiblehydrocolloids 19

L

Latex 28

Lightbody 21,33

M

Macromonomer 16,17

Mediumbody 21

Metalsalts 11,20

Methacrylatecomposite 12,20

Monophasetechnique 34

O

Occlusalstops 23,36

Oralhygiene 10,11

P

Pentamix™AutomaticMixingUnit 27,30,31,32

Periodontium 10,42,46

Permanentdeformation 13

Platinumcatalyst 15

PolyetherRetarder 27,41

Polysulfides 18

Pulls 33

Putty 20,21,22,23,27,28,33,34

R

Retractionsolutions/liquid 11,36

Reversiblehydrocolloids 14,15,18

S

Sandwichtechnique 33

Sectionedmodel 46

Settingprocess 11,12,37

Singlecordretractiontechnique 11

Smearlayer 20

Snapset 16,17

Standardisedworkflow 9,27,34

Staticmixing 29,31

Sulcusbleeding 10,12

Surfactants 14,15

Syringing 17,29,36

T

Temporaryrestorations 19,20,49

Tensilestrength 16

Tissuedisplacement 11

Toothaxes 13,22

Trayadhesive 24,25,26

U

Undercuts 22,25,33,34

V

Vasoconstrictor 11,12

VPS 12,15,16,20

1-stepputty/washtechnique 33

2-stepputty/washtechnique 34

54 | Overview

Indications•Crownandbridgeimpressions

•Inlayandonlayimpressions

15. Overview 3M ESPE impression materials

•Functionalimpressions

•Implantimpressions

Impregum™Penta™Soft/QuickPolyetherImpressionMaterial

Excellentfitduetofirst-classprecision.

Benefits•Precise and void-free impressionsthroughoutstandinginitialhydrophilicityinmoistenvironments

•First-rate detail reproductionthankstoexcellentflowproperties

•Constant flow behaviour throughout working period and less distortionsbyunique“snap-set”behaviour

•Quick material cuts working and setting timesbyatleast33%

•Fresh minty flavour and easier removabilityof“Soft”materials

Overview | 55

Indications

•Crownandbridgeimpressions

•Inlayandonlayimpressions

Indications•Preliminaryimpressions

•Provisionalcrownandbridgeimpressions

•Opposingdentitionimpressions

•Impressionsforbleachingtraysandmouthguards

•Studymodelimpressions

•Impressionsfororthodonticmodels

Position™Penta™/QuickVPSAlginateReplacement

Lesspreptime.Moreworkingtime.Astress-freealginatereplacement.

Express™2VPSImpressionMaterial

Outstandingbalanceofclinicallyrelevantpropertiesforuncompromisingimpressionaccuracy.

Benefits• Precise impressions throughhigheraccuracy

•Fast working and setting times atroomtemperature

•Less distortions thankstoelasticrecovery

•Easy and thorough disinfection becausematerialcanbecompletelysubmersedindisinfectantsolution

•Long-term storage ability duetohighdimensionalstability

•Suitable for multiple pouring plusnoneedofimmediatecasting

Benefits•Extraordinarily well balanced propertiescomparedtootherleadingVPSproducts

•Great detail reproduction throughsuperiorhydrophilicityandflowbehaviour

•Distortion-free removal from the mouth duetoexcellenttoughness

•Reduced chance of costly remakes duetoalmost100%recoveryfromdeformation

•Faster setting of wash materials without reduced working time throughthermallyactiveputtytechnology

Your notes

3M ESPE AGESPE Platz82229 Seefeld · GermanyE-Mail: [email protected]: www.3mespe.com

EUR 49.00 Recommended price.

3M, ESPE, DuoSoft, Express, Garant, Impregum, Impresept, Imprint, Lava, Palgat, Penta, PentaMatic, Pentamix, Permadyne, Position and Ramitec are trademarks of 3M or 3M ESPE AG.

Acculoid, Affinis, Alginot, Aquasil, Boder-Lock, CEREC, Expasyl, Hongum, Identic, Invisalign, Optosil, P2, Peridenta, Permalastic, Plicafol, Speedex, Triple Tray and Xantopren are not trademarks of 3M or 3M ESPE AG.

© 3M 2008. All rights reserved.

70200956095/01 (5.2008)

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