TheEffectofArtificialToothMaterialson StressDistributioninCompleteDentures

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1 ORİJİNAL ARAŞTIRMA TheEffectofArtificialToothMaterialson StressDistributioninCompleteDentures Oğuz ERASLAN, a Özgür İNAN, a Gürcan ESKİTAŞCIOĞLU a a Department of Prosthodontics, Selçuk University, Faculty of Dentistry, Konya Ge liş Ta ri hi/received: Ka bul Ta ri hi/accepted: PresentedattheJointMeetingofthe ContinentalEuropean(CED)and Scandinavian(NOF)Divisionsofthe IADR,Amsterdam,Netherlands, September2005. Ya zış ma Ad re si/correspondence: Oğuz ERASLAN Selçuk University, Faculty of Dentistry, Department of Prosthodontics, Konya, TÜRKİYE/TURKEY oguzeraslan@selcuk.edu.tr ABSTRACTObjectives:Theartificialtoothmaterialforanedentulouspatienthasanimportanteffect onsuccessoftreatment;however,informationabouttheinfluenceofartificialtoothmaterialonforcestransmittedtotheresidualridgeislimited.theaimofthisstudywastocomparethestressdistributiononsupportingboneofporcelainandhardacrylicresinmaterials,andtocomparephotoelastic andfiniteelementmethodsbythismanner.materialandmethods:threedimensionalfiniteelement modelsandphotoelasticmodelssimulatingtwocompletedentureswithporcelainandhardacrylicresinteethwereprepared.300nocclusalloadwasappliedatbothmethodstotheflattenedocclusalsurfacesofmodeledteeth.thedifferencesinocclusalloadtransferabilityofacrylicandporcelainteeth wereinvestigated.results:maximumstresseswereconcentratedonforceapplicationareas(28mpa) andcervicalregionsofartificialteeth(24mpa).thestressvaluesobservedwiththeuseofporcelain teeth(4-8mpa)werelowerthanthehardacrylicresinteeth(4-12mpa).thestressdistributionon supportingbonewassimilarforbothmodels.conclusion:theresultofthisstudyshowedthattheuse ofporcelainasartificialteethincompletedenturesreducesthecompressivestresslevelsonsupportingbonestructure.finiteelementmethodprovidedmoredetailedinformationaboutthestressdistributionthanphotoelasticmethod,andgaveinformationaboutallofthemodelcomponents. KeyWords:Artificialtooth;finiteelementanalysis;completedenture ÖZETAmaç:Tamdişsizhastalardayapaydişmateryalitedavibaşarısındaönemlibiretkiyesahiptir; bununlabirlikte,yapaydişmateryalininalveolisırtınailetilenkuvvetlerüzerindekietkisiyeterince bilinmemektedir.buçalışmanınamacı,porselenveakrilikrezinmateryallerinindestekkemikdokularındakistresdağılımlarınıkarşılaştırmakvebuyollafotoelastikvesonluelemanstresanalizyöntemlerinikıyaslamaktır.gereçveyöntemler:porselenvesertakrilikrezindişleresahipikitamprotezi betimleyenüçboyutlusonluelamanvefotoelastikmodellerhazırlandı.herikiyöntemdedemodellenendişlerindüzleştirilenokluzalyüzeyinden300nokluzalyüklemeyapıldı.akrilikveporselendişlerinokluzalyüktransferkabiliyetlerindekifarklılıklarincelendi.bulgular:kuvvetuygulamaalanları (28MPa)veyapaydişlerinservikalbölgelerinde(24MPa)enyüksekstresdeğerlerigözlendi.Porselendişlerkullanıldığındagözlenenstresdeğerleri(4-8MPa)sertakrilikrezindişlerdegözlenenlerden (4-12MPa)dahadüşüktü.Destekkemikyapısındakistresdağılımşekliherikimodeldedebenzerdi. Sonuç: Buçalışmanınbulguları,porselenintamprotezlerdeyapaydişolarakkullanılmasınındestek kemikyapısındakisıkıştırmatipistresseviyelerinidüşürdüğünügöstermiştir.sonluelemanstresanalizyöntemifotoelastikanalizyöntemindenstresdağılımıhakkındadahadetaylıbilgisağlamışvemodeldekitümyapılardakidağılımınincelenebilmesineolanakvermiştir. AnahtarKelimeler: Yapaydiş;sonluelemananalizi;tamprotez TurkiyeKlinikleriJDentalSci2009;15(2):81-6 Cop yright 2009 by Tür ki ye Kli nik le ri he selection of artificial teeth for an edentulous patient requires knowledgeandunderstandingofanumberofphysicalandbiologic factorsthataredirectlyrelatedtothepatient.dynamicbehaviorof TurkiyeKlinikleriJDentalSci2009;15(2) 81

2 OğuzERASLANetal THEEFFECTOFARTIFICIALTOOTHMATERIALSONSTRESSDISTRIBUTIONINCOMPLETEDENTURES thedentureunderocclusalforcehasanimportant effectonsuccessoftreatment.thedentistmustaccumulate,correlate,andevaluatethebiomechanicalinformationinselectionofartificialteethto meettheindividualestheticandfunctionalneeds ofthepatient. 1 Notonlythemasticatingefficiency considerationbutalsocomfort,esthetics,andpreservation of the underlying bony and soft tissue structuresareimportantinselectionofposterior teeth. 2 Vacuum-firedporcelain,acrylicresin,and hardacrylicresinareusedinfabricationofartificialteeth,butallhavesomeadvantagesanddisadvantages. Avarietyoffactorsareinvolvedinresidual ridgeresorption,somelocal,otherssystemic. 3,4 For example, compressive forces are known to be harmfultobone. 5 Therefore,itisimportanttolessenthepressureonthesupportingtissues.Since theloadsaretransferredthroughtheteethtothe restofprosthesis, theselectionofartificialteeth materialhasanimportantroleonstressdistributioninsupportingstructures. 6 Inthiscontextofforcestransmittedtotheresidualridgethequestionarisesofwhetheramaterialwithahighercoefficientofelasticity,suchas thatusedinacrylicresinartificialteeth,wouldbe lessharmfultotheresidualridges. 5 Variationsindenturetechniquethatmayaffectbonelosshavebeeninvestigated. 7 Nodifferencesofstatisticalsignificancewerefoundinthe amountofbonelost,whetherasimpleoraconventionaldenturetechniquewasused. 5 Unfortunately, theauthorsofthestudydidnotspecifywhether theteethweremadeofacrylicorporcelain. 5 Theeffectofthesettingofartificialteeth, and theeffectofthecuspanglehavealsobeeninvestigated. 8,9 Butthereislittleknowledgeabouttheeffect of artificial teeth material in the literature. Furthermore,areviewofliteraturerevealedthat thequestionofridgeresorptioninrelationtothe materialusedinartificialteeth(porcelainoracrylicresin)remainsunsolvedtodate. 5,10,11 Granthassummarizedtheadvantagesanddisadvantagesofporcelainandacrylicresinartificial teeth. 10 Thesimplicityofadjustmentstoacrylicte- eth,whichcanbegroundwithoutanysevereef- fectontheiradhesiontothedenturebase,aswell astheeaseofdenturefabricationandpolishingafteradjustments,standoutasthemainfactorsfor thechoiceoftheseteethbymostclinicians. 5 The greatpopularityofacrylicresinteethwasalsoacknowledgedinasurveyofnorthamericandental schools. 11 Nevertheless,porcelainremainsanoutstandingmaterial,recognizedinparticularforits durability,whichissuperiortothatofacrylic,despiteprogressinthedevelopmentofhighlycrosslinked acrylic resins that are less susceptible to wearthanconventionalones. 5 Butitisnecessary fordenturestobeusedforalongperiodoftimebecauseoftheprematurecontactscausedbytheabrasion of artificial teeth and absorption of the alveolarridge. 12 Inthelightofthisinformation,thepurposeof thisstudywastocomparethestressdistributionon supportingboneofporcelainandhardacrylicresin materials, and to compare photoelastic method (PM) and finite element method (FEM) by this manner. MA TE RI AL AND MET hods Inthisstudy,three-dimensionalFEMandthephotoelasticstressanalysismethodswereused.Two typesofmathematicalmodelssimulatingtwocompletedentureswithporcelainandhardacrylicresin teeth have been prepared with supporting structures.porcelainandhardacrylicresinteeth havebeenalsousedinpm. Photoelastic Method: Acrylic resin (Major Dent,MajorProdottiDentariS.p.A.,Moncalieri, Italy)andporcelain(Real,ENTAB.V.,Holland)artificialfirst-secondpremolarandfirstmolarteeth havebeenused.occlusalplaneofteethhavebeen flattenedtoapplyauniformload.thicknessofbasepartofdenturewaspreparedas1.5mm.tosimulatesupportingstructureparta30x50mmwax modelwith10mmthicknesshasbeenprepared. ThenimpressionofthiswaxpatternhasbeenacquiredbyaPolysiloxanesilicon-basedimpressionmaterial (Zetaplus, Zhermack Italy). PL-2 (MeasurmentsGroup,Inc.,Raleigh.NC)epoxyresinhasbeenusedinfabricatingmodel(Figure1). 82 TurkiyeKlinikleriJDentalSci2009;15(2)

3 THEEFFECTOFARTIFICIALTOOTHMATERIALSONSTRESSDISTRIBUTIONINCOMPLETEDENTURES OğuzERASLANetal FIGURE 1: Model prepared for photoelastic stress analysis. FIGURE 2: (A) 3D finite element model. (B) Boundary conditions of FE model. 300NocclusalloadhavebeenappliedbyaPolariscope(SharplesStressEngineersLtd.,Preston, UK)uniformlytoflattenedocclusalsurfaceofteeth. FiniteElementMethod: Thestudywasconducted using a three-dimensional FEM and the SAP2000Advanced9.0.3structuralanalysisprogram(ComputerStructuresInc.,Berkley,CA). Thegeometryofstructuresinthemodelwas acquiredfromthephotoelasticmodel.thestandardmodelcomposedof17283nodesand15360 eightnodesbricksolidelementswiththreedegree offreedompernode(figure2a).pointsatbottom borderofmodelwereconsideredfixedinalldirectionsforresistanceofthefemmodel totheocclusalloads. Total300Nloadhavebeenapplieduniformly toflatocclusalsurfacesofallthreeteeth.theappliedforceswerestatic(figure2b). Mechanicalpropertiesofthematerialswere takenfrompreviousliterature(table1). 13,14 ToenablethelogicalcomparisonoftheresultsofFEM andpm,mucosatissuewasignored.allmaterials werepresumedhomogenousandisotropic.elastic modulusandpoisson sratioofthematerials,along withthecoordinateandgeometryofeachnodeand element,wereenteredtocomputer.sap2000struc- TABLE 1: Mechanical properties of materials. Material Elastic Modulus (E) (GPA) Poisson s Ratio (Ц) Acrylic artificial teeth Porcelain artificial teeth Acrylic resin Compact bone turalanalysisprogramwasusedtosolvethestress analysisproblems.calculatednumericdatawere transformedintocolorgraphicstobettervisualize mechanicalphenomenainthemodels.stresslevels werecalculatedusingvonmisesstressvalues. 15 RE SULTS Photoelastıcmethod Inpresentationofthestressdata,thefollowingterminologyhasbeenused: a)lowstress 1fringeorless; b)moderatestress-between1and3fringes;and c)highstress morethan3fringes. 16 Afterapplyingthesameverticalloadtotwo differentmaterials,fringeordershavebeenevaluated.inevaluationofbothmodelshighstressvalues have been observed at alveolar ridge region (Figure3,4). TurkiyeKlinikleriJDentalSci2009;15(2) 83

4 OğuzERASLANetal THEEFFECTOFARTIFICIALTOOTHMATERIALSONSTRESSDISTRIBUTIONINCOMPLETEDENTURES FI GU RE 3: Stress dis tri bu ti on of por ce la in te eth mo del in pho to e las tic met hod. FI GU RE 4: Stress distribution of acrylic teeth model in photoelastic method. Incomparisonofporcelain(Figure3)andacrylic(Figure4)teethmodels,morefringeordershave been observed at acrylic teeth models than porcelainteethmodel. Fınıteelementmethod Theanalysisofstressvaluesforallmodelsrevealed thatmaximumstresseswereconcentratedonforce applicationareas,cervicalregionsofartificialteeth andmesial-distalalveolarridgeregion. Whentheporcelainandacrylicteethmodels werecompared,lowerstressvalueswereobserved withtheuseofporcelainteeth(figure5)thanthe hardacrylicresinteeth(figure6). Inporcelainteethmodel,stresseswereaccumulatedinporcelainstructure,andstressestransferredtothebonestructurewereminimal.Butin acrylicteethmodelstressesweredirectlytransferredtothebonestructure WhenFEMandPMmodelswerecompared, thestressdistributiononsupportingbonewassimilar.butfemmethodgaveinformationaboutthe typeandamountofstressadditiontothedistribution. FI GU RE 5: Stress distribution of porcelain teeth model in FE method. FI GU RE 6: Stress distribution of acrylic teeth model in FE method. 84 TurkiyeKlinikleriJDentalSci2009;15(2)

5 THEEFFECTOFARTIFICIALTOOTHMATERIALSONSTRESSDISTRIBUTIONINCOMPLETEDENTURES OğuzERASLANetal DIS CUS SI ON Although finite element analysis was originally usedinshipbuildingandcivilengineering,ithas beenutilizedforstressanalysisindentistry. 13 Inthe presentstudy,usingtheoretical(fem)technique, theeffectoftheartificialteethmaterialonstress amountanddistributionwasevaluated.directexperimentalmeasurementsofthestressdistribution attheselocationsaredifficult.however,atheoreticalwellknownmethodforcalculatingstressdistribution within complex structures is the FEM whichallowstheinvestigatortoevaluatetheinfluenceofmodelparametervariationoncethebasic modelhavebeencorrectlydefined. 17 TheFEMresultsarepresentedintermsofthe vonmisesstressvalues.vonmisesstressesdepend ontheentirestressfieldandareawidelyusedindicatorofthepossibilityofdamageoccurrence. 18 It wasobservedthatartificialteethmaterialhasan effectonstressdistributiononsupportingstructures. Theadvantagesanddisadvantagesofporcelainandacrylicresinartificialteethwerereported previously. 5,10,11 Despitetheprogressinthedevelopmentofhighlycross-linkedacrylicresinsthat arelesssusceptibletowearthanconventionalones, porcelainremainsanoutstandingmaterialasitis muchmoreresistanttowear. 5 Itisnecessaryfor denturestobeusedforalongperiodoftimebecauseoftheprematurecontactscausedbytheabrasionofartificialteethandabsorptionofthealveolar ridge. 12 Landa statedthat90%ofthetroubleresultingfromdenturesiscausedbytraumaticocclusion. 19 Thus, a strong material like porcelain is neededintreatment,andinthelightoffindingsof currentstudythatthelowerstressvalueswereobservedwiththeuseofporcelainteeth,porcelainteeth can be recommended as an option for treatment. Therewerenopreviouspublicationsaboutthe comparisonofinfluenceofporcelainoracrylicartificialtoothmaterialonstressdistribution.the FEMmodelcreatedforthisstudywasamultilayered complex structure involving artificial tooth, denturebase,andsupportingstructures.itisimportanttonotethatthestressfollowingloading may be influenced greatly by the materials and propertiesassignedtoeachmaterial.itisknown, thatwhenforceisappliedtocompositeorlayered materials,stressestendtomaximizewithinthematerialwiththehighestelasticmodulus. 20 Therefore, the stresses were more concentrated in the porcelain tooth material and less transmitted to supportingstructuressinceporcelainhasahigher elasticmodulusthanotherstructuresandacrylic. PMcangivesimilarstressdistributionpattern on supporting bone, but FEM gave information aboutthetypeandamountofstressadditiontothe distribution.furthermore,withfem,stressdistributionsofallstructuresinvestigatedinstudycan beevaluated. Themodelusedinthisstudyimpliedseveral assumptions regarding the simulated structures. Thestructuresinthemodelwereallassumedtobe homogeneous,andisotropic.thepropertiesofthe materialsmodeledinthisstudy,particularlythelivingtissues,however,aredifferent.also,itisimportant to point out that the stress distribution patternsmayhavebeendifferentdependingonthe materialsandpropertiesassignedtoeachlayerof themodelandthemodelusedintheexperiments. 21 Also,theeffectofmucosalayerwasignoredtoenablethecomparisonofFEMandPMresults.Thus, the inherent limitations in this study should be considered. Theinvivogreatnessofocclusalforceisselectedstandard300Nvalue.However,itisnotnecessary for this force to match the reality exactly becauseofthestandardizationbetweenconditions hasbeenensuredincurrentstudyandtheconditionshavebeencomparedqualitativelywitheachother.chenandxuhaveemphasizedthatthevalue offemmodelingisinrelativevaluescalculatedat distributionpattern. 22 Aswithmanyin-vitrostudies,itisdifficultto extrapolatetheresultsofthisstudydirectlytoaclinicalsituation.theloadapplicationareacaninfluence the stress distribution pattern. Thus, to simulateequalconditionsfordifferentmaterials TurkiyeKlinikleriJDentalSci2009;15(2) 85

6 OğuzERASLANetal THEEFFECTOFARTIFICIALTOOTHMATERIALSONSTRESSDISTRIBUTIONINCOMPLETEDENTURES theocclusalsurfacesofteethhavebeenassumedas flat,thishavealsostandardizedtheconditionsfor PMandFEM.Theseflatocclusalsurfaceshavebeenspecificallydescribedasthelocationsforthe forceapplications.consideringthelimitationsof currentstudy,furtherstudiesthatbettersimulate theoralenvironmentandincludingfatigueloading arerecommended. CONC LU SI ON Withinthelimitationsofthistheoreticalstudy,the followingconclusionsweredrawn: Thisstudyshowedthattheuseofporcelainas artificialteethincompletedenturesresultedinless stresslevelsonsupportingbonestructure. Wheninvestigatingthestressdistributionson multilayereddentalcomplexes,althoughpmgives similar results, FEM allow detailed information aboutstresstransferanddistribution.thus,femis advantageouscomparedtopm. Acknowledgement ThisstudyissupportedbyResearchProjectCounsilof UniversityofSelçuk. 1. Me şe A, Gün düz Gü zel K, Ka le E. 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