* M.Shash , H.Nazha , W.Abbas Bone: A 3D-FEA Behavior of One-Piece Zirconia Dental Implants and Their Surrounding Inﬂuence of Different Abutment Designs on the Biomechanical IRBM

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Contents lists available atScienceDirect

IRBM

www.elsevier.com/locate/irbm

Original Article

Inﬂuence of Different Abutment Designs on the Biomechanical

Behavior of One-Piece Zirconia Dental Implants and Their Surrounding Bone: A 3D-FEA

M. Shash

^a^,^b

, H. Nazha

^a^,^b^,^∗

, W. Abbas

^c

aFacultyofTechnicalEngineering,UniversityofTartous,Tartous,Syria

bFacultyofBiomedicalEngineering,Al-AndalusUniversityforMedicalSciences,Tartous,Syria cFacultyofMechanicalEngineering,CzechTechnicalUniversity,Prague,CzechRepublic

h i g h l i g h t s g r a p h i c a l a b s t ra c t

•^3D^finiteêlement^models^wereconstructed forfiniteelementanalysis.

•Theocclusalloadingforcewasappliedon theprostheticabutments.

•^Thebiomechanicalbehaviorofthesystem wasinvestigated.

•^Model⁰¹^presented^the^bestbiomechani- calbehaviorintheperi-implantbone.

a r t i c l e i n f o a b s t ra c t

Articlehistory:

Received28September2018 Receivedinrevisedform4April2019 Accepted17July2019

Availableonline5August2019 Keywords:

Dentalimplants Abutmentdesigns Finiteelementanalysis Zirconiamaterial Biomechanicalbehavior

Background: Inadentalimplant/bonesystem,thedesignfactorsaffectthevalueanddistributionsofstress and deformations that playsa pivotalrole on the stability, durabilityand lifespan of the implant/bone system.

Objective: The aim of this study was to compare the inﬂuence of different abutment designs on the biomechanical behavior of one-piece zirconia dental implantsand their surrounding bone tissues using three-dimensionalﬁniteelementanalysis.

Methods: A three-dimensionalgeometricalmodel ofazirconia dental implant and itssurrounding bone tissuewerecreated.Theocclusalloadingforceappliedtotheprostheticabutmentswasacombinationof 114.6Nintheaxialdirection,17.1Ninthelingualdirectionand23.4Ntowardthemesialdirectionwhere thesecomponentsrepresentmasticatoryforceof118.2Nintheangleofapproximately75°totheocclusal plane.

Results: ThesystemincludedimplantabutmentModel01showedadecreaseof9.58%,9.92%and3.62%at leastintheaveragevalueofmaximumvonMisesstresscomparedtoModel02,Model03andModel 04 respectively.TheresultsalsoshowedthatthesystemincludedimplantabutmentModel 01decreasesthe averagevalueofmaximumdeformationof16.96%,7.17%and9.47%atleastcomparedtoModel02,Model 03andModel04respectively.

Conclusion: The one-piece zirconia dental implant abutment Model 01 presents a better biomechanical behaviorintheperi-implantbonethanothers.Itcaneﬃcientlydistributetheappliedloadandpresentmore

*

Correspondingauthorat:FacultyofTechnicalEngineering,UniversityofTartous,Tartous,Syria.

E-mailaddress:Hasannazha15@gmail.com(H. Nazha).

https://doi.org/10.1016/j.irbm.2019.07.001

1959-0318/©²⁰¹⁹ÂGBM.^Published^byÊlsevier^Masson^SAS.Âll^rights^reserved.

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homogeneousbehaviorofstressdistributionandhaslessdeformationthanothers,whichwillenhancethe stabilityofimplant/bonesystemandprolongitslifespan.

©²⁰¹⁹ÂGBM.^Published^byÊlsevier^Masson^SAS.Âll^rights^reserved.

1. Introduction

Implantationalludes tonon-livingmaterialsintothebody and setinlivingtissue[1].Dentalimplantsupportedrestorationshave been generallyutilized as a typical treatment method to restore edentulousness in recent years [2]. Numerous individuals have practicedwithmissingteethimplantationforremoval. Theessen- tial treatment objective is the re-establishment of function. Fur- ther, objectives include the long-term functional stability of the implants, lessened surgical and prosthetic procedures, high pre- dictabilityofthetreatmentresults,andidealstructuredesign[3].

Thetransference oftheocclusal loadsto thebone-implant in- terfaceis a crucial factor to determine the resultof the implant treatment [4]. Numerous factors inﬂuence load transfer at the bone-implant interface, for example, the type of loading, surface structure,amountofsurroundingbone, materialpropertiesofthe implantandimplantdesign[5].Astheproperdesigncandecrease thedeformation,thestressoritsdistributioncanbehomogenized, itwouldbemorelikelytoincreasethesuccessoftheimplant[6].

The kind of the load exerted on the implant inﬂuences the mode distribution of stress andthe deformation. The excess ap- pliedload encompassingthe implant causesvery smallcracks in the bone that leads to loosening and probable breaking of the implant. In term of implant material, a perfect implant material oughttobebiocompatible,withsuitabletoughness,durability,cor- rosion,wearandfracture resistance[7].Theutilizationofzirconia isconcernedwiththedurability,corrosionresistanceandaesthet- icsanticipation.Besides,Zirconiahasbeenprovenhighly biocom- patible in numerous investigations [8–10], and the gathering of bacteriahasbeenreportedlowerthantitanium[11].Furthermore, thebeforehanddescribed animalinvestigations uncoveredsimilar or even better bone growth onto zirconia when contrasted with titaniumsurfaces[12–14].

Some research focuses on failure of zirconia dental implant.

Gahlert etal.[15] studied the failure mechanismof13 fractured dental zirconia implants by clinical, macroscopic and scanning electronmicroscopic (SEM) methods.They foundthat 92% ofthe fracturedimplants wereso-calleddiameterreducedimplants (diameter 3.25 mm), thus they concluded that these diameter re- ducedimplantscannotberecommendedforclinicaluse.Kammer- meier et al. [16] studied zirconia dental implant systems. Their studywas to investigate the long-termin vitro performance and fractureresistanceofone-pieceandbondedtwo-piecezirconiaim- plant systems for anterior application. They found that bonded two-piece zirconia implant systems show more failure rates and lowerfractureresistancethanwell-provenscrewedtwo-piecetita- niumsystemsandhencemaynot beacceptable forclinicalante- rior necessaries. While Individual one-piece zirconia systems exhibit high variations in failure rates and fracture resistance and mayinthismannerbeappliedinanteriorapplication.

Osman et al. [17] studied titanium versus zirconia implants to compare the stress and strain occurring in peri-implant bone andimplantsusedtosupportmaxillaryoverdentureswhereThree- dimensionalﬁniteelementanalysis(3DFEA)wasusedtocompare one-piecezirconiaandtitaniumimplants.Theyfoundthatceramic implants made from zirconia might be a potential alternative to conventional titanium implants for the support of overdentures.

Pevidaetal.[18] studiedbiomechanicalconsequencesoftheelas- ticpropertiesofdentalimplantalloyson thesupporting boneby

ﬁniteelementmethod,wherethecompareddentalimplantswere made of rigid (Y-TZP), conventional (Ti-6Al-4V), and hyperelastic (Ti-Nb-Zr)materials.Theyfoundthatrigidalloy(Y-TZP)dentalim- plantproducelessmicrodeformationintheperi-implantboneand implant itself compared to other materials. Wu et al. [19] used three-dimensional ﬁnite-element (FE) simulations to analyze the stresses inboth theimplant andthesurroundingbone whenus- ing one-piece and two-piece small-diameter implants, with the aim of understanding theunderlying biomechanical mechanisms.

Theyfoundthat themechanicalstressintheimplantishigherin atwo-piecesmall-diameterimplantcomparedtoone-piecesmall- diameterimplant.

Inliterature,biomechanicalbehaviorhasbeenanalyzedtocom- paredifferentdentalimplantmaterials,differentdesignsbasedon diameterorlengthofimplants,orone-pieceversustwo-piecedental implants. To our knowledge, this is the ﬁrst investigation to underline the effectofdifferentabutmentdesigns on thebiome- chanical behavior ofone-piece zirconiadentalimplants andtheir surrounding bone tissues. Therefore, the aim of this study is to validate, using 3D ﬁnite element method, the design concept by comparingthemagnitudeanddistributionofstressandthedefor- mation ofperi-implantboneandtheimplantitselfcorresponding tofourdifferentabutmentmodelsofone-piecezirconiadentalim- plantsunderstaticocclusalloads.

2. Materialsandmethods 2.1. Modelingandmeshing

Inthisstudy,3DFEmodelsofmandibularsectionsofbonewith amissingsecondpremolartootharecreated.Aboneblockwithdi- mensionsof15mm×²⁰^mm×¹⁵^mm,representingthesectionof the mandiblebonethat consistsofacancellousbone surrounded bya2-mm-thicklayerofcorticalboneintheupperpart.Fourdif- ferent models ofimplant abutments with variousgeometries are specifiedinFig.1,wherethe3D modeloftheimplantswas con- structed by the Autodesk^® Inventor^TM software. Then, Models of the bone,thecrownandtheimplant wereexported to ANSYS^TM, wheretheywereassembledintoasinglefiniteelement(FE)model asshowninFig.2.ElementsforFEAweretetrahedrons.Themesh was refinedandacceptedwhentherelative errorswerelessthan 1%. Theresultsofconvergenceanalysisare showninTable1and Fig.3.

2.2. Boundaryconditions

The occlusalloading forceapplied tothe crownisacombina- tionof114.6Nintheaxialdirection,17.1Ninthelingualdirection and23.4Ntoward themesial directionwherethesecomponents represent masticatory force of 118.2 N in the angle of approxi- mately75°totheocclusalplane[20].

Allthecontactsmodeled inthisstudyareconsideredlinear.The crown-abutment, The bone-bone and The bone-implant contact conditionsestablishedinthisFEManalysisareconsideredbonded where the bone-implant interfacesare assumedto be bondedor osseointegrated [1,17,21,22]. The FEM model is ﬁxed at the bot- tomsurfaceofmandibularasshowninFig.4.

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2.3.Materialproperties

Inthepresentstudy,thecorticalandcancellousboneisconsid- eredorthotropic materials. The orthotropic materials exhibit dif- ferentmechanicalpropertiesbasedontheloadingdirection, such asaxialortransversal[23].However,isotropicmaterialsshowthe same mechanical properties regardless of loading direction [24].

Fig. 1.Dimensions of the implant models used in the study.

Thereferencevaluesaretakenfromtheliterature[25–31].Table2 showsasummaryofthemechanicalpropertiesusedinthenumer- icalanalysis.

3. Results

Thedataobtainedfromtheﬁniteelementanalysiscanbepre- sentedina deformation andstress distribution mapwitha color scale,whichmakes itpossibletodirectlycomparethemagnitude anddistributionofstress andthe deformationofvarious zirconia dentalimplantmodelsandsurroundingbonetissues.Theseresults demonstratetherelationshipbetweenthestressdistributioninthe implant/bonesystem, the geometrical characteristics ofthe abut- mentmodelsanddeformations.

One ofthe theoriesmost usedto determine the stress isvon Misestheory.Thistheoryhasbeenappliedtodeterminethestress distribution oftheimplant modelsandsurroundingbone tissues.

From the FE analysis, numerical results of maximum von Mises stressobtainedfordifferentmodelsunderstaticloadingcondition havebeentabulatedinTable3.

Thestress inthe implantsishighestinthe areanearthe ﬁrst thread for all models as shown in Fig. 5. It could be observed that the von Misesstress of implant Model02 (109.03MPa) are much higher than those of other implants, whileimplant Model 04(99.38MPa)andModel01(100.59MPa)havetheloweststress compared toother models. Afterthe transferring ofstress tothe surroundingbones, themaximumstress incorticalboneislarger

Table 1

Totalnumberofelementsandnodesforeachsystem.

Model 01 Model 02 Model 03 Model 04

Elements 53255 55281 63677 57615

Nodes 84839 87765 100278 91031

Fig. 3.Mesh sensitivity results in terms of the maximum von Mises stress.

Fig. 2.Assemblies including four models used in the study.

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Fig. 4.Mesh and boundary conditions.

Table 2

Mechanicalpropertiesofthematerialsusedinthestudy.

Properties Porcelain crown

Zirconia (Y-TZP)

Cortical bone Cancellous bone Density

[g/cm³]

2.4 6.05 1.8 1.2

Elastic modulus (E)[MPa]

68900 205000 9600 (Ex) 144(Ex)

9600 (Ey) 99(Ey) 17800 (Ez) 344(Ez) Shear

modulus (G)[MPa]

26914 78846 3097 (Gxy) 53(Gxy)

3510 (Gyz) 63(Gyz) 3510 (Gxz) 45(Gxz) Poisson’s

ratio(ν)

0.28 0.30 0.55 (νxy) 0.23(νxy)

0.30 (νyz) 0.11(νyz) 0.30 (νxz) 0.13(νxz)

Table 3

MaximumvonMisesstressindifferentimplantmodelsandsurroundingbones.

Von Mises stress [MPa]

Description Model 01 Model 02 Model 03 Model 04

Implant 100.59 109.03 104.88 99.38

Cortical 21.03 25.43 30.07 26.78

Cancellous 0.7 0.8 0.83 0.75

than that of cancellous bone in the surrounding bone tissue as showninFig. 6.The highestvon Misesstress is concentratedon thebonearoundtheimplantneckforallmodels.Theimplant/bone systemincludedimplantabutmentModel01hastheloweststress atcortical(21.03MPa)andcancellousbone(0.7MPa)comparedto others.

It is obvious that the design of the implant abutments has a predominate inﬂuence on the von Mises stress of bone-implant interface. Implant Model02 hasa high trendto causethe stress concentration, whileimplant Model 01can eﬃcientlyreduce the interfacestress.

In comparison offour implant/bone systems included various implantabutmentmodels,itcouldbeobservedthatModel03has the highest average value of maximum von Mises stress (45.26

Fig. 5.Distribution of the stress in different implant models.

Table 4

Maximumtotaldeformationindifferentimplantmodelsandsurroundingbones.

Total deformation [μm]

Description Model 01 Model 02 Model 03 Model 04

Implant 9.76 12.43 10.8 11.05

Cortical 7.35 8.36 7.72 7.91

Cancellous 6.97 8.21 7.43 7.65

MPa) as shown in Fig. 7, while Model 01 has the lowest aver- agevalueofmaximumvonMisesstress(40.77MPa)comparedto othermodels.

Numericalresultsoftotaldeformation ofeach modelanalyzed are listedintheTable4.Fig.8presentsdistribution ofthedefor- mation in different implant models. As shown, the value of the deformation decreases as the deformation position goes to the bottomofimplant.Thehighestdeformationisobservedintheim- plantModel02(12.43 μm),whilethelowestdeformationisfound intheimplantModel01(9.76 μm).Inthecorticalbone,thehigh- estdeformationisobservedinModel02(8.36 μm)andthelowest inModel 01(7.35 μm)asshowninFig.9.Similar resultsareob- tainedforthecancellousbone,thehighestdeformationisfoundin Model02(8.21 μm),butthelowestinModel01(6.97 μm).

In comparison of four implant/bone systems included various implantabutmentmodels,itcouldbeobservedthatModel02has the highestaveragevalue ofmaximumdeformation (9.67 μm)as showninFig.10,whileModel01hasthelowestaverage valueof maximumdeformation(8.03 μm)comparedtoothermodels.

4. Discussions

In orderto maintainthe bone levelorenhance thelong-term successratesofimplantsystem,asigniﬁcantobjectivefordentists is to reduce the stress anddeformation to the bone around the implant and the implant itself [19]. When implant/bone system is subjected to stresses,a few changes in formdeformation may occur, where their points bear dislocations, beingthese, changes fromtheinitialpositionsandbetweenthemselves[32].

FEA is a useful method to understand the biomechanical be- haviors ofrestorativeandprosthetic treatmentsunder simulation ofloadingconditionsintheoralenvironment[33].Furthermore,it isapowerfulapproachtoestimate thestressanddeformationoc- curringindentalimplantsandsurroundingbone.Itisusuallyused to determinetheforces thatinﬂuence thebone-implantinterface ortoevaluatedifferentclinicalandprostheticoptions[34–39].

Inmanystudies,researcheshaveemployed FEAinconjunction withimplant/bonesystemandmadeanefforttointroduceanew design that can eﬃciently reduce the interface stress anddeformation [17–19,40–43].However,their workislimitedtocompare different dentalimplant materials, different designs basedon diameterorlengthofimplants,orone-pieceversustwo-piecedental implants.

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Fig. 6.Distribution of the stress in the peri-implant bone.

Therefore,inthepresentwork,a3DFEAhaveemployedonfour differentmodelsofone-piecezirconiadentalimplantabutmentsto explore biomechanicalbehavior and comparethe magnitude and distribution of stress and the deformation of peri-implant bone andtheimplant itselfbasedon thegeometrical characteristicsof one-piece zirconia dental implant abutment models under static occlusalloads.

SincethevonMisesstressisacombinationofnormalandshear stressesoccurringinalldirections,itisimportanttoinvestigateit

Fig. 7.AveragevaluesofmaximumvonMisesstressofdifferentimplant/bonesys- temsincludedvariousabutmentmodels.

Fig. 8.Distribution of the deformation in different implant models.

inimplant/bonesystems[44].Fromobtainednumericalresults,the systemincludedimplantabutmentModel01showedadecreaseof 9.58%,9.92%and3.62%atleastintheaveragevalue ofmaximum von Misesstress comparedto Model02,Model03andModel 04 respectively asshowninFig. 7.The resultsalsoshowed that the systemincluded implant abutmentModel 01decreases the aver- agevalueofmaximumdeformationof16.96%,7.17%and9.47%at leastcomparedtoModel02,Model03andModel04respectively asshownin Fig.10.These results achieveddue tothe abutment design that enable to distributethe applied load, thus the using ofimplantModel01willpresentmorehomogeneousbehavior of stressdistributionandhaslessdeformationthanothers,itwillalso enhancethestabilityofimplant/bonesystemandprolongitslifespan.

Since thediameterreducedimplants cannot be recommended forclinicaluseduetoits tendencytothefailure[15],itisimpor- tanttousetheproperdiameterimplantthat achievethestability andloaddistributioninthesystem. Therefore,theuseofimplant Model 01 with 5 mm neck diameter seems to present a better performanceinthesystem,soitcouldeﬃcientlyenhancethesta- bilityofimplant/bonesystem, the stressdistribution andprolong itslifespan.

Fig. 10.Averagevaluesofmaximumdeformationofdifferentimplant/bonesystems includedvariousabutmentmodels.

Fig. 9.Distribution of the deformation in the peri-implant bone.

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Inthisstudy,inordertoachievereliabledata,theconvergence andaccuracyofthefiniteelementresultswasexamined,evaluated andvalidated. Twofundamental verifications were made; first, a meshstudytoensure aboutthe sizeofmeshaspreviously men- tioned andshowed in Table 1 and Fig. 3. Second, a comparison withrespecttoanexistingrelatedworkinliteratureregardingthat no earlierstudies haveexamined theinfluence ofdifferent abut- mentdesignsonthebiomechanicalbehaviorofone-piecezirconia dentalimplantsandsurroundingbonetissues.

MahajanandPatil[45] showedthatthestressindentalimplant concentrated in the area near the ﬁrst thread, while it concentrated on the bone around the implant neck. They also showed that the value of the deformation decreases as the deformation positiongoes tothe bottomof implant,which was inagreement withthepresentedresultsinthisstudy.

Gahlertetal.[15] showedthatdiameterreducedimplants(diameter 3.25 mm)have high failure risk caused by highconcen- tratedstress,andSantiagoetal.[46] foundthatthelarge-diameter implants (diameter 5 mm)improved thetransference ofocclusal loads to bone tissue and decreased stress. These results were in agreement with the presented results, where the stress was the highestintheimplant/bonesystemwithabutmentModel02(diameter 3.5 mm), while the lowest stress was observed in the implant/bonesystemwithabutment Model01 (diameter5 mm), comparedtoModel03(diameter4.16mm)andModel04(diame- ter4.28mm).

Wuelal.[19] showedthatthestress inducedinzirconiaden- tal implant is higher than bone stress. They alsofound that the stress in the cortical bone is higherthan cancellous bone stress, thatcouldbeexplainedbecausethecorticalbonehasthetendency ofconcentrategreater strain[47].Despitethefactthattheystud- ied two designs differ fromthe models studied in this research, thisresult wasinagreementwiththepresentedresults.

Some limitations remain in the current study and must be taken into account in the model in order to optimize computa- tionalresourceswithoutaffectingfundamentalanalysis.Giventhat theproposeddesignconceptisbasedonimplant/bonesystemwith crown,thebothofmetalframeworkunderthecrownandcement layer were neglected. Perfect osseointegration between implants andbonewasassumedandﬁniteelementanalysiswasperformed understaticocclusalloads.However,FEAislikeanyotherbasicre- searchtool,whichaidsinplanningfurtherinvitroandinvivotests whenusedasaninitialstep.

Nevertheless,asmentioned, the one-piece zirconiadental im- plantabutmentModel01presentsabetterbiomechanicalbehavior inthe peri-implant bone than others.It can eﬃciently distribute theappliedloadandpresentmorehomogeneousbehaviorofstress distribution and has less deformation than others. That will enhancethestabilityofimplant/bonesystemandprolongitslifespan.

5. Conclusion

Withinthe limitations ofthis study,it can be concluded that theone-piecezirconiadentalimplantabutmentModel01caneﬃ- cientlydistributetheappliedloadintheimplant/bonesystemand presentsamorehomogeneousbehaviorofstressdistribution,and havelessdeformationthanothers.Thatwillenhancethestability, durabilityandlifespanofthesystem.Furtherinvestigationsstudy- ingthe modelsunderdynamicloadings arerequiredtoachieve a betterunderstandingofthebiomechanicalbehavior.

Funding

Thiswork did not receiveany grantfromfunding agencies in thepublic,commercial,ornot-for-proﬁtsectors.

Authorcontributions

AllauthorsattestthattheymeetthecurrentInternationalCom- mitteeofMedicalJournalEditors(ICMJE)criteriaforAuthorship.

DeclarationofCompetingInterest

Theauthorsdeclarethattheyhavenoknowncompetingﬁnan- cial orpersonalrelationships that couldbe viewedasinﬂuencing theworkreportedinthispaper.

CRediTauthorshipcontributionstatement

M. Shash:Conceptualization, Formal analysis,Supervision,Val- idation,Visualization, Writing - originaldraft, Writing - review&

editing.H. Nazha: Conceptualization,Formal analysis,Supervision, Validation, Visualization,Writing- originaldraft,Writing - review

& editing.W. Abbas: Conceptualization, Formal analysis, Supervi- sion, Validation, Visualization, Writing - original draft, Writing - review&editing.

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