Effects of fiber-glass-reinforced composite restorations on fracture resistance and failure mode of endodontically treated molars

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Article

Reference

Effects of fiber-glass-reinforced composite restorations on fracture resistance and failure mode of endodontically treated molars

NICOLA, Scotti, et al.

Abstract

OBJECTIVES: The study evaluated the fracture resistance and fracture patterns of endodontically treated mandibular first molars restored with glass-fiber-reinforced direct composite restorations. METHODS: In total, 60 extracted intact first molars were treated endodontically; a mesio-occluso-distal (MOD) cavity was prepared and specimens were then divided into six groups: sound teeth (G1), no restoration (G2), direct composite restoration (G3), fiber-post-supported direct composite restoration (G4), direct composite reinforced with horizontal mesio-distal glass-fibers (G5), and buccal-palatal glass-fibers (G6). Specimens were subjected to 5000 thermocycles and 20,000 cycles of 45° oblique loading force at 1.3Hz and 50N; they were then loaded until fracture. The maximum fracture loads were recorded in Newtons (N) and data were analyzed with one-way ANOVA and post-hoc Tukey tests (p

NICOLA, Scotti, et al . Effects of fiber-glass-reinforced composite restorations on fracture resistance and failure mode of endodontically treated molars. Journal of Dentistry , 2016, vol.

53, p. 82-87

PMID : 27492772

DOI : 10.1016/j.jdent.2016.08.001

Available at:

http://archive-ouverte.unige.ch/unige:89711

Disclaimer: layout of this document may differ from the published version.

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Effects of ﬁ ber-glass-reinforced composite restorations on fracture resistance and failure mode of endodontically treated molars

Scotti Nicola

^a,

*, Forniglia Alberto

^a

, Michelotto Tempesta Riccardo

^a

, Comba Allegra

^a

, Saratti Carlo Massimo

^b

, Pasqualini Damiano

^a

, Alovisi Mario

^a

, Berutti Elio

^a

aDepartmentofSurgicalSciences,DentalSchoolLingotto,UniversityofTurin,ViaNizza230,Turin,Italy

bDivisionofCariologyandEndodontology,SchoolofDentistry,UniversityofGeneva,RueBarthèlemy-Menn,Geneva,Switzerland

ARTICLE INFO

Articlehistory:

Received12March2016

Receivedinrevisedform17July2016 Accepted1August2016

Keywords:

Endodonticallytreated Fractureresistance Glass-ﬁber Directcomposite Fractography

ABSTRACT

Objectives:Thestudyevaluatedthefractureresistanceandfracturepatternsofendodonticallytreated mandibularﬁrstmolarsrestoredwithglass-ﬁber-reinforceddirectcompositerestorations.

Methods:Intotal,60extractedintactfirstmolarsweretreatedendodontically;amesio-occluso-distal (MOD)cavitywaspreparedandspecimenswerethendividedintosixgroups:soundteeth(G1),no restoration(G2),directcompositerestoration(G3),fiber-post-supporteddirectcompositerestoration (G4),directcompositereinforcedwithhorizontalmesio-distalglass-fibers(G5),andbuccal-palatalglass- fibers(G6).Specimensweresubjectedto5000thermocyclesand20,000cyclesof45obliqueloading forceat1.3Hzand50N;theywerethenloadeduntilfracture.Themaximumfractureloadswererecorded inNewtons(N)anddatawereanalyzedwithone-wayANOVAandpost-hocTukey tests(p<0.05).

Fracturedspecimenswereanalyzedwithascanningelectronmicroscope(SEM).

Results:Themeanstaticloads(inNewtons)were:G1,831.83;G2,282.86;G3,364.18;G4,502.93;G5, 499.26;andG6,582.22.FractureresistancedidnotdifferamongG4,G5,andG6,butwassignificantly higherthanG3(p=0.001).Allspecimensfracturedinacatastrophicway.InG6,glassfibersinducteda partialdeflectionofthefracture,althoughtheywerenotabletostopcrackpropagation.

Conclusions:Forthedirectrestorationofendodonticallytreatedmolars,reinforcement ofcomposite resinswithglass-fibersorfiberpostscanenhancefractureresistance.TheSEManalysisshowedalow abilityofhorizontalglass-fiberstodeviatethefracture,butthiseffectwasnotsufficienttoleadtomore favorablefracturepatternsabovethecement-enameljunction(CEJ).

Clinical significance: The fractureresistance of endodontically treated molars restored with direct compositerestorationsseemstobeincreasedbyreinforcementwithfibers,evenifitisinsufficientto restoresoundmolarfractureresistanceandcannotavoidverticalfractures.

ã2016ElsevierLtd.Allrightsreserved.

1.Introduction

Providingfractureresistancetoocclusalloadinendodontically treatedposteriorteethrepresentsoneofthemaingoalsofpost- endodonticrestorations,becausetheyaregenerallymoresuscep- tibletofracturesthanvitalteethduetothelossofalargeamountof tissueasaconsequenceofcariouslesionsorcoronalfracture[1,2].

Recentstudieshavereportedthatthelongevityofendodontically treatedteethdependsdirectlyontheamountofremainingtooth structureandtheefﬁcacyoftherestorativeproceduresinreplacing fracturestructuralintegrity[3].Thesefactorsshowtheimportance of highly conservative endodontic and restorative procedures

preserving a sound structure as much as possible. The clinical outcomesofdirectresincompositerestorations,whichrepresenta lessinvasiveapproachtorestoringendodonticposteriorteeth,are variableintheliterature,rangingfromcatastrophictoacceptable [4–6]. More recently, the insertion of fiber posts within direct composite restorations has been tested with the intention of providingincreasedfractureresistance[7–9].Indeed,withinthe radiculardentin,thefiberpostservesasadistributorofstresses and loads applied tothe composite restoration [10], providing reinforcementeveninthepresenceofsufficientresidualcoronal dentin[11,12].Moreover,postandcoreshouldhavesimilarelastic moduli torootdentin tobetterabsorbthe forces concentrated along the root and, consequently, decrease the probability of fracture [13,14]. However, fiber post insertion presents some limitations: the post-space preparation tends to weaken the radicularstructure,becausesomedentintissueshouldberemoved

*Correspondingauthorat:ViaNizza230,10100,Turin,Italy.

E-mailaddress:[email protected](S.Nicola).

http://dx.doi.org/10.1016/j.jdent.2016.08.001 0300-5712/ã2016ElsevierLtd.Allrightsreserved.

ContentslistsavailableatScienceDirect

Journal of Dentistry

j o u r n a lh o m e p a g e : w w w . i n t l . e l s ev i er h e a l t h . c o m / j o u r n a l s / j d e n

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this network changed the stress dynamics at the enamel- composite material interface [19], but the effect on fracture resistanceof endodonticallytreatedteethremains controversial [20,21].

Recently, UDMA-TEGDMA pre-impregnated parallel glass- fibers were introduced, but as yet there is limited knowledge abouttheireffectonfractureresistancewhenusedtogetherwith an extensive composite restoration on endodontically treated posteriorteeth.Thus,theaimofthisinvitrostudywastoevaluate the fracture resistance and failure patterns of endodontically treated mandibular first molars restored with glass-fiber rein- forcedcomposite.Thenullhypothesiswasthatglass-fibersdonot increasethefractureresistanceofdirectcompositerestorationsin endodonticallytreatedteeth.

2.Materialsandmethods

Intotal,60non-cariousmandibularﬁrstmolars,extractedfor periodontalreasons,wereselected.Theinclusioncriteriawereas follows:soundteeth,withnearlysimilarcrownsizesandnocracks under transillumination and magniﬁcation, extracted within 1 month.Ahandscalinginstrumentwasusedforsurfacedebride- ment,followedbycleaningwitharubbercupandslurryofpumice.

Thespecimensweredisinfectedin0.5%chloraminefor48hand thenstoredin4%thymolsolutionatroomtemperatureuntiluse.

endodonticsealer(PulpCanalSealerEWT;Kerr,Orange,CA,USA).

Backﬁlling was performedwith theObturaIIIsystem (Analytic Technologies,Redmond,WA,USA).

Theteethwerestoredindistilledwateratroomtemperaturefor at least 72h. For the simulation of 0.3-mm-thick periodontal ligament, each root was immersed in melted wax up to the demarcationline2mmapicaltothecement-enameljunction[18]

(CEJ;checkedwithadigitalcaliper).Ametalcubicmoldwasused toembedallthespecimensinacrylicself-curingresin(StickRESIN;

StickTechLtd.,Turku,Finland)upto1mmapicaltotheCEJ,their long axes were oriented perpendicular tothe horizon using a custom-made parallelometer. Eachroot was removed fromthe resinblockwhenprimarysignsofpolymerizationwerenoticed.

Thewaxspacerwasremovedwithhotwaterandthenreplacedby a silicone-based impression material (Light Body, Flexitime;

Heraeus Kulzer,Hanau, Germany), which was injected intothe acrylicresinblockpriortoreinsertionofthespecimen.

After 48h in distilled water, standardized class II mesio- occluso-distal (MOD) cavities were prepared by the same experiencedoperatorinallspecimensexceptthepositivecontrol group. For cavity preparation, cylindrical diamond burs (#806314014; Komet, Schaumburg, IL, USA) under copious air- watercoolingwereusedinahigh-speedheadpiece(KavoDental GmbH,Biberach,Germany).Theresidualthicknessofbuccaland lingualcuspsattheheightofthecontourwas2.50.2mminall specimens, withthe medial and distal cervical margin located

Fig.1.Schematicrepresentationofthecavitypreparationusedinthisexperiment.

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1.5mmcoronaltotheCEJ(Fig.1).Afterﬁnishingthepreparation, allinternaledgesweresmoothedandrounded.

Theteethwereassignedrandomlytosixgroups(n=10each) accordingtothepost-endodonticrestoration.

Group 1 (G1) (positive control): sound teeth (no cavity preparationorrootcanaltreatment).

Group 2 (G2) (negative control): the MOD cavity was not restored.

Group 3 (G3): the MOD cavity was restored with a direct composite restoration. A three-step etch-and-rinse adhesive system(OptibondFL, Kerr)was appliedfollowing themanufac- turer’sinstructions,and thencuredfor 60swithanLED curing light (Valo; Ultradent Products Inc., South Jordan, UT, USA) at 1400mW/cm².Thecavityﬂoorwascoveredwitha1mmlayerof highviscosityﬂowablecomposite(GrandioSoHeavyFlow;Voco, Cuxhaven, Germany), and the cavity was then incrementally restoredwithcompositeresin(GrandioSo;Voco)usinganoblique layeringtechnique.Eachlayer,1.5–2mmthick,waslight-curedfor 20swithanLEDcuringlamp(Valo)at1400mW/cm².

Group4(G4):theMODcavitywasrestoredwithafiberpost- supporteddirectcompositerestoration.Apostspacewasprepared toadepthof7mm,measuredfromthepulpalchamberfloor,using drillsfromthepostmanufacturer(RebildaPost15;Voco)onthe distalcanalofthespecimen.Therootcanal wallswerecleaned with10% EDTA for 30swith a continuous brushingtechnique, washedusingawatersyringewithanendodonticneedleandthen gentlyair-dried.Excesswaterwasremovedfromthepostspace usingpaperpoints,preventingthedentinfromdehydrating.The postwascoveredwithalayerofsilane(SilaneCouplingAgent;3M, St.Paul,MN,USA)andthenfixedintothepostspacewithaself- adhesiveresincement(Rely-XUnicem2;3M).Afteraninitialset for1min,irradiationwasperformedwithanLEDcuringlightfor 60s(Valo).Then,adirectcompositerestorationwasperformedas describedinGroup3.

Group 5 (G5): the MOD cavity was restored with a direct compositerestorationreinforcedwithhorizontallyplacedglass- ﬁbers(unidirectionalﬁbers,size2mm5mm,12

m

^m^diameter).

Afterthethree-stepetch-and-rinseadhesiveapplicationdescribed forGroup3,ahorizontallayerofhighviscosityﬂowablecomposite (GrandioSoHeavyFlow)wasplacedoverthepulpalchamberﬂoor untilreachingtheheightofthemesialanddistalcervicalboxes.

Then, pre-impregnatedglass ﬁbers (GranTEC; Voco)were hori- zontallyplacedfromthemesialtothedistalbox,withouttouching theenamelmargins.Afterlight-curingfor20swithanLEDlamp (Valo),adirectcompositerestorationwasperformedasdescribed inGroup3.

Group 6 (G6): specimens were restored with the same procedure described for Group 5 except with respect to the placement of the glass ﬁbers, which werepositioned over the ﬂowable composite ina buccal-palataldirection, withtheends bondedtothebuccalandoralwallstoachieveaheightof2mm.

All these direct restorations were performed by the same experiencedoperator,whoaimedtoobtainanintercuspidalangle

of 90 to standardize cusp inclination and allow reproducible positioningofthesteelsphereduringthecompressivetests.Allthe restored specimens were finished using a fine diamond bur (8379314016;Komet)andpolishedwithfineSof-Lex discs(3M) andsiliconecups.

2.1.Loadingofthespecimens

Afterstorageindistilledwaterat37Cfor1week,allspecimens weresubjectedto5000thermalcyclesbetween5Cand55Cfor 60sandthenexposedto20,000cyclesof45obliqueloadingforce onthecenterofthespecimens(MiniBionicsII;MTSSystems,Eden Prairie,MN,USA),atafrequencyof1.3Hzand50N,totallyresting onthecompositerestoration.

Specimenswerethensubmittedtoastaticfractureresistance testusingauniversaltestingmachine(Instron;Canton,MA,USA) witha6-mm-diametersteelspherecrossheadweldedtoatapered shaft and appliedtothe occlusalsurfaceof thespecimens ata constantspeedof0.5mm/minandanangleof45tothelongaxis of the tooth. Specimens were loaded until fracture and the maximumfractureloadswererecordedinNewtons(N).

2.2.Fractographicanalysis

Fracturedspecimenswereﬁrstanalyzedunderastereomicro- scope(SZX9;Olympus OpticalCo.,Ltd., Tokyo,Japan).Different magniﬁcations(from 6.3 to50)andangled illuminationwere usedtobetterviewthefracturesurface.Thetypesoffailurewere determinedandcompared;inparticular,adistinctionwasmade betweencatastrophicfractures(non-reparable,belowtheCEJ)and non-catastrophicfractures(reparable,abovetheCEJ).

Subsequentlya scanning electronmicroscope (SEM) (Digital SEMXL20;Philips,Amsterdam,Netherlands)wasusedformore detailedanalysesofthefracturedsurfaces.Tocleanthespecimens ofimpurities,allfragmentswereimmersedinanultrasonic10%

NaOCLbathfor3min,rinsedwithwater,driedandthenfixedon thesupportforthemicroscope.Thespecimensweregold-coated priortoanalysiswiththeSEM.Allrecognizablefeatures,suchas compression curl, hackle, and arrest line [22,23], were photo- graphedanddocumented.Magnificationsupto2000wereused toobtainhigherdefinitionimagesofidentifiedcrackfeaturesin selectedareasofinterest.

2.3.Statisticalanalysis

Data are expressed as meansstandard deviation (SD) and frequency (%). The Kolmogorov-Smirnov test for normality revealedanormal datadistribution.The statisticalanalysiswas thenconductedwithaone-wayanalysisofvariancetest(ANOVA) andaposthocTukeytest.Ap-valueof<0.05wasconsideredto indicate statistical signiﬁcance. All statistical analyses were performed using STATA software (ver. 12.0; StataCorp, College Station,TX,USA).

Table1

Meanfractureloadvalues,expressedinNewtons,ofeachgroup.Differentsuperscriptlettersindicatestatisticaldifferencesbetweengroups(p<0.05).

Group n FractureLoad(MeanSD) Median Minimum Max

G1(controlgroup) 10 831.8350.94^A 849 756.40 879.60

G2(norestoration) 10 282.8630.33^B 299.3 234.87 314.48

G3(directcompositerestoration) 10 364.1848.55^C 359.86 298.51 448.77

G4(ﬁber-postsupportedcompositerestoration) 10 502.9343.49^D 507.23 445.98 567.89

G5(mesio-distalglass-ﬁberreinforcedcompositerestoration) 10 499.2661.77^D 487.98 426.65 587.52

G6(buccal-oralglass-ﬁberreinforcedcompositerestoration) 10 582.2276.50^D 565.023 499.67 703.31

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(p=0.001).

Intheanalysisperformedwiththestereomicroscope,fractures wereevaluatedascatastrophicinallspecimens,becausetheywere allbelowtheCEJ.Ingroupswhere arestorationwas performed (i.e.,G3–G6),thefractureswerealwaysadhesive.Thedebondingof therestorationoccurredonthewallchargedwiththeload;the debonding started fromthe occlusal surface and determined a deﬂection of thewallof thetooththatsubsequently induceda lateral fracture of the same wall, leaving a “compression curl”

teeth would improve their mechanical resistance and prevent unfavorable fractures, thereby restoring anatomy and function.

This invitro studyaimedto evaluatethe effects of glass ﬁber- reinforcedresincompositeonthefractureresistanceofendodon- ticallytreatedmolarswithMODcavities,comparedwithdifferent directadhesiverestorationtechniques.Ithasbeenreportedthat mandibular molars are the teeth involved most frequently in endodontic treatments[24] and areoften extractedbecause of secondarycariesandcuspsorradicularfractures[25].Therefore,a

Fig.2.Afracturedspecimenfromgroup6.(a)Stereomicroscopeimageofthepatternofthefracture.(b)Scanningelectronmicroscope(SEM)imageshowingthemixed fracture:marksproducedbythediamondbur(whitecircle)werestillvisibleontheinternalpartofthepalatalwall.Thefractureendedatthelevelofthepalatalroot,whereit produceda“compressioncurl”(whitestar).Thewhiterectanglecin(b)represents(c).(c)Hacklelines(whitearrows)indicatethepresenceofapartialcohesivefractureofthe build-up,andshowthedirectionofthecrackpropagation.Thewhiterectangledin(c)represents(d).(d)Thelayerofglassﬁber,whichleftanimpression(whitestar)onthe resincompositebuild-up,causedapartialinterruptionofthepropagationofthefracture.However,thiswasnotenoughtocompletelystopthecrack.

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restorationtechniquethatcanreinforcetheweakenedremaining tooth structure is fundamental to reducing the possibility of fractures. Moreover, in the selected teeth, standardized MOD cavities were prepared because this clinical condition strongly reducesresistancetocuspalfractures[2,26–29]duetotheabsence ofmesialanddistalwalls,whichcauseahighstrainonvestibular and lingual cusps [18]. Soares et al. conﬁrmed that MOD preparationand endodontictreatment accentuatedtheconcen- trationof stress inside the dental structure, mainlydue tothe greaterremovalofthedentalstructure[30].

Toevaluatethedistributionofocclusalandmasticatoryloads onmolarcrowns,forcesareusuallyappliedtothecentralpitand parallel [31] or oblique tothe tooth axis. Nevertheless, recent studieshavedemonstratedthatduringmaximumintercuspidation withinthe second phase of chewing, higher stresses are more concentratedalong thecervicaldentalportionandmesiolingual radicularareaofthemandibularmolars.Jiangetal.[32] useda ﬁnite elementmodel toanalyzestressconcentrationinvital or endodonticallytreatedmandibularmolarsrestoredwithindirect adhesiverestorations.Specimensreceivedaverticalor45oblique occlusalloadataconstantintensityof45Ntosimulatemasticatory loads.Inallspecimensreceivinglateralloadapplication,thestress wasconcentratedmainlyalongthecervicalradicularportionofthe toothandattheﬂoorofthepreparation,aswellasattheloading site.Thus,inthepresentstudy, specimensweresubmittedtoa lateralloadwitha45angletodistributethestressesinareasof higherfracturerisk.

Theresultsofthepresentinvitrostudyledustorejectthenull hypothesis,becausetheinsertionofglassfibersindirectcomposite restorationssignificantlyincreasedthefractureresistanceofthe endodontically treated molars. However, it is important to highlightthatnoneofthedirectrestorationtechniquestestedin thisstudycouldrestorethefractureresistancetothatofasound mandibular molar. This finding emphasizes the importance of maintainingasmuchsoundtissueaspossibleduringendodontic andrestorative procedures,becausethestructuralstrengthof a tooth strictly depends on the quantity and integrity of its anatomical form [33]. Traditionally, to prevent tooth fracture, cuspalcoverage, preceded by custom cast post and cores, has commonlybeenusedasasystemtoimproveteethresistanceand loaddistribution.Aquilino&Caplan[34]showedthatatoothwith crownrehabilitationhadasix-foldhigherrateofsuccessthana directly restored tooth. At present, a conservative approach is preferredtopreservesoundtissue,whichisdirectlyrelatedtothe fractureresistanceofatooth.

The presentfindings clearlyshowedhowadirect composite restorationwasabletoprovideasignificantimprovementinthe fracture resistanceof endodonticallytreated molars with MOD cavities.Ithasbeenreportedthatadhesiverestorationsarebetter ableto transmit and distribute functional stresses throughthe restorativematerial-toothinterface,withthepotentialtoreinforce the weakened tooth structure [35,36]. However, a significant reinforcementeffect wasobtainedwiththeinsertion ofa glass fiber post within the direct composite restoration. Fiber post insertionwithinacompositerestorationcanimprovetheabilityof thetooth-restorationcomplextoabsorbtheocclusalloadsalong themajoraxisofthetooth[37];couldincreasetheresistanceofthe endodonticallytreatedtoothtoocclusalloads[38,39];andmay cause less cuspal deflection, thus reducing the possibility of marginal leakage that creates a gap at the tooth-restoration interfacewithconsequentmarginalinfiltration[40].Afavorable effect of a fiber post-supported composite restoration in the longevityof post-endodonticrestorationshas beenreported in severalinvivostudies[6,41].Nevertheless,someinvitrostudies haveshownhowendodonticallytreatedpremolarswithoutfiber postplacementhadfracturetoughnesssimilartothosewithafiber

post.Krejcietal.[42]confirmedthatanyrestorationavoidingpost space preparation, with less sacrifice of residual sound tissue, might result in greater resistanceto fracture regardless of the degree of impairment of the dental structure. Another recent study,bySoaresetal.[30],concludedthattheuseofglassfibers postsdidnotreinforcethetoothrestorationcomplex.

Theseconflicting results,togetherwith theneed to find less invasiverestorativesolutions,promptedstudiesonfiber-reinforced compositerestorations. In thepresentstudy, glassfibers where insertedwithinadirectcompositerestorationtobetterunderstand their effects on fracture resistance and crack propagation. Our findings showed a significant increase in fracture resistance, obtainingastrengtheningeffectcomparabletothatobtainedwith fiberpost insertion.Thepresenceofglass-fibersinsidetheresin compositecouldaltertheelasticmodulusofthematerialitself,thus modifyingthestressdistributionandtransmissiontoresidualcavity walls.In fact,the higherthe elastic modulusof therestorative materialattherestorationinterface,thelowerthedeformationof dentalstructures[36].These results areconsistent with other studies [20,43],showingthattheuseofpolyethylenefibersunder composite restorations in root-filled teeth with large MOD preparations producedstatisticallygreaterfractureresistancethanresincompos- iterestorations.Theauthorssuggestedthatthepolyethylenefibers hadastress-modifyingeffectalongtherestoration-dentininterface, andthebondingabilityoffibersincombinationwiththeresinmight haveincreasedthefracturestrengthofthetoothbykeepingboth cuspstogether.However,Rodriguesetal.[21]concludedinarecent paperthatfibersplacedintoMODcavitiesdidnotreinforceteeth,but theymayhaveaprotectiveeffectonfracturepropagationtowards thepulpchamberfloor.Theseinconsistenciescouldberelatedtothe differentanglewherebythespecimenswereloaded.Anirrelevant effectoffiberreinforcementwasalsoshowninarecentstudyby Roccaetal.[31],inwhichbi-directionalE-glassfiberswereplaced overthepulpalchamberarea,asinthepresentstudy,butindirect LavaUltimate overlayswereemployedto restoreendodontically treatedmolars.

Aslight,althoughnotstatisticallysignificant,improvementin fractureresistancewasfoundwhenglassfiberswereplacedina buccal-palataldirection.Theconnectionoftheresidualwallsofthe specimensthroughthefibersmaycontrastthecompressiveload thatinducedtensioninthecervicalarea.Asimilareffectwastested byKarzounetal.[44],whoplacedahorizontalfiberpostinapost- endodonticcompositerestoration,joiningthepalatalandbuccal wallsof theMOD cavity.Thistechnique showedan increasein fracture resistance, although the horizontal post didnot avoid catastrophicfractures.

To evaluate the fracture pattern, a combined stereo and scanning electron microscopy technique was used [31]. The stereomicroscope showed the whole surface of the fractured specimens. SEM images gave information on fractographic markers,suchashacklelines,arrestlines,andcompressioncurl, which are indicators of the crack propagation direction. A fractographic analysis of the pattern of a fragment provides important information when a cohesive fracture occurs. In adhesivesfractures,mostof thefeatures leftbythecrack,such as the origin, the “mirror” and the “hackles,” are not visible.

However,theendoftheeventwasindicatedbythepresenceofthe

“compression curl,” leftonthecracked rootsof thespecimens, meaningthattheoriginwasinanupperregion.Somesecondary cohesive fractures were also recognizable. In G6, the denuded ranksoffibersleftamarkonthesurfaceofthebuild-upaftertheir debonding(Fig.2).Thisindicatesthatthemainfrontofthefracture waspartiallydeviatedonceittouchedthelayeroffibers,following theirhorizontaldirection.However,thiseffectwasnotsufficientto avoidacatastrophicbreak:thechargedwallalwaysdeflecteduntil fracture.

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-Glassﬁberswithabuccal-palatalorientationshowedapartial deviation of the fracture pattern, even if it did not prevent catastrophicfractureofthespecimen.

Acknowledgment

Theauthorsdenyanyconﬂictofinterestrelatedtothisstudy.

References

[1]J.M.Carter,S.E.Sorensen,R.R.Johnson,R.L.Teitelbaum,M.S.Levine,Punch sheartestingofextractedvitalandendodonticallytreatedteeth,J.Biomech. 16 (1983)841–848.

[2]E.S.Reeh,G.K.Ross,Toothstiffnesswithcompositeveneers:astraingaugeand ﬁniteelementevaluation,Dent.Mater.J.10(1994)247–252.

[3]S.Fernandes,G.S.Dessai,Factorsaffectingthefractureresistanceofpost-core reconstructedteeth:areview,Int.J.Prosthodont.14(2001)355–363.

[4]B.Toure,B.Faye,A.W.Kane,C.M.Lo,B.Niang,Y.Boucher,Analysisofreasons forextractionofendodonticallytreatedteeth:aprospectivestudy,J.Endod.37 (2011)1512–1515.

[5]P.K.Gohring,O.A.Peters,Restorationofendodonticallytreatedteethwithout posts,Am.J.Dent.16(2003)313–317.

[6]N.Scotti,C.Eruli,A.Comba,D.S.Paolino,M.Alovisi,D.Pasqualini,etal., Longevityofclass2directrestorationsinroot-ﬁlledteeth:aretrospective clinicalstudy,J.Dent.43(2015)499–505.

[7]B.Akkayan,T.Gülmez,Resistancetofractureofendodonticallytreatedteeth restoredwithdifferentpostsystem,J.Prosthet.Dent.87(2002)431–437.

[8]F.Hurmuzlu,A.Kiremitci,A.Serper,E.Altundasar,S.H.Siso,Fractureresistance ofendodonticallytreatedpremolarsrestoredwithormocerandpackable composite,J.Endod.29(2003)838–840.

[9]F.Hurmuzlu,A.Serper,S.H.Siso,K.Er,Invitrofractureresistanceofroot-ﬁlled teethusingnew-generationdentinebondingadhesives,Int.Endod.J.36 (2003)770–773.

[10]L. Pierrisnard, F. Bohin, P. Renault, M. Barquins, Corono-radicular reconstructionofpulplessteeth:amechanicalstudyusingﬁniteelement analysis,J.Prosthet.Dent.88(2002)442–448.

[11]L.A.Goncalves,L.P.Vansan,S.M.Paulino,M.D.SousaNeto,Fractureresistance ofweakenedrootsrestoredwithatransilluminatingpostandadhesive restorativematerials,J.Prosthet.Dent.96(2006)339–344.

[12] R.S.Schwartz,J.W.Robbins,Postplacementandrestorationofendodontically treatedteeth:aliteraturereview,J.Endod.30(2004)289–301.

[13]G.A.Freedman,Estheticpost-and-coretreatment,Dent.Clin.NorthAm.45 (2001)103–116.

[14]J.P.Standlee, A.A. Caputo, E.W. Collard, M.H. Pollack, Analysis of stress distributionbyendodonticposts,OralSurg.OralMed.OralPathol.33(1972) 952–960.

[15]I.Radovic,C.Mazzitelli,N.Chiefﬁ,M.Ferrari,Evaluationoftheadhesionof ﬁberpostscementedusingdifferentadhesiveapproaches,Eur.J.OralSci.116 (2008)557–563.

[16]C.Goracci,S.Grandini,M.Bossù,E.Bertelli,M.Ferrari,Laboratoryassessmentof theretentivepotentialofadhesiveposts:areview,J.Dent.35(2007)827–835.

[17]M.P.Newman,P.Yaman,J.Dennison,M.Rafter,E.Billy,Fractureresistanceof endodonticallytreatedteethrestoredwithcompositeposts,J.Prosthet.Dent.

89(2003)360–367.

[18]F.K. Cobankara, N. Unlu, A.R. Cetin, K.B. Ozkan, The effectof different restorationtechniquesonthefractureresistanceofendodontically-treated molars,Oper.Dent.33(2008)526–533.

[24]J.A.Skupien,N.Opdam,R.Winnen,E.Bronkhorst,C.Kreulen,T.Pereira-Cenci, M.C.Huysmans,Apractice-basedstudyonthesurvivalofrestored endodonticallytreatedteeth,J.Endod.38(2013)1335–1340.

[25]W.M. Fennis, R.H. Kuijs, C.M. Kreulen, F.J. Roeters, N.H. Creugers, R.C.

Burgersdijk,Asurveyofcuspfracturesinapopulationofgeneraldental practices,Int.J.Prosthodont.15(2002)559–563.

[26]C.T.Smith,N.Schuman,Restorationofendodontically-treatedteeth:aguide fortherestorativedentist,QuintessenceInt.28(1997)457–462.

[27]M.N.Gelb,E.Barouch,R.J.Simonsen,ResistancetocuspfractureinClassII preparedandrestoredpremolars,J.Prosthet.Dent.55(1986)184–185.

[28]R.B.Joynt,G.WieczkowskiJr.,R.Klockowski,E.L.Davis,Effectsofcomposite restorationsonresistancetocuspalfractureinposteriorteeth,J.Prosthet.

Dent.57(1987)431–435.

[29]R.Pilo,T.Brosh,H.Chweidan,Cuspreinforcementbybondingofamalgam restorations,J.Dent.26(1998)467–472.

[30]P.V.Soares,P.C.Santos-Filho,L.R.Martins,C.J.Soares,Inﬂuenceofrestorative techniqueonthebiomechanicalbehaviorofendodonticallytreatedmaxillary premolars.PartI:fractureresistanceandfracturemode,J.Prosthet.Dent.99 (2008)30–37.

[31]G.T.Rocca,C.M.Saratti,M.Cattani-Lorente,A.J.Feilzer,S.Scherrer,I.Krejci,The effectofaﬁberreinforcedcavityconﬁgurationonloadbearingcapacityand failuremodeofendodonticallytreatedmolarsrestoredwithCAD/CAMresin compositeoverlayrestorations,J.Dent.43(2015)1106–1115.

[32]W. Jiang,H.Bo,G. Yongchun,N.LongXing,Stress distributioninmolars restoredwithinlaysoronlayswithorwithoutendodontictreatment:athree- dimensionalﬁniteelementanalysis,J.Prosthet.Dent.103(2010)6–12.

[33]Assif, C. Gorﬁl, Biomechanicalconsiderations in restoring endodontically treatedteeth,J.Prosthet.Dent.71(1994)565–567.

[34]S.A.Aquilino,D.J.Caplan,Relationshipbetweencrownplacementandthe survivalofendodonticallytreatedteeth,J.Prosthet.Dent.87(2002)256–266.

[35]P.Ausiello,S.R.DeGee,C.L.Davidson,Fractureresistanceofendodontically- treatedpremolarsadhesivelyrestored,Am.J.Dent.10(1997)237–241. [36]P.Magne,U.C. Belser,Porcelainversuscompositeinlays/onlays:effectsof

mechanicalloadsonstressdistribution,adhesion,andcrownﬂexure,Int.J.

Periodont.Restor.Dent.23(2003)543–555.

[37]P.Panitvisai,H.H.Messer,Cuspaldeﬂectioninmolarsinrelationtoendodontic andrestorativeprocedures,J.Endod.21(1995)57–61.

[38]N.Mohammadi,M.A.Kahnamoii,P.K.Yeganeh,E.J.Navimipour,Effectofﬁber postandcuspcoverageonfractureresistanceofendodonticallytreated maxillarypremolarsdirectlyrestoredwithcompositeresin,J.Endod.35 (2009)1428–1432.

[39]N.Scotti,M.Scansetti,R.Rota,F.Pera,D.Pasqualini,E.Berutti,Theeffectofthe postlengthandcuspcoverageonthecyclingandstaticloadofendodontically treatedmaxillarypremolars,Clin.OralInvest.15(2011)923–929.

[40]P.A.Acquaviva,L.Madini,A.Krokidis,M.Gagliani,F.Mangani,A.Cerutti, Adhesiverestorationofendodonticallytreatedpremolars:inﬂuenceofposts oncuspaldeﬂection,J.Adhes.Dent.13(2011)279–286.

[41]F.Mannocci,A.J.Qualtrough,H.V.Worthington,T.F.Watson,T.R.PittFord, Randomizedclinicalcomparisonofendodonticallytreatedteethrestoredwith amalgamorwithﬁberpostsandresincomposite:ﬁve-yearresults,Oper.Dent.

30(2005)9–15.

[42]I.Krejci,D.Dietschi,F.U.Lutz,Principlesofproximalcavitypreparationand ﬁnishingwithultrasonicdiamondtips,Pract.Periodont.Aesthet.Dent.10 (1998)295–298.

[43]H.Kemaloglu,S.Belli,A.Erdemir,M.Ozcopur,G.Eskitascioglu,Theeffectof ﬁbreinsertiononfractureresistanceofrootﬁlledmolarteethwithMOD preparationsrestoredwithcomposite,Int.Endod.J.38(2005)73–80.

[44]A. Karzoun, A. Abdulkarim, Fracture strength of endodontically treated maxillarypremolarssupportedbyahorizontalglassﬁberpost:aninvitro study,J.Endod.41(2015)907–912.