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การเสรมความแขงแรงของรากฟนแทปลายรากเปดทไดรบการรกษาดวยวธเอเพกซฟเคชน: ทบทวนวรรณกรรมRoot Reinforcement of Immature Permanent Teeth Treated with Apexification: A Literature Review

เอธส อ�ำพนนวรตน1, อำณต เดว2, ธนดำ ศรสวรรณ2, ภมศกด เลำวกล2

1ภำควชำทนตกรรมครอบครวและชมชน คณะทนตแพทยศำสตร มหำวทยำลยเชยงใหม2ภำควชำทนตกรรมบรณะและปรทนตวทยำ คณะทนตแพทยศำสตร มหำวทยำลยเชยงใหม

Aetas Amponnawarat1, Anat Dewi2, Tanida Srisuwan2, Phumisak Louwakul21Department of family and community dentistry, Faculty of Dentistry, Chiang Mai University

2Department of Restorative Dentistry and Periodontology, Faculty of Dentistry, Chiang Mai University

ชม. ทนตสาร 2562; 40(3) : 43-53CM Dent J 2019; 40(3) : 43-53

Received: 24 January, 2019Revised: 18 April, 2019Accepted: 8 May, 2019

บทคดยอ การรกษาดวยวธเอมทเอ เอเพกซฟเคชน (MTA apexification) เปนหนงในทางเลอกการรกษาฟนแทปลาย

รากเปดทมการตายของเนอเยอใน อยางไรกตามแมจะพบ

วาการรกษาดงกลาวใหผลการรกษาทด ฟนแทปลายราก

เปดทรกษาดวยวธการดงกลาวนน มผนงเนอฟนทบางและ

เสยงตอการเกดการแตกหกของรากฟน ในปจจบนมการ

ศกษาเพอลดความเสยงของการแตกหก เพอใหฟนทไดรบ

การรกษาดวยวธเอเพกซฟเคชนสามารถคงอยในชองปาก

ไดนานขน นกวจยคนพบวธการเสรมความแขงแรงของ

รากฟนดวยการใชวสดหลายชนดเพอเสรมในคลองรากฟน

แททปลายรากเปด และการศกษาในปจจบนมงเนนศกษาถง

ผลของวสดชนดตางๆ ตอความแขงแรงของฟนทไดรบการ

รกษาดวยวธเอเพกซฟเคชน บทความนไดรวบรวมขอมล

Abstract Mineraltrioxideaggregate(MTA)apexifica-tionisoneofthetreatmentoptionsforimmature,permanentteethwithnecroticpulps.Althoughapexificationmaybesuccessful,thecanalwallsofimmatureteetharestillthinandvulnerabletofracture.Attemptshavebeenmadetoreducetheriskoffractureofsuchteethsothattheycanremaininfunctionforalongerperiodoftime.Researchers have come across the idea of intraradicular reinforcementwithvariousmaterials.Theresearchtrendnowadaysisfocusedmainlyonmethodswhichyieldthegreateststrengthtotheimma-tureteethtreatedwithapexification.Thisarticle

Corresponding Author:

อาณต เดวอำจำรย ภำควชำทนตกรรมบรณะและปรทนตวทยำ คณะทนตแพทยศำสตร มหำวทยำลยเชยงใหม 50200

Anat DewiLecturer, Department of Restorative Dentistry and Periodontology, Faculty of Dentistry, Chiang Mai University, Chiang Mai 50200, ThailandE-mail: [email protected]

บทความปรทศนReview Article

ชม. ทนตสาร ปท 40 ฉบบท 3 ก.ย.-ธ.ค. 2562 CM Dent J Vol. 40 No. 3 September-December 201944

Introduction Traumaticdentalinjuriesoccurinbothchildren andadults.(1)A12-yearreviewof theliterature suggeststhatonefourthofschoolchildrenandaboutonethirdofadultssufferfromtraumatotheperma-nentdentition.(1)Suchinjuriescanbringaboutlossofpulpvitalitybeforethedevelopmentoftherootiscompleted.(2)Immatureteethwithnecroticpulpsoftencausedifficultyforcliniciansinperformingrootcanaltreatment,duetoaninabilitytocontroltheextrusionofroot-canal-fillingmaterialsthroughtheapex.(3)Furthermore,thethindentinalwallsofsuchimmatureteethalsocompromisetheirsurvivalrate.Apexificationisamethodthathasbeenwidelyusedtoovercomethepreviouslydescribedsituation,aiming toinducethenaturalapicalclosureor tocreate anapicalplug.(3,4)After successfulcreationofanapicalbarrier,aconventionalrootcanalfilling materialcanbeplaced.Andthoughtheapexification maybesuccessful,thedentinalwallsarestillthinand,therefore,susceptibletofracture.(5)Theresearchtrendnowadaysisfocusedmainlyonintraradicularreinforcement,inhopeofdisclosingmaterialsorprocedureswhichyieldthegreateststrengthtotheimmatureteethtreatedwithapexification.Theteethwithgreaterstrengthmeanthattheycanwithstandgreaterforce,thusreducingtheriskoffracture,there-fore,theycanremaininfunctionforalongerperiodoftime.

Apexification Thetraditionalapexificationprocedurerequirestheuseofcalciumhydroxideasanintraradicularmedicament.The time required forhard tissue formationattheapexisbetween6and18months.(5) Duringthisperiodoftime,calciumhydroxidemighthavetoberepeatedlyreplacedbecauseitcanbewashedoutbytissuefluidsthroughthewide-openapex.(5)Aradiographismadeatthebeginningofeveryfollow-upappointmentinordertoevaluatethepresenceofcalcificbarrier.Calciumhydroxideapexificationhasaclinicalandradiographicsuccessraterangingfrom87%to100%and87%to93.3%,respectively.(6-8)

Despitethehighsuccessrateandthefavorableoutcomeoftraditionalcalciumhydroxideapexifi-cation,therearesomedrawbacks,whichneedtobediscussed.(9)Suchdrawbacksincludeanextendedperiodoftimerequiredtoformahardtissuebarrier,requiringpatientcompliancefor6to17visits,(5,10) andithasbeenprovedthatlongtermusageofcalcium hydroxidedressingweakenstherootstructure,and,therefore, increasestheriskofrootfracture.(11) Tomakeupforthesedrawbacks,theconceptofanimmediateapicalbarrierhasbeenintroduced.Successfuloutcomesofimmediateapicalbarrierformationhavebeenobservedwithouttheneedofinducinganaturalapicalbarrier.(12)Inthepast, researchershavestudiedseveralmaterials,e.g. tricalciumphosphate,freeze-driedcorticalbone,dentinalplugs,orevencalciumhydroxide,touseasimmediateapicalbarriers.(3,4,13,14)Recently,mineral

เกยวกบวธการและวสดทใช ในการเสรมความแขงแรงของ

ฟนแทปลายรากเปดทไดรบการรกษาดวยวธเอเพกซฟเคชน

ค�ำส�ำคญ: เอเพกซฟเคชน ฟนแทปลายรากเปด เอมทเอ

การเสรมความแขงแรงของรากฟน

reviewsthereinforcementmethodsandmaterialsusedforreinforcingimmature,permanentteethwithnecroticpulpstreatedwithapexification.

Keywords:apexification,immaturepermanentteeth,mineraltrioxideaggregate,reinforcement


trioxideaggregate(MTA)hasbeenusedextensivelyasanalternativetocalciumhydroxideapexification,duetoitssuperiorcharacteristics:sealingabilityandbiocompatibility,forexample.(15)Thesurvivalandclinical-radiographicsuccessratesofMTAapexifi-cationhavebeenreportedtobe96.9%and90.2%ofcases,respectively,inoneretrospectivestudy,(16)

andthelongterm(meanfollow-uptime,8.29years)survivalandsuccessrateshavebeenreportedtobe100%and95.6%ofcases,respectively.(17) Eventhoughtheapexificationprocedureresultsinastoundingclinicaloutcomes,thethindentinalwallsstillpresentamajorconcern.Teethwiththindentinalwallsarevulnerabletorootfracture,espe-ciallyinthecervicalregion.(11)Suchvulnerabilitymayhavetodowiththefactthatwhenforcesarenotloadedparalleltothelongaxisoftheanteriorteeth,marginalbonebecomesafulcrum.Together with thindentinalwalls in thecervicalareaof immatureteeth,fracturesoftenoccuratthispreciselocation.(18)Inaretrospectiveclinicalstudy,Cvek,in1992,revealedthatcervicalrootfractureoccursmorefrequentlyinimmatureteeththaninmatureteeth.(19)Amongsuchimmatureteeth,thestageofrootdevelopmentplaysanimportantroleintermsofincidenceoffracture,whichrangedfrom77%inteethwiththeleastdevelopedrootsto28%inteethwiththemostdevelopedroots.(19)Attemptshavebeenmadeinordertoreinforcetherootstructuresandtopreventfracture.(20)

Root reinforcement Variousroot-reinforcementmethodsforimma-ture,permanentteetharementionedinthelitera- ture.(21,22)Suchmethods include intraradicular reinforcementwithmaterialssuchasresin-modifiedglassionomer(RMGI),compositeresin,fiberpost,MTA,orBiodentine.(Fig.1)

Intraradicular reinforcement AfterestablishingasuccessfulMTAapicalplug,rootcanalsareusuallyobturatedwithguttaperchainconjunctionwitharootcanalsealer.Cervicalrootfracture,oneofthemajorcomplicationsassociatedwithapexification,canbeobservedfollowingthetreatment.Cvek(19)hasreportedthattheprevalenceofcervicalrootfractureafterguttaperchaobturationisashighas8.5%.Thus,intraradicularreinforcementshouldbeconsidered. Regardingintraradicularreinforcement,rootcanals can be obturatedwith various types of materialstoprotectthemagainstpossiblefracture.(20) EarlyintraradicularreinforcementwithRMGIorcompositeresinwascarriedoutwiththehelpofatranslucentcuringposttoensurethattheentirelengthoftheresinwaspolymerized.Thepostwasremovedafterwards;thus,thecenteroftherootcanalwasusuallyleftempty(Fig.2).Followingthecontinued

รปท 1 แสดงฟนแทปลำยรำกเปดทมกำรตำยของเนอเยอในและ

ไดรบกำรรกษำดวยวธเอเพกซฟเคชน และไดรบกำรเสรม

ควำมแขงแรงของรำกฟนดวยวสด เชน เอมทเอ เรซนคอม-

โพสต หรอเดอยฟน

Figure 1 Diagram showing an immature permanent tooth

with necrotic pulp treated with MTA apexification.

The tooth was reinforced with material such as MTA,

composite resin, or fiber post.


developmentofresinmaterials,resinreinforcementisnowperformedbyfillingtheentirerootcanalwithself-curedordual-curedcompositeresin.Moreover,fiberpostsarealsousedtostrengthentherootbycementingthemtotherootwithresincement.Anewpolycaprolactone-basedmaterial,Resilon,developed toreplaceguttapercha,isusedtofilltherootcanal of immature teeth treatedwithapexification, in conjunctionwitharesin-basedsealer.(20,23)Mostrecently,MTAandBiodentinehavebeenusedtofilltheentirerootcanalofimmatureteethforthesamepurpose.(24)Inordertoanswerwhichmaterialisthebestintermsofstrengtheningimmatureroots,manyexperimentalstudieshavefocusedlargelyonthefractureresistanceofsimulatedimmatureteethreinforcedwiththesedifferentmaterials. Asbioceramicmaterialshavebecomeavailableinthemarketinrecentyears,cliniciansareinterested toseeifdifferentmaterialsusedasanapicalplugaffectthefractureresistanceofthetooth.Evren, et al.(25)comparedthefractureresistanceofMTA,

Biodentineandcalcium-enrichedmixture(CEM)whenusedasanapicalbarrier.Afterthesuccessful creationofbarriers,allrootcanalswerereinforcedwithglass-fiberposts(UniCore®size4)andcemented withself-adhesiveresincement(BifixSE;Voco,Cuxhaven,Germany).Theloadtofracturerevealedthatnosignificantdifferenceswerefoundbetweenanymaterials.TheauthorsconcludedthatMTA,Biodentine,andCEMcanbeusedasanapicalpluginimmatureteethwithequaleffect,andspeculated thatthefractureresistanceofthetoothtendsto dependontherootcanalwallthicknessratherthantheapicalplugmaterial.

Resin reinforcement Earlyexperimentalstudiesfocusmainlyonthefractureresistanceofendodonticallytreatedteeth.Onestudycomparedeightdifferentmethodsof restoringendodontically-treatedteethandreportedthatfillingtherootcanalspacewithcompositeresinafteracidetchingyieldedthegreateststrength.(26) Theauthorssuggestedthattheideacouldbeusedinimmatureteethwiththindentinalwalls.Rabie, et al.(22)usedtheacidetchingtechniquetorestoretheimmaturemaxillaryincisorsandtheresultsweresatisfactory.Afterwards,researchersturnedtheirattentiontowardtheintraradicularreinforcementofimmatureteethinhopesofdiscoveringthebestmaterialtobeusedinsuchcircumstances. In1998,Katebzadeh,et al.(27)simulatedthethindentinalwallsofimmaturehumancentralincisors and tested the reinforcingabilityofcomposite resin.Therootcanalsoftheexperimentalteethwereeithercoatedwithcompositeresin(XRVHerculite,DentinshadeB2)orcementedwithametalpost(Luminex®,DentatusAB)usingaresincement.Theresultsshowedthatthereinforcedimmatureteethcanwithstandgreaterforces,regardlessofthematerialsused.

รปท 2 แสดง (a) ฟนแทปลำยรำกเปดทมกำรตำยของเนอเยอใน

(b) ภำยหลงจำกกำรท�ำกำรกนปลำยรำกฟนดวยเอมทเอ

(c) เสรมควำมแขงแรงของรำกฟนดวยวสดเรซน คอม-

โพสต หรอ อำรเอมจไอ (d) รปตดขวำงของรำกฟนท

ไดรบกำรเสรมควำมแขงแรงดวยวสดเรซน คอมโพสต

หรอ อำรเอมจไอ

Figure 2 Diagram showing (a) immature permanent tooth with

necrotic pulp. (b) after MTA apical plug placement.

(c) intraradicular reinforcement with composite resin

or RMGI. (d) cross-section of the tooth reinforced

with composite resin or RMGI.


Despitesuchpromisingresultsfromtheuseofacomposite,otherresearchers(28)carriedoutanexperi- ment similar toKatebzadeh’s using anRMGI (Vitremer™3MDentalProducts,StPaul,MN,USA)insteadofacompositeresin.TheyconcludedthattheRMGIcansignificantlyincreasestheresistancetofractureoftheimmatureteeth,and,therefore,canbeusedasanalternativetocompositeresin. Furthermore,Rani,et al.(29)studiedthereinforc-ingeffectofanRMGI(Vitremer™3M),aflowablecompomer(PrimaFlow®),andaflowablecompositeresin(Filtek™Z350)bycoatingeachmaterialontotherootcanalwallsofsimulatedimmaturehumanincisorsafter15,30,90,and180daysofthecalciumhydroxidemedicament.Theresultsrevealedthatallmaterialssubstantiallyincreasedfractureresistance of the reinforced teethcomparedwith thenon- reinforcedteeth.At180daysaftercalciumhydroxidemedicament,theflowablecompositeresinyielded the greatest reinforcement effect among the materials;nonetheless,thereinforcingeffectwasnotdifferentbetweentheRMGIandtheflowablecompomer.Theauthorspointedoutthateventhoughthefailureloadof thenon-reinforcedteethwas significantlyreducedbyalmost40%attheendofsixmonths,significantreductioninthereinforcementvalueswasnotfoundintheflowable-composite- reinforcedteethattheendof180dayscomparedwith thoseat15days, indicating thatflowable composite resin is effective in reinforcing the immatureteeth.(29) Attempts have beenmade to determine if differenttypesofcompositeresinofferdifferent reinforcingresults.(2,30)Karapinar-Kazandag,et al.(2) experimentedonsimulatedimmatureteethbyfillingtheentirerootcanalwitheitherself-curedhybridcompositeresin(BisFilII)orself-curedflowablecompositeresin(BisFil2B).Asignificantdifferenceinthefractureresistancewasnotfoundintheteethreinforcedwitheitherofthematerials.Wilkinson

et al.(30),however,testedthesametwocompositeresinsandrevealedthatonlythehybrid-compositeresin-reinforcedteethexhibitedsignificantlygreater fractureresistancethandidthenon-reinforcedteeth.Theyexplainedthatthefractureloadoftheflow-able-composite-resin-reinforcedteethintheirstudywas,infact,similartothatofthehybrid-compositeresin-reinforcedteeth.Thelargerangeofresultswithin theflowable-composite-resin-reinforcedtoothgroup,however,didnotindicateasignificantdifferencecomparedwiththenon-reinforcedtoothgroup.Thislargevariabilitywasprobablyduetotwofactors:alowfillerloadintheflowablecompositeresinandthehighC-factorsoftherootcanals.Thesefactorsresultintheshrinkageoftheflowablecom-positeresinwhich,inturn,affectthebondingandfractureload.(30)

Thereisareportontheeffectofirrigatingsolution onfractureresistanceofteethrestoredwithcomposite resinandglassionomer.(31)Sodiumhypochlorite(NaOCl),whenusedasarootcanalirrigant,doesnotaffectthefractureresistanceofteethsubsequently restoredwitheitheracompositeresinoraglass ionomer.However,chelatingagents,suchaslacticacidorEthylenediaminetetraaceticacid(EDTA),whenusedas rootcanal irrigants, significantly increasethefractureresistanceofsuchteeth.(31)These datahighlightanimportantstepthatmayhelpprolong thesurvivalofcomposite-resin-reinforcedteeth. Thelimitationofusingacompositeresinistheinabilitytolight-curetheentirelengthofthematerialwithintherootcanal.Twomethodsareavailabletoovercometheproblem:transmittingthelightthroughaclearplasticpost(27)andusingaself-curedora dual-curedcompositeresin.(30)Thefirstmethodmerelycoatstherootcanalwall,whereasthesecondmethodobturatestheentirerootcanalspacewithacompositeresin.Incaseswhereapostisneededforthepermanentrestoration,thelatteroptionisnotapplicable.


Post reinforcement Metal,ceramic,andfiberpostsareusedinroot-filledteethforcore-retentionandroot-reinforcementpurposes.Regardingtheroot-reinforcementpurpose,ceramicormetalpostsarenotfrequentlymentionedintheliterature,despitetheirefficientreinforcementabilityinimmatureteeth.(32,33)Themainreasonisbecausefiberpostsarebetter,sincetheyperform better than ceramicormetalposts in termsof fractureresistance.(34)Additionally,inscenarioswhererootfracturesoccur,teethrestoredwithfiberpostsoftenshowrestorablefractures,whereasteethwithmetalorceramicpostsoftenshowcatastrophicfractures.(34)

Fiberpostshavebeenusedinendodontically- treated teeth for core-retentionpurposes, long beforetheywereusedforreinforcementpurposesintheimmatureteeth.(34)Schmoldt,et al.(35) evaluated thefractureresistanceofsimulatedimmatureteethrestoredwithacompositeresin(Pentron),ProRoot® MTA(DensplyTulsaDental,Tulsa,OK),gutta percha, and a fiber post (FiberKor™Pentron, Wallingford,CT).Onlytheteethrestoredwithafiberpostexhibitedasignificantincreaseinfracture resistancecomparedwithallothermaterials.In addition,Tanalp,et al.(36)experimentedonsimulated immaturerootsanddiscoveredthatUniCorequartzfiberpost-reinforcedteethprovidedthegreatest fractureresistancecomparedtotheteethreinforcedwithallothertestedmaterials.Linsuwanont,et al.(37) alsoconfirmedtheabilityoffiberpoststoreinforceimmatureteeth;however,theydisclosedthattheteethreinforcedwithothermaterials,i.e.,MTAorcom-positeresin(dual-curePermaFlo™DC)provided asimilareffect.Apossibleexplanationfor this disputablefindingmayhavetodowiththefactthatthermocyclingwasperformedin thatparticular study.Thermocyclingisamethodusedtoexposetheteethatdifferent temperaturesforhundredsofcyclestomimictheprocessinwhichtheteeth

areexposedtoafluctuationoftemperatureduring eatinganddrinking.Thermocyclinghasbeenfoundtoreducetheflexuralstrengthofacompositeresin.(38) Theauthorsexplainedthatthisprocessisprobablywhyasignificantdifferenceinthefractureresistanceofteethreinforcedwithdifferentmaterialswasnotfoundintheirstudy.(37) Theeffectsofreinforcingtherootcanalwithmultiplefiberpostshavealsobeeninvestigated.Kim,et al.(39)reportedtheuseofacustomizedfiberpost,multipleEverStick®glassfiberpostsbondedtoeachother,asanintraradicularreinforcementmaterial.Theyshowedthatteethrestoredwithacustomized fiberpostyieldslightlygreaterfractureresistancethando teeth restoredwitha singlefiberpost. However,statisticaldifferenceswerenotfound.Theauthorsconcludedthatacustomizedfiberpostdoesnotofferanyadditionaladvantagesoverasingleglassfiberpost. Severalfactorsassociatedwithpostshavealsobeenstudied.Postfitisonesuchfactor,andpostlengthisacontroversialfactor.Büttel,et al.(40) eval-uatedtheeffectofpostfitandpostlengthonthefractureresistanceofendodontically-treatedteeth,andfoundthatpostfithasnoinfluenceonfractureresistance,andthatlongpostsyieldgreaterfractureresistancethandoshortones.Seto,et al.(41)ontheotherhand,disclosedthatbyrestoringanimmaturepermanenttoothwithafiberposttoadepthof3mmbelowthecemento-enameljunction(CEJ),thetoothcansustaingreaterforcethancanatoothwithafiberpostrestoredtoadepthof7mmbelowtheCEJ.Theyexplainedthatimmatureteethhaveathinnerdentinalwallapically;therefore,teethwithashorterpostcanwithstandgreaterforce.Posttypeandpostsizeareadditionalfactorsthathavebeenstudied.Kim,et al.(39)evaluatedtheeffectofpost typeandpostsizeonthefractureresistanceofimmature teeth.Theirresultsrevealedthatpost-reinforcedteethshowsignificantlygreaterfractureresistance


thandonon-reinforcedteeth.However,neithertheposttypenorpostsizeaffectthefractureresistanceofimmatureteeth.

Resilon reinforcement Resilonisasyntheticpolycaprolactone-polymer- basedmaterialusedforobturationoftherootcanalsinasimilarmannertothatofguttapercha.Itisusedinconjunctionwithadual-cureresin-basedsealer.(20) Severalstudieshaveevaluatedthereinforcingabilityofresilonintheimmaturetooth.(20,23,30)Wilkinson,et al.(30)revealedthatresilon-obturatedteethshowagreaterfractureresistancethandogutta-percha- obturatedteeth;however,thedifferencewasnot significant.Furthermore,thedifferenceinfracture resistanceofbothgutta-percha-andresilon-obturated teethwasnotsignificantfromthatofnon-obturated teeth,therefore,suggestingthatneitherresilonnorguttaperchahavetheabilitytoreinforceimmatureteeth.(30)Moreover,Hemalatha,et al.(23)agreedthatneitherresilonnorguttaperchacanstrengthen immatureteeth.

MTA reinforcement AfterMTAbecameavailableinthemarket,recentexperimental studieshavesimulated the immaturerootnotonlybythinningthedentinalwallsbutbycreatinga4-mmbarrierofMTAattheapextoimitatetheclinicalsituationafterestablishinganMTAapicalbarrier.(20,23,30,35,37)Additionally,MTAcanalsobeusedtofilltheentirerootcanalspaceofimmatureteeth.(2,35,37)Cauwels,et al.(42)foundthatMTA-reinforcedteethshowsignificantlygreater fractureresistancethandonon-reinforcedteeth,suggestingthatanMTAcanbeusedtoreinforce immatureteeth.ThisresultwaslaterconfirmedbyKarapinar-Kazandag,et al.(2)andLinsuwanont, et al.(37)showingthatMTA-reinforcedteethyieldagreaterfractureresistancethandonon-reinforcedimmatureteeth.EventhoughMTAhasprovento

beabletoreinforceimmatureteeth,Linsuwanont, et al.(37)discovered that the reinforcingability betweenMTAandguttaperchawasnotsignificantlydifferent.ThisfindingwasspeculatedtobetheeffectofthermocyclingonMTAsincethereisareportonMTAdisintegrationbeingobservedafterMTA-rein-forcedteethunderwentathermocyclingprocess.(43)

DespitethereinforcementabilityofMTA,afewdrawbacksneedtobeconsidered.Whenestheticsisaconcern,MTAshouldnotbeusedbecauseitcancausetoothdiscoloration.(44)Moreover,incaseswhereapostisrequiredforapermanentrestoration,MTAreinforcementisnotapracticalmethod.(37)

Biodentine reinforcement ApartfromMTA,Biodentinehasalsobeenstudiedforitsabilitytofortifyimmatureroots.IthasbeendiscoveredthatthereisnodifferenceinreinforcingabilitybetweenBiodentine,guttapercha, andadual-curedcomposite resin,when tested immediatelyandthreemonthsafterthereinforce-ment.However,only the teeth reinforcedwith Biodentine showed a statistically significant reductioninfractureresistancethreemonthsafterthereinforcement.(45)Inagreement,Topçuoglu,et al.(46) evaluatedthefractureresistanceofimmatureteethreinforcedwithvariousmaterials,usingBiodentine asanapicalplug, and revealed thatonly teeth reinforcedwithafiberpostshowedsignificantlygreaterfractureresistancethandidteethreinforcedwithBiodentineorguttapercha,ornon-reinforcedteeth.(46) AmorerecentreportbySawyer,et al.(47)reported that theflexural strengthof dentin exposed to BiodentineandMTAsignificantlydecreasesafter twoand threemonths, respectively.Moreover, Leiendecker, et al.(48)reportedcollagendegradationoftherootdentinafterexposuretoBiodentineforanextendedperiodoftime.Thisdegradationwas speculatedtobethereasonwhythestrengthof


theBiodentine-reinforced teeth in the studyofZhabuawala,et al.(45)wasdrasticallyreducedafterthreemonths. Duetothescarcityofstudiesavailable,using Biodentine as an intraradicular reinforcement materialcannotberecommended.

Trends of future studies Severallimitationsanddrawbackshavebeenidentifiedinthepreviousstudies.Inordertoobtainthemostreliableoutcomes,influencingfactors,suchasdentinalwallthickness,simulationoftheperi-odontalligamentandwhethertousethermocycling,needtobeconsidered.

Dentinal wall thickness Stuart, et al.(20)simulatedimmatureteethby instrumentingtherootcanalofextractedteethwithaPeesoreamerwithadiameterof1.5mm,leavinganaverageof2.63mmofdentinalwallthickness,anddisclosedthatthismighthavebeeninsufficienttoadequatelyweakenthetoothstructurebecauseasignificantdifferenceinreinforcingabilitywasnotfoundbetweenanyofthetestingmaterials.There-fore,theysuggestedthatreinforcementofimmatureteethwithrootcanaldiametersof1.5mmorless,anddentinalwallthicknessesof2mmormore,may not be necessary. Recent studies(23,24,45) then consideredpreparingtheimmaturerootcanalwitha3mm-diameterinstrumenttosimulatestagethreeofCvek’sclassificationinordertoobtaintheroot- to-canalratiointhemesiodistaldimensionattheCEJofapproximately1:1.(19)Largerinstrumentwasusedtoobtaintheremainingdentinalwallthicknessofaround1-1.5mm.(45)

Themocycling process Thethermocyclingprocesshasbeenusedinrecentexperimentalstudies,(29,35,37)sinceithasbeenfoundtoaffecttheresistancetofractureofmany

intraradicularreinforcementmaterials:resincom-positeandMTA,forexample.(38,43)

Simulation of periodontal ligament Periodontal ligament simulation and root embedmentmaterialsusedduringanexperimentareamongthefactorsthatmayaffecttheoutcomesofexperiments.IthasbeenestablishedinastudybySoares,et al.(49)thatboththeperiodontalligamentsimulationandrootembedmentmaterialsalteredthefracturepatternoftheexperimentalteeth;therefore,iffracturepatternistobedetermined,simulationofperiodontalligamentisnecessary.

Conclusion Despitesuccessfuloutcomesofapexificationofimmaturepermanentteethwithnecroticpulps,athindentinalwallcanstillresultinrootfracture, especiallyinthecervicalregion.Theincidenceofrootfractureinsuchteethdependsmostlyonthestageofrootdevelopmentandtheamplitudeofforceloadsonthetooth.Preventionofsuchrootfracture mustbeconsidered.Amyriadofstudiesshows differentresults.Themethodologyofeachstudywasextremelydifferentintermsofsamplesource,directionofforceloading,simulationofimmature roots,etc.Comparingtheresultsfromthesestudies is,therefore,hardlypossible.Thebestsolution, however,seemstobepointingtowardsintraradicularreinforcementwithdentinadhesivematerials,suchascompositeresinorfiberpostswithresincement.Furtherstudiesshouldbeconducted,replicatingtheclinicalscenariosascloselyaspossible,sothatthelong-termreinforcingeffectcanbefullyunderstood.

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