上颌第三磨牙根管形态：Maxillary Fusioned Molars

Fusioniscommonlyidentifiedastheunionoftwodistinctdentalsproutswhichoccursinanystageofthedentalorgan.Theyarejoinedbythedentine;pulpchambersandcanalsmaybelinkedorseparateddependingonthedevelopmentalstagewhentheunionoccurs.Thisprocessinvolvesepithelialandmesenchymalgermlayersresultinginirregulartoothmorphology(1).Moreover,thenumberofteethinthedentalarchislessthannormal.Areviewoftheliteraturerevealsgreatdifficultyincorrectlydifferentiatingfusionandgemination.Foradifferentialdiagnosisbetweentheseanomalies,thedentistmustcarryoutahighlyjudiciousradiographicandclinicalexamination.Theaetiologyoffusionisstillunknown,buttheinfluenceofpressureorphysicalforcesproducingclosecontactbetweentwodevelopingteethhasbeenreportedasonepossiblecause(2).Geneticpredispositionandracialdifferenceshavealsobeenreportedascontributingfactors.Thisanatomicirregularityoccursmoreofteninthedeciduousthaninthepermanentdentition.Onlyafewcasesoffusioninvolvingmolarandpremolarteethhavebeenreported(3-5)whereas,inbothdentitions,theprevalenceishigherintheanteriorregion(6-9).Casesofbilateralfusionarelessfrequentthanunilateralfusion(6).TurellandZmener(3)describedacaseoffusioninvolvingamandibularthirdmolarandfourthmolar(distomolar).Unfortunately,mostofthesefusionsrequiresurgicalremovalbecauseoftheirabnormalmorphologyandexcessivemesiodistalwidth,whichcauseproblemswithspacing,alignmentandfunction(6,8).Intheanteriorregionthisanomalyalsocausesanunpleasantaesthetictoothshapeduetotheirregularmorphology.Theseteethalsotendtobegreatlypredisposedtocariesandperiodontaldiseaseand,insomecases,endodontictreatmentisverycomplicated(7,10).Fusioncanoccurbetweenteethofthesamedentitionormixeddentitions,andbetweennormalandsupernumeraryteeth(3,7-9,11,12).Inthesecases,thenumberofteethinthedentalarchisalsonormalanddifferentiationfromgeminationisclinicallydifficultorimpossible.Adiagnosticconsideration,butnotasetrule,isthatsupernumeraryteethareoftenslightlyaberrantandpresentacone-shapedclinicalappearance.Thus,fusionbetweenasupernumerarynormaltoothwillgenerallyshowdifferencesinthetwohalvesofthejoinedcrown.However,ingeminationcasesthetwohalvesofthejoinedcrownarecommonlymirrorimages.Fusedteethusuallypresentasymptomatically.Infact,theco-operationofpractitionerswithexpertiseinmultipleareasofdentistryisimportanttocreateorachievefunctionalandestheticsuccessinthesecases.Severaltreatmentmethodshavebeendescribedintheliteraturewithrespecttothedifferenttypesandmorphologicalvariationsoffusedteeth,includingendodontic,restorative,surgical,periodontaland/ororthodontictreatment(3-9,12).(Source:Nunesetal.2002.Fulltext).。

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