下颌较好磨牙根管形态：Mandibular First Molar

Theearliestpermanentposteriortoothtoerupt,themandibularfirstmolarseemstobethemostfrequentlyinneedofendodontictreatment.Itusuallyhastworootsbutoccasionallythree,withtwocanalsinthemesialandoneortwocanalsinthedistalroot.Thedistalrootisreadilyaccessibletoendodonticcavitypreparationandmechanicalinstrumentation,andthecliniciancanfrequentlysecdirectlyintotheorifice(s).Thecanalsofthedistalrootarelargerthanthoseofthemesialroot.Occasionallytheorificeiswidefrombuccaltolingual.Thisanatomyindicatesthepossibilityofasecondcanaloraribbonlikecanalwithacomplexwebbingthatcancomplicatecleaningandshaping.Themesialrootsareusuallycurved,withthegreatestcurvatureinthemesiai-buccalcanal.Theorificesareusuallywellseparatedwithinthemainpulpchamberandoccurinthebuccalandlingualunderthecusptips.Thistoothisoftenextensivelyrestored.Itisalmostalwaysunderheavyocclusalstress;thusthecoronalpulpchambersarefrequentlycalcified.Thedistalcanalsareeasiesttolocate;oncetheselocationsarcpositivelyidentified,themesialcanalswillbefoundintheaforementionedlocationsinthesamehorizontalplane.Becausethemesialcanalopeningslieunderthemesialcusps,theymaybeimpossibletolocatewithconventionalcavitypreparations.Itwillthenbenecessarytoremovecuspalhardtissueorrestorationtolocatetheorifice.Aspartoftheaccesspreparation,theunsupportedcuspsofposteriorteethmustbereduced.Remember,thistooth,likeallposteriorteeth,shouldalwaysreceivefullocclusalcoverageafterendodontictherapy.Thereforeawideraccesscavitytolocatelandmarksandorificesisbetterthanignoringoneormorecanalsforthesakeofa"conservative"preparation,whichmayleadtofailure.SkidmoreandBjørndalstatedthatapproximatelyonethirdofthemandibularfirstmolarsstudiedhadfourrootcanals.Whenatoothcontainedtwocanals,"theycitherremainedtwodistinctcanalswithseparateapicalforamina,unitedandformedacommonapicalforamen,orcommunicatedwitheachotherpartiallyorcompletelybytransverseanastomoses.Ifthetraditionaltriangularoutlinewerechangedtoamorerectangularone,itwouldpermitbettervisualizationandexplorationofapossiblefourthcanalinthedistalroot."Multipleaccessoryforaminaarelocatedinthefurcationareasofmandibularmolars. Theyareusuallyimpossibletocleanandshapedirectlyandarerarelyseen,exceptoccasionallyonpostoperativeradiographsiftheyhavebeenfilledwithrootcanalsealerorwarmedgutta-percha.Itwouldbepropertoassumethatifirrigatingsolutionshavethepropertyof"seekingout"anddisposingofproteindegenerationproducts,thenthefurcationareaofthepulpchambershouldbethoroughlyexposed(calcificadhesionsremoved,etc.)toallowthesolutionstoreachthetinyopenings.Allcaries,leakingrestorations,andpulpalcalcificationsmustberemovedpriortoendodontictreatment,andfullcuspalprotectionandinternalreinforcementarerecommended(BurnsRC,BuchananLS.ToothMorphologyandAccessOpenings.PartOne:TheArtofEndodonticsinPathwayofPulp,6thEd.p.160).。