permanent mandibular molars：永久的下颌磨牙

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1、PERMANENTMANDIBULARMOLARSMANDIBULAR1stMOLARthelargestandthestrongestmandibularmolarsnotconsideredsuccedaneousfirstpermanentmolarstoerupt=sixyearmolars5cusps2rootsD&M(3canals:1-D,2-M)UNIQUEFUTURESlargestmesiodistalcrowndimensionofanytoothheocclusocervicalandfaciolingualdimensionsofthefir

2、stmolararegreaterthananyothermandibularmolarMandibularfirstmolarshavethreefacialcuspsasdosomemandibularthirdmolarsthelongestrootsofanymolarthegreatestmesiodistalrootseparationofanymolarThemesialroothasthegreatestfaciolingualdimensionofanyrootinthemouthBuccalviewThemesiofacial(mesiobucca

3、l)cuspisthelargest,widest,andhighestofthe3facialcuspsThefacial(buccal)cervicallineisnearlystraightbuttherecanbeenamelthatdipscervicallynearlyintothefurcationThetwolingualcusps(mesiolingualanddistolingual)arevisiblebecausetheyaretallercuspsThemesialrootaveraged1mmlongerthanthedistalrootB

4、othrootshaveanoveralldistalinclinationThedistalrootisstraighterthanthemesialrootLingualviewThegreaterheightofthelingualcuspshidethefacialcuspsportionsoftheproximalsurfacesarevisiblefromalingualviewThelingualcervicallineisnearlystraightMesialviewTwocuspscanbeseen(ML&MB)Onlyonerootcanbese

5、en(FLlengthtwiceMD)ThemesialcervicallinecurvesocclusallyThelingualheightofcontour(areaofgreatestconvexity)hasbeenlocatedinthemiddlethirdofthecrownThefaciolingual(buccolingual)crown,root,cuspsdimensionisgreaterMthanDThetwomajormesialcusps(mesiofacialandmesiolingual)arelargerthanthedistal

6、cuspsDistalviewDistolingualcuspislargestdistalproximalcontacthasbeenlocatedfacialtothecrowncenter(Fuller/Denehy/Schulein;Renner),centeredovertherootFromadistalview,moreofthefacialsurfacecanbeseenthanfromamesialviewbecausethecrowntapersdistallyMoreoftheocclusalsurfaceisvisiblefromadistal

7、viewthanmesialviewbecausethedistalsurfaceisshorterocclusocervicallyOcclusalview5cusps.AllofthemfunctionalThemesiofacialcuspisthelargestcuspThecrowntaperslinguallyTheoutlineformhasbeendescribedaspentagonalTherearefourdevelopmentalgroovesontheocclusalsurface:central;mesiofacial(m