口腔解剖生理学之国外ppt--下颌第二磨牙

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1、DESCRIPTIVEANATOMYOFMANDIBULARSECONDMOLARProf.A.ElsahnInitialcalcification2½–3yearsCompletionofcrown7–8yearsEruption11–13yearsCompletionofroots14–15yearsProf.A.ElsahnCHRONOLOGYItsdisto-buccalcuspislargerthanthatfoundinthelowerfirstmolar.Prof.A.ElsahnGEN

2、ERALCHARACTERISTICSThismolaristheseventhtoothfromthemiddleline.Thecrownisusuallysmallerthanthefirstmolarinthesamemouth.Ithasfourcusps.1234567DDMLLBB4321Thecervicalridgeislesspronouncedthanonthefirstmolarsinmostinstances,butaprominentbulgecervicallyonthe

3、mesio-buccalcuspiscommon.Prof.A.ElsahnGENERALCHARACTERISTICSThereisonlyonebuccalgroove.BDMLTherootsareaslong(ormaybelonger),lessbroadbucco-linguallythanonthefirstmolarandarelesswidelyseparatedormoreparallel.Prof.A.ElsahnGENERALCHARACTERISTICSTheroottrun

4、kisslightlylongerthanonthefirstmolar.BTHECROWNThecrownappearstobewideratthecervixthanthefirstmolar(lesstapertowardthecervixbelowthecontactareas),duetoabsenceofadistalcusp.Prof.A.ElsahnBUCCALASPECTAsinthefirstmolar,thecrownismuchlargermesiodistallythance

5、rvico-occlusally.CCOODDMMesialoutline:Isnearlystraightfromthecervicallinetothemesialcontactarea.Distaloutline:Isconvexfromthecervicallinetothedistalcontactarea.Prof.A.ElsahnBUCCALASPECTTHECROWNMDCONTACTAREASMESIALIsataboutthejunctionofthemiddleandocclus

6、althirds.DISTALIsatthecenterofthemiddlethird.Prof.A.ElsahnBUCCALASPECTTHECROWNBothcontactareasareatslightlylowerlevel,especiallyinthedistalareathanthoseofthefirstmolar.Prof.A.ElsahnBUCCALASPECTTHECROWNOCCLUSALOUTLINEThetwobuccalcusps(mesio-buccalanddist

7、o-buccal)andthetipsofthetwolingualcusps(mesio-lingualanddisto-lingual)arevisiblefromthebuccalsidebecausethelingualcuspsareslightlylonger.Prof.A.ElsahnBUCCALASPECTTHECROWNDMThebuccaldevelopmentalgrooveseparatesthetwobuccalcusps,anditmayendinapitonthemidd

8、leofthebuccalsurface.Thetwobuccalcuspsareaboutequalmesio-distallybutthemesio-buccalisusuallywider.Prof.A.ElsahnBUCCALASPECTTHECROWNMDCERVICALLINEItmaypointsharplytowardtherootbifurcation.Prof.A.ElsahnBUCCALASPECTTHECROWNItisnearl