口腔解剖生理学之国外PPT--MANDIBULAR FIRST PREMOLAR(下颌4).ppt

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1、MANDIBULARFIRSTPREMOLARProf.A.El-SahnInitialCalcification1¾–2yearsCompletionofCrown5–6yearsEruption10–12yearsCompletionofRoot12–13yearsCHRONOLOGYProf.A.El-SahnBuccalAspectThegeometricaloutlineofthecrownisroughlytrapezoidalwiththeshortestoftheunevensidesiscervically.Themesialanddis

2、taloutlinesareslightlyconcavefromthecervixtothecontactareas.Prof.A.El-SahnTheCrownThemesialanddistalcontactareasarenearlyatthesamelevelinthemiddlethird,justocclusaltothemiddleofthecrown.Thecurvatureofthedistalcontactareaisbroaderthanthatofthemesialone.Prof.A.El-SahnBuccalAspectThe

3、CrownContactareas:Thebuccalcuspislongandsharp,andlooksmuchlikeamaxillarycaninefromthebuccalaspect.Thetipofthebuccalcuspis,inmostcases,locatedalittlemesialtothecenterofthecrownbuccally,similartothemandibularcaninetoagreaterdegree.Prof.A.El-SahnBuccalAspectTheCrownOcclusaloutline:Th

4、ebuccalcuspislongerandmorepointedthatthebuccalcusponmandibularsecondpremolars.Prof.A.El-SahnBuccalAspectTheCrownTheCrownThemesialcuspridgeisshorterthanthedistalcuspridges.Eithercuspridges(orslopes)usuallyshowshallownotches(concavities)ofunwornteeth.Prof.A.El-SahnBuccalAspectTheCro

5、wnThenotchesonthemesialcuspridgesaremorepronounced.ThesenotchesserveasspillwaysforfoodduringmasticationandaresometimescalledThomasnotches.DMProf.A.El-SahnMorphologyofthebuccalsurface:Thebuccalsurfaceofthecrownismarkedlyconvex(morethaninmaxillarypremolars),especiallyatthecervicalan

6、dmiddlethirds.Prof.A.El-SahnBuccalAspectTheCrownTheCrownThereisacontinuousridgefromthecervicalmargintothecusptip,whichiscalledthebuccalridge(itisnotasprominentasthatonthemaxillaryfirstpremolar).Prof.A.El-SahnBuccalAspectTheCrownVerticaldevelopmentaldepressionsareoftenseenintheoccl

7、usalthirdofthebuccalsurfaceoneithersideofthebuccalridge(betweenthethreebuccallobes).Prof.A.El-SahnBuccalAspectTheCrownCervically,thecrownisnarrowermesio-distallythanatthecontactareas.Prof.A.El-SahnBuccalAspectTheCrownThecervicalline:Isslightlyconvextowardstheroot.Prof.A.El-SahnBuc

8、calAspectTheCrownTheapicalthirdof