口腔解剖生理学之国外PPTMANDIBULAR FIRST PREMOLAR下颌

口腔解剖生理学之国外PPTMANDIBULARFIRSTPREMOLAR下颌InitialCalcification1¾–2yearsCompletionofCrown5–6yearsEruption10–12yearsCompletionofRoot12–13yearsCHRONOLOGYProf.A.El-SahnBuccalAspectThe

geometricaloutlineofthecrownisroughlytrapezoidal

withtheshortestoftheunevensidesiscervically.Themesialanddistaloutlinesareslightlyconcavefromthecervixtothecontactareas.Prof.A.El-SahnTheCrownThemesialanddistal

contactareasarenearlyatthesamelevelinthemiddlethird,justocclusaltothemiddleofthecrown.Thecurvatureofthedistalcontactareaisbroaderthanthatofthemesialone.Prof.A.El-SahnBuccalAspectTheCrownContactareas:Thebuccalcuspislongandsharp,andlooksmuchlikeamaxillarycaninefromthebuccalaspect.Thetipofthebuccalcuspis,inmostcases,locatedalittlemesialtothecenterofthecrownbuccally,similartothemandibularcaninetoagreaterdegree.Prof.A.El-SahnBuccalAspectTheCrownOcclusaloutline:Thebuccalcuspislongerandmorepointedthatthebuccalcusponmandibularsecondpremolars.Prof.A.El-SahnBuccalAspectTheCrownTheCrownThemesialcuspridgeisshorterthanthedistalcuspridges.Eithercuspridges(orslopes)usuallyshowshallownotches(concavities)ofunwornteeth.Prof.A.El-SahnBuccalAspectTheCrownThenotchesonthemesialcuspridgesaremorepronounced.ThesenotchesserveasspillwaysforfoodduringmasticationandaresometimescalledThomasnotches.DMProf.A.El-SahnMorphologyofthebuccalsurface:Thebuccalsurfaceofthecrownismarkedlyconvex(morethaninmaxillarypremolars),especiallyatthecervicalandmiddle

thirds.Prof.A.El-SahnBuccalAspectTheCrownTheCrownThereisacontinuousridgefromthecervicalmargintothecusptip,whichiscalledthebuccalridge(itisnotasprominentasthatonthemaxillaryfirstpremolar).Prof.A.El-SahnBuccalAspectTheCrownVerticaldevelopmentaldepressionsareoftenseenintheocclusalthirdofthebuccalsurfaceoneithersideofthebuccalridge(betweenthethreebuccallobes).Prof.A.El-SahnBuccalAspectTheCrownCervically,thecrownisnarrowermesio-distallythanatthecontactareas.Prof.A.El-SahnBuccalAspectTheCrownThecervicalline:Isslightlyconvextowardstheroot.Prof.A.El-SahnBuccalAspectTheCrown

Theapicalthirdoftherootisoftenbentdistallyandsometimesmesially.Therootofthistoothisshorterthanthatofthelowercanine.Prof.A.El-SahnBuccalAspectTheRootThesinglerootisconvexonitsbuccalsurfaceandtapersgraduallytoanear-lypointedapex. DMTheLingualAspectThecrowntaperslingually,sothelingualsideisnarrowerthanthebuccalside.Prof.A.El-SahnTheCrownThelingualcuspisalwayssmall,short,reachingabouttwo-thirdsthelengthofthecrownandoftenhasapointedtip.Prof.A.El-SahnTheLingualAspectTheCrown2\3TheLingualAspectTheCrownMuchoftheocclusalsurfaceofthistoothcanbeseenfromthelingualaspectbecauseoftheshortnessofthelingualcusp.Prof.A.El-SahnThemesialanddistaloutlinesareslightlyconcavebetweenthecervicallineandthecontactareas.Thecontactareasandmarginalridgesarepronouncedandextendoutabovethenarrowcervicalportionofthecrown.Prof.A.El-SahnTheLingualAspectTheCrownThetipofthelingualcuspisinalignmentwiththetriangularridgeofthebuccalcusp.Themesialanddistalocclusalfossaeareoneachsideofthetriangularridge.Prof.A.El-SahnTheLingualAspectTheCrownDMThereisamesio-lingualdevelopmentalgrooveseparatingthemesialmarginalridgefromthemesialslopeofthesmalllingualcusp.Thisgrooveactsasalineofdemarcationbetweenthemesio-buccallobeandthelinguallobeandextendsintothemesialfossaoftheocclusalsurface.Prof.A.El-SahnTheLingualAspectTheCrownDMThecervicalportionofthecrownlinguallyisnarrowandconvex.Thecervicallineisslightlyconvextowardstheroot.Prof.A.El-SahnTheLingualAspectTheCrownCervicallyTheRootTherootismuchnarroweronthelingualsurfacethanonthebuccalsurface.Ittapersfromthecervixtoapointedapex.Prof.A.El-SahnTheLingualAspectTheMesialAspectThegeometricoutlineofthecrownproximallyisroughlyrhomboidalasallmandibularposteriorteeth.Prof.A.El-SahnTheCrownThecrownistiltinglingually

muchmorethananyotherpremolar.So,thetipofthebuccalcuspisnearlycentered

overtheroot.Prof.A.El-SahnTheMesialAspectTheCrownLLThelingualcuspisshorterthanthebuccalcuspbyaboutonethirdofthecrownlength,whichisfromthecervicallinebuccallytothetipofthebuccalcusp.TheCrownTheMesialAspectBProf.A.El-SahnThetipoftheshortlingualcuspisusuallyinline

verticallywiththelingualborderofthecervicalportionoftheroot.Thisdiffersfromtheconditionfoundinmaxillaryposteriorteeth,wherebothbuccalandlingualcusptipsarewellwithintheconfinesoftheroottrunks.Prof.A.El-SahnTheMesialAspectTheCrownThelingualcusp,beingshort(andnarrowmesio-distally)isanonfunctioningcusp.Prof.A.El-SahnTheMesialAspectTheCrownThebuccaloutlineofthecrownisprominentlycurved,thecrestofcurvatureisusuallyjustocclusaltothecervicalline,nearthemiddlethirdofthecrown.Prof.A.El-SahnTheMesialAspectTheCrownThelingualoutlineofthecrownisacurvedoutlineoflessconvexitythanthatofthebuccalsurface.Thecrestofcurvatureisaboutinthecenterofthecrownlengthnotfarfromthetipofthelingualcusp.Prof.A.El-SahnTheMesialAspectTheCrownThelingualsurfaceofthecrownextendslinguallybeyondthelingualsurfaceoftherootduetoextremelingualtiltingofthecrownmakingalingualoverhangabovetherootlingually.Prof.A.El-SahnTheMesialAspectTheCrownThetriangularridgeofthebuccalcuspinclines

sharplyfromthecusptiptowardthecenteroftheocclusalsurface,whilethetriangularridgeofthelingualcuspisshortandisinanearlyhorizontalplane.Prof.A.El-SahnTheMesialAspectTheCrownOcclusalOutlineThemesialmarginalridgeinclinessharplyfromthebuccaltothelingualsurfaceinacervicaldirectionandisnearlyparalleltothetriangularridgeofthebuccalcusp.Prof.A.El-SahnTheMesialAspectTheCrownOcclusalOutlineThemesialmarginalridgeisshorterandusuallylocatedmorecervicallythanisthedistalmarginalridge.Thisistheonlyposteriortoothinwhichthisistrue.Prof.A.El-SahnTheMesialAspectTheCrownOcclusalOutlineDMWhenpresent,themesio-lingualdevelopmentalgroovebetweenthelingualborderofthemesialmarginalridgeandthemesialslopeofthelingualcusp(inthelingualthirdofthecrown).Prof.A.El-SahnTheMesialAspectTheCrownOcclusalOutlineThecervicallineisconvexocclusaIIy.Thecrestofcurvatureiscenteredbucco-linguaIIy.Themesialcurvatureaveragedabout1mm.However,thecervicallinemaybestraightacrossbucco-lingually,andisinamoreocclusalpositionlinguallythanbuccallybyabout2mm.Prof.A.El-SahnTheMesialAspectTheCrownThesurfaceofthecrownmesiallyissmoothexceptforthemesio-lingualgroove.Thesurfaceisconvexatthemesialcontactarea.Prof.A.El-SahnTheMesialAspectTheCrownMorphologyoftheMesialsurfaceImmediatelybelowtheconvexityofthecontactarea,thesurfaceissharplyconcavetillthecervicalline.Themesialcontactareaiscenteredonalinewiththetipofthebuccalcuspandalittleocclusaltothemiddleofthecrownlength.Prof.A.El-SahnTheMesialAspectTheCrownMorphologyoftheMesialsurfaceTheRootThebuccalandlingualsidesoftherootarenearlystraightinthecervicalhalf.Thentherootoutlinetapers

apicallytoabluntapex.Therootapexisinlinewiththetipofthebuccalcusp.Prof.A.El-SahnTheMesialAspectBThemesialsurfaceoftherootissmoothandflatwithalongitudinaldeepdevelopmentalgrooveinthemiddleandapicalthirds.Shallowgroovesmaybeevidence.Prof.A.El-SahnTheMesialAspectTheRootOccasionallytheapicalthirdoftherootmaybedividedintoabuccalandlingual

portionbyadeepdevelopmentalgrooveendinginthebifurcation,i.e.themandibularfirstpremolarwillhaveabifurcatedroot.Prof.A.El-SahnTheMesialAspectTheRootMDProf.A.El-SahnTheCrownTheDistalAspectThegeneralshaperesemblesthatofthemesialaspect.DistalmarginalridgeisThelongerbucco-linguallyandisinamorehorizontalpositionthanthemesialone(itisnearlyatrightangletotheaxisofthetooth).Prof.A.El-SahnTheDistalAspectTheCrownThedistalmarginalridgeishigherormoreocclusallylocatedthanthemesialmarginalridge(whichisauniquecharacteristicofthistooth).DMProf.A.El-SahnTheDistalAspectTheCrownUsuallythereisnodevelopmentalgroovebetweenthedistalmarginalridgeandthedistalslopeofthelingualcusp.Prof.A.El-SahnTheDistalAspectTheCrown?ThecervicallineDistallymaybelesscurvedthanonthemesial.ItmayslopeoccIusallyfrombuccaltolingualasitdidonthemesialbyabout2mm.DMProf.A.El-SahnTheDistalAspectTheCrownThedistalsurfaceofthecrownissmoothlyconvex.Alinearconcavityextendsbucco-linguallyjustabovethecervicalline.Prof.A.El-SahnTheDistalAspectTheCrownThedistalcontactareaisbroaderthanthemesial.Thecenterofthedistalcontactareaisatapointmidwaybetweenbuccalandlingualcrests

ofcurvatureandmidwaybetweenthecervicallineandthetipofthebuccalcusp.Thedistalcontactareaismorelinguallysituated

thanthemesialone.Prof.A.El-SahnTheDistalAspectTheCrownThesurfaceoftherootdistallyshowsmoreconvexitythanmesially.Ashallowdevelopmentaldepressioniscenteredontheroot,whichmaycontainalongitudinaldevelopmentalgroove

lessmarkedthanmesially.MDProf.A.El-SahnTheRootTheDistalAspectUsualdifferencesbetweenthemesialanddistalaspectsThefrequentpresenceofamesio-lingualdevelopmentalgroove.Thedifferenceintheslope,length,andheightofthemarginalridges.Thelongitudinaldevelopmentalgrooveonthemesialsurfaceoftherootismoremarkedthanonthedistalsurface.DMProf.A.El-SahnTheOcclusalAspectTheocclusalaspectsoflowerfirstpremolarshowmuchvariationinthegrossoutline.Becauseoflingualinclinationofthiscrownovertheroot,mostofthebuccalsurfacemaybeseenfromtheocclusalaspect,whereaslittleofthelingualsurfaceisinview.Prof.A.El-SahnTheCrownTheusualoutlineformisroughlydiamond-shaped,orroughlycircular.Prof.A.El-SahnTheOcclusalAspectTheCrownTheproximalsides

convergesharplyfromthecontactareastothecenterofthelingualsurface.Themesialoutlineofthecrownisflatorslightlycurved.Thedistalcrownoutlineismoreconvex.Prof.A.El-SahnTheOcclusalAspectTheCrownLLThecontactareasocclusallyarerepresentedbycurvaturesjustlingualtothebuccallineangles.Theyarerelativelybroad,thedistalareaisbroaderthanthemesialcontactarea.Prof.A.El-SahnTheOcclusalAspectTheCrownThebuccalcuspisverymuchlargerthanthelingualcuspanddominatestheocclusalsurface.Prof.A.El-SahnTheOcclusalAspectTheCrownLBTheocclusalsurfaceshowsalongbuccaltriangularridgeandashortlingualtriangularridge.Prof.A.El-SahnTheOcclusalAspectTheCrownLLBBThetwotriangularridgesoftenuniteandformatransverseridge.Oneachsideofwhichthereisafossa,themesialanddistalocclusalfossae.Prof.A.El-SahnTheOcclusalAspectTheCrownLBSometimesthetransverseridgeiscrossednearthecenteroftheocclusalsurfacebyashallowcentralgroove,whichextendsfromthemesialtothedistalfossa.Prof.A.El-SahnTheOcclusalAspectTheCrownWell-markedmesialanddistalmarginalridgesareseenocclusalIy

boundingthemesialanddistalfossae.Themesialand

distalocclusalfossaearetwodepres