国外口腔解剖乳牙.ppt

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1、THEDECIDUOUSDENTITIONINTRODUCTIONTheworddeciduouscomesfromaLatinwordmeaningtofalloff.Deciduousteethfallofforareshedlikeleavesfromadeciduoustree.Thedeciduous,primary,or,astheyoftenreferredtocolloquially,(MILK)teeth,havearelativelyshortlife-spanbeforetheyexfoliatedtobereplacedb

2、ythepermanentteeth.Thisusuallyoccursbetweentheagesof6and13years.Thedeciduousincisorsandcanineshavepermanentsuccessorbutthefirstandseconddeciduousmolarsarereplacedbythefirstandsecondpremolarsrespectively.Thedeciduousdentitioncomprisesfewerteeththanthepermanentdentitionwithatot

3、alofTENmaxillaryandTENmandibularteeth.Theyareasfollows,inorderofpositionfromthemidline:A-First(central)incisor.B-Second(lateral)incisor.C-Canine.D-Firstmolar.BCDEAE-Secondmolar.Theshorthandformulaforthedeciduousteethisasfollows:I2C1M2=10212GENERALCHARACTERISTICSThedeciduouste

4、ethgenerallyhaveseveralimportantdifferencesinmorphology,composition,sizecolouraslistedbelow:1-Thedeciduousteetharesmallerthanthepermanentteeth.PRINCIPALDIFFERENCESBETWEENDECIDUOUSANDPERMANENTTEETHPRINCIPALDIFFERENCESBETWEENDECIDUOUSANDPERMANENTTEETH2-Theenamelofthedeciduouste

5、ethiswhiterandmoreopaque,whichgivesthecrownalightercolourthanthatofthepermanentteeth.3-Theenamelofthedeciduousteethismorepermeableandmoreeasilyworndown.Thedegreeofpermeabilityislessenedafterthestartofrootresorption.PRINCIPALDIFFERENCESBETWEENDECIDUOUSANDPERMANENTTEETH4-TheDEP

6、THOFENAMELismoreconsistentandthinnerthaninthepermanentteeth,beingfrom0.5mmto1.00mmthick.PRINCIPALDIFFERENCESBETWEENDECIDUOUSTEETHANDPERMANENTTEETH5-Deciduousteethhaveapronouncedcervicalmargin.Theenamelbulges,insteadoftaperinggently,atthecemento-enamljunction,whichisstraighter

7、thaninthepermanentteeth.Thiscervicalbulgeisaccentuatedinthemesiobuccalareaofdeciduousmolars.PRINCIPALDIFFERENCESBETWEENDECIDUOUSANDPERMANENTTEETH6-Innewlyerupteddeciduousteeth,thecuspstendtobemorepointed.PRINCIPALDIFFERENCESBETWEENDECIDUOUSANDPERMANENTTEETH7-Therootsofthedeci

8、duousteethareshorter,lessstrongandlighterincolourthanthoseoftheperma