文案综合二讲课pathway 10

PathwayofthePathwayofthePulp10thEdition第二后，医生应该评估是否此时直线通图。7-45镍钛锉器械分离。因为Straight-lineaccessAfterthelingualshoulderhasbeenremovedandtheorifice(s)flared,theclinicianmustdeterminewhetherstraight-lineaccesshasbeenachieved.Ideally,anendodonticfilecanapproachtheapicalforamenorthefirstpointofcanalcurvatureun-deflected.Unnecessarydeflectionofthefilecanresultinnumerousconsequencesrelatedtolossofinstrumentcontrol.Deflectedinstrumentsfunctionundermorestressthanun-deflectedinstrumentsandaremoresusceptibletoseparationduringtheshapingandcleaningprocess(Fig.7-FIG.7-45Separationofarotaryendodonticinstrumentasaresultofunder-extendedaccesspreparationratherthancanalbinding.键部位的通道，会影响成型和清洗作，容易形成台阶，偏移和尖部被键部位的通道，会影响成型和清洗作，容易形成台阶，偏移和尖部被如图7-46不合适的通道预备。方向，型成了台阶。外壁被过度预备了，并形成了拉直Deflectedinstrumentsalsolackaccesstocriticalareasofthecanalandthereforedonotshapeandcleaneffectively.Attemptstoshapeandcleanwithoutstraight-lineaccessoftenleadtoproceduralerrorssuchasledging,transportation,andzipping(Fig.7-46).FIG.7-46Inadequateaccesspreparation.Thelingualshoulderwasnotremoved,andincisalextensionisincomplete.Thefilehasbeguntodeviatefromthecanalintheapicalregion,creatingaledge.Aledgeisaniatrogenicallycreatedrootcanalwallirregularitythatmayimpedeplacementofanintra-canalinstrumenttotheapex.Transportationoccursintheportionofthecanalapicaltoacurvaturewhencanalwallstructureoppositethecurveisremoved,tendingtostraightenthecanalcurvature.Zipping,orellipticationoftheapicalforamen,occurswhenanoverextendedfiletransportstheouterwalloftheapicalforamen.Conversely,un-deflectedinstrumentsprovidebettertactilesensation,whichisnecessaryfor“feeling”thecanalanatomyand的锉（初尖锉）无压迫地到达根尖孔或者第一个弯曲时，锉针在根管的锉（初尖锉）无压迫地到达根尖孔或者第一个弯曲时，锉针在根管以获得直线如路。如图7-47所示。图7-47A,部分牙本质的舌侧肩和清洗。B.舌侧肩全部去除后，得“feeling”howthefileisperformingintherootcanalsystem.Straight-lineaccessisevaluatedbyinsertingintothecanalthelargestfilethatfitspassivelytotheapicalforamenorthepointofthefirstcanalcurvature.Thisinternallengthcanbedeterminedbymeasuringadiagnosticpretreatmentperiapicalradiograph.Thefileisinsertedgentlyandwithdrawnastheclinician“feels”forcanalbindingordeflection.Ifdeflectionisdetected,theclinicianmustreevaluatetheadequacyoflingualshoulderremovalbeforechangingtheincisaledgepositionoftheaccesspreparation.Inadequateremovalofthelingualshouldercausesthefiletodeflectinafacialdirection,andaninexperiencedclinicianmayoverextendtheincisaledgeoftheaccesspreparationinanattempttoachievestraight-lineaccess(Fig.7-47).FIG.7-47A,Thelingualledgeofdentinremains,deflectingthefiletowardthelabialwall.Asaresult,portionsofthelingualcanalwallwillnotbeshapedandcleaned.B,removalofthelingualledgeresultsinstraight-line如图7-14所示。Visualinspection如图7-14所示。VisualinspectionoftheaccessTheclinicianshouldinspectandevaluatetheaccesscavity,usingappropriatemagnificationandillumination.Althoughthiscanbedoneduringanystageofthepreparation,itshouldalwaysbedoneatthispoint.Theaxialwallsattheirjunctionwiththeorificemustbeinspectedforgroovesthatmightindicateanadditionalcanal.Theorificeandcoronalcanalmustbeevaluatedforabifurcation(seeFig.7-14).RefinementandsmoothingofrestorativemarginsThefinalstepinthepreparation继续向切端预敞，直到锉能站直。Ifthelingualshoulderhasbeenadequatelyremovedandthefilestillbindsontheincisaledge,theaccesscavityshouldbeextendedfartherincisallyuntilthefileisnotdeflected.Thefinalpositionoftheincisalwalloftheaccesscavityisdeterminedbytwofactors:(1)completeremovalofthepulphornsand(2)straight-lineaccess.咬合力过大时，容易形成冠部的渗anaccesscavityistorefineandsmooththecavosurfacemargins.Roughorirregularmarginscancontributetocoronalleakagethroughapermanentortemporaryrestoration.Properrestorativemarginsareimportantbecauseanteriorteethmaynotrequireacrownasthefinalrestoration.Definite,smoothcavosurfacemarginsallowthecliniciantoplaceandfinishacompositeresinfinalrestorationwiththeprecisionnecessarytominimizecoronalleakage.Suchleakagecouldjeopardizethesuccessoftherootcanalprocedure.Anotherfactortheclinicianmustconsiderwhenfinalizingtheaccessmarginsofamaxillaryanteriortoothisthatthefinalcompositeresinrestorationwillbeplacedonafunctionaltoothsurface.Theincisaledgesofthemandibularanteriorteethslideoverthesemaxillarylingualsurfacesduringexcursivejawmovement.Thereforetherestorativemarginsofmaxillaryanteriorteethshouldbecreatedtoallowabulkofmaterialatthemargin.Buttjointmarginsareindicatedratherthanbeveledmargins,whichproducethincompositeedgesthatcanfractureunderexcursivefunctionalloadsandultimatelyresultincoronalleakage.Obviously,iftheanteriortoothrequiresacrownasthefinalrestoration,theaccesscavosurfacemarginbecomesalesscriticalfactor.、Removalof、RemovalofCariesandPermanentThediscussionofcariesandpermanentrestorationremovalpresentedintheprevioussection,AnteriorAccessCavityPreparations,appliesequallytoposteriorteeth.Posteriorteethrequiringrootcanaltherapytypicallyhavebeenheavilyrestoredorthecariousprocessisextensive.Suchconditions,alongwiththecomplexpulpanatomyofposteriorteeth,canmaketheaccessprocesschallenging.但是也有很多区别，值得单独的讨PosteriorAccessCavityTheprocessofpreparingaccesscavitiesonposteriorteethissimilartothatforanteriorteeth,butenoughdifferencesexisttowarrantaseparatediscussionIndividualanteriorPleaseseethefiguresinthesectionMorphologyandAccessCavityPreparationsforIndividualTeeth,laterinthechapter.颗完好的牙齿，开髓的位置必须认真思考。如图7-48所示，上前磨牙而如图7-49，由于下前磨牙的冠面要适当进行补偿性调整（图7-InitialexternaloutlineTheremovalofcariesandexistingrestorationsoftenaccomplishesthecreationofaninitialexternaloutlineform.Aswithanteriorteeth,thepulpchamberofposteriorteethispositionedinthecenterofthetoothattheleveloftheaccessstartinglocationmustbedeterminedforanintacttooth.Inmaxillarypremolarsthispointisonthecentralgroovebetweenthecusptips(Fig.FIG.7-48A,Startinglocationforaccesstothemaxillarypremolar(X).B,Initialoutlineform(darkarea)andprojectedfinaloutlineform(dashedline).B,Buccal;L,lingual.Crownsofmandibularpremolarsaretiltedlinguallyrelativetotheirroots(Fig.7-49),andthestartinglocationmustbeadjustedtocompensateforthistilt(Fig.7-50).7-49下前磨牙的冠沿牙根的纵轴7-49下前磨牙的冠沿牙根的纵轴7-A下颌第一前磨牙通道口位置B下颌第一前磨牙通道口位置C下颌第二前磨牙通道口位置D下颌第二前磨牙通道口位置FIG.7-49Thecrownofamandibularpremolaristiltedlinguallyrelativetotheroot.B,Buccal;L,lingual.FIG.7-A,Mandibularfirstpremolarandaccessstartinglocation(X)(occlusalview).B,Mandibularfirstpremolarandstartinglocation(proximalview).C,Mandibularsecondpremolarandaccessstartinglocation(X)(occlusalview).D,Mandibularsecondpremolarandstartinglocation(proximalview).B,Buccal;DL,distolingual;L,lingual;ML,mesiolingual.牙因为向舌侧倾斜的角度较小，所7-51所示，为了决定磨牙Inmandibularfirstpremolarsthestartinglocationishalfwayupthelingualinclineofthebuccalcusponalineconnectingthecusptips.Mandibularsecondpremolarsrequirelessofanadjustmentbecausetheyhavelesslingualinclination.ThestartinglocationforthistoothisonethirdthewayupthelingualinclineofthebuccalcusponalineconnectingthebuccalcusptipandthelingualgroovebetweenthelingualcuspsTodeterminethestartinglocationformolaraccesscavitypreparations,theclinicianmustestablishthemesialanddistalboundarylimitations(Fig.7-51).Evaluationofbite-wingradiographsisanaccuratemethodofassessingthemesiodistalextensionsofthepulpchamber.Themesialboundaryforboththemaxillaryandmandibularmolarsisalineconnectingthemesialcusptips.Rarelyarepulpchambersfoundmesialtothisimaginaryline.Agoodinitialdistalboundaryformaxillarymolarsistheobliqueridge.Formandibularmolarstheinitialdistalboundaryisalineconnectingthebuccalandlingualgrooves.Formolarsthecorrectstartinglocationisonthecentralgroovehalfwaybetweenthemesialanddistalboundaries.7-A7-A上磨牙的髓室近远中边界和开B下磨牙的髓室近远中边界和开FIG.7-51A,Mesialanddistalboundaryofamaxillarymolarshowingtheaccessstartinglocation(X).B,Mesialanddistalboundaryofamandibularmolarshowingtheaccessstartinglocation(X).D,Distal;M,mesial;MB,mesiobuccal;ML,PenetrationofthepulpchamberContinuingwiththesameroundortaperedfissurebur,theclinicianchangestheangleofpenetrationfromperpendiculartotheocclusaltabletoanangleappropriateforpenetrationthroughtheroofofthepulpchamber.Inpremolarstheangleisparalleltothelongaxisoftheroot(s)bothinthemesiodistalandbuccolingualdirections.Failuretoanalyzethispenetrationanglecarefully2号球钻，磨牙用号球钻，打穿牙釉质并穿透牙本质1毫米左右，然后改用带锥度的裂做到最终大小的一半或者四分之三管的开口形状为菱形。无论如何，口的实际位置之前，髓腔轮廓暂时Penetrationthroughtheenamelintothedentin(approximately1mm)isperformedwitha#2roundburforpremolarsanda#4roundburformolars.Ataperedfissureburmaybeusedinsteadofroundburs.Theburisdirectedperpendiculartotheocclusaltable,andaninitialoutlineshapeiscreatedataboutonehalftothreefourthsitsprojectedfinalsize.Thepremolarshapeisovalandwidestinthebuccolingualdimension.Themolarshapeisalsoovalinitially;itiswidestinabuccolingualdimensionformaxillarymolarsandinamesiodistaldirectionformandibularmolars.Thefinaloutlineshapeformolarsistriangular(forthreecanals)orrhomboid(forfourcanals);however,thecanalorificesdictatethepositionofthecornersofthesegeometricshapes.Therefore,untiltheorificeshavebeenlocated,theinitialoutlineformshouldbeleftasanoval.7-52上磨牙的开髓角度朝向最大的根管口（腭侧）有感受到落空感，医生应该立即停canresultingougingorperforationbecausepremolarrootsoftenaretiltedrelativetotheocclusalplane.Inmolarsthepenetrationangleshouldbetowardthelargestcanal,becausethepulpchamberspaceusuallyislargestjustocclusaltotheorificeofthiscanal.Therefore,inmaxillarymolarsthepenetrationangleistowardthepalatalorifice,andinmandibularmolarsitistowardthedistalorifice(Fig.7-FIG.7-52Angleofpenetrationtowardthelargestcanal(palatal)inamaxillarymolar.B,Buccal;P,palatal.Aswithanteriorteeth,penetrationislimitedtothedistancemeasuredonapretreatmentradiographtojustpenetratetheroofofthepulpchamber.Ifthedrop-ineffectisnotfeltatthisdepth,theclinicianshouldcarefullyevaluatetheangleofpenetrationbeforedrillingdeeper.Inmulti-rootedposteriorteeth,theclinicianmustguardagainstlateralandfurcationperforations.Aggressiveprobingwithanendodonticexploreroftencanhelplocatethepulpchamber.A、BDGG钻去牙本质肩领/安全车针修边CompleteroofAroundbur,ataperedfissurebur,orasafety-tipdiamondorcarbideburisusedtoremovetheroofofthepulpchambercompletely,includingallpulphorns(Fig.7-53,AandB).Visibilityproblemscausedbyvitalpulphemorrhageshouldbehandledasdescribedintheprevioussectionforanteriorteeth(seeAnteriorAccessCavityPreparations).Thegoalistofunnelthecornersoftheaccesscavitydirectlyintotheorifices,andasafety-tipdiamondorcarbideburperformsthistasknicely;itcanbesetonthepulpfloorandtheentireaxialwallshapedatonetimewithlittlechanceofgouging(Fig.7-54).Thesafety-tipdiamondorcarbideburispassedbetweentheori-ficesalongtheaxialwallstoremovetheroof,tapertheinternalwalls,andcreatethedesiredexternaloutlineshapeFIG.7-53A,Pulproof/pulphornremoval.Theroundburhooksunderthelipofthepulphorn.B,Theburisrotatedandwithdrawninanocclusaldirectiontoremovethelip.C,removalofacervicaldentinbulge.AGates-Gliddenburisplacedjustapicaltotheorificeandwithdrawninadistoocclusaldirection.D,Asafety-tiptapereddiamondburisusedtoblendandfunneltheaxialwallfromthecavosurfacemargintotheorifice.7-557-55所示，部分根管口从IdentificationofallcanalInposteriorteethwithmultiplecanals,thecanalorificesplayanimportantroleindeterminingthefinalextensionsoftheexternaloutlineformoftheaccesscavity.Ideally,theorificesarelocatedatthecornersofthefinalpreparationtofacilitatetheshapingandcleaningprocess.Internally,theaccesscavityshouldhaveallorificespositionedentirelyonthepulpfloorandshouldnotextendintoanaxialwall.Extensionofanorificeintotheaxialwallcreatesamouseholeeffect(Fig.7-55),whichindicatesinternalunderextensionandimpedesstraight-lineaccess.Insuchcasestheorificemustberepositionedontothepulpfloorwithoutinterferencefromaxial FIG.7-54Safety-tipcarbideburisusedtoshapetheaxialwallinoneplanefromtheorificetothecavosurfacemargin.B,Buccal;P,palatal.FIG.7-55AFIG.7-55AMouseholeeffectcausedbyextensionoftheorificeintotheaxialwall.OrificethatliescompletelyonthepulpB该使用安全车针或者GG钻来去7-53C,DRemovalofthecervicaldentinbulgesorificeandcoronalInanteriorteeththelingualshoulderistheinternalanatomicstructurethatmustberemovedasanimpedimenttostraightlineaccess.Inposteriorteeththeinternalimpedimentsarethecervicaldentinbulgesandthenaturalcoronalcanalconstriction.Thecervicalbulgesareshelvesofdentinthatfrequentlyoverhangorificesinposteriorteeth,restrictingaccessintorootcanalsandaccentuatingexistingcanalcurvatures.Thesebulgescanberemovedwithsafety-tipdiamondorcarbidebursorGates-Gliddenburs.Theinstrumentsshouldbeplacedattheorificeleveland在牙本质凸起被去除之后，用GG在牙本质凸起被去除之后，用GG预敞。使用GG钻时，向根分叉相反操作。另一个选项就是使用10%或者12%锥度的机用镍钛开口锉预敞根管口。预敞后的根管口，需要有7-56从髓室通道向下滑的时候，不会遭leanedtowardthedentinbulgetoremovetheoverhangingshelf(seeFig.7-53,CandD).access.Insuchcasestheorificemustberepositionedontothepulpfloorwithoutinterferencefromaxialwalls.Aftertheshelfhasbeenremoved,theorificeandconstrictedcoronalportionofthecanalcanbeflaredwithGatesGliddenburs,whichareusedinasweepingupwardmotionwithlateralpressureawayfromthefurcation.Analternativemethodistousea#.10or#.12taperedengine-drivennickel–titaniumfiletoestablishtheuppercanalshape.Astheorificeisenlarged,itshouldbetaperedandblendedintotheaxialwallsothatthecliniciancanslidefromthecorneroftheexternaloutlineformdowntheaxialwallintotheorificewithoutencounteringanyobstructions(Fig.7-56)FIG.7-57AfiberopticlightFIG.7-57Afiberopticlightcanappliedtothecervicalaspectofthecrowntohelpobtainmaximalvisibilitywithmagnification.Trans-illuminationoftenrevealslandmarksotherwiseinvisibletotheunaidedeye.7-57光纤光源投射到牙颈部位VisualinspectionofthepulpchamberPleaserefertotheearliersectionunderAnteriorAccessCavityPreparations;andFig.7-57.Straight-lineaccessAswithanteriorteeth,straight-lineaccessisparamounttosuccessfulshaping.Filesmusthaveunimpededaccesstotheapicalforamenorthefirstpointofcanalcurvaturetoperformproperlyduringshapingandcleaning.Theclinicianmustassesseachcanalforstraight-lineaccessandmakealladjustmentsnecessarytoachievethisgoal(seeFig.7-56,O).挑战髓腔通道预备：CHALLENGING挑战髓腔通道预备：CHALLENGINGACCESSTeethwithminimalornoclinicalSeveralfactorscancausethelossofasignificantportionofatooth’sclinicalcrown.Cariesleftuntreatedcancauselossofcoronaltoothstructure.Badlydecayedteethtypicallycanfractureunderocclusalfunctionbecauseoftheunderminedandunsupportedremainingtoothstructure.Similarly,teeththathavebeenheavilyrestoredwithamalgam,compositeresin,orglassionomerrestorativematerialscanhaveminimalcoronaltoothstructure.individualposteriorPleaseseethefiguresinthesectionMorphologyandAccessCavityPreparationsforIndividualTeeth,laterinthechapter.RefinementandsmoothingoftherestorativemarginsInbothtemporaryandinterimpermanentrestorations,therestorativemarginsshouldberefinedandsmoothedtominimizethepotentialforcoronalleakage.Thefinalpermanentrestorationofchoiceforposteriorteeththathaveundergonerootcanaltherapyisacrownoronlay.7-58所示。髓7-59所Xrestorativematerialsprovidenoextra-coronalsupportforthetooth,andthefillingscanfalloutduringocclusalfunction,leavinglittleornoclinicalcrownremaining.Externaltraumacancausetheclinicalcrowntofracture,sometimesshearingofftothefreegingivalmargin.Creatinganaccesscavityonatoothwithlittleornoclinicalcrownmightseemtobeasimpleprocedure.Inyoungteeth,traumaticfracturesoftenexposethepulpchamber,makingpreparationeasy.However,inolderteeththathavehadcariesorlargerestorations,thepulpchamberstypicallyhaverecededorcalcified.Lossofsignificantcoronalanatomytoguidepenetrationanglescanmakeaccessquitedifficult.Beforebeginninganaccesscavityontheseteeth,theclinicianshouldstudytheirrootangulationonpretreatmentradiographsandexaminethecervicalcrownanatomywithanexplorer(Fig.7-58).PulpchambersarelocatedatthecenterofthecrownattheleveloftheCEJ.Accessoftenisstartedwithoutadentaldaminplacesothatrooteminencescanbevisualizedandpalpatedasaccessisattempted(Fig.7-59).Becausetheexternalrootanatomyisformedbyodontoblastsinthepulp,byvisualizingtherootanatomybothradiographicallyandclinically,theclinicianshouldhaveagoodideaofaccesspenetrationangles.EveryeffortismadetostaycenteredwithintherootforFIG.7-58TheFIG.7-58Thecervicalareaofthetoothexploredbeforeaccessis7-58向在近远中方向上有了偏差，再转角拍片，看是否在颊舌向有偏差。观察了这两张片子后，如果发现偏橡皮障，按照前面所述的操作指thebestchanceoflocatingthepulpcanal.Thedepthofpenetrationneededtoreachthepulpcanalismeasuredonapretreatmentradiograph.Iftheclinicianreachesthisdepthwithoutlocatingthecanal,tworadiographsshouldbetakenbeforetheprocessproceeds.Astraight-onradiographshowswhetherthepreparationisdeviatinginamesialordistaldirection.Applyingthebuccal-objectrule,anangledradiographshowsabuccalorlingualdeviationinpenetration.Aftercheckingtheseradiographs,thecliniciancanredirectthepenetrationangleifnecessaryandmovethepreparationapically.Assoonasthepulpcanalisidentified,thedentaldammustbeplacedandtheaccesspreparationfinalized,usingtheguidelinesdiscussedearlierinthisFIG.7-59FIG.7-59Accesspreparationwhentheanatomiccrownismissing.A,Amandibularfirstpremolarwiththecrownmissing.B,Anendodonticexplorerfailstopenetratethecalcifiedpulpchamber.C,Along-shankroundburisdirectedintheassumedlongaxisoftheroot.D,Perforationoftherootwall(arrow),resultingfromtheclinician’sfailuretoconsiderrootangulation.E,Palpationofthebuccalrootanatomywithoutadentaldaminplacetodeterminerootangulation.F,Correctburangulationafterrepairoftheperforationwithmineraltrioxideaggregate(MTA;DENTSPLYTulsaDentalSpecialties,Tulsa,OK).Thedentaldamisplacedassoonasthecanalisidentified.重度修复的的牙齿（包括瓷贴面重度修复的的牙齿（包括瓷贴面全冠，很少会精确复制牙冠的固有形的时候，冠-根角度通常也会变化。如图7-60所示正常进入牙齿内部，造成髓室通道预备的视线极差。所有这些因素，单独图7-57光纤光源的透光照明，可以帮HeavilyRestoredTeeth(IncludingThoseWithFullVeneerCrowns)Restorativematerialsoftenaltertheexternalanatomiclandmarksonthecrownofatooth,makingaccesspreparationdifficult.restorativematerialsandfullcrownsrarelyreproducetheoriginaltoothanatomyintheexactsameposition.Thecrown-to-rootangulationoftenisalteredwhenlargerestorationsorcrownscorrectocclusaldiscrepancies(Fig.7-60).FIG.7-60Accesscavityerrorresultingfromalterationoftheoriginaltoothcontoursbyafullveneercrown.A,Originalcrowncontourofthetooth.B,Afullveneercrownisusedtochangetheoriginalcrowncontourforestheticpurposes.C,AccessperforationresultingfromrelianceonthefullveneercrowncontourratherthanthelongaxisoftheBC,依据瓷贴面的形状（没有依据牙根方向）开髓，导致了侧穿Mostrestorativematerialsblockthepassageoflightintotheinternalaspectsofthetooth,resultinginpoorvisibilityduringpreparationoftheaccesscavity.Allthesefactors,singlyortogether,complicatethe大块的修复体。（如图7-61）大块的修复体。（如图7-61）preparationofaccesscavitiesonheavilyrestoredteeth.TheDOMandtransilluminationofthecervicalareaofaheavilyrestoredtoothcangreatlyimprovevisibilityandreveallandmarksthatotherwisewouldbemissed(seeFig.7-57).Inmostcases,completeremovaloflargerestorationsisthewisestcourse(Fig.7-61).7-A7-A需要根管治疗的重度修复的第二上磨B，FIG.7-61A,Inaheavilyrestoredmaxillarysecondmolarthatrequiresrootcanaltherapy,theclinicianmayattemptaccesstothecanals.Pretreatmentradiographsdemonstratethreeimportantfactors:(1)areinforcingpinisinplace(arrow);(2)atleasttwothirdsofthecoronalportionisrestorativematerial;and(3)themesiobuccalcanalappearscalcified(arrow).Thesefactorssuggestcompleteexcavation.B,Apatientmayaskthecliniciantoattemptanunexcavatedsearchforthecanals;thismayresultinafurcalperforation,C,C,更安全保守的方法是去除银汞合D,医生可以更顺畅地进行根管治疗，有。去除这些修复体，可以帮助医生性会增加40%。良好的视线，也可以到根管中。（7-74D）。完全去除compromisingtheprognosis.Insuchcasesthepatientshouldbeengagedinthedecisiontocontinuetreatment,whichunquestionablyinvolvesremovaloftheexistingrestoration.C,Asafer,moreconservativeapproachistoremovetheamalgam,thepin,andanyoldcements.Carefulexcavation,usingenhancedvision,resultsinaccesstothepulpchamber.D,Thecliniciannowcanperformsoundrootcanaltherapy,followedbyinternalreinforcementandfullcoverage.Theserestorationsoftenhaveleaky,defectivemarginsorrecurrentcariesorboth.Removingtherestorationallowstheclinicianbettervisibilityoftheinternalanatomicstructuresthroughdirectvisualizationandincreasedlightpenetration.Withincreasedvisibilitythecliniciancancheckforrecurrentcariesandfracturelinesonthepulpchamberwallsorfloor.Asstatedearlierinastudy,cliniciansare40%morelikelynottodetecttheseanomalieswhenrestorationsarenotremovedcompletely.Bettervisibilityalsomakeslocatingrecededorcalcifiedcanalseasier.Coronalleakageoftenoccurswhenpartsoflargerestorationsareleftinthetoothbecausetherestorationsareloosenedbythevibrationoftheaccessdrilling.Anotherreasontoremovetheserestorationremnantscompletelyistopreventpiecesoftherestorativematerialfromfallingintotherootcanal.Instrumentscanrubagainstrestorationfragmentsduringshapingandcleaning,creatingfilingsthatcanbecarriedintothecanalsystem(seeFig.7-74,D).Completeremovalpreventstheseproblems.管。例如，第五类洞冲天修复经常引管。例如，第五类洞冲天修复经常引62所示，剩余的根管部分都可以通过7-A根面龋和牙周病引起的钙化情况下，进行的第五类修复B,钙化的根管口阻碍进入根管。从颊Completeremovalofanextensiverestorationfromthecervicalregionofthetoothpermitsmoredirectaccesstotherootcanal(s).Forexample,classVrestorationsoftencausecalcificationofthecoronalcanal,makinglocationofthecanalthroughtheocclusalapproachquitedifficult.removaloftheclassVrestorationallowsmoredirectaccesstothecalcifiedcanal,whichmakeslocationandtreatmentmucheasier.Anyremainingcanalscanbetreatedthroughtheconventionalocclusalaccesscavity(Fig.7-62).FIG.7-62A,ExtensiveclassVrestorationnecessitatedbyrootcariesandperiodontaldiseasethatledtocanalcalcification(arrow).B,Accesstothecanalisoccludedbycalcification.removalofthefacialrestorationmayberequiredtoobtainaccessfromthebuccalsurface.Whenanextensiverestorationisafullorpartialveneercrown,therestorationmustbeevaluatedthoroughly.Ifanyconcernsariseaboutrecurrentdecayorleakymargins,the住髓室。此时，只能靠医生全神贯开髓。金刚砂球钻也许好用，但是混可能导致瓷裂。如图7-63crownshouldberemovedbeforetheaccesscavityisprepared.Removalofthecrownallowseliminationofallrecurrentcariesandimprovesthevisibilityofthepulpspaces.Creationofanaccessthroughanintactfullorpartialveneercrownshouldbedonewithcaution.Whensuchrestorationsareplaced,theyoftenchangethecrown-to-rootangulationtocorrectpre-existingocclusaldiscrepancies.Fullveneercrownsalsocanaltertoothrotation.Boththesesituationsmakethepreparationofaccesscavitieschallenging.Pretreatmentradiographscanbehelpful,butthemetalinthefullveneercrownoftenmaskstheunderlyingpulpchamber.Inthesesituationstheclinician’sbestapproachistostayascenteredinthetoothaspossible,usingallavailableclinicalandradiographicinformation.TheDOMandtransilluminationoftheCEJarevaluableaidesinthisprocess.Metalveneercrownsarebestpenetratedwithnew,sharpcarbideburs.Roundbursworkwell,buttungstencarbidetransmetalbursaremoreefficient.Thesecrosscutfissurebursarespecificallydesignedtocutthroughmetalrestorativematerials.Porcelainorceramometalrestorationsmustbehandleddelicatelytominimizethepotentialforfracture.Theclinicianshouldusearounddiamondburandcopiouswaterspraytopenetratetheporcelain.Afterporcelainpenetration,atransmetalburandcopiouswatersprayshouldbeusedtopenetratethemetalcoping;thewatersprayminimizesheatbuildup,whichcouldfracturetheporcelain(Fig.7-63).A,B,在用金刚砂球钻预备出初始开髓口后，改用钨钢合金裂钻切割金属层C,建立直线通道，保证器械可以直接,循。在完成髓室通道的时候，医生应洗，并使全冠就位。FIG.7-63Accesscavitypreparationthroughaceramometalcrown.A,Arounddiamondburisusedtopenetratetheporcelain.B,Aftertheaccessoutlinehasbeenmadewiththerounddiamondbur,atransmetalburisusedtocutthroughthemetal.C,Preparedaccesscavity,whichallowsadirectapproachtothecanals.D,TestfilescanbeplacedontheaccesscavitywallswithoutimpingementManyclinicianstendtobetooconservativewhenpreparinganaccesscavitythroughaveneercrown.Anattempttosavethecrownoftenleadstoanunder-extendedpreparation.Alltheguidelinesforaccesscavitypreparationsdiscussedearliermustbefollowed.Whenthepreparationiscomplete,theclinicianshouldsearchthemarginsandinternalspacesforcaries,leakage,andfractures.Ifnoproblemsarediscovered,theclinicianmayproceedwithshapingandcleaning,leavingthefullveneercrowninplace.钙钙的全部或者局部钙化。如图7-64所和老化）经常会引起根管系统的狭窄。在根管通向根尖的方向，钙化程存在，并且应该全部被预备，冲洗，充填直至根尖。7-64有临床症状（冷热过敏和酸甜过敏）的术前片。第一下磨牙没有进行根管治疗，因为牙髓测试有活力。TeethWithCalcifiedApretreatmentradiograph(Figs.7-64and7-65)oftenappearstorevealtotalornearlytotalcal