UnitEightOPERATIVEPROCEDURESInthefuturetheneedofoperativedentistrywillbereducedinassociationwiththereductionincariesincidenceandprevalence.However,itisunlikelythatthecariesdiseasewilldisappeartotally.Duetothereducedcariesincidenceandimprovedunderstanding'ofthecariousprocess,thecriteriaforoperativetreatmenthavechangeddramaticallytowardsamoreprophylacticattitudeinrecentyears.Thusoperativetreatmentmaybecometheexceptionratherthantherule.Evenso,patientswhohavenotbeenexposedtoprophylacticmeasuresorpatientswithapreviouslyhighcariesexperiencewillrequireoperativedentistry.Furthermore,traumas,excessiveattrition,abrasionorerosion,cervicalwedgeshapeddefectmaycallforrestorativeprocedures.Becauseoftheintimaterelationbetweenthedentinandthepulpthroughtheodontoblasticprocesses,thesetissuesareconsideredtobeoneorganintheirreactiontocariesandoperativeprocedures.Cariesgenerallyprogressesratherslowly,leavingthedentinandthepulptimetorespondwithmineraldeposition.Theoperativeonthecontraryisacutetraumasandmayassuchbemoredeleterioustothepulpthanthecariousprocess.Inoperativedentistryitisthereforeoftheutmostimportancetosupportthehealingpotentialofthepulpandnottoaddfurtherdamagetothedentin/pulporgan.Differentfactorsmaycontributetopathologicchangesinthedentinandinthepulpwhenrotatinginstrumentsareused.Themainfactorscausingharmfulreactionsare:speed-desiccation-heat-pressure,incombinationwithcuttingtime,depthofthecavityandareaofprepareddentin,Efficientwaterspraykeepingthepreparedareaunderconstantwatercoverhasbeenshowntobecrucialinminimizingpulpaldamage.Manywaterspraynozzlesdonotsecurewetpreparation,partlyduetotheshapeofpreparation,theshapeoftheburortheabrasiveandthequalityandpowerofthewatersprayapplied.Providedthereiseffectivewatersupply,onlyminorpulpalchangescanbeobservedevenincaseswithaveryshortdistancefromthecavitybottomtothepulptissue.Itiswellknownthatdrypreparationismorepainfultothepatientthanwetpreparation.InConclusion:keepingthedentinmoistseemstobeofmajorimportanceillminimizingthehazardsofpulpaldamageduringpreparation.Thisalsoimplyavoidanceofexcessiveairdryingpriortoliningofthecavityorimpressiontaking.Thediscussionconcerningcleaninganddisinfectionofthedentinbeforefillingthecavityorcementingarestorationhasflourishedagaininrecentyears.Theprocedureismeanttodestroybacteriaandtoremovethesmearlayercreatedduringcuttingandgrindingofdentinandenamel.Followingexcavationofcariouslesions,bacteriahavebeenfoundinthedentinin25-50%ofthecases.Thesmearlayerconsistsoforganicandinorganicmaterialandbacteriamaybepresent.Thislayermayinterferewiththeadaptationofthefillingmaterialsandpersistentbacteriamaymultiplyandcausepulpaldamage.Thelayeristhereforeconsideredariskbysomeauthorsandshouldberemoved.Water-spray,hydrogenperoxideandsomecommercialcleansingagentsdonotremovethesmearlayerfromthedentin,whereasanEDTA-solutionremovesitpartly.Thesmearlayermaybetotallyremovedbycitricorphosphoricacid,butsomenegativesideeffectsmayoccur:Thesmallplugsofdebrisinthedentinaltubulesareoftenremoved.Theseplugsmayactasabarrierandshouldthereforenotberemovedintentionally.Demineralizingsolutionsmaywidenthediameterofthedentintubuleopenings,facilitatingthedentinalinvasionofbacteriaortheirmetabolicproductsandtherebyincreasethepathologicpulpchangesfollowingrestoration.Somestrongacidsusedfor60secondsmaybetoxictothepulptissue.Generallythesmearlayermaydecreaseadaptationbetweenfillingmaterialanddentin.Ifthesmearlayerhastoberemoved,aweakEDTA-solutionseemstoremovemostofitwithoutdisturbingtheplugs.Restorativematerials:AmalgamCondensationpressureandhighmercury-andcopper-contenthavebeenofmajorconcernexplainingtheminorpulpalchangesunderunlinedamalgamfillingiswellcondensed,microleakagewilloccurandsomebacteriamaybefoundonthedentinalwallunderunlinedfillings.Themicrospaceisnormallyconsideredtobesealedoffaftersometimebecauseofthedepositionofcorrosionproducts.Thefilling,however,percolatesduringmasticationandheatthuscausinginvasionofbacteriaeveninthepresenceofcorrosionproducts.Butgenerally,amalgamisconsideredratherharmlesstothepulpexceptforproductswithanexcessivehighcoppercontent.Themainreasonforinsulationunderamalgamfillingsshouldthereforebetoprotectthepatientfrompainsensationscausedbythethermalconductivityofthematerial.Allergicortoxicreactionstowardsmercuryorelectrogalvanicreactionshavetobeconsideredbyusingamalgam.Allergicreactionsareveryrare,andsystemictoxicreactionstomercuryfromamalgamfillingsisclaimedtobeimpossible,Oralgalvanismisduetothedifferentelectrochemicalpotentialsofvariousmetals.Directcontactbetweenamalgamandgoldorfollowinginsertionofanewamalgamfillingamongolderfillingsmaycausepainsensation.Thesensationdisappearsnormallyassoonaspassivationofthemetaloccurs.Oralgalvanismhasbeenlinkedtolocalsymptomssuchaswhitelesionsoftheoralmucosa,burningsensations,thetasteofmetal.Andchangesinsecretionofsaliva,aswellasgeneralsymptomssuchaspaininhead,ears,jointsandmusclesaswellasindigestionandsleepingproblems.Thesymptoms,however,aremostoftenshowntohaveotheroriginsasforexampledysfunctionalandpsychogenicdisorders.Glassionomorcement(GIC)Besidescomposites,glassionomercementsaretoday'salternativetosilicatecementasatooth-colouredfillingmaterial.Butincontrasttocompositestheglassionomercementreleasesfluoride,whichininvitrostudieshaveshownacariostaticeffect.Thecementseemslesstoxictothepulpthansilicatecementbutslightlymoretoxicthanzincoxide-eugenolcement.Thelowtoxicityhasbeenassociatedwiththepolacrylicacid.Thisispoorlydissociatedanddiffusionintodentinaltubulesisrestrictedbyhighmolecularweightandentanglementofpolymerchains.Releaseoffluorideinrelationtotoxicityhasnotbeeninvestigated.Thefillingmaterialreactswithenamelanddentintoformphysico-chemicaladhesion.Therearesomedisagreementsaboutthepresenceofbacteriabeneathglassionomercementfillingsandattentionshouldbedrawntotherelativelyhighfailureratereportedinclinicaltrials,whichindicatemanipulativeandadhesiveproblems.CompositesAccordingtosomestudiesthedifferentcomponentsofcompositesaremoreorlessharmlesstothepulptissuesalthoughunlinedcompositefillingshavebeenshowntobetoxic.Thepolymerizationofcompositesisanincompletereactionandalaterdecompositionandformationoftoxicproductsmaygiverisetopathologicalchangesinthepulp.Moreover,bacteriabeneathcompositefillingsareanimportantfactorinelicitingpulpaldamage.Theacidetchtechniquereducesmicroleakage,providedtheenamelispresentallaroundthecavitymargin.However,thisisoftennotthecaseintheclinicalsituation.Invivostudieshavefurthermoreshownacombinationofaddetchingandanintermediateresinlayertobeinsufficientinthetotalpreventionofmarginalleakage.Atpresent,agreatdealofresearchisdevotedtothedevelopmentofchemicals,whichmaymediateachemicalbondingbetweenthecompositeresinandthetoothstructure.Severalfactorshavetobeconsideredinevaluatingthelong-termresultsoftheseefforts,suchasforexamplepolymerizationcontractioninrelationtohygroscopicexpansion,cavosurfacedesign,cracksintheenamel,deformationofthecavitiesduringmastication,andpracticaldifficultieswiththeclinicalprocedures.VOCABULARYl.operativedentistry牙體外科學2.cariesincidence齲增長率3.traumas創傷、外傷4.abrasion磨損5.wedge-shapeddefect楔狀缺損6.dentin牙本質7.odontoblasticprocesses造牙本質細胞突8.cavitypreparation窩洞預備9.cutting切割10.bur鉆針11.cavitylining窩洞襯墊12.impressiontaking取印模13.excavator挖匙挖器14.filling充填15.plugs拴，塞16.adaptation適合性17.amalgam銀汞合金18.microleakage微漏19.microspace微隙20.percolation滲透(作用)21.mercury汞22.galvanism流電反應23.whitelesions白色病損24.glassionomercement(GIC)玻璃離子水門汀25.composites復合樹脂26.polymerization聚合反應27.acidetchtechnique酸蝕技術28.marginalleakage邊緣滲漏29.cavosurface洞斜面30.invitro離體，體外31.operativetreatment牙體(手術)治療32.cariostatic抑齲的33.excesseveattrition過度磨耗34.erosion酸蝕35.dentinaltubules牙本質小管36.pulp牙髓37.thedentin/pulporgan牙本質牙髓官(complex)牙本質牙髓復合體38.rotatinginstrument轉磨器械39.waterspray噴霧水40.abrasive