專業(yè)英語(yǔ) Unit 33教案.docx

UnitThirtyThreeTypesofbridgeTheappliancesusedtoreplacemissingteethweredefinedinChapter7.Someofthetermsusedinbridgeworkarcalsousedinrelationtopartialdentures.Anabutmentisatoothtowhichabridge(ofpartialdenture)isattached. Aretainerisacrownorotherrastorationthatiscementedtotheabutment.Thetermsretainerandabutmentshouldnotbeconfusedorusedinterchangeably. Aponticisanartificialtoothaspartofabridge. Aspanisthespacebetweennaturalteeththatistobefilledbythebridge. Thesaddleistheareaoftheedentulousridgeoverwhichtheponticwilllie. Apierisanabutmenttoothstandingbetweenandsupportingtwopontics.Eachponticbeingattachedtoafurtherabutmenttooth. Aunit,whenappliedtobridgework,meanseitheraretainerorapontic.Abridgewithtworetainersandoneponticwouldthereforebeathree-unitbridge. Aconnector(orjoint)connectsapontictoaretainer,ortworetainerstoeachother.Connectorsmayeitherbefixedorallowsomemovementbetweenthecomponentsthattheyjoin.Basicdesign,combinationsandvariationsTherearefourbasicdesignsofbridge,thedifferencebeingthetypeofsupportprovidedateachendofthepontic.Thesamenameisgiventothedesignhowevermanyponticsinthespanandabutmentteethsplintedatoneendofthespan(secFigure85).Thefourbasicdesignsarethesamewhetherthebridgeisaconventionaloraminimalpreparationtype.Itispossibletocombinetwoormoreofthefourbasicdesignsandtocombineconventionalandminimal-preparationretainersinthesamebridge.Ofthefourbasicdesigns,thefirstthreemaybeeitherconventionalorminimal-preparationtype.Ilwouldbeunusualtohaveaminimal-preparationversionofthespringcantileverbridge.ThefourbasicdesignsFixed-fixedbridgeAfixed-fixedbridgehasarigidconnectoratbothendsofthepontic.Theabutment(eetharethereforerigidlysplintedtogetherandforaconventionalbridgemustbepreparedparalleltoeachothersothat(hebridge,whichisaminimumofthreeunits,canbecementedinoneplace.Theretainersshouldhaveapproximatelythesameretentionaseachothertoreducetheriskthatforcesappliedtothebridgewilldislodgeoneretainerfromitsabutment,leaving(hebridgesuspendedfromtheotherabutment.Tominimizethisriskitisalsoimportantfortheentireoccludingsurfaceofalltheabutmentteethforaconventionalbridgetobeco4eredbytheretainers.Theopposingteethcannotthencontactthesurfaceofanabutmenttooth,depressitinitssocketandbreakthecementlute.Ifthisshouldhappen,theretainerwillnotappearloose,asitwillstillbeheldinplacebytherestof(hebridge.However,oralfluidswillenterthespacebetweentheretainerandtheabutmentpreparationandcarieswillrapidlydevelop(seeFigure86).Thisruledoesnotapplytominimal-preparationbridgesinwhichthebondbetweenthe,200110n700Bonoingahoycastingtemc1200,Bonarnpalloymeltingtemp»)bu,r-rie-ceramicsoiaenng炬m。U1075-112。*-ueoasstn<i970JPorcelainlinno940-9/0nTOS(-ceramicSCHQenng5notal-ceramicunits<i>«>atcmoy201Yellowuoldcastinotemp970Yellowgoldmeitinotemp850°OSt-ceramrcsoldering10ypiiowMOKlum(j,75c-«00»00Figure91Typicaltemperaturerangesforthemetal-ceramicprocess.Theevaryaccordingtothemetal,porcelainandsolderused,andwiththetypeoffurnace,Inparticularitsrateoftemperaturerise.Figure92showsasimpleclassificationofminimal-preparationbridges;variationsofthistechniqueareshowninFigures94,95-b.MINIMALPREPARATIONBRIDGESDIRECTINDIRECT11MacroMechanical1MediumMechanical1MicroMechanical1ChemicallyRetention-Retention-e.g.VinginiaSaltRetention-e.g.Adhesive-e.g.e.g.RochetteMeshCrystalBondMarylandInavia-ex(seeFig.94)(seeFig.92)(seeFig.96)(seeEig.97)Figure92Asimpleclassificationofminimal-preparationbridgesDirectbridgesmaybeusingthecrownofthepatient'sowntooth.Thiscanoftenbedoneasasimpleandrapidwayofreplacingatoothlostthroughinjury(whichcannotbereimplanted)orwhichhastobeextractedurgently.Sometimesmetalmeshorwireisaddedtothelingualsurfacetoincreasestrength,butthisisnotalwaysnecessary.Ifthenaturalcrownofthetoothisnotavailableorisnotsuitable,anacrylicdenturetoothcanbeusedinthesameway. Macro-mechanicallyretentivebridges(Rochette,seeFigure94)havelargeundercutperlorationsthroughthecast-metalplate,throughwhichthecompositeflows.Theseholesarecutinthewaxoracrylicpatternwithaburandarethencountersunk. Medium-mechanicalretentivesystemsallinvolveretentivefeaturescastaspartofthemetalframework(seeFigure95).Theyalladdsignificantlyto(hecementfilmthicknessinsomeareas,atleast,oftheretainerandtheyallproducelarge,non-undercutlumpsofmetalonthefitsurfacewhichdonotcontributetoretentionbutwhichnecessitatearelativelythickretainer.Thesizeoftheretentivefeaturesisintermediatebetweenmacroandmicromechanicalretentivesystems.Figure94Arochettebridgereplacingonecentrelincisor.Theporcelainisyettobeaddedandthepalatalspurontheponticwillactasahandleuntilthebridgeisfinished,whenitwillberemoved.Figure95Acast-meshbridge.Itisdifficulttoachievegoodadaptationofthemeshovertheentireretainersurfaceandneitheroftheseretainershasretentivefeaturesrightuptotheperiphery.Theaddedthicknessoftheretainercanalsobesee.Castingthemetalretainerandthenetchingthefitsurfaceproducesmicro-mechanicalretentionbyoneofthreemethods:electrolyticetchinginacidinthelaboratory,electrolyticetchingusingchairsideequipment.Orchemicaletchingwithahydrofluoricacidgeleitherin(helaboratoryoratthechairside.Althoughthesethreesystemsproducedifferentetchpatterns,theyareallveryretentive.Thesizeoftheretentivefeaturesisapproximatelyone-tenththatofthemedium-mechanicalretentivesystemsandtheretentivefeaturesareundercutfromthesurface.Thesmallersizeoftheseetchpitsandtheabsenceofunnecessarynon-retentivefeatures(asinthemedium-mechanicalretentivesystems)allowthinnermetalretainersandathinnercementfilmthickness.Figure96aAMarylandbridge,thedesigneisunsatisfactoryinthattheextensiondistallyontothethirdmolartoothtoincreaseretentionwouldgiverisetnanimpossiblecleaningproblembetweenthesecondandthirdmolar.ThisIsatechniquebridge,notmadeforepatient.Itisshowntoillustrateacommondesignerror.Chemicallyretentiveresinsarenowavailable.Severalhavebeenmarketedandsome(forexample.Panavia-Ex)haveperformedwellinsomelaboratoryandshort-termclinicaltrials.Theyadherechemicallytorecentlysandblastedmetalsurfacesandarcretainedonthetoothbyconventionalacid-etchingof(heenamel.Comparisonofindirectminimal-preparationretentionsystemsAnumberoflaboratorystudiesandclinicaltrialshaveshown(ha(themicro-mechanicalandchemicaladhesivesystemsarethemostretentive.However,thechemicaladhesivesystemshaveonlybeenavailableforashorttimeandlonger-termclinicaltrialsarenecessarybeforeitissafetorelytooheavilyonthissystem.ThedisadvantageofthemiciO-mcchanicalretentionsystemisthatthemetalframeworkshouldnotbetriedin(hemouthafterthesurfacehasbeenetched.Thisisbecause(heverydelicateetchpatternmaywellbedamagedorcloggedbydepositsfromsaliva.Thismeansthattheidealistotryintheunetchedframeworkandtheneitherreturnittothelaboratoryforetchingoretchita(thechairsidc.Thistakestimeandthereforeaddstothecost.Themacro-mechanicalretentivedesign(Rochette)overcomesthisproblembutislessretentiveinmostcasesandbecauseitiscementedwithaconventionalcompositeandthecompositecomesthroughtheperforationstothemouth,itispronetodegradationoveraperiodofyears.However,themainadvantageoftheRochettebridgeisthatilcanberemovedfromthemouthfairlyeasily.Thecompositeisdrilledoutfromtheholesandthebridgecanusuallyberemovedwithout(oomuchforce.For(hisreasontheRochettebridgeisstillusedwhentheabutmentteethhaveapoorprognosisandwhenfurthermodificationsarelikelytobenecessaryforexample,whenonelowerincisorisbeingreplacedforperiodontalreasonsandtheotherteetharestillreceivingperiodontaltreatment.TheRochettedesignisalsousedforimmediateinsertionbridgessothatthebridgecanberemovedwhenthetissueshavehealedandtheponticadaptedtotheridgeorthebridgeremade.Historically,themcdium-mcchanicalretentivesystemsweredevelopedaftertheRochetteandMarylanddesignsinanattempttoovercomethedisadvantagesofthesedescribedabove.However,theyhavedisadvantagesoftheirowninbeinglessretentivethanthemicro-mechanicalsystemandyethavingthickermetalretainersandathickercementfilm.Oneadvantage,however,isthattheycanbemadeinanymetal,includingpreciousmetals,whereastheetchedsystemscanonlybemadeinbasemetalalloyswhichareetchable.Disadvantageofminimal*preparationbridgesingeneralAsthemetalplateisaddedtothesurfaceofthetoothratherthanreplacingpartofit,thethicknessofthetoothisincreasedandmay-forexample,inanonnalClassincisorrelationshipinterferewiththeocclusionunlessspaceiscreatedonhodonticallyorbygrindingtheopposingteeth.Themarginoftheretainerinevitablyproducesaledgewhereplaquecancollect.Thisisaproblemespeciallyinthereplacementoflowerincisors.Hereplaqueandcalculusdepositsarecommononthelingualsurfacetowardsthegingivalmarginandthepresenceofsuchaledgecanonlymakeitmoredifficultforthepatienttocleaninthisarea.AnotherexampleofadesignthatwouldpreventgoodoralhygieneisshowninFigure96a.PracticalPoints Thefourbasicbridgedesignsdifferinthesupportprovideateachendof(hepontic.Thebasicdesignscanbecombinedtogive,forexample,afixed-fixed/cantileverdesign. Simpler,lessdestructiveminimal-preparationbridgesareuseful,particularlyinyoungerpatiens. Bridgesthatarcmadetoberemovablebythedentistmakefurtherendodonticorperiodontaltreatmentpossible;thosepatientscanremovemakecleaningeasier. Inexperiencedoperatorsshouldnotusespringcantileverdesignsasasoftoptiontopreparingsoundanteriorteeth.VOCABULARY1.Abridge橋2.Aminimal-preparationbridge最小預(yù)備的橋3.Aremovablebridge活動(dòng)橋4.Aprecisionattachmentpartialdenture精密附著局部義齒5.Apartialdenture局部義齒6.Occlusalstability合穩(wěn)定7.retention固位8.dentition牙列9.Periodontalsplinting牙周夾板10.Secondarycaries繼發(fā)翻11.microleakage微漏12.abutment基牙13.pontic橋體14.retainer固位體15.span跨度、橋距16.saddle橋鞍17.pier橋墩18.unit單位19.connector連接體20.fixed-fixedbridge固定一固定橋21.fixed-moveablebridge固定一活動(dòng)橋22.Cantileverbridge懸臂橋23.springcantileverbridge彈性懸臂橋24.Conventionalbridge傳統(tǒng)橋25. MetalBridgeMetal-ceramicbridge26. Ceramicbridge橋烤橋力屬屬瓷桿金金烤杠橋烤橋力屬屬瓷桿金金烤杠27. leverageforceretainerandtheabutmenttoothismuchstronger.However,itissometimesnotstrongenoughanddebondingsometimesoccursasaresultofamechanismsimilartothatshowninFigure86.Thisprobablypartlyaccountsforthehigherincidenceofretentionfailurewithminimal-preparationbridgesthanwithconventionalbridge.Atonetimeitwasthoughtthatthesupportfortheabutmentteethateachendofafixed-fixedbridgeshouldbesimilar.Inotherwords,therootsurfaceareaoftheabutmentsshouldbeapproximatelythesame.Todaythisisnotconsiderednecessary.Afixcd-movcablcbridgehasarigidconnector,usuallyatthedistalendoftheponticandamoveableconnectorthatallowssomeverticalmovementofthemesialabutmenttooth.Themoveableconnectorshouldresistbothseparationoftheponticfromtheretainerandlateralmovementof(hepontic(seeFigure87).Figure85Fourbasicbridgedesignsofconventionalbridges.aFixed-fixeddesignBothupperandlowerbridgewillbefixed-fixed,thelowerretainedbyfullcrownsonthecaninetoothandcentralincisor.Theupperbridgewillberetainedbythecanineteethonly.Fixed-moveablebridgeOccasionallythefixedandmoveableconnectorsarereversedbutthishasanumberofdisadvantages.Theretainerwiththemoveableconnector(theminorretainer)issmallerandlessvisibleandsoisbetterinthemoreanteriorabutmenttooth.Mesialdrifttendstounseatdistalmoveableconnectors,butisresistedbymesialones.Themoveableconnectorcanbeseparatedbeforethebridgeiscementedandsothetwopartsofthebridgecanbecementedseparately.Theabutmentteethdonotthereforehavetobepreparedparalleltoeachotherand(heretentionfortheminorretainerdoesnotneedtobeasextensiveasforthemajorretainer.Neitherdoesitneedfullocclusalprotection,(occlusalforcesappliedtothetoothsurfacenotcoveredbytheretainerwilldepressthetoothinitssocketandtherewillbemovementatThemoveablejointratherthanrupturingofthecementlute(seeFigure86).bFixed-moveabledesignwithDoinlayinthelowerseenpremolarandfullcrownonthemolartooth.Thisbridgehasbeenpresentfortwentyyears,infeetsolongthattheocclusalsurfaceofthecrownhaswornthrough(seeChapter13).ThemoveableJointcanbeseenbetweentheponticandtheminorretainer.Itwouldnotnormallybeasobviousasthis.CCantileverdesignBothlateralincisorsareponticssupportedbycrownsonthecanineteeth.Bothbridgesareall-porcelainandtherightonehasbeenpresentforfourteenyears.Theleftonefracturedfatersevenyearsandwasreplacedwithanotherallporcelainbridge,whichisstillpresent.dSpringcantileverdesignwithfirstmolartoothasabutment.Thereisamidlinediastemaandadiastemabetweenthelateralincisorandcanineonthesideofthemissingcentralincisor.Anyotherbridgedesignwouldhaveinvolvedclosingoneorbothofthesespecs.Afixcd-movcahlcminimal-preparationbridgecannothavethemoveablejointwithinthecontourof(heoriginalabutmenttooth,asthisisnotpreparedsufficientlyforthemoveableconnector.Thismeansthatthemoveableconnectorisintheponticofthebridgeandisusuallyathroughandthroughtubeandpinarrangement.Thismeansthatthe(wopartsofthebridgeareconnectedbutifeitherdebondsthenitcanberemovedwithoutdisturbingtheotherpartofthebridgeandrecemented.However,thisdesignofmoveablejointiscumbersomeandtheundersurface,whichapproximatestheridge,isdifficulttoclean.Itisthereforenotcommonlyused.Figure86Aconventionalfixed-fixedbridgeshouldhavealltheoccludingsurfacesoftheabutmentteethprotectedbytheretainers,otherwiseanocclusalforcedirectedattheunprotectedareawilldepresstheabutmenttoothinitssocketwhilethebridgeandtheotherabutmenttoothholdtheretainer.Thiswillbreakdownthecementlute,causingleakage.Theretainerisheldinplacebythebridgeandsosecondarycariesdevelopsrapidly(seeFigure146.page232)Figure87aAniveablecibbectirmseorated.bAcrylicburn-outpatternsforpatternsformoveableconnectors.TheblueIsverytapered,theredmoreparallel-sided.CantileverbridgeAcantileverbridgeprovidessupportfortheponticatoneendonly.Theponticmaybeattachedtoasingleretaineror(otwoormoreretainerssplintedtogether,buthasnoconnectionattheotherendofthepontic.Theabutmenttoothorteethforacantileverbridgemaybeeithermesialordistaltothespanbutforsmallbridgesareusuallydistal.SpringcantileverbridgeSpringcantileverbridgesarcrestrictedtothereplacementofupperincisorteeth.Onlyoneponticcanbesupportedbyaspringcantileverbridge.Thisisattachedtotheendofalongmetalarmrunninghighintothepalateandthensweepingdowntoarigidconnectoronthepalatalsideofasingleretainerorapairofsplintedretainers.Thearmismadelongandfairlythinsothatitisspringy,butnotsothinthatitwilldeformpermanentlywithnormalocclusalsurfaces(i.e.,exceedtheelasticlimit).Forcesappliedtotheponticareabsorbedbythespringinessofthearmandbydisplacementofthesofttissuesofthepalatesothatexcessiveleverageforcesdonotdisturbtheabutmentteeth.Theabutmentsareusuallythetwopremolarteethsplintedtogether,orasinglepremolarormolartooth.CombinationdesignsThefourbasicdesignscanbecombinedinavarietyofways.Inparticular,thefixed-fixedandcantileverdesignsareoftencombined.Inlargerbridgesadditionalcantileverpoliticsmaybesuspendedfromtheendofalargefixed-fixedsection(seeFigure88).Similarly,itispossibletocombinefixed-fixedandfixed-moveabledesigns.Itislesscommonforspringcantileverbridgestobecombinedwithothertypesofbridge,butoccasionallyaspringcantileverarmisattachedtoaposteriorfixed-fixedbridge.Itispossibletocombineabridgewitharemovablebuccalflangethatreplaceslostalveolartissue.HybriddesignsTherearethreedifferenlhybriddesigns: Fixed-fixedwithoneconventionalandoneminimal-preparationretainer Fixed-moveablewithaminimal-preparationretainercarryingthemoveableconnector Fixed-movablewiththeconventionalretainercarryingthemoveableconnector.Thefirsttwodesignsshouldnotbeused.Ineithercaseiftheminimal-preparationretainerbecomesdebondedthenitwillnotbepossibletorecementitwithoutremovingtheconventionalretainerwhomaywellinvolvedestroyingthebridge.Thethirddesignisacceptableandmaywellbe(heoneofchoicegivencircumstancesinwhichoneoftheabutmentteeth(usuallythemesialone)alreadyhasarestorationwhichcouldbereplacedbymeansofaninlayorotherconventionalretainer.Theotherabutmenttoothisunrestoredortherestorationdoesnotinvolvethesurfacestobecoveredbyaminimal-preparationretainer.Thesecircumstancesoccursurprisinglycommonlyandsothisdesignofbridgeisbeingusedincreasing.VariationsRemovablebridgesAllthedesignsdescribedsofararepermanentlycementedinthepatient'smouth.Withlargebridges(herearedisadvantagesinpermanentcementationinthatthemaintenanceandfurtherendodonticorperiodontaltreatmentofabutmentteethisdifficult,andifsomethinggoeswrongwithonepartofthebridgeorwithoneoftheabutmentteeth,usuallythewholebridgehastobesacrificed.Forthisreasonlargerbridges,includingfullarchbridges,aresometimesmadesothatthedentistwithoutbeingdestroyedcanremovethem.Cementingindividualcastgoldcopingstoeachoftheabutmentteethdoesthis.Someofthecopingshavethreadedsleevessolderedintothem,andthebridgeisthencementedtothesecopingswithweakcement.Itisheldinplacewithlinescrewsthatpasthroughholesin.theretainersofthebridgeintothethreadedsleeves.Figure88Alargesplint/bndgewithcantileveredpontics.aTheworkingdies.Figure88bThemetalframeworkshowingtwocantileveredponticsontherightofthepicture.Inothercasesthebridgeisremovablebythepatientandhasnocementorscrews.Theadvantageofthisisthatcleaningaroundtheabutmentteethandundertheponticsismucheasier.Thebridgehastowithstandhandlingbythepatientandsoitisusuallymadeinabasemetalwithacrylicfacings.Thebasemetalismorerigidthanapreciousmetalframeworkandtheacrylicfacingsarclessliabletochipifthebridgeisdropped.Theycanalsobereplacedwithouttheriskofdistortingtheframework.AdvantagesanddisadvantageofthefourbasicdesignsAcomparisonofconventionalfixed-fixed,fixed-moveableandcantileverbridgesisshownonpage240-241Springcantileverbridgesarediscussedseparately.SpringcantileverbridgeThesearedealtwithseparatelybecausetheyareusedonlytoreplaceupperincisorteeth,usuallywhentherearcspacesbetweentheincisorteethandtheadjacentpotentialabutmentteetharesound.Theyshouldnotbeusedtoreplacelowerincisorsastheshapeoftheridgeandtheresilienceofthesofttissuesarcnotsuitedtoabsorbingpartoftheocclusalloading.Theadvantagesofthedesignare:theponticnotbeingattachedtoadjacentteeth,spacescanbepreservedbothsidesofit,andthesoundnaturalanteriorteethdonotneedtobepreparedasabutments.Disadvantages:somepatientsfindthepermanentbarrunningacrossthepalateintolerable.Althoughmostgetusedtothissurprisinglywell,itisverydifficulttopredictthosewhowillnotbecomeaccustomedtoit.Ithasonoccasionbeennecessarytoremoveaperfectlysoundspringcantileverbridgefornootherreasonthanthatthepatientcouldnottoleratethefeelingof(hebar.Amorecommonproblemisthedifficultyofcleaningunderthebar,particularlyatitsconnectorwiththeretainer.Theeffectivewayofcleaningtheareaistopassdentaliloss,superfloss,orotherthreadmaterialovertheponticandalongthebarandtocleanbothunderitandundertheconnector.Thisrequiresconsiderabledexteritybythepatient.Anumberofspringcantileverbridgeshavefailedbecauseofperiodontaldiseaseonthepalatalsideoftheabutmentteeth.Theponticmayalsotraumatizethegingivalpapillaeoneithersideofitbecausethespringinessofthebarallowsthepontictomoveupanddownslightlyinuse.Thedesignofthebridgerequiresretentionoftheabutmentpreparationstobeverygood.Inexperiencedoperatorsshouldnotfallintothetrapofusingspringcantileverdesignsbecausetheylacktheconfidencetopreparesoundanteriorteethandprefertopractisebridgeworkusingposteriorabutmentsonly.Thedesignchosenshouldbethebestoneinthepatient'sinterest,andiftheoperatorisnotsufficientlyexperiencedtocarryitoutheshouldreferthepatienttoacolleagueorseekguidanceindesigningandmakingthebridge.ADVANTAGESFixed-fixed Robustdesignwithmaximumretentionandstrength Abutmentteetharesplintedtogether,maybeanadvantage,particularlywhenteethareuncomfortablymobilefollowingbonelossthroughperiodontaldiseaseThedesignisthemostpracticalforlargerbridges,particularlywhentherehasbeenperiodontaldisease Theconstructionisrelativelystraightforwardinthelaboratory CanbeusedforlongspansFixed-moveable Preparationsdonotneedtobeparalleltoeachother,sodivergentabutmentteethcanbeused Becausepreparationsdonotneedtobeparallel,eachpreparationcanbedesignedtoberetentiveindependentlyoftheotherpreparation(s