专业英语 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。*-ueoasstni970JPorcelainlinno940-9/0nTOS(-ceramicSCHQenng5notal-ceramicunitsatcmoy201Yellowuoldcastinotemp970Yellowgoldmeitinotemp850OSt-ceramrcsoldering10ypiiowMOKlum(j,75c-0000Figure91Typicaltemperaturerangesforthemetal-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-preparationbridgesDirectbridgesmaybeusingthecrownofthepatientsowntooth.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桥2.Aminimal-preparationbridge最小预备的桥3.Aremovablebridge活动桥4.Aprecisionattachmentpartialdenture精密附着局部义齿5.Apartialdenture局部义齿6.Occlusalstability合稳定7.retention固位8.dentition牙列9.Periodontalsplinting牙周夹板10.Secondarycaries继发翻11.microleakage微漏12.abutment基牙13.pontic桥体14.retainer固位体15.span跨度、桥距16.saddle桥鞍17.pier桥墩18.unit单位19.connector连接体20.fixed-fixedbridge固定一固定桥21.fixed-moveablebridge固定一活动桥22.Cantileverbridge悬臂桥23.springcantileverbridge弹性悬臂桥24.Conventionalbridge传统桥25. MetalBridgeMetal-ceramicbridge26. Ceramicbridge桥烤桥力属属瓷杆金金烤杠桥烤桥力属属瓷杆金金烤杠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.VariationsRemovablebridgesAllthedesignsdescribedsofararepermanentlycementedinthepatientsmouth.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.Thedesignchosenshouldbethebestoneinthepatientsinterest,andiftheoperatorisnotsufficientlyexperiencedtocarryitoutheshouldreferthepatienttoacolleagueorseekguidanceindesigningandmakingthebridge.ADVANTAGESFixed-fixed Robustdesignwithmaximumretentionandstrength Abutmentteetharesplintedtogether,maybeanadvantage,particularlywhenteethareuncomfortablymobilefollowingbonelossthroughperiodontaldiseaseThedesignisthemostpracticalforlargerbridges,particularlywhentherehasbeenperiodontaldisease Theconstructionisrelativelystraightforwardinthelaboratory CanbeusedforlongspansFixed-moveable Preparationsdonotneedtobeparalleltoeachother,sodivergentabutmentteethcanbeused Becausepreparationsdonotneedtobeparallel,eachpreparationcanbedesignedtoberetentiveindependentlyoftheotherpreparation(s