專業(yè)英語 Unit 33教案.docx

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1、UnitThirtyThreeTypesofbridgeTheappliancesusedtoreplacemissingteethweredefinedinChapter7.Someofthetermsusedinbridgeworkarcalsousedinrelationtopartialdentures.Anabutmentisatoothtowhichabridge(ofpartialdenture)isattached. Aretainerisacrownorotherrastorationthatiscementedtotheabutment.Thetermsretaineran

2、dabutmentshouldnotbeconfusedorusedinterchangeably. Aponticisanartificialtoothaspartofabridge. Aspanisthespacebetweennaturalteeththatistobefilledbythebridge. Thesaddleistheareaoftheedentulousridgeoverwhichtheponticwilllie. Apierisanabutmenttoothstandingbetweenandsupportingtwopontics.Eachponticbeingat

3、tachedtoafurtherabutmenttooth. Aunit,whenappliedtobridgework,meanseitheraretainerorapontic.Abridgewithtworetainersandoneponticwouldthereforebeathree-unitbridge. Aconnector(orjoint)connectsapontictoaretainer,ortworetainerstoeachother.Connectorsmayeitherbefixedorallowsomemovementbetweenthecomponentsth

4、attheyjoin.Basicdesign,combinationsandvariationsTherearefourbasicdesignsofbridge,thedifferencebeingthetypeofsupportprovidedateachendofthepontic.Thesamenameisgiventothedesignhowevermanyponticsinthespanandabutmentteethsplintedatoneendofthespan(secFigure85).Thefourbasicdesignsarethesamewhetherthebridge

5、isaconventionaloraminimalpreparationtype.Itispossibletocombinetwoormoreofthefourbasicdesignsandtocombineconventionalandminimal-preparationretainersinthesamebridge.Ofthefourbasicdesigns,thefirstthreemaybeeitherconventionalorminimal-preparationtype.Ilwouldbeunusualtohaveaminimal-preparationversionofth

6、espringcantileverbridge.ThefourbasicdesignsFixed-fixedbridgeAfixed-fixedbridgehasarigidconnectoratbothendsofthepontic.Theabutment(eetharethereforerigidlysplintedtogetherandforaconventionalbridgemustbepreparedparalleltoeachothersothat(hebridge,whichisaminimumofthreeunits,canbecementedinoneplace.There

7、tainersshouldhaveapproximatelythesameretentionaseachothertoreducetheriskthatforcesappliedtothebridgewilldislodgeoneretainerfromitsabutment,leaving(hebridgesuspendedfromtheotherabutment.Tominimizethisriskitisalsoimportantfortheentireoccludingsurfaceofalltheabutmentteethforaconventionalbridgetobeco4er

8、edbytheretainers.Theopposingteethcannotthencontactthesurfaceofanabutmenttooth,depressitinitssocketandbreakthecementlute.Ifthisshouldhappen,theretainerwillnotappearloose,asitwillstillbeheldinplacebytherestof(hebridge.However,oralfluidswillenterthespacebetweentheretainerandtheabutmentpreparationandcar

9、ieswillrapidlydevelop(seeFigure86).Thisruledoesnotapplytominimal-preparationbridgesinwhichthebondbetweenthe,200110n700Bonoingahoycastingtemc1200,Bonarnpalloymeltingtemp)bu,r-rie-ceramicsoiaenng炬m。U1075-112。*-ueoasstni970JPorcelainlinno940-9/0nTOS(-ceramicSCHQenng5notal-ceramicunitsatcmoy201Yellowuol

10、dcastinotemp970Yellowgoldmeitinotemp850OSt-ceramrcsoldering10ypiiowMOKlum(j,75c-0000Figure91Typicaltemperaturerangesforthemetal-ceramicprocess.Theevaryaccordingtothemetal,porcelainandsolderused,andwiththetypeoffurnace,Inparticularitsrateoftemperaturerise.Figure92showsasimpleclassificationofminimal-p

11、reparationbridges;variationsofthistechniqueareshowninFigures94,95-b.MINIMALPREPARATIONBRIDGESDIRECTINDIRECT11MacroMechanical1MediumMechanical1MicroMechanical1ChemicallyRetention-Retention-e.g.VinginiaSaltRetention-e.g.Adhesive-e.g.e.g.RochetteMeshCrystalBondMarylandInavia-ex(seeFig.94)(seeFig.92)(se

12、eFig.96)(seeEig.97)Figure92Asimpleclassificationofminimal-preparationbridgesDirectbridgesmaybeusingthecrownofthepatientsowntooth.Thiscanoftenbedoneasasimpleandrapidwayofreplacingatoothlostthroughinjury(whichcannotbereimplanted)orwhichhastobeextractedurgently.Sometimesmetalmeshorwireisaddedtothelingu

13、alsurfacetoincreasestrength,butthisisnotalwaysnecessary.Ifthenaturalcrownofthetoothisnotavailableorisnotsuitable,anacrylicdenturetoothcanbeusedinthesameway. Macro-mechanicallyretentivebridges(Rochette,seeFigure94)havelargeundercutperlorationsthroughthecast-metalplate,throughwhichthecompositeflows.Th

14、eseholesarecutinthewaxoracrylicpatternwithaburandarethencountersunk. Medium-mechanicalretentivesystemsallinvolveretentivefeaturescastaspartofthemetalframework(seeFigure95).Theyalladdsignificantlyto(hecementfilmthicknessinsomeareas,atleast,oftheretainerandtheyallproducelarge,non-undercutlumpsofmetalo

15、nthefitsurfacewhichdonotcontributetoretentionbutwhichnecessitatearelativelythickretainer.Thesizeoftheretentivefeaturesisintermediatebetweenmacroandmicromechanicalretentivesystems.Figure94Arochettebridgereplacingonecentrelincisor.Theporcelainisyettobeaddedandthepalatalspurontheponticwillactasahandleu

16、ntilthebridgeisfinished,whenitwillberemoved.Figure95Acast-meshbridge.Itisdifficulttoachievegoodadaptationofthemeshovertheentireretainersurfaceandneitheroftheseretainershasretentivefeaturesrightuptotheperiphery.Theaddedthicknessoftheretainercanalsobesee.Castingthemetalretainerandthenetchingthefitsurf

17、aceproducesmicro-mechanicalretentionbyoneofthreemethods:electrolyticetchinginacidinthelaboratory,electrolyticetchingusingchairsideequipment.Orchemicaletchingwithahydrofluoricacidgeleitherin(helaboratoryoratthechairside.Althoughthesethreesystemsproducedifferentetchpatterns,theyareallveryretentive.The

18、sizeoftheretentivefeaturesisapproximatelyone-tenththatofthemedium-mechanicalretentivesystemsandtheretentivefeaturesareundercutfromthesurface.Thesmallersizeoftheseetchpitsandtheabsenceofunnecessarynon-retentivefeatures(asinthemedium-mechanicalretentivesystems)allowthinnermetalretainersandathinnerceme

19、ntfilmthickness.Figure96aAMarylandbridge,thedesigneisunsatisfactoryinthattheextensiondistallyontothethirdmolartoothtoincreaseretentionwouldgiverisetnanimpossiblecleaningproblembetweenthesecondandthirdmolar.ThisIsatechniquebridge,notmadeforepatient.Itisshowntoillustrateacommondesignerror.Chemicallyre

20、tentiveresinsarenowavailable.Severalhavebeenmarketedandsome(forexample.Panavia-Ex)haveperformedwellinsomelaboratoryandshort-termclinicaltrials.Theyadherechemicallytorecentlysandblastedmetalsurfacesandarcretainedonthetoothbyconventionalacid-etchingof(heenamel.Comparisonofindirectminimal-preparationre

21、tentionsystemsAnumberoflaboratorystudiesandclinicaltrialshaveshown(ha(themicro-mechanicalandchemicaladhesivesystemsarethemostretentive.However,thechemicaladhesivesystemshaveonlybeenavailableforashorttimeandlonger-termclinicaltrialsarenecessarybeforeitissafetorelytooheavilyonthissystem.Thedisadvantag

22、eofthemiciO-mcchanicalretentionsystemisthatthemetalframeworkshouldnotbetriedin(hemouthafterthesurfacehasbeenetched.Thisisbecause(heverydelicateetchpatternmaywellbedamagedorcloggedbydepositsfromsaliva.Thismeansthattheidealistotryintheunetchedframeworkandtheneitherreturnittothelaboratoryforetchingoret

23、chita(thechairsidc.Thistakestimeandthereforeaddstothecost.Themacro-mechanicalretentivedesign(Rochette)overcomesthisproblembutislessretentiveinmostcasesandbecauseitiscementedwithaconventionalcompositeandthecompositecomesthroughtheperforationstothemouth,itispronetodegradationoveraperiodofyears.However

24、,themainadvantageoftheRochettebridgeisthatilcanberemovedfromthemouthfairlyeasily.Thecompositeisdrilledoutfromtheholesandthebridgecanusuallyberemovedwithout(oomuchforce.For(hisreasontheRochettebridgeisstillusedwhentheabutmentteethhaveapoorprognosisandwhenfurthermodificationsarelikelytobenecessaryfore

25、xample,whenonelowerincisorisbeingreplacedforperiodontalreasonsandtheotherteetharestillreceivingperiodontaltreatment.TheRochettedesignisalsousedforimmediateinsertionbridgessothatthebridgecanberemovedwhenthetissueshavehealedandtheponticadaptedtotheridgeorthebridgeremade.Historically,themcdium-mcchanic

26、alretentivesystemsweredevelopedaftertheRochetteandMarylanddesignsinanattempttoovercomethedisadvantagesofthesedescribedabove.However,theyhavedisadvantagesoftheirowninbeinglessretentivethanthemicro-mechanicalsystemandyethavingthickermetalretainersandathickercementfilm.Oneadvantage,however,isthattheyca

27、nbemadeinanymetal,includingpreciousmetals,whereastheetchedsystemscanonlybemadeinbasemetalalloyswhichareetchable.Disadvantageofminimal*preparationbridgesingeneralAsthemetalplateisaddedtothesurfaceofthetoothratherthanreplacingpartofit,thethicknessofthetoothisincreasedandmay-forexample,inanonnalClassin

28、cisorrelationshipinterferewiththeocclusionunlessspaceiscreatedonhodonticallyorbygrindingtheopposingteeth.Themarginoftheretainerinevitablyproducesaledgewhereplaquecancollect.Thisisaproblemespeciallyinthereplacementoflowerincisors.Hereplaqueandcalculusdepositsarecommononthelingualsurfacetowardstheging

29、ivalmarginandthepresenceofsuchaledgecanonlymakeitmoredifficultforthepatienttocleaninthisarea.AnotherexampleofadesignthatwouldpreventgoodoralhygieneisshowninFigure96a.PracticalPoints Thefourbasicbridgedesignsdifferinthesupportprovideateachendof(hepontic.Thebasicdesignscanbecombinedtogive,forexample,a

30、fixed-fixed/cantileverdesign. Simpler,lessdestructiveminimal-preparationbridgesareuseful,particularlyinyoungerpatiens. Bridgesthatarcmadetoberemovablebythedentistmakefurtherendodonticorperiodontaltreatmentpossible;thosepatientscanremovemakecleaningeasier. Inexperiencedoperatorsshouldnotusespringcant

31、ileverdesignsasasoftoptiontopreparingsoundanteriorteeth.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.microl

32、eakage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

33、屬屬瓷桿金金烤杠27. leverageforceretainerandtheabutmenttoothismuchstronger.However,itissometimesnotstrongenoughanddebondingsometimesoccursasaresultofamechanismsimilartothatshowninFigure86.Thisprobablypartlyaccountsforthehigherincidenceofretentionfailurewithminimal-preparationbridgesthanwithconventionalbridg

34、e.Atonetimeitwasthoughtthatthesupportfortheabutmentteethateachendofafixed-fixedbridgeshouldbesimilar.Inotherwords,therootsurfaceareaoftheabutmentsshouldbeapproximatelythesame.Todaythisisnotconsiderednecessary.Afixcd-movcablcbridgehasarigidconnector,usuallyatthedistalendoftheponticandamoveableconnect

35、orthatallowssomeverticalmovementofthemesialabutmenttooth.Themoveableconnectorshouldresistbothseparationoftheponticfromtheretainerandlateralmovementof(hepontic(seeFigure87).Figure85Fourbasicbridgedesignsofconventionalbridges.aFixed-fixeddesignBothupperandlowerbridgewillbefixed-fixed,thelowerretainedb

36、yfullcrownsonthecaninetoothandcentralincisor.Theupperbridgewillberetainedbythecanineteethonly.Fixed-moveablebridgeOccasionallythefixedandmoveableconnectorsarereversedbutthishasanumberofdisadvantages.Theretainerwiththemoveableconnector(theminorretainer)issmallerandlessvisibleandsoisbetterinthemoreant

37、eriorabutmenttooth.Mesialdrifttendstounseatdistalmoveableconnectors,butisresistedbymesialones.Themoveableconnectorcanbeseparatedbeforethebridgeiscementedandsothetwopartsofthebridgecanbecementedseparately.Theabutmentteethdonotthereforehavetobepreparedparalleltoeachotherand(heretentionfortheminorretai

38、nerdoesnotneedtobeasextensiveasforthemajorretainer.Neitherdoesitneedfullocclusalprotection,(occlusalforcesappliedtothetoothsurfacenotcoveredbytheretainerwilldepressthetoothinitssocketandtherewillbemovementatThemoveablejointratherthanrupturingofthecementlute(seeFigure86).bFixed-moveabledesignwithDoin

39、layinthelowerseenpremolarandfullcrownonthemolartooth.Thisbridgehasbeenpresentfortwentyyears,infeetsolongthattheocclusalsurfaceofthecrownhaswornthrough(seeChapter13).ThemoveableJointcanbeseenbetweentheponticandtheminorretainer.Itwouldnotnormallybeasobviousasthis.CCantileverdesignBothlateralincisorsar

40、eponticssupportedbycrownsonthecanineteeth.Bothbridgesareall-porcelainandtherightonehasbeenpresentforfourteenyears.Theleftonefracturedfatersevenyearsandwasreplacedwithanotherallporcelainbridge,whichisstillpresent.dSpringcantileverdesignwithfirstmolartoothasabutment.Thereisamidlinediastemaandadiastema

41、betweenthelateralincisorandcanineonthesideofthemissingcentralincisor.Anyotherbridgedesignwouldhaveinvolvedclosingoneorbothofthesespecs.Afixcd-movcahlcminimal-preparationbridgecannothavethemoveablejointwithinthecontourof(heoriginalabutmenttooth,asthisisnotpreparedsufficientlyforthemoveableconnector.T

42、hismeansthatthemoveableconnectorisintheponticofthebridgeandisusuallyathroughandthroughtubeandpinarrangement.Thismeansthatthe(wopartsofthebridgeareconnectedbutifeitherdebondsthenitcanberemovedwithoutdisturbingtheotherpartofthebridgeandrecemented.However,thisdesignofmoveablejointiscumbersomeandtheunde

43、rsurface,whichapproximatestheridge,isdifficulttoclean.Itisthereforenotcommonlyused.Figure86Aconventionalfixed-fixedbridgeshouldhavealltheoccludingsurfacesoftheabutmentteethprotectedbytheretainers,otherwiseanocclusalforcedirectedattheunprotectedareawilldepresstheabutmenttoothinitssocketwhilethebridge

44、andtheotherabutmenttoothholdtheretainer.Thiswillbreakdownthecementlute,causingleakage.Theretainerisheldinplacebythebridgeandsosecondarycariesdevelopsrapidly(seeFigure146.page232)Figure87aAniveablecibbectirmseorated.bAcrylicburn-outpatternsforpatternsformoveableconnectors.TheblueIsverytapered,theredm

45、oreparallel-sided.CantileverbridgeAcantileverbridgeprovidessupportfortheponticatoneendonly.Theponticmaybeattachedtoasingleretaineror(otwoormoreretainerssplintedtogether,buthasnoconnectionattheotherendofthepontic.Theabutmenttoothorteethforacantileverbridgemaybeeithermesialordistaltothespanbutforsmall

46、bridgesareusuallydistal.SpringcantileverbridgeSpringcantileverbridgesarcrestrictedtothereplacementofupperincisorteeth.Onlyoneponticcanbesupportedbyaspringcantileverbridge.Thisisattachedtotheendofalongmetalarmrunninghighintothepalateandthensweepingdowntoarigidconnectoronthepalatalsideofasingleretaine

47、rorapairofsplintedretainers.Thearmismadelongandfairlythinsothatitisspringy,butnotsothinthatitwilldeformpermanentlywithnormalocclusalsurfaces(i.e.,exceedtheelasticlimit).Forcesappliedtotheponticareabsorbedbythespringinessofthearmandbydisplacementofthesofttissuesofthepalatesothatexcessiveleverageforce

48、sdonotdisturbtheabutmentteeth.Theabutmentsareusuallythetwopremolarteethsplintedtogether,orasinglepremolarormolartooth.CombinationdesignsThefourbasicdesignscanbecombinedinavarietyofways.Inparticular,thefixed-fixedandcantileverdesignsareoftencombined.Inlargerbridgesadditionalcantileverpoliticsmaybesus

49、pendedfromtheendofalargefixed-fixedsection(seeFigure88).Similarly,itispossibletocombinefixed-fixedandfixed-moveabledesigns.Itislesscommonforspringcantileverbridgestobecombinedwithothertypesofbridge,butoccasionallyaspringcantileverarmisattachedtoaposteriorfixed-fixedbridge.Itispossibletocombineabridg

50、ewitharemovablebuccalflangethatreplaceslostalveolartissue.HybriddesignsTherearethreedifferenlhybriddesigns: Fixed-fixedwithoneconventionalandoneminimal-preparationretainer Fixed-moveablewithaminimal-preparationretainercarryingthemoveableconnector Fixed-movablewiththeconventionalretainercarryingthemo

51、veableconnector.Thefirsttwodesignsshouldnotbeused.Ineithercaseiftheminimal-preparationretainerbecomesdebondedthenitwillnotbepossibletorecementitwithoutremovingtheconventionalretainerwhomaywellinvolvedestroyingthebridge.Thethirddesignisacceptableandmaywellbe(heoneofchoicegivencircumstancesinwhichoneo

52、ftheabutmentteeth(usuallythemesialone)alreadyhasarestorationwhichcouldbereplacedbymeansofaninlayorotherconventionalretainer.Theotherabutmenttoothisunrestoredortherestorationdoesnotinvolvethesurfacestobecoveredbyaminimal-preparationretainer.Thesecircumstancesoccursurprisinglycommonlyandsothisdesignof

53、bridgeisbeingusedincreasing.VariationsRemovablebridgesAllthedesignsdescribedsofararepermanentlycementedinthepatientsmouth.Withlargebridges(herearedisadvantagesinpermanentcementationinthatthemaintenanceandfurtherendodonticorperiodontaltreatmentofabutmentteethisdifficult,andifsomethinggoeswrongwithone

54、partofthebridgeorwithoneoftheabutmentteeth,usuallythewholebridgehastobesacrificed.Forthisreasonlargerbridges,includingfullarchbridges,aresometimesmadesothatthedentistwithoutbeingdestroyedcanremovethem.Cementingindividualcastgoldcopingstoeachoftheabutmentteethdoesthis.Someofthecopingshavethreadedslee

55、vessolderedintothem,andthebridgeisthencementedtothesecopingswithweakcement.Itisheldinplacewithlinescrewsthatpasthroughholesin.theretainersofthebridgeintothethreadedsleeves.Figure88Alargesplint/bndgewithcantileveredpontics.aTheworkingdies.Figure88bThemetalframeworkshowingtwocantileveredponticsontheri

56、ghtofthepicture.Inothercasesthebridgeisremovablebythepatientandhasnocementorscrews.Theadvantageofthisisthatcleaningaroundtheabutmentteethandundertheponticsismucheasier.Thebridgehastowithstandhandlingbythepatientandsoitisusuallymadeinabasemetalwithacrylicfacings.Thebasemetalismorerigidthanapreciousme

57、talframeworkandtheacrylicfacingsarclessliabletochipifthebridgeisdropped.Theycanalsobereplacedwithouttheriskofdistortingtheframework.AdvantagesanddisadvantageofthefourbasicdesignsAcomparisonofconventionalfixed-fixed,fixed-moveableandcantileverbridgesisshownonpage240-241Springcantileverbridgesarediscu

58、ssedseparately.SpringcantileverbridgeThesearedealtwithseparatelybecausetheyareusedonlytoreplaceupperincisorteeth,usuallywhentherearcspacesbetweentheincisorteethandtheadjacentpotentialabutmentteetharesound.Theyshouldnotbeusedtoreplacelowerincisorsastheshapeoftheridgeandtheresilienceofthesofttissuesar

59、cnotsuitedtoabsorbingpartoftheocclusalloading.Theadvantagesofthedesignare:theponticnotbeingattachedtoadjacentteeth,spacescanbepreservedbothsidesofit,andthesoundnaturalanteriorteethdonotneedtobepreparedasabutments.Disadvantages:somepatientsfindthepermanentbarrunningacrossthepalateintolerable.Although

60、mostgetusedtothissurprisinglywell,itisverydifficulttopredictthosewhowillnotbecomeaccustomedtoit.Ithasonoccasionbeennecessarytoremoveaperfectlysoundspringcantileverbridgefornootherreasonthanthatthepatientcouldnottoleratethefeelingof(hebar.Amorecommonproblemisthedifficultyofcleaningunderthebar,particu

61、larlyatitsconnectorwiththeretainer.Theeffectivewayofcleaningtheareaistopassdentaliloss,superfloss,orotherthreadmaterialovertheponticandalongthebarandtocleanbothunderitandundertheconnector.Thisrequiresconsiderabledexteritybythepatient.Anumberofspringcantileverbridgeshavefailedbecauseofperiodontaldise

62、aseonthepalatalsideoftheabutmentteeth.Theponticmayalsotraumatizethegingivalpapillaeoneithersideofitbecausethespringinessofthebarallowsthepontictomoveupanddownslightlyinuse.Thedesignofthebridgerequiresretentionoftheabutmentpreparationstobeverygood.Inexperiencedoperatorsshouldnotfallintothetrapofusing

63、springcantileverdesignsbecausetheylacktheconfidencetopreparesoundanteriorteethandprefertopractisebridgeworkusingposteriorabutmentsonly.Thedesignchosenshouldbethebestoneinthepatientsinterest,andiftheoperatorisnotsufficientlyexperiencedtocarryitoutheshouldreferthepatienttoacolleagueorseekguidanceindes

64、igningandmakingthebridge.ADVANTAGESFixed-fixed Robustdesignwithmaximumretentionandstrength Abutmentteetharesplintedtogether,maybeanadvantage,particularlywhenteethareuncomfortablymobilefollowingbonelossthroughperiodontaldiseaseThedesignisthemostpracticalforlargerbridges,particularlywhentherehasbeenpe

65、riodontaldisease Theconstructionisrelativelystraightforwardinthelaboratory CanbeusedforlongspansFixed-moveable Preparationsdonotneedtobeparalleltoeachother,sodivergentabutmentteethcanbeused Becausepreparationsdonotneedtobeparallel,eachpreparationcanbedesignedtoberetentiveindependentlyoftheotherpreparation(s