專(zhuān)業(yè)英語(yǔ) Unit 33教案.docx

11、ce,Inparticularitsrateoftemperaturerise. Figure92showsasimpleclassificationofminimal-preparationbridges;variationsofthistechniqueareshowninFigures94,95-b. MINIMALPREPARATIONBRIDGES DIRECT INDIRECT 1 1 MacroMechanical 1 MediumMechanical 1 MicroMechanical 1 Chemically Retention- Ret

12、ention-e.g.VinginiaSalt Retention-e.g. Adhesive-e.g. e.g.Rochette MeshCrystalBond Maryland I^navia-ex (seeFig.94) (seeFig.92) (seeFig.96) (seeEig.97) Figure92Asimpleclassificationofminimal-preparationbridges ?Directbridgesmaybeusingthecrownofthepatient'sowntooth.Thiscanoftenbedon

13、easasimpleandrapidwayofreplacingatoothlostthroughinjury(whichcannotbereimplanted)orwhichhastobeextractedurgently.Sometimesmetalmeshorwireisaddedtothelingualsurfacetoincreasestrength,butthisisnotalwaysnecessary.Ifthenaturalcrownofthetoothisnotavailableorisnotsuitable,anacrylicdenturetoothcanbeusedint

14、hesameway. ? Macro-mechanicallyretentivebridges(Rochette,seeFigure94)havelargeundercutperlorationsthroughthecast-metalplate,throughwhichthecompositeflows.Theseholesarecutinthewaxoracrylicpatternwithaburandarethencountersunk. ? Medium-mechanicalretentivesystemsallinvolveretentivefeaturescastasparto

15、fthemetalframework(seeFigure95).Theyalladdsignificantlyto(hecementfilmthicknessinsomeareas,atleast,oftheretainerandtheyallproducelarge,non-undercutlumpsofmetalonthefitsurfacewhichdonotcontributetoretentionbutwhichnecessitatearelativelythickretainer.Thesizeoftheretentivefeaturesisintermediatebetweenm

16、acroandmicromechanicalretentivesystems. Figure94 Arochettebridgereplacingonecentrelincisor.Theporcelainisyettobeaddedandthepalatalspurontheponticwillactasahandleuntilthebridgeisfinished,whenitwillberemoved. Figure95 Acast-meshbridge.Itisdifficulttoachievegoodadaptationofthemeshovertheentirer

17、etainersurfaceandneitheroftheseretainershasretentivefeaturesrightuptotheperiphery.Theaddedthicknessoftheretainercanalsobesee. ?Castingthemetalretainerandthenetchingthefitsurfaceproducesmicro-mechanicalretentionbyoneofthreemethods:electrolyticetchinginacidinthelaboratory,electrolyticetchingusingchai

18、rsideequipment.Orchemicaletchingwithahydrofluoricacidgeleitherin(helaboratoryoratthechairside.Althoughthesethreesystemsproducedifferentetchpatterns,theyareallveryretentive.Thesizeoftheretentivefeaturesisapproximatelyone-tenththatofthemedium-mechanicalretentivesystemsandtheretentivefeaturesareundercu

19、tfromthesurface.Thesmallersizeoftheseetchpitsandtheabsenceofunnecessarynon-retentivefeatures(asinthemedium-mechanicalretentivesystems)allowthinnermetalretainersandathinnercementfilmthickness. Figure96aAMarylandbridge,thedesigneisunsatisfactoryinthattheextensiondistallyontothethirdmolartoothtoincr

20、easeretentionwouldgiverisetnanimpossiblecleaningproblembetweenthesecondandthirdmolar.ThisIsatechniquebridge,notmadeforepatient.Itisshowntoillustrateacommondesignerror. ?Chemicallyretentiveresinsarenowavailable.Severalhavebeenmarketedandsome(forexample.Panavia-Ex)haveperformedwellinsomelaboratorya

21、ndshort-termclinicaltrials.Theyadherechemicallytorecentlysandblastedmetalsurfacesandarcretainedonthetoothbyconventionalacid-etchingof(heenamel. Comparisonofindirectminimal-preparationretentionsystems Anumberoflaboratorystudiesandclinicaltrialshaveshown(ha(themicro-mechanicalandchemicaladhesivesyst

22、emsarethemostretentive.However,thechemicaladhesivesystemshaveonlybeenavailableforashorttimeandlonger-termclinicaltrialsarenecessarybeforeitissafetorelytooheavilyonthissystem. ThedisadvantageofthemiciO-mcchanicalretentionsystemisthatthemetalframeworkshouldnotbetriedin(hemouthafterthesurfacehasbeenet

23、ched.Thisisbecause(heverydelicateetchpatternmaywellbedamagedorcloggedbydepositsfromsaliva.Thismeansthattheidealistotryintheunetchedframeworkandtheneitherreturnittothelaboratoryforetchingoretchita(thechairsidc.Thistakestimeandthereforeaddstothecost. Themacro-mechanicalretentivedesign(Rochette)overco

24、mesthisproblembutislessretentiveinmostcasesandbecauseitiscementedwithaconventionalcompositeandthecompositecomesthroughtheperforationstothemouth,itispronetodegradationoveraperiodofyears.However,themainadvantageoftheRochettebridgeisthatilcanberemovedfromthemouthfairlyeasily.Thecompositeisdrilledoutfro

25、mtheholesandthebridgecanusuallyberemovedwithout(oomuchforce.For(hisreasontheRochettebridgeisstillusedwhentheabutmentteethhaveapoorprognosisandwhenfurthermodificationsarelikelytobenecessaryforexample,whenonelowerincisorisbeingreplacedforperiodontalreasonsandtheotherteetharestillreceivingperiodontaltr

26、eatment.TheRochettedesignisalsousedforimmediateinsertionbridgessothatthebridgecanberemovedwhenthetissueshavehealedandtheponticadaptedtotheridgeorthebridgeremade. Historically,themcdium-mcchanicalretentivesystemsweredevelopedaftertheRochetteandMarylanddesignsinanattempttoovercomethedisadvantagesofth

27、esedescribedabove.However,theyhavedisadvantagesoftheirowninbeinglessretentivethanthemicro-mechanicalsystemandyethavingthickermetalretainersandathickercementfilm.Oneadvantage,however,isthattheycanbemadeinanymetal,includingpreciousmetals,whereastheetchedsystemscanonlybemadeinbasemetalalloyswhichareetc

28、hable. Disadvantageofminimal*preparationbridgesingeneral Asthemetalplateisaddedtothesurfaceofthetoothratherthanreplacingpartofit,thethicknessofthetoothisincreasedandmay-forexample,inanonnalClassincisorrelationshipinterferewiththeocclusionunlessspaceiscreatedonhodonticallyorbygrindingtheopposingtee

29、th. Themarginoftheretainerinevitablyproducesaledgewhereplaquecancollect.Thisisaproblemespeciallyinthereplacementoflowerincisors.Hereplaqueandcalculusdepositsarecommononthelingualsurfacetowardsthegingivalmarginandthepresenceofsuchaledgecanonlymakeitmoredifficultforthepatienttocleaninthisarea.Another

30、exampleofadesignthatwouldpreventgoodoralhygieneisshowninFigure96a. PracticalPoints ? Thefourbasicbridgedesignsdifferinthesupportprovideateachendof(hepontic. ?Thebasicdesignscanbecombinedtogive,forexample,afixed-fixed/cantileverdesign. ? Simpler,lessdestructiveminimal-preparationbridgesareuseful,

31、particularlyinyoungerpatiens. ? Bridgesthatarcmadetoberemovablebythedentistmakefurtherendodonticorperiodontaltreatmentpossible;thosepatientscanremovemakecleaningeasier. ? Inexperiencedoperatorsshouldnotusespringcantileverdesignsasasoftoptiontopreparingsoundanteriorteeth. VOCABULARY 1.Abridge 橋

32、 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

33、 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-ceramicbridge 26. Ceramicbr

34、idge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. leverageforce retainerandtheabutmenttoothismuchstronger.However,itissometimesnotstrongenoughanddebondingsometimesoccursasaresultofamechanismsimilartothatshowninFigure86.Thisprobablypartlyaccountsforthehigherincidenceofretentionfailurewithminimal-prepara

35、tionbridgesthanwithconventionalbridge. Atonetimeitwasthoughtthatthesupportfortheabutmentteethateachendofafixed-fixedbridgeshouldbesimilar.Inotherwords,therootsurfaceareaoftheabutmentsshouldbeapproximatelythesame.Todaythisisnotconsiderednecessary. Afixcd-movcablcbridgehasarigidconnector,usuallyatth

36、edistalendoftheponticandamoveableconnectorthatallowssomeverticalmovementofthemesialabutmenttooth.Themoveableconnectorshouldresistbothseparationoftheponticfromtheretainerandlateralmovementof(hepontic(seeFigure87). Figure85Fourbasicbridgedesignsofconventionalbridges. aFixed-fixeddesignBothupperand

37、lowerbridgewillbefixed-fixed,thelowerretainedbyfullcrownsonthecaninetoothandcentralincisor.Theupperbridgewillberetainedbythecanineteethonly. Fixed-moveablebridge Occasionallythefixedandmoveableconnectorsarereversedbutthishasanumberofdisadvantages.Theretainerwiththemoveableconnector(theminorretai

38、ner)issmallerandlessvisibleandsoisbetterinthemoreanteriorabutmenttooth.Mesialdrifttendstounseatdistalmoveableconnectors,butisresistedbymesialones. Themoveableconnectorcanbeseparatedbeforethebridgeiscementedandsothetwopartsofthebridgecanbecementedseparately.Theabutmentteethdonotthereforehavetobeprep

39、aredparalleltoeachotherand(heretentionfortheminorretainerdoesnotneedtobeasextensiveasforthemajorretainer.Neitherdoesitneedfullocclusalprotection,(occlusalforcesappliedtothetoothsurfacenotcoveredbytheretainerwilldepressthetoothinitssocketandtherewillbemovementatThemoveablejointratherthanrupturingofth

40、ecementlute(seeFigure86).  bFixed-moveabledesignwithDoinlayinthelowerseenpremolarandfullcrownonthemolartooth.Thisbridgehasbeenpresentfortwentyyears,infeetsolongthattheocclusalsurfaceofthecrownhaswornthrough(seeChapter13).ThemoveableJointcanbeseenbetweentheponticandtheminorretainer.Itwouldnotnorma

41、llybeasobviousasthis. CCantileverdesignBothlateralincisorsareponticssupportedbycrownsonthecanineteeth.Bothbridgesareall-porcelainandtherightonehasbeenpresentforfourteenyears.Theleftonefracturedfatersevenyearsandwasreplacedwithanotherallporcelainbridge,whichisstillpresent. dSpringcantileverde

42、signwithfirstmolartoothasabutment.Thereisamidlinediastemaandadiastemabetweenthelateralincisorandcanineonthesideofthemissingcentralincisor.Anyotherbridgedesignwouldhaveinvolvedclosingoneorbothofthesespecs. Afixcd-movcahlcminimal-preparationbridgecannothavethemoveablejointwithinthecontourof(heorigina

43、labutmenttooth,asthisisnotpreparedsufficientlyforthemoveableconnector.Thismeansthatthemoveableconnectorisintheponticofthebridgeandisusuallyathroughandthroughtubeandpinarrangement.Thismeansthatthe(wopartsofthebridgeareconnectedbutifeitherdebondsthenitcanberemovedwithoutdisturbingtheotherpartofthebrid

44、geandrecemented. However,thisdesignofmoveablejointiscumbersomeandtheundersurface,whichapproximatestheridge,isdifficulttoclean.Itisthereforenotcommonlyused. Figure86 Aconventionalfixed-fixedbridgeshouldhavealltheoccludingsurfacesoftheabutmentteethprotectedbytheretainers,otherwiseanocclusalforcedir

45、ectedattheunprotectedareawilldepresstheabutmenttoothinitssocketwhilethebridgeandtheotherabutmenttoothholdtheretainer.Thiswillbreakdownthecementlute,causingleakage.Theretainerisheldinplacebythebridgeandsosecondarycariesdevelopsrapidly(seeFigure146.page232) Figure87 aAniveablecibbectirmseorated.

46、 bAcrylicburn-outpatternsforpatternsformoveableconnectors.TheblueIsverytapered,theredmoreparallel-sided. Cantileverbridge Acantileverbridgeprovidessupportfortheponticatoneendonly.Theponticmaybeattachedtoasingleretaineror(otwoormoreretainerssplintedtogether,buthasnoconnectionattheotherendofthe

47、pontic.Theabutmenttoothorteethforacantileverbridgemaybeeithermesialordistaltothespanbutforsmallbridgesareusuallydistal. Springcantileverbridge Springcantileverbridgesarcrestrictedtothereplacementofupperincisorteeth.Onlyoneponticcanbesupportedbyaspringcantileverbridge.Thisisattachedtotheendofalongm

48、etalarmrunninghighintothepalateandthensweepingdowntoarigidconnectoronthepalatalsideofasingleretainerorapairofsplintedretainers.Thearmismadelongandfairlythinsothatitisspringy,butnotsothinthatitwilldeformpermanentlywithnormalocclusalsurfaces(i.e.,exceedtheelasticlimit).Forcesappliedtotheponticareabsor

49、bedbythespringinessofthearmandbydisplacementofthesofttissuesofthepalatesothatexcessiveleverageforcesdonotdisturbtheabutmentteeth.Theabutmentsareusuallythetwopremolarteethsplintedtogether,orasinglepremolarormolartooth. Combinationdesigns Thefourbasicdesignscanbecombinedinavarietyofways.Inparticular

50、,thefixed-fixedandcantileverdesignsareoftencombined.Inlargerbridgesadditionalcantileverpoliticsmaybesuspendedfromtheendofalargefixed-fixedsection(seeFigure88).Similarly,itispossibletocombinefixed-fixedandfixed-moveabledesigns. Itislesscommonforspringcantileverbridgestobecombinedwithothertypesofbrid

51、ge,butoccasionallyaspringcantileverarmisattachedtoaposteriorfixed-fixedbridge. Itispossibletocombineabridgewitharemovablebuccalflangethatreplaceslostalveolartissue. Hybriddesigns Therearethreedifferenlhybriddesigns: ? Fixed-fixedwithoneconventionalandoneminimal-preparationretainer ? Fixed-movea

52、blewithaminimal-preparationretainercarryingthemoveableconnector ? Fixed-movablewiththeconventionalretainercarryingthemoveableconnector. Thefirsttwodesignsshouldnotbeused.Ineithercaseiftheminimal-preparationretainerbecomesdebondedthenitwillnotbepossibletorecementitwithoutremovingtheconventionalreta

53、inerwhomaywellinvolvedestroyingthebridge. Thethirddesignisacceptableandmaywellbe(heoneofchoicegivencircumstancesinwhichoneoftheabutmentteeth(usuallythemesialone)alreadyhasarestorationwhichcouldbereplacedbymeansofaninlayorotherconventionalretainer.Theotherabutmenttoothisunrestoredortherestorationdoe

54、snotinvolvethesurfacestobecoveredbyaminimal-preparationretainer.Thesecircumstancesoccursurprisinglycommonlyandsothisdesignofbridgeisbeingusedincreasing. Variations Removablebridges Allthedesignsdescribedsofararepermanentlycementedinthepatient'smouth.Withlargebridges(herearedisadvantagesinpermanen

55、tcementationinthatthemaintenanceandfurtherendodonticorperiodontaltreatmentofabutmentteethisdifficult,andifsomethinggoeswrongwithonepartofthebridgeorwithoneoftheabutmentteeth,usuallythewholebridgehastobesacrificed.Forthisreasonlargerbridges,includingfullarchbridges,aresometimesmadesothatthedentistwit

56、houtbeingdestroyedcanremovethem.Cementingindividualcastgoldcopingstoeachoftheabutmentteethdoesthis.Someofthecopingshavethreadedsleevessolderedintothem,andthebridgeisthencementedtothesecopingswithweakcement.Itisheldinplacewithlinescrewsthatpasthroughholesin.theretainersofthebridgeintothethreadedslee

57、ves. Figure88 Alargesplint/bndgewithcantileveredpontics.aTheworkingdies. Figure88bThemetalframeworkshowingtwocantileveredponticsontherightofthepicture. Inothercasesthebridgeisremovablebythepatientandhasnocementorscrews.Theadvantageofthisisthatcleaningaroundtheabutmentteethandundertheponticsi

58、smucheasier.Thebridgehastowithstandhandlingbythepatientandsoitisusuallymadeinabasemetalwithacrylicfacings.Thebasemetalismorerigidthanapreciousmetalframeworkandtheacrylicfacingsarclessliabletochipifthebridgeisdropped.Theycanalsobereplacedwithouttheriskofdistortingtheframework. Advantagesanddisadvant

59、ageofthefourbasicdesigns Acomparisonofconventionalfixed-fixed,fixed-moveableandcantileverbridgesisshownonpage240-241Springcantileverbridgesarediscussedseparately. Springcantileverbridge Thesearedealtwithseparatelybecausetheyareusedonlytoreplaceupperincisorteeth,usuallywhentherearcspacesbetweenthe

60、incisorteethandtheadjacentpotentialabutmentteetharesound.Theyshouldnotbeusedtoreplacelowerincisorsastheshapeoftheridgeandtheresilienceofthesofttissuesarcnotsuitedtoabsorbingpartoftheocclusalloading. Theadvantagesofthedesignare:theponticnotbeingattachedtoadjacentteeth,spacescanbepreservedbothsidesof

61、it,andthesoundnaturalanteriorteethdonotneedtobepreparedasabutments. Disadvantages:somepatientsfindthepermanentbarrunningacrossthepalateintolerable. Althoughmostgetusedtothissurprisinglywell,itisverydifficulttopredictthosewhowillnotbecomeaccustomedtoit.Ithasonoccasionbeennecessarytoremoveaperfectly

62、soundspringcantileverbridgefornootherreasonthanthatthepatientcouldnottoleratethefeelingof(hebar. Amorecommonproblemisthedifficultyofcleaningunderthebar,particularlyatitsconnectorwiththeretainer.Theeffectivewayofcleaningtheareaistopassdentaliloss,superfloss,orotherthreadmaterialovertheponticandalong

63、thebarandtocleanbothunderitandundertheconnector.Thisrequiresconsiderabledexteritybythepatient.Anumberofspringcantileverbridgeshavefailedbecauseofperiodontaldiseaseonthepalatalsideoftheabutmentteeth. Theponticmayalsotraumatizethegingivalpapillaeoneithersideofitbecausethespringinessofthebarallowsthep

64、ontictomoveupanddownslightlyinuse.Thedesignofthebridgerequiresretentionoftheabutmentpreparationstobeverygood. Inexperiencedoperatorsshouldnotfallintothetrapofusingspringcantileverdesignsbecausetheylacktheconfidencetopreparesoundanteriorteethandprefertopractisebridgeworkusingposteriorabutmentsonly.T

65、hedesignchosenshouldbethebestoneinthepatient'sinterest,andiftheoperatorisnotsufficientlyexperiencedtocarryitoutheshouldreferthepatienttoacolleagueorseekguidanceindesigningandmakingthebridge. ADVANTAGES Fixed-fixed ? Robustdesignwithmaximumretentionandstrength ? Abutmentteetharesplintedtogether,m

66、aybeanadvantage,particularlywhenteethareuncomfortablymobilefollowingbonelossthroughperiodontaldisease ?Thedesignisthemostpracticalforlargerbridges,particularlywhentherehasbeenperiodontaldisease ? Theconstructionisrelativelystraightforwardinthelaboratory ? Canbeusedforlongspans Fixed-moveable ? Preparationsdonotneedtobeparalleltoeachother,sodivergentabutmentteethcanbeused ? Becausepreparationsdonotneedtobeparallel,eachpreparationcanbedesignedtoberetentiveindependentlyoftheotherpreparation(s