\ Atlas of Principlesand icalApplications Preface AtlasofOrthodontics:PrinciplesandCl inicalApplicationswaswrittenwiththe intentiontointroducetotheworldof clinicalorthodonticsitsfirstillustratedtext. Thiscolorful .methodologicalpresentationofthemostup-tartAPreliminary Examination of till!Patient Iocclusion.Ifthereisexcessmaxillarytoothmaterial,wewillendupwithan excessiveOJ(secFig.FS.8);iftheexcessisinthemandibulararch,thenminimal OB/ OJwillexist and the cuspids willocclude in a slightclass IIIrelation. Alargepercentageof patientshavemesial-distaltooth-sizediscrepancies,approxi-mately13.8%and9.2%forthemandibularandmaxillarydentitions,respectively. I I Suchdiscrepancies,ifleftunt reated,couldleadtofutureposttreatmentrelapse,espe-ciall yinthemandibularincisorarea.Interproximalreductionwi ll ,inmostcases, alleviate such discrepancies. AmethodusedtoassessTSDisBollon'sanal ysis.1,llIf alterations of toothsizeare tobedoneintheupperarch,thesumofthewidthoftheloweranteriorteethis multipliedby1.3togivethedi mensionsoftheidealupperarchfortheseparticul ar lower anteriors.IO If alterat ionsof toothsizearetobe doneinthelower arch, thenthe widthof theupperanteriorteethismultipliedby.775togi vetheideallowerarch.1O IftheTSDisint heposteriorteeth,thentheymaybeselectivelyreducedinwidth, enoughtoobtai naclassI cuspidrelation(seeFigs.F3.7,F3.8).Interproxi malreduc-tionshouldbedoneintheupperorlowerarchinordertomaketheseteethfitin relation totheir counterparts. References I.OkesonIP: Managementof TemporomandibularDisorders and Occ/usion,2nded.St.Louis.MO:C. V. Mosby Co..1989. 2.MolalNO,urb GA,CarlssonGE,andRughSO:ATexlbookof Occ/usiOll.Chicago:Quintessence Publishing,1988. 3.AmericanAcademyof CraniomandibularDisorders:Craniomandibufar{Jisordcrs: Guidelines for ~ a f uotion, Diagnosis and Management.McNeillC, ed.Chicago:QuintessencePublishing,1990. 4.ParkerWS:Centricrelationandcentri cocclusion - Anorthodonticresponsibility.AmJOrthod Dentofacial Orthop 74:481-500,1978. 5.HarrisEF,andJohnsonMG:Heritabili tyof craniometricandocclusalvariables:Alongitudi nalsib anal ysis.Am JOrthod Dentofacial Orthop 99:258-26g,1991. 6.Carlson G: AdvancesinOrthodontics:Seminar Series (Course Syllabus). Minneapolis.MN.1988. 7.ProffitWR: Contemporary Orlhodonlics.St.Louis,MO:C. V. Mosby Co.,1986. 8.RichardsonME: Theroleof thethirdmolarinthecauseof latelowerarchcrowding:Areview.AmJ OrthodDcntofacialOrthop 95:79- 83.1989. 9.VadiakasG,andViazisAD:Anteriorcrossbiteconnecti onintheprimarydentition.AmJOrthod Dentofacial Orthop102: 160 - 162,1992. 10.WolfordLM:Surgical- onhodonticoom:ct ionof dentofacialandcraniofacialdeformities-Syllabus. Baylor Col lege of Dentistry,Dallas. TX,1990. II.CrosbyDR.andAlexanderRG:Theoccurrenceof toothsizediscrepanciesamong differentmalocclu-siongroups.AmJOrthod Dentofacial Orthop 95:457 - 461,1989. 12.BoltonWA:Theclinicalapplicationof toothsi zeanal ysis.AmJOrthodDcntofacialOrthop48:504 -529,1962. Ii , ellaler JRadiographicEvaluation A carefuldentalandrndiographic (panoramic or peri apical) evaluationmay revealanumber of situationsthatneedtobeaddressedbeforetheinitiationoforthodonticmechano-therapy. Ankylosis Ankylosis, 'alocalizedfusionofalveolarboneandcementum,istheresultofa defectiveordiscontinuousperiodontalmembraneandisapparentl ycausedbyme-chanical,thermal,ormetabolictraumatotheperiodontalmembraneduringorafter toot heruption.Itoccursmostoftenintheprimarydentition(seeFig.010.8)inthe mandibularteeth,andinmolars.Itcansometimesbedetectedfromradiographic evidenceof periodontalmembraneobliterationorbyasharporringingsoundupon percussionandbylackof toothmobilityorsoreness,evenwi thheavy,continuous orthodontic forces.' Inthepri marydentition, ankylosisisusuallytreatedby simpleneglect,restoration, orextraction.l Ankylosisofapermanenttooth,however,ismorecomplicatedif orthodontictreatmentisplanned.Interventioncanincludeluxation,corticotomy,or ostectomy. I Mostinfra-occludedandankyloscdprimarymolarswithapermanentsuccessor exfoliatenormall y.2Thedecreasedheightof thealveolarbonelevel atthesi teof the infra-occludedprimarymolarhas beenreponedtonormali zeafterthe eruption of the permanentsuccessor.Infra-occlusionandankylosisofprimarymolarsdocsnotcon-stitute a general riskof futurealveolar bonelossmesial to thefi rstpermanent molars. Primary Failure of Eruption Primaryfailureoferuptiondescribesaconditioninwhichnonankylosed,usuall y posteriorteethfailtoerupt,eitherfull y or partially,becauseof fai lureof theeruption mechanism.l-S Theteethmostcommonl yinvolvedarethedeciduousandpermanent molars,althoughpremolarsandcuspidsmay alsobeaffected.$Thereappearstobeno mechanicalimpedimenttoeruptioninthesecases. 'Unilateral situationsoccurmore frequentlythanbilateralones.Aposterioropenbite,causedbyaprimaryfailureof eruption,willnotrespondtoorthodontictreatment ;asegmentalalveolarosteotomy offersthe only possibletreatmentmodality. Diastemas Midlinediastemasarcquitecommonamongindividuals(seeFig.F4.11).Closing themposesnoproblemorthodontically,butinmanypatientstheylendtore-open, especially if causedbyanabnormallabial frcnum.6 14PartAI'fI'fimi nary Examination oj lhePath'nl Itisimportanttoclosethespaceorthodonti call yassoonaspossibleandthen performthesurgicalprocedureof abnonnallabialfrenum,thusallowinghealingof thetissuestooccurwiththeteethintheirnewlyestablishedpositions.6 Itissuggested thatwhenthefrenumiswideandattachedbelowthemucogi ngivalj uncti onin ker'J.tinj zedtissue,itoftenwillregenerateafterfrenectomy. 'Topreventthisfrom occurring,epi thelialgraftfromthepalateisplacedovertheareaonremovalof the frenum,preventing itsingrowth.' Root Resorption Rootresorptionoccursineverypatientwhoundergoesorthodontictreatment.Inthe majorityof cases,itisamereblunting of therootapices.Insomepati ents,itismore severeforreasonsthatseemtobeidiopathic.wit htheexceptionof previousl ytrau-mat izedteeth,whicharemoresusceptibletoresorpti onandlossofvital it y(Fig. A4. 1).'Around16.5%ofpatientshaveapproximatelyImmofresorpti onofthe maxillaryincisorteeth.'Maxillaryincisorshavebeenreportedtobethemostsuscep-tibletothissevereresorpti on,withotherteethlessaffected.Arecentstudyshowed that3%ofpatientshavesevereresorption(greatertha noneq uarteroftheroot length) of bothmaxillary centralincisors (Fig. A4.2). Lessresorpti onisobservedinpatientstreatedbeforeageIIyears,perhapsduetoa preventiveeffectofthethicklayerof predentinonyoung,undevel opedrool s.9 Con-tactofmaxi ll aryincisorswit hthelingualcort icalplatemaypredisposetoresorption.' ClassIII patients are overrepresentedinthe group withsevereresorption.' FigureA4.1Traumatothesecentralincisorsfromabicycle accidentledtotheirsevererootresorptionandlossof vitality. F I ~ of roo , A4,2 FigureA4.2Resorpt ionof centralincisorteethafter2years of orthodontictreatment.One quarter toonethirdof these roolShavebeenlost. Chapter 4Radiographic EI'afliation15 Thelongertheactivetreatmenttime,thegreaterthechanceof severeresorption. Obviously,apatientwit hsmall,roundedrootsisnotagoodcandi dateforexcessive toothmovement.Iatrogenicrootresorpti oniscausedbyj igglingteethoverlong periodsoftime,indecisivetreatmentthatcausescha ngesinthedirectionoftooth movement,andproximatingofthecorticalplate.1O Norelationhasbeenfound betweentheamountof rootshorteninganddegreeof intrusionachieved,!1Ingeneral, treatmenttimeisthemostsignificantfactorforoccurrenceof rootshortening.Ina recentlong-tennevaluationofrootresorpti onoccurringduringorthodontictreat-ment,itwasshownthattherearenoapparentchangesafterapplianceremovalexcept remodeling of roughand sharp edges.!2 Impacted Cuspids Impacti onof the cuspidtccthll-20 iscausedprimarilybytheraleof rootresorpti onof thedeciduoustccth,disturbancesintootheruption.toothsize/ archlengthdiscrepan-cies,rotationortraumaof toothbuds,prematurerOOIclosure,ankylosis,cysticor neoplasti cformation, clefts,andidiopathiccauses.Mostoftheimpacti onsarcuni lat-eralandonthepalatalside. 16Theevidenceof maxillaryimpactionrangesfrom0.92% to2.2%;maxill aryimpactionistwi ceascommoninfemalesthaninmales, I6The incidenceofmandibularimpactionismuchless,0.35%,16Impactedcuspidsmay causeresorpti onof theadjacentincisorteeth;thus,theirextractionor uncovering and movementintothcdentalarchisnecessary(Fig.A4.3).Potentialincisorresorption casesfromimpactedcuspidsarethoseinwhichthecuspidcuspinperiapicaland panoramicfilmsispositionedmediall ytothemidlineofthelateralincisor(0.71 %).!6 The ri skof resorptionalso increases withamoremesial hori zontal pathof eruption.2! 16J'art "Prriimmar}' Examinalioll of/hI' I'miml M.3 FigureA4.3 Animpacted cuspidhas causedalmostcomplete resorptionofthelateralincisortoothandsignificantde-structi on of the centralincisor tooth. Surgicaluncovering of theseteethisthestandardtreatmentprocedure,followedby directbondingof anorthodonti cbracketontothetoothandmechanicaltractionwit h elasti csorspringstobringtheteethintothearch(seeFig.F4.58).Anapicall y reposit ionednapforlabiallysituatedcuspidsisrecommended. I.Adequateattached gingivaneedbepresent(orsurgicallyplaced)toavoidmucogingivalproblems.Wire ligation("lasso"type)insteadof directbracketplacementonto theuncoveredtoothis prohibitedbecauseitleadstolossof attachmentandtoexternalrootresorptionand ankylosisYInaddition,anysurgicalexposurebeyondthecement - enamel junction leads tobone loss. Treatmentofcaseswithimpactedcuspidsisquitelengthy,dependingonthe positionandorientationof theimpactedtoothinthebone.'6'7 Itmaytakebetween 12and30months.Also, attheendof treatment, theseteethwillshowthepresenceof a5- to7-mmpocket,usuall yonthedistalside.Theydisplaysignificantl ymoreloss ofperiodontalsupportonthebuccalandpalatalsurfacesthandonormalteeth.11 Excellentoralhygiene wi llpreserve these teeththroughoutlife withoutfurthersequelae. Analternativetosurgicaluncoveringandlengthyorthodontictreatmentofim-pactedteethistheautotransplantationof theseteeth.Autotransplantationshouldbe performedatastagewhenoptimalrootdevelopmentofthetransplantmaybe expected;namely,onehalf tothreequartersof thefullrootlength. I' Whentransplan-tationisperformedatanearli erstageof rootdevelopment,thefinalrootlengthmay beshorterthandesirable.If autotransplantationisperformedatalaterstageof root development.theri skof rootresorpti onincreases.Thesurgicalprocedureshouldbe asatraumatic as possible andrequires a surgeon wellacquainted withthemethod. Teethtransplantedwithincompleteandcompleterootformationshow96%and 15%pulphealing,respcctively.'9Thesizeoftheapicalforamenandpossibl ythe avoidanceofbacterialcontaminationduringthesurgicalprocedureareexplanatory factorsforpulpalhealing.Traumatotheperiodontalligament(PDL)ofthetrans-plantisthe explanatoryfactorforthe development of rootrcsorption. '9 .'" in&! cu. Cliapll'r 4Radiographicf :l'ulliulion17 Arairlynewtechnique,transalveolartransplantation,isusedtoremovelarge amountsorbonewithaburexceptrorathinlayerclosetotherootsurface.20This boneisthenverygent lyremovedwithanelevator toavoiddamagetothecement um. Thetoothisstoredinthesocketthroughouttheoperativeprocedure.Finally.the cuspidismovedthroughthealveolarprocessintoitsdeterminedposition.Asecti onal archwireisusedtostabilizebutnotimmobil izethetransplantedcuspid.Sometimes, grindingor theantagonisttoothisrequiredtoavoidtraumaticocclusion.Apostoper-ati veorthodonticappliancecheckisperrormedIweeklater,whenthesuturesare removed.Further orthodonti c controls areperformedevery 2 weeksror 6to 8 weeks. Tooth Transpositions A4.4 Transpositionhasbeendescribedasaninterchangeinthepositionor twopermanent teethwithinthesamequadrantorthedentalarch.22-nThemaxillarypermanent cuspidisthetoothmostrrequentl yinvolvedintranspositionwiththefirstbicus-p i d . 2 2 , 2 ~lessortenwiththelateralincisor(Fig.A4.4).1224Theretaineddeciduous cuspidmaybetheprimarycausefordeviationofthepermanentcuspi dfromits normalpath of erupti on. Ifthemandibularcuspidandlateralincisorhavealreadyeruptedintheirtrans-posedposition,correcti ontotheirnonnalpositionshouldusuall ynotbeattempted.22 Al ignmentintheirtransposedpositionwi threshapingof theirincisalsurraceswilln01 damagethetcct horsupportingstructuresandwillpresentanacceptableesthetic result .Ifoneorthetransposedoradjacentteethisseverelyaffectedbycariesor traumaorifthereisaseverelackorspace,extractionofthattoothshouldbe considered.2223 Ir toothmovementisundertakentocorrectthetranspositi on,inorder toavoidrootinterferenceorresorptionduringtreatmentandtopreventbonylossat thecorticalplateof thelabiallypositionedcuspid,thetransposedtooth(premolaror lateralincisor)shouldfirstbemovedpalatally,enoughtoallowrorafrcemovement of thecuspidtoitsnormalplace.22.23Thislastmet hodistheleastdesirabletreatment of choice. FigureAU Transposedmaxillaryrightcuspid.asitis erupt-ingdistaltothefirstbicuspid.Notetheretainedprimary cuspKl . 18Part APrelimi/Jaf}' Examinalionoj/he Paliem Supernumerary Teeth Supernumerary(extrateeth)orcongenitall ymissingteethoccurQuitefrequentl y amongpatients.u Themostcommonsituationof asupernumerarytoothisameso-densbetweenthecentralincisors,whichmaypreventtheirnonnaleruption.The mostfrequentmissingteetharetheupperlaterals(seeFig.F5.30),followedbythe lowersecondbicuspids,theuppersecondbicuspids, andlower incisors.Of course,the thirdmolars (wisdomteeth) arcmissing inalargepercentage of thepopulation. Third Molars Theroleofmandibularthirdmolarsintherelapseof loweranteriorcrowdingafter thecessationof retentioninorthodonticall ytreatedcaseshasprovokedmuchspecu lationinthedentalliteratureovermanyyears.21Mostpractitionersareof theopinion thatthirdmolarssometimesproducecrowdingof themandibularanleriorteeth.2A numberof studiesoverrecentyearshavesubstantiatedveryclearlythatthepresence of thirdmolarsdoesnotappeartoproduceagreaterdegreeof loweranteriorcrowd ingthanthatwhichoccursinpatientswithnothirdmolars. 21 . 29Therefore,the recommendationformandibularthirdmolarremovalwiththeobjectiveof relieving interdentalpressureandthus alleviatingor preventingmandibularincisorcrowdingis not justified.28,29 References I.PhelanMK,MossRBJr..PowellRS,andWombleBA: Orthodonticmanagement of ankyloseartCGrQw/1! Cl .S FigureCl.5Amandibular advancementorthognathicproce-dureisthesurgeryperformedonpatientswithmandibular rctrognathia. Cl .6 FigureCl .6 ThesamepatientasinFigureCU afterortho-donti ctreatmentandsurgery.NotetheimprovementintM patient'Sprofile. FigureCl.7Thedentitionaftersurgeryinthepalientseen inFigure CU. Ct.8 FigureCUSue rognathia.N o t ~ isafun(100\ 150% OS!). FigureCUI onhodontio (mandibula molar relat CI .8 FigureC1.8Buccalviewof apatientwithmandibularrel-rognathia.NotetheISmmoverjet.Themolarrelationship isafull(I()()C\()classII.Thebiteisverydeep(morethan 150%OB!). CUD FigureCUD Buccalviewof thepatientinFigureCL8after CI1hodontictreatmentfollowedbyonhognathicsurgery (mandibularadvancement).NotetheclassIcuspidand molarrelationship. Chaptt'lIGro ....thCOIlsidl'rat ions83 C1.9 FigureC1 .9Anteriorvicwof thesamepatientasinFigure C I.8. C1.11 FigureCl .11Anteriorviewof thepatientinFigureCLIO. Note the dramati c improvement inthe overbiterelationship. 84Part CGrow/h FigureC1.12AIO-year-oldgirlwithevidentmandibular prognathism. FigureCl .14SamepatientasinFigureC1.l2afterpuberty andcessationofmandibulargrowth.Notetheprognathic profile. FigureC1.13Samepati entasinFigureC1.12.Rightbuccal viewof theocclusion.Notetheret roclinedlowerinci sors andthe cnd-to-endmultiple crossbites. Cl .15 FigureC1.15SamepatientasinFigureC1.I 4.Fued onho-donlicappli ances in prepamtion forsurgery. CU6 FIgureC1. ularselba a positi ve AgureC1. viewoftI inthe00 relatio nsll .. C1.16 FigureC1.1BSame patienlasinFigure CJ.l4.Inamandib-ularsetbackprocedure,themandibleisbroughtbackuntil a positiveoverjetis achieved. FigureC1.1BSamepatientasinFigureC1.I 7.Rightbuccal ,iewof theoccl usionaftersurgery.Notetheimprovement intheocclusion.Thecuspidteet hareinasolidclassI rdationship. Ch. plerIGrQwthConsiderations85 F"l{IureC1 . 17Patient shown inFigure CI.I 4 after surgery. C1.19 FigureC1.19Cephalometricradiographofapatientwit ha signifi cant verticalproblem. 86Part CGrowth -n _OP E>BITE Cl .20 FigureCl .20SamepatientasinFigure C 1.I 9.Thecephalo-metrictracingrevealsa6.5-mmopenbite,highmandibular plane angle (32"), and averylong lower face. FigureCl .21Rightbuccalviewof thesamepatientasin FigureCI. 19.Notetheextentof theopenbitealltheway to theposterior teeth. FigureCl.22Anteriorviewof thesamepatientasinFigurt C1.I9.Notethe"rainbow"appearanceof theskeletalopec bite. FigureCl.23Incaseswithsuchasignificantverticalprob-lem, aleFortI osteotomy ispcrfonned above themaxilla . FigureCl.24Asegmentof boneisremovedandthewhol maxillaisrepositionedsuperiorly.Inmostinstances,tb: mandibleautorotatesandaidsintheclosingoftheOpe! bite. Fig...,.Cl posterior problem): ....... C1.25. FIgureCl .25Patientwithmandibularprognathism(antero-posteriorprobl em)andaverylonglowerface(vert ical problem). C1.27 f9Jl1lCl .27Anteriorviewof thesamepatientasinFigure e1.25.Thiscaserequiresadouble-jawort hognathicap-proach(three-pi ecemaxi ll aryleFortIosteotomyanda mandibularprocedure). napier 1GrowthCOfuidcralions87 Cl .26 FIgureC1.26SamepatientasinFigureCL2S.Rightbuccal viewoftheocclusion.Notethattheopenbi teextends posteriorly tothemolar area. Cl .26 FtgureCl .28Cephalometricradiographofthepatientin Figure CI.2S. 88Plrt CGrQI'I1h n ' Cl.29 , ,1. " FigureC1.30Skeletalasymmetryorthejawsasaresultof mandibularprognathism.Amandibularorthognathicpro-cedure is thetreatment of choice. FigureC1.29Thecephal ometrictracing andanalysisreveals averyhi ghmandibularplane(37 ).alargemandiblerela-ti vetothesizeor themaxilla(ratio,1: 2. 15),anda1-mm openbite.Suchacaseisalmostimpossibletotreatwith orthodonticmeans alone atany age. References I.SkieUerV.BjOrkA.andLinde-HausenT:Predictionor maodibular growthrotat ionevaluatedfroma longilUdinal implant sample.Am JOrthod 86:359- ) 10,1984. 2.SolowB:Thedentoalveolarcompensatorymechanism:Backgroundandclinicalimplication.BrJ Orthod 1: 145- 16 1, 1980. 3.NielsenIL:Ven icalmalocclusions:Etiology,development,diagnosisandsomeaspectsof treatment. Angle Onhod 61:241-260, 1991. 4.KomEL,andBaumrindS:Transversedevelopmentof thehumanjaws betweentheages8.5and15.5 years.studied longitudinallywithuseof implants. J DentRes 69:1298- 1306,1990. 5.lseriH,andSolowB:Growthdisplacementof themaxillaingi rlsstudiedbytheimplantmethod.Eur JOnhod12:389-398,1990. 6.Behrents R: Adult craniofacialgrowth. JClinOrthod 20:842-847,1986. 7.LoveRJ,MurrayTM,andMamandrasAH:Facialgrowt hinmales16to20yearsof age.AmJ OrthodDentofacial Onhop 97:200- 206,1990. 8.Bp kA:Variationsinthegrowthpatternsof thehumanmandible:LongitudinalradiOKl1lphicstudyby the:implant method. J Dent 42:400- 411.1963. 9.Bpk A: Prediction ofmandibular growthrotat ion. Am J Onhod 55:585- 599,1969. 10.Bp kA,andSkiellerV:Facialdevelopmentandtootheruption:Animplantstudyaltheageof pubert y.AmJOnhod 62:339-383,1972. II.BjOrkA:Theraceinprofile:AnanthropologicalJIO -tayinvestigationonSwedishchildrenandcon-scripts.SvenskTandlakare Tidskrift. 4{)(Suppl ) (5B).1947. 12.Enlow DH: Facial Growth. Philadelphia: W.B. Solllnden Co ..1990. 13.ProffitWR, and WhileRP, Jr. : Surgical-Orthodontic Treatment.SI.Louis, MO:C. V. Mosby Co.,1991. 14.BellWH:ModernPracticeinOrthognathicandRt"-VlIstrllctivl'Surgery,vols.1-3.Philadelphi a:W.B. Saunders Co ..1992. Ith Growth Superimposition/ Evaluation ell IIhasbeenwelldocumentedthattheanteriorwallofthesellaturcicaandthecribriformplate remai nunchangedafterthefifthyearof life. L_. Thismeansthatnogrowthorremod elingchangesaffecttheseareasof thecranialbasebythetimethefirstpermanent tootheruptsintheoralcavity,whichismostlikelytheearliesttimeanorthodontic consultationor interventionmaybeneeded.Growthchangesof thefacialskel etoncan becarefull yevaluatedbysuperimposingcephalometricradiographsonthesestable structures.Yetthevariousexistingsuperi mpositiontechniquesdonotconcent rateon usingthisportionofthecranialsubstratc.5-16 Allof theother arcaspresentlyusedarc subjecttogrowthchangesYEvcnthemostpopularsuperi mpositiontechniquc-superimpositionontheSNlinebyregisteringonS(sella)-expressesgrowthmore anteriorlythanitactuall yoccurs.9-11 Areasonforavoidingtheuseof theaforemen-tionedstableareashasbeenthedifficultyinaccuratelocationof thecribriformplate andthe small dimensionof the anterior wallof the sellaturcica. Thefollowingsuperimpositionapproachoffersasoundandpracticalwayof incor-poratingthesestructuresintheevaluationof facialgrowth.17 Threepointsareusedto define the triangle (Fig.C2.I): I.T-poilll :Themostsuperiorpointoftheanteriorwallofthesellaturcicaatthe junctionwithtuberculumsella.Itcanbequicklylocatedontheradiographand doesnot changewi thgrowth, as does the sella (S). 2.C-poilll:Themostanteri orpointofthecribriformplateatthejunctionwit hthe nasalbone.Eventhoughthecribriformplateisnoteasily detectable,theC-pointis alwaysveryclearonthecephalomet ricradiographatthemostposteriortipof the nasal bone. 3.L-poilll: Themostinferior(lower)poi ntof thesellaturcica.Thispointalsodefines themostposterior point of the anterior wallof the sellaturcica. The triangleincorporatesinitsareathewholeanteriorwallof theselJaturcicaand extendsoveralargeareathatincludesalloftheanteriorandpartofthemiddle cranialbase.Thethreepointsselectedareatthegreatestdistancefromeachother wi thinstablestructures.Thisprovidestheclinicianwithalargemarkingarea.By registeringontheT-pointandsuperimposingontheanteriorwallof thesellaturcica andthestableTCline(cranialbaseli ne),asolidformati onisprovidedthroughthe shapeof thetriangleinboththeanteroposteriorandtheverticalplanesforapractical anddependableevaluati onof facialgrowth.Thepurposeof thetriangleistoprovide theclinicianwithaquick,solid,visualori entationofthemoststableareasofthe cranial base. Itispreferabletoobtainacephalometricradiographof allgrowingpatientsatthe ageof9or10yearsorattheinitialvisitattheoffice.Justbeforeorthodontic treatmentistobegi nandatleast6monthsaftertheinitialradiograph,asecond cephalometricradiographwillgivethecliniciantheabilitytocomparethetwoand evaluatefacialgrowth.Whensuperimposingthetwotrianglesasdescribedabove,the twolowersidesofthetrianglesmaynotnecessarilyfitrightontopof eachother, , 90PIlr1CGrOluh C2.1 , , "':.--------FIgureC2.1The cranialbasetriangle(TLC),theG(growt h) line, and 0(directi onal) angle. especiallybecauseof theL-point(duetoslightremodelingchangesinthearea)(see Fig.C2. J).Focusshouldbeplaced,intheorderofregistering.on( I)theT-point and superimposingon(2)theinnerstructureofthetriangle(anteriorwallofthesella turcica)and(3)theTCline.Thisrecommendedmethodologysi mplifiestheproce-dureof the"best-fit"approachwhilerecognizingthelimits of reali sticex.pectationsof asuperimpositiontechnique. AlineconnectingtheT-pointwithgnathion(Gn)isdefinedastheG-Iine,which maybeusedasagrowthline(seeFig.C2.I).Theadvantageof theG-lineoverthe otheronesthatusesellaisattributedtothestablepositionof theT-pointversusthe unstableS(sellapoint)duetogrowthandremodeling.Inaddition,theT-pointisan anatomiclandmark,whereasthesellaisaconstructedone(asthemiddleof sella turcica). Themean SDof theangleformedbetweentheG-lineandthetruehorizontal (D-angle)is58degrees 4degreesl7 (seeFig.C2. 1).Growthisdownwardandfor-wardalong thisline (D-anglestable withgrowth).BackwardrotationoftheG-line(by registeringattheT-point)withgrowthindicatesverticalgrowth(D-angleincreases) (Fig.C2.2).AnteriorrotationoftheG-linewithgrowthindicates aforwardhori zontal growt h pattern (D-angle decreases) (Fig. C2.3). TheanglebetweentheTCline(stablecranialbaseline)andthe(mevertical (TV) maybeestablishedonthefirsttraci ngofapatient(Fig.C2.4).AnyadditionaJ radiographsofthispatienttakentoevaJuateeithergrowthchangesortreatment effectsmaybeorientedsothattheTC- Til angleremainsconstant.Inthisway,the patientistreatedtohisorherinitiaJnaturalheadposition(NHP),establi shedinthe beginningoftreatment,illespectiveofpostural,behavioral,orsurgicaleffects.In otherwords,thepatientistreatedtoaconstantNHPbasedsolelyonthelineof vision,whichisestablishedwhenthepupilisinthemiddleoftheeyeandthe individualis looking straight ahead. Inunderstandingtheimportance of craniofacialgrowthanditsroleinthe develop-mentofanindividual'smalocclusion,oneneedsonl ytocomprehendtheroleof dentalcompensationto the skeletal growthpattern. C2.' ""'" opn C2. ""'. , on, pati '. " "' -'il,-C2.2 Fill"'.C2.2Backwardorclockwiserotat ionandthedevel-opmentof an open bite. - .... C2.' r... C2.4TheanglebetweenTCandTVcanbeusedto OIlentanyfuturecephalometricradiographsofthesame pati(nt. C2.3 Chapter 2GrowthSIIJX'rimposilion/E"ulllatioll91 '\ \)' ----- --Figur.C2.3Forwardorcounlerclockwiserolationandthe development of a deep bi te. 92Part CGrO ....1h C2.5 --, C2.6 FigureC2.6Dentalcompensationindeep-bitecases.The lowerincisorshaveflared(110")inaneffontoreducethe overbite (normal, 92 5"). FIgureC2.5Dentalcompensationinopenbites:theanterior teethtiplinguallyandsupererupt.Here,thelowerincisor to the mandibular plane angleis 75 " (normal, 92"+5"). Malocclusionsstemfromtheinabilityofteethtocompensateforanabnormal skeletalpattern. IIIf weweretolookatsevereskeletalopen-bitecases,wewould noticethattheanteri ordentition(i ncisors)isretroclined(ti ppedlinguall y)andhas supereruptedinthemajorityof thesecases"(Fig.C2.5).Thisisnature'sattemptto compensatefortheabnormalskeletalgrowthpatternthathascreatedtheopenbite (backwardrotation)withdentalmovementthatdecreasestheextentof theopenbite overtheyears. The oppositewouldtakeplaceinadeep-bitepatient.Theteethwould flarelabiall yinanefforttodecreasethedeepoverbiterelationshi p18(Fig.C2.6).Of course,thisisnotclearlyvisibleinallcases,becauseotherfactorsplayaroleinthe overallappearanceofthedentition(muscles,softtissue,tongue- lipequili bri um, tongue function, parafunctionalhabits, etc.). Theaforementioneddifferencesinnature's dentalcompensationsinvolvetheverti-calplane.If weweretolookatskeletaldevelopmentproblemsintheanteroposterior dimension,wewouldnoticeasimilar compensatorypattern.InaclassIIImandibular prognathismpatient,asthenegativeoverjct(underjet)develops,theupperincisors tip labiallyandthelowerincisorstiplinguall yinanefforttokeepasnormalanoverjet relationshipaspossible.It is asif theteetharetrying to"holdon" whilethemandible grows excessively anteriorly (Fig. C2.7). Thediagnosisofsuchproblemsmaybecomemorecomplicatedwhenwehave abnormalskeletaldevelopmentinbothdimensions,verti call yandanteroposteriorly, suchastheclassIII,open-bitepatientpresentedpreviously(seeFigs.Cl.2Sthrough CI. 29).Athoroughcephalometricevaluationalongwi thpropersuperimpositionof serialradiographs willhelpinlocating the extentof the probleminboth dimensions. -. , C2.7 FIgureC2.71 themandil maxillary11oftipping). theteeth( compensati Cbaptcr 2Groll1h SU{Jerimpositionj Elolualion93 I e2.7 FigureC2.7Asthemandiblecontinuestogrowanteri orly, !bemandibularteethgraduallyliplingually,whereasthe maxillaryteethtiplabially(thearrowsshowthedirection of tipping).Notetheanglesfonnedfromthelo ngaxesof theteeth(theseaxeswouldremai nparallelifnodental compensation occurred). Anexampleof dentalcompensationisgiveninthesituationof twopatientswho mayhavethesame skeletalopen-bitetendency,butonehasanormalopenbite/ over-jetof 2mmandtheother anopenbite.Theteethof thefirstpatient compensatedby supereruptionoftheanteriors,whereastheydidnotforthesecondpatient.Inthe past,whenorthognathicsurgeryhadnotyetdevelopedtoitscurrentlevel,cli nicians wouldcorrectsuchmalocclusionsbycompletingnature' swork;i.e.,extrudetheteeth (inthe case of an openbite)to closethe bite. Anotherexampleoftheroleofdentalcompensationsinvolvesthedecisionof extracti onversusnonextractionontwoindividualswhohavethe exactsame crowdi ng anddentalappearance,butonehasanopen-bitetendency(backwardrotation)and theotheradeepbite(forwardrotation).Nat uretendstocompensateinopen-bite casesbysupereruptingtheanteri or teethandtippingthemlingually.Nat urecompen-satesadeepbitebyflaringtheanteriorslabiall y.Wewouldratherextractteethto resolvethecrowdinginanopen-bitecase,becausethistreatmentmodalit ywould allowustotiptherestof theteethlingually(workingalongwi thnature' sattemptto compensate)toclosethebite.Extractionsinadeep-bitecaseshouldbeavoidedif possible,bci:ausetheremainingteethwouldmovelinguall yandmakethebite deeper. Therefore,nonextraction approaches shouldbeinvestigatedfordeep-bite cases. Finally,if weweretoconsidertwopatientswi thidenticalmalocclusionbuttotally differentgrowthpatterns,wewouldattempttotreatthemintwodifferentways becauseitisnotthemalalignmentof teeththatdirectsourtreatmentplanning,but the individual growthpatterns (Figs.C2.8through C2. IO). 94Part CGrowlh FIgureC2.B This100year-oldgirldemonstrates severedental projecti onof theupperanteriorteeth.Noteherlonglower faceheight (Sn toMe'). FigureC2.9This100year-oldboydemonstratesadental problemsimilartothatofthegi rlshowninFigureC2.g, Notehisshonlowerfaceheight(SntoMe').Alsonotethe deeplabiomentalfold,indicativeofadeep-bite,class11malocclusion. , -"'-- co -,.. C2.10 FigureC2.10Arbitrarysuperimpositi on of the cephalometri radiographsofthetwopatientspresentedinFiguresOJ andC2.9.Althoughaverycrudemethodof eval uating* growthofdifferentindividualsof thesameage,oneCD noticethe differenceintheirgrowthpatterns. The girt lIlm thelonglowerfacehas0mmoverbiteandisabachmd growthrotator(venicalgrower).Theboyisaforwzn! growthrotatorandhasadeepbiteof6mm.Altboup thesepatientshavethesamedentaJproblem(severeprojct. tionof theupperincisorsandaQassIItit treatmentapproachwillbedifferentaccordingto their it dividual growthpattems. Chapl 2Growlh SuperimposiliOllj EvaluOIioll95 References I.Melsen8 :Thecranialbase.Thepostnataldevelopmentof thecranialbasestudiedhistologicallyon human autopsymaterial.Acta Odontol Sc:and32(Suppl):62,1974. 2.RocheAF,andLewis AB:Lategrowth changes inthe cranialbase.InDevelopmem of theBasimmiuln. edited by JF Bosma.Bethesda:DHEW1976, pp 22 1-239. 3.BjOrkA,andSkielk:rV:Normalandabnormalgrowthof themandible.Asynthesisof longitudinal cephalometric implant studies over aperiod of 25yeaB.Eur J Onhod 5: I - 46.1983. 4.BuschansPH,LaPalmeL,TanguayR,andDemirjianA:Thetechnicalreliabi lityofsuperimposition on cranialbase and mandibular structures.Eur JOnhod 8: I 52 - 156,1986. S.de Coster L: The familialline,studies byanewlineof reference. Trans Eur Onhod Soc28:50- 55.1952. 6.Brodie G:Late growth changes inthehuman face. AngleOrthod 23: 147 - I 57,1953. 7.BjOrk A: Cranialbase development. Am JOnhod 41 : 198- 255,19S5. 8.Coben SE: The integration of facial skelctalvariants. Am J Onhod 41 :407 _434,1955. 9.IUcketls RM: Afoundationof cephalometric communication. Am JOrthod 46:330- 357,1960. 10.Ricketts RM: Cephalometricanalysis and synthesis. Am J Onhod 3 1; 141 - 156,1961 . II.IUckettsRM:Thevalueof andoomputeri.u:dtechnology.AngleOnhod42: 179-199, 1972. 12.RickettsRM: Perspecti ves in clinicalapplicationofAngle Onhod 5 I: II 5-150,1981 . 13.Bj OrkA:Variationsinthe growthpatternof thehumanmandible:Longitudinalradiographicstudyby theimplant method. J Dent Res 42: 400- 411.196J. 14.SolowB,andTallgrenA:Naturalheadpositioninstanding subjects.ActaOdontolScand29:59 1- 607, 1971. 15.CobenSE:Basion horizontal coordinate tracing film. Jain Onhod13:598 - 605,1979. 16.FrankelR:Theapplicabili tyof theoccipitalreferencebaseincephalometries.AmJOnhod77:379-]95,1980. 11.Viazis AD: The cranial base t riangle.J ain Orthod 25:S65 -570,1991. 1&.BjOrkA,andSkillerV:Facialdevelopmentandtootheruption.Animplantstudyattheageof puberty. Am J Orthod 62:]] 1- 383,1912. Hand-Wrist Radiograph Evaluation ell Thecourseof ort hodontictreatmentoftendependsontheintensityoffacialgrowth;thus,the knowl edgeofthegrowthvelocityvariationsof thejawsisofimportanceinclinical orthodontics.1.2Theclinicianwouldliketoknowt heonsctofthegrowingpatient's pubertalgrowthspurtsothatheorshemayintervenewithmaximumresultsinthe minimumtimeframc.The physicalmaturit y showninahand - wristradiographof the individualchildcanbevisuallycomparedwiththatofnormalchildrenofthesame ageandgenderusingGreulichandPyle'sAtlas.)whereanumberofhand-wrist radiographsarcpresented.l,lConsequently,thepractitionermayevaluatethestageof developmentofthepatientbymatchingtheindividualradiographtooneintheAt/as. Conversely,onemayassessahand-wristradiographwithouttheAtlas.basedonthe following guidelines:l.2 I.Whenthewidthof theepiphysisof thesecondproximalphalanx( PP2)isequalto thatofitsdiaphysis( PP2= ),wearecloseto,butcertainlybeforetheonsetof puberty. 2.Whenthewidthoftheepiphysisof thethirdmiddlephalanx(MP3)isequalto thatof itsdiaphysis (MP3=) andthesesamoid(s)bonehasbeguntoossifyand can besecnontheradiograph,wearerightattheonsetof pubertyorslightl ypastits onset(Fig.C3. 1).Onemustrememberthatinonefifthofpatients,thesesamoidis visi ble2yearsbeforemaximumgrowthisreached.I2 Thisiswhytheinformation obtainedfromMP3 isvery critical. 3.CappingofMP3(wheretheepiphysiscoverscompletelythediaphysis)occurs almostinvariablysimul taneouslywiththemaximumofIyearafterthepeak growth.12 4.Themostintenseperiodof growthmaybeexpectedbetweenossificationof the sesamoidand onset of the capping stage. Menarcheingirlsoccurswellafterthepubertalgrowthpeak.'Dentaldevelopment isoflillievalueasacriteri onofpuberty.'Themeansesamoidboneappearance precedesmeanpeakmandibularvelocity(puberty)by0.72yearinmalesand1.09 yearsinOneshouldnotethatinonequarterofmalesandonefifthof females. the adductor sesamoidappears after pUberty.' Onemaystarthisorherobservationof thepatient' shand - wristradiographby lookingattheadductorsesamoidof thethumb.6 Ifitisnotossified,wethenlookat thewidthof theepiphysisof tbemiddlephalanxof thethirdfinger(MP3).Ifthisis equaltoorlessthanthewidthof the diaphysisof MP3,thenweknowthepatienthas notyetreachedpuberty.If thesesamoidisossifiedandwecanseccappingof MP3 (i.e ..theepiphysisiswiderthanthediaphysisandstartstocapit),thenweknowthe patienthasprettymuch justreachedpubeny.Within2yearsafterthis,fusionof MP3 willoccur,andthisisanindicatorthatthereisverylittlegrowthleft.Finally,if we seefusionof theradius,wecan besurethat growthfor this patienthas been completed. 98Pin CGrowth References FigureCl.1Thisradiographof thethirdfi ngershowsthat capping of MP)is j ust begi nni ng. I.HelmS,Siersbael NelsonS,SlcidlerY,andBjOrkA:Skeletalmaturationof thehandinrdationto maximum pubertal growth inbody height.Tandlaegebladet 6: 1223- 12]4,1911. 2.BjOrkA,andHelmS:Predictionof theageof maxi mumpubenalgrowthinbodyheight.AngleOnhod ]1:1]4- 143, 1961. ].GreulichWW,andPyleSI:Radiographic Atlll$of SkeletalDevelopmemof the"and andWrist,2nded. Stanford, CA: Stanford UniversityPress,1959. 4.Enlow DH: Facial Growth.Philadelphia: W.B. Saunders Co.,1990. 5.Pile:skiRCA,Woodside00, andJamesGA:Relationshipof theulnarsesamoidboneandmax.imum mandibular growthvelocity. Angle Onhod 4]: 162- 110,1973. 6.FishmanLS:Radiographi cevaluationof skeletalmaturation:Aclinicallyorientedmethodbasedon hand - wristfilms. Angle Onhod 52:88- [ II ,1982. [ 1 Nasal Growth Thegrowthofthenosehasbeenthefocusofmanyinvcstigationsoverthepast30years,due totheimportantrolethatnasaldevelopmentplaysinorthodontictreatment planni ng.l-Il ClassIsubjcctstendtohavestraighternoses,classIIIsubjectsreveala concaveconfi gurationofthenosealongthedorsum,andclassIIindividualsexhi bita morcpronouncedelevationofthenasalbridge(greaterdorsalhump),leadingtothe increasedconvexityobservedintheclassIIpatient.Mostinvestigatorsstatethatnasal growthforgirlscontinuesuntiltheageof16years.19 Inaddition,verysmallincre-mentsof nasa)growthhavebeenreportedbetweentheagesof18to22years,andas lale as 26to 29years of age. 10, 11 Thetipofthenoseprogressivelyattainsamoreforwardanddownwardposition withage(duetoforwardgrowthof thenasal, septalcartilages)andtheforwardgrowt h of thenoseisgreaterinproportionthanthatof othersonti ssuesof theface.2,)Nasal growthincreasesatarateof about25%greaterthanofthemaxilla.4 Thiscont ributes significantl ytotheincreasedconvexityof thesoft -tissueprofilewithage.Inarecent study,itwasconcludedthatpatientswithmarkedhorizontalmax.illarygrowthhave morehorizontalgrowthofthenosethanthosepatientswi thverti calgrowthofthe maxilla (whohavemoreverti calnasal development). 12 Developmentally,thegreatestchangeoccursintheanteroposteri orprominenceof thenasaltipinbothsexes,andbecausetheforwardpositioningof thenoseisgreater thanthatof thesoft-tissuechin,itappearsthattheli psarerecedingwithinthefacial profile.2s Havi ngfailedtoexplainthepossibilityof excessivenasalgrowt hpotential, thecli nicianfindsitdifficulttoconvincetheparents or thepatientthattheunesthetic profi leisduetotheexcessivenoseandnottoorthodonticmechanotherapythat resultedinretrusive lip position 12(Figs. C4. !throughC4.3). 100Plrt CGro ....th FigureC4.1Profileof apatientatage12years,beforeorth odonti c treatment. FigureC4.2Same patientasinFigureC4. 1, atage14years, afterorthodontictreatment.Thenasallengthappearsto have remai nedthesame. C4.3 F"tgur.C4.3 Samepatient asinFigureC4. 2.6yearslater, at age20years.Notetheexcessivelatenasalgrowththat resultedinthe"' false"appearanceof retrudedlips(attrib-utedby the patient to the orthodontic treatment). Chapter 4Nasa/Gro ....th .10 1 References LPosenTM: A longitudinal study of the growth of the nose. Am J Orthod53:746- 756,1967. 2.Sublenly 10 :A longitudinal swdy of softtissuefacialstructures andtheirprofilecharacterist icsdefined inrelation to underl ying skelet.alstructures. Am1 Orthod 45: 481- 507,1959. 3.Subtenly JD: The soft tissueprofile, growthand treatment changes. Angle Orthod31: 10S- 122,196 1. 4.ProffitWR:Contemporary Orthodontics.SI.Louis.MO:C. V. Mosby Co.,]986. S.RudeeDA:Proportionalprofikchangesconcurrentwithorthodontictherapy.AmJOrthod50:421. ]964. 6.Charonas SJ: A statisticalevaluation of nasa]growth. Am J Orthod56:4{I 3- 4 14,1969. 7.OementsBS;Nasalimbalanceandtheonhodonticpatient.AmJOrthod55:244 - 264,329- 352, 477 - 497,1969. 8.BurstoneCJ: The integumentalprofile.AmJ Orthod 44: ] - 25.1958. 9.MengHP,GoorhulsJ,Kapi laS,andNaridaRS:Growthchangesinthenasalprofilefrom7to18 yeaB of age. AmJ Orthod 94:911-926, 1988. 10.SamasKY,andSolowB:Earlyadultchangesintheskeletalandsofttissueprofile.EurJOnhod 2:1-12. 1980. II.FosbergCM:Facialmorphologyandaging:Orlongi tudi naltq)halometricinvestigationofyoung adullS.Eur 1 Onhod 7:15-23, 1979. 12.BusehangPH,YiazisAD,DelaCruzR,andOakesC:Horizontalgrowthof thesoft-tissuenoserelative to maxillary growth. JCl inOrthod 26: 111 - 118.1992. Par t Orthodontic Mechanotherapy elller Biomechanics of Tooth Movement ToothMovement Simplified If "'e takeapencil,andplaceitflatonadesk, andtrytomoveitwithafingerby contacting it initsmiddle,wewillnoticethatthepencilrollsandmovesparalleltoitself (Figs. 01.1and01.2).Ifwetrytomoveitfromitssharpenededge,wewillseethatit moves,butitalsorotates slightly (Figs. 01 .3and01.4). Nowif weimaginethetoothasthepencil,theorlhodomic forcesasourfmger,the middleof thepencilasthe center of resistanceof the tooth, andthesharpenededgeof thepencilasthecrownof thetooth, andif wedefineasbodilymovementtheparallel motionof anobjecttoitselfandtippingasthemovementoftheobjectasitrotates andspinsarounditself,thenwemayappreciatethefollowingwhenitcomestotooth movementin orthodonticsl-1: Becausethecenterof resistanceof thetoothisfourtenthsawayfromitsapex,i.e., withinthealveolarbone,itwouldbeimpossibleforustoapplyadirectforceonthe toothinorder tomakeitmoveparallel toitself (Figs.01.5and01.6).Thus,our only optionistoattempttomoveteethbyapplyingaforceonthecrown, which, according totheaforementionedcorrelationwiththepencil,willcausethetoothtotip.This happensbecausethereisaMoment ""ForceXDistancethatrotatesthetooth(Figs. DJ.7and01.8).Inordertomoveatoothbodily,weneedtoapplyacountennoment equaltoandintheoppositedirectionof theonethatiscreatedbytheorthodontic force. This canbedone only withrectangular wires.I-1 Letusimaginetheupperincisorsaswetrytoretractintotheavailablespacethat wehaveobtainedfromtheextractionof thefirstbicuspids(Fig.01.9).Thebracket thatisbondedonto thecrownof thetoothhasanopeninginit,calledtheslot,where thearchwireisplaced.Anelasticchaincanbeusedtopullthebracketstogetherand thusapplythenecessaryforcetomovethetooth.Assoonastheforceisapplied,the toothtendstotip,asexplainedpreviously.Whenthathappens,theedgesofthe rectangularwiregrabholdofthebracketslotandthusapplyacouple(equaland oppositeforces),whichtendstospinthetoothintheoppositedirectionthanthe momentfromtheforceisattemptingtotipit(Fig.01.10).Inotherwords,the rectangularwirehascreatedacountennoment.Ifthemomentandcountermoment areequal ,theywillcanceleachotherout. I,)Thismeansthatthetoothwillmove bodily(translation,parallelmovement)fromtheactionof theforcefromtheelastic chainand solely fromit. Thesameprinciplesapplyif weweretolookatatoothfromitsocclusalsurface, withanorthodonticbracketbondedontoitsbuccalsurfacel-3 (Fig.01.11).Thi s time,thetoothwilltendtospinarounditslongaxisifthemainarchwireisnot securelywiretiedwithaligatureinthebracketslot.Inthis dimensionwedonothave muchcontrol.whetherweusearoundorrectangularwire,unlessweuscadeltoid bracket. 106Part DOrrhodOlllic MlXhflrwtherupy FigUffl01.1Aforce (fromour finger)isappliedinthemid-dle of the pencilatpointA. Figure 01.3 Try to movethe pencilfromone of its ends. Figure01.2NoticethaIthepencilmovesparalleltoitself ro pointB. 01 .4 Figure 01.4 II rotates asitmovesfrompoi ntA to B. flo'" a\tl bod; F " " ~ appl y t heI( appl ic looth. 01 .5 fI\lUf"01.5 and01.6It isimpossibletoappl yadirectforce atthecenterofresistanceofatooth(andthusmoveit bodily), becauseitis inthe alveolarbone. Apt. 01.1and01.8Asweattempttomovethetoothby appl)ingaforce( F)onitscrown,amoment( M)rotates thetoothasitmoves;(d)isthedistanceofthepointof iIIlPIicationoftheforcefromthecenterofresistanceof the ,.,th. Chapter IBiomt"Chanics Qj TOOthMovement107 01.8 108PartDOrthodonticMer:hanQlherapy 0 1.9 Figures01.9and01.10Aswetrytomovet heupper incisor posteriorl ybyapplyi ngaforceonitfrompointAtopoint 8,thetoothmovesbodil yifthecountermomentapplied fromtherectangulararch wireisequaltothemomentthat tends totip the tooth. 01.1 0 F 01 .11 Figure01.11Asthisbi cuspidtoothispulledfromanortho-donticelastic ' wirechaintoclosetheextracti onspaceme sialtoit,thetoothtendstorotatefromt hemoment( M) thatiscreated.CR is the center of resistance of the tooth. B (: 01 .12 Figure~ standarc in-and-c enceIn preadju! etscom; mayusc: ness has ChaplerIBiomechanics O/TOOlh Mow!"Jent1 09 Bracket Prescriptions (I ) 01.12 Conlemporaryorthodonticmcchanotherapy4- 9leadstotreatmentresultsthatare basedonthesixkeystonormalocclusion6:(I)aclassImolarrelationship(as describedprevi ously);(2)crownangulation(Iip)- thegingi valportionofthecrown ofteethisdistaltotheincisalportioninmostindividuals;(3)crowninclination (Iorque) - anteriorcrownshaveananteriorinclination,whereasposteriorcrowns havealingualinclination;(4)absenceor rotations;(5)absenceorspaces;and(6)the planeorocclusionshoul dvaryrromgenerall yfl attoaslightCijrveor $pee.Inorder toachievetheseresults,weneedtounderstandtherelationshipsandposilionsof teeth inthe arches. If oneweretocloselyobserveanidealdentalarch,itwouldimmediatelybecome apparentthatthepositionoreachtoothintbealveolusisdefinedbythree parameters4-6:( I)the"in - out"position(Fig.DI.I2),(2)thecrownangulationto "tip"(Fig.DI.I 3),and(3)thecrowninclinationor" torque"( Fig.DI.I4).These threeparametersdefineIhethree-di mensionalpositionof eachtoothinilsspace.In thepast,allorthodonticbracketswerethesameforallteeth,withthesameslot.The clinicianshadtoincorporateintothemainarch wirethreebendsroreachtooth,in ordertomaneuvereachtoothinitsidealposition:(I)the" in-out"orfirst-order bend,(2)the" tip"orsecond-orderbend,and(3)the" torque"orthird-orderbend. Modemfixedapplianceshaveallthesebendsbuiltintotheirslots,thusmaki ngeach bracketspecifi cforeachtoot h.Providingthatthebracketispositionedideall yonthe toothsurface(inthemiddleorthecrown,alongthelongaxis,andparalleltothe incisaledge),thesepreadj ustedprescriptionappbancestheoreticall yhavethecapability tofinishthetreatmentwithnobendsinthearchwireswhatsoever!Obviously.thisislike sayingthateveryone'sfeetshouldfitinthesamesizeshoe.Nomailerhowperfect bracketplacementiswithpreadjustedappliances.compensatingbendswillalwaysbe needed at the end of treatment forfinaldetailing andfinishing of the ocdusion. Asuggestedprescriptionis given4-8 (Fig.D 1. 15): t + (Jr) f91reD1 .12Intheoriginalonhodonticbracketsofonc ltandardsizeandprescription(/), theclinicianhadtoplace inand-outbendsinthewiretocompensateforthediffer-metin thebuccolingualthi cknessof teeth.Inthemodem, prtadj ustedappliances(II),differentthicknessinthebrack-dScompensatesforthatof theteethsothattheclinician mayuseastraightwirewithoutbends(thebracketthick-ahas been exaggeratedforpurposes ofillustrat ion). 110Pan0Of/hot/I)nlic M('ChwJolherapy -~ a _ (I) 01 .13 FIgure01.13Thedifferenceintheangulationoftheteeth (tip)inthepastforcedthecliniciantocompensatewithan up-and-downbend(I ).Incontemporary,preadjustedappli-ances,thi sisnotnecessarybecausethetipisbuiltintothe bracket.If AisperpendiculartoP (Pforms90"withinci-saledge)and8isperpendiculartothebaseof thebracket slot,thentheanglefonnedbetweenthetworepresentsthe compensatingbendthatneeds10beplacedwiththestan-dard appliances (I ).A and8 coincidein II. II 1I 1 I I 1 I I 1 -- I I I 1 I > I II I I I - -L ... I (I) Ill) 01 .14 Figure01.14Thetorqueorincl inationof teethinthebone isagaincompensatedforbythepreadjustedappliance (II). Notethattheangl eformedbetweentheperpendicular(B) tothebaseof theslotandtheperpendiculartolineP, (A), coi ncide(A- 8)forthepreadjustedappliances(II). whereasthetwoperpendicularsBandAfonnananglein the standard brackets (/). BRACKET PRESCRIPTIOSS 1 ..~ " ,~ . , ..... , ~ - . , ~ --'- -,- , " , " "" , , " ., " , " , ., .,, ., , .,,, , " , " ." ".+ . ~ , " " .,,,,, , ,, , ,, , ." , " , ." " , " , " n , n , n , , , ~ , n , , ." DLlS Figure01.15Bracketprescriptions.V - Viazis;A-Andrews;firstR- Roth;S- Swain;W-"Wick"Alex-ander; 11- Hilgers:secondR - Ricketts. " .-. '--.. '--. '-.......... -- - -, " , " , " ., , " " ... " " , " , , ., ., , , ." ." , ." ,.,,, , , ,, ,, , ., , ."." ." ." ." ,n n ., .. , ., n n ., , Figu.., thebn bracke Upper central Incisor First-order bend (in -out ):Standard Second-order bend(tip):5 degrees Third-order bend(torque):20 degrees OuIplerIBiom('Chanics ofTOQlhMon'ment111 Aspecificthicknessisgiventotheupperincisorbracketof aregularsize.The 5-degreeangulationissimilartotheoneproposedbyAndrews'classicwork.6 Itis alsowidelyusedinotherprescriptions.The20-degreetorqueisdefinitelygreaterthan thetorqueproposedbyRoth,'andAlexander,1andclosetothe22degrees suggestedbyHilgers.'Becauseslidingmechanicsareused,itwouldbequiteeasyto "dump"theanteriorteethlinguallyduringretractionandspaceclosure(Figs.DI.16 through01.18).Accentuatedtorquewouldreducethisand,itishoped, bytheend of treatmenttheteethwouldbeintheareaof10degreesoftorque,similartothat proposedbyAndrewsfortheidealocclusion(7degrccs).Inaddition,itiseasierto alleviatethetorqueeffectbyundersizedrectangularwiresthantoaddtorqueinthe wire.BecauseO.c)QIinchofplay(tolerance)relatestoapproximately4degreesof torquelost,spaceclosurewitha.016- X .022-inch2stainlesssteelwirewouldtheoreti-call yhave8 degrees of torque effectlost, if desired. Accentuatedlingualroottorque of theuppercentralincisorsisneededinthemajorityof casesduringslidingmechano-therapy, and thisprescription offersthis advantage. figulesD1 .16andD1 .17Theeffectof additionaltorquein thebracket(notethetwi stedrectangulararchwireinthe blacketslot)rotates thetooth fromA toB. 112PartJ)Orthodontic MechanOJhl>rapy Upper LateralIncisor First-order bend(i n-out):Morethi ckness Second-order bend(tip):10degrees Third-order bend(torque):10 degrees /, I\ I \ # I I , I " I , , , 01.18 FigureDU8IfAistheOOITttIincl inat ionoftheupper incisorteethintheboneandBisthepositiontheywould assumeif theytippedlinguall yduringspaceclosureif the countermomentprovidedby thewireisnotenough,then C shouldbeincreasedtorquethatisincorporatediniothe preadjusledappliancesothatthetoothmayendupin position Aafter space closure. Morebracketthicknessisneededtocompensateforthebuccal- lingualrelationship ofthelateralincisorcomparedtothecentralincisor.TheIO-degrccangulationis slight lygreaterthanthatsuggestedbyAndrews6andR o t h ~(9degrees)orAlexander1 andHilgers'(8degrees),butsimi lartothatrecommendedbyRicketts8 (10degrees). Thisadditionalangulationisneededtoprcvcntcloseproximityofthecentraland lateralincisorroots,especiallyduringspaceclosure.The10-dcgrcetorqueisagain greaterthanthatinothe_ prescriptionsforthesamereasonsaddressedforthecentral incisor bracket. Upper Cuspid First-order bend (in -out):Thinner thancentralincisor Second-order bend (tip):15 degrees Third-order bend (torque):5 degrees Thebracketthicknessonthecuspidhastobethinnerthantheregularsizeof the uppercentralincisorduetothebulkinessofthecuspid.The15degreesoftipare similartothatproposedbyRoth5 ( 13degrees).Itpositionstherootof thetoothmore di stall y,thusenhanci ngbodilymovementandreducingthetippingeffectof sliding mechani cs.A5-degreetorqueisnecessarybecause,assupport edbyHilgers,B thereisa ChapterIBiomechanics o/ TOOIhMQI'emem11 3 mechanicaltendencytodetorquetheupper cuspidsastheyareretractedinextraction cases,andthereisalwaysthepossibilityofimpactingtherootonthedensecortical labialplateonspaceclosure.Innonextracti oncases,whereaslightexpa nsionoccurs inallcasesandthetoot histippedoutwardanyway,theeffectof thetorquecanbe mini mizedbyplacinganundersizedfi nishingwire(i.e..a0.01 6- X 0.022-inchlwire in the 0.0 18 slot system). Highli ngualtorqueontheuppercuspidisalsoadvocatedintheprescriptionsby Hilgers!andRicketts' inordertomaintaintheintegri tyof thelabialsurfacecont ours betweenthecuspida ndthelateralbykeepingtheirtorquedifferentialtoaminimum. Inaddition,amoreverticalinclinati onof theuppercuspidsalleviatesthedet rimental effectsofthe" narrowcuspid"look,whichisalsodetrimentaltofu ncti onaljaw movementsandtheperiodontalhealt hof thetissues overlyingprominentroots.Thus, ani ce,broad" Holl ywood"typesmileiscreatedwithagentleriseinexcursionsand stabilit y throughreduction of excessivelateralforces. Upper Bicus pids First-order bend(in - out ): Simi lar tothe cuspid Second-order bend (tip): 0degrees Thi rd-order bend (torque): - 5 degrees Thefi rst-order compensati onisthesameasthecuspidonebecauseof theirsimi lar prominence.TheO-degreetipagreeswi ththeovercorrectedpositionsuggestedinmost prescri pti ons.The- 5-degreetorqueplacedonthebicuspids,alt houghitencourages "dropping down"ofthelingualcusps,doesso j ustenoughtoensuregoodintercuspa-tionofthebicuspidteethwiththeir counterpartsoftheopposing arch.Thiscomesas thercsultofnumerousobservati onsoffi nishedcasesthatappearedfinefromthe buccalsidebutfromthelingualsidelackedtheni ce,solidoccl usionofanideally finishedcase.Undersizedwires can beusedinopen-bitetendency cases. Upper Molars Fi rst-order bend (in -out ):Very thinmesiall y/ very thi ck distall y (20 degrees) Second-order bend(tip):0degrees Third-order bend(torque):- 10degrees AssuggestedbyHilgers,!aIS-dcgrcedistalrotat ionofthistoothensuresthe shortestarchlengthoccupi edbythe molartooth,whichisSdegreesmorethan Andrews"recommendat ion.Thus.,thebracketshoul dbeverythinaroundtheme-siobuccalcuspandverythi ckonthedistobuccal cusp.A20-degrecdistaloverrotati on isespeciall yhelpfulintheovercorrectionofclass11 ,divisionIcases,anditcounter-actsthemovementsplacedonthemolarteethfromthesideeffectsof slidi ngme-chanolherapywithelasti cchains.TheO-degree angulationissimilartootherprescri p-tions.The- IO-degreetorqueall owsagoodintercuspalocclusion,especiall yof the li ngualcusps.Incorporat ionof thesecondmolarteethisadvisableonl yif absolutely necessary. Lower Incisors First-orderbend (in - out ): Thick Second-order bend (tip):0degrees Third-order bend(torque): - S degrees Thi ckbracketsonthelowercompensatefortheirlingualrelationship relati vetotheupperanteri ors.TheO-degrecti ppositionsthesetccthina nupright positionwhilethe- 5-degrcctorque,similartothatsuggestedbyAlexander,1hasbeen showntoholdthemandi bularincisorsintheirori gi nalposition,thusensuringmaxi-mumretention stability. 114PIIrlDOrthodontic Ml'ChanOlherapy Lower Cuspid First-orderbend (in-out ):Thinner thanregul ar Second-order bend (tip): 5 degrees Third-order bend(torque):- 5 degrees Athinbracketisnecessarytocompensatefortheprominenceorthistooth.The 5-degreetipissimilartothatproposedbyAndrews,'Alexander,'a ndHilgers.'The - 5-degreetorquegivesthelower cuspidamorelabialversionthaninotherprescrip-tionsinordertoarticulatewiththeuppercuspid,asdefinedbythisprescripti on,and offertheproper cani negui danceduri ngexcursivemovements.Inaddi ti on,byhavi ng si milartorquetotheincisors,thecuspidtoothispositionedslightl ylingualtothe incisors(beingatthecornerofthearch).Thissupportstheloweranteriordentition andenhancespost-retention stabilit y. Lower FirstBicuspid First-order bend(i n-out):Asthinas the lower cuspid Second-order bend(tip):0 degrees Third-order bend (torque):- 15 degrees Athinbracketisrequiredduetothesimilarityofthistoothtothecuspid.The O-degrcctipisagainsimilartothatsuggestedbytheprescriptionsofAlexander,1 Hilgers,'andRicketts.s The- 15-degreetorqueprovidesasli ghtlygreater elevationof thelingualcuspthanthatsuggestedbyAndrews'( 17degrees)inordertoprovidea sol idocclusionwiththe opposing dentition. Lower SecondBicuspid First-order bend(in - out):Same as the lower firstbicuspid Second-order bend (tip):0 degrees Third-order bend (torque):-20degrees Allcompensationsforthistootharemadeforthesamereasonsasforthelower firstbicuspid. Lower Molars First-order bend(in - out): Mesially verythin/ distall y verythick Second-order bend (tip):- 5 degrees Third-order bend(torque):- 30 degrees Forthesamereasonsdescribedforthemaxillarymolars,anovercorrectionof the first-ordercompensationof10degreesisneededtocounteractthemesialrotation imposedonthemolarsbytheclasticchainsofslidingmechanotherapy.The - 5-degreetipmaximizesthelowermolarresistancetomesialtippingfromthesliding mechanicsandoffers' tip-back" effectbyplaci ng therootsmesially,thuscontri buting toanchoragecontrolduringspaceclosure.The- JO-degrcetorqueallowsforgood intercuspation of the lingual cuspswithout allowing unnecessary extrusion. Ch.pl erIBiomechanicHI/TOOlh}.{/J\'i'rllI'nt115 References I,Smi thRJ, andBumone CJ: Mechanics of toothmovement.AmJ Orthod 85:294- 307.1984. 2.StaggersJA.andGennaneN:ainieal considerationsintheuseof retractionmechanics.J ain Orthod 25:364-369,1991. 3.ProffitWR:COnli'mporary Onhadon/ics. S1.Louis, MO: C. v. Mosby Co"1986. 4.SwainBF:Straightwiredesignstrattg.i es:Five-year evaluationof theRothmodificationof theAndrews straightwireappliance,Chapttr18,pp.279-298.inGraberlW:Onhadonlics-SJaJe0/ theAn, Essence of the Scien((', St , Louis. MO: C. V. Mosby Co.1986. 5.RothRH:Treatmentmechanicsforthest raightwireappl iance.ChapterII ,pp.665 _ 716,inGraber TM.andSwainBF: O"hodomicr-CIirr/>fIIPrinciples andTechniques.St.louis,MO: C. V.Mosby Co., 1985, 6.AndrewsIF: StraightWire -Conceptand Appliances.SanDiego: L.A.Wells Co.,1989, 7.AlexanderRG: The Alexander Discipline.Glendora, CA: Onnco Co.,1986. 8,HilgersJJ:Beginwitht ~endinmind:Bioprogrcssivesimplified.Jain Onhod9:618-627.10:716-734. 11 :794-804.12:857-870, 1987. 9,MclaughlinRP.andBennetTC:Thetransitionrromstandardedgewisetopreadjustedappliance systems.Jain Orthod 23:1 42- 153.1989, Orthodontic Metal Fixed Appliances Cha Orthodonticfixedappliancesareusedtoapplycorrecti veforcestomalalignedteeth.I-4 These appl iancesgenerallyincludebrackets,whicharebondedontothefacialsurfaceof the crownoftheteeth,andamainarchwire,whichisinsertedinthebrackct(slot portion).The wireisall owedtoslidethroughthebracketsduring toothmovementand guidestoothmovementwhileappl yi ngacertainforcetothebracket(a ndthusthe tooth)ifitisacti ve(Fig.02.1).Additionalforcesmaybeappliedtotheteethby elasti cs(rubberbands)and/orelastomericchainmodul es,especiall y duringtheclosing of spaces (Fig. 0 2.2). Conventionalbracketshave(1)abase,whichhasameshconfigurationthatall ows foradequatebondstrengthtothetoothsurface;(2)a slot,whichreceivesthewire; and (3)wingsorhooks,onwhichclasti cs,elastomericmodules.,ligatures,andcoilsprings, etc.,can beattached(Fig.02.3). Thetwi n-typebracketsarebasicallymadeof twoverticall yorientedparallelbars thatarespacedapartwithaslotcutineachbartoreceivethemainarchwire(Fig. 02.3).Thesingle-typebracketsaremadeof oneverticalbar,withasmallersizeslot thanthetwinbrackets.,and" wings"thatarcacti vatedtocontactthemainarch wire forrotationalcontrol,asneeded(Fig.02.4).Themajordisadvantageofthetwi n bracketsisthenarrowinterbrackctdistance(betweenadjacentteeth),thusresultingin asmallspanof wirebetweent hebrackets.whichreducestheOexibilityof thearch-wire.Conversely,therotati onalwingsof thesinglebracketsaretoobig;rotationsare noteasilycorrcctedandteethmaytipintotheextractionsidemoreeasil y during space closure. Thedeltoidbracketprovidesanarrowslotof thesamedimensions of asingle-wing bracketanddeliversthesameinterbracketdistance(seeFigs.02.3and02.4).It offers excell entrotationalcontrolduetothehorizontalsegmentofthebracketandthe triangularmanner withwhichthe0ringsor theligaturewires encompassthebracket. Itissmall erthanthetwinbracketsandsuperiortothesi nglebracket'srotational wings,whichcauseproblemswiththepati ent'soralhygiene.Itiseasytoorientonto thetoothsurface(theverticalbarisalong thelong axis of thetoothandthehorizontal parall eltoitsincisaledge).Slidingmechanicsaregreatl yfacilitatedthroughtherota-tionalandti pcontrolthatthehorizontalbaroffersduri ngspaceclosure.Itgreatl y reduces frictionduring space closure due tothe elevatedslot. Thesizeof anybracketslotcanbeeitherO.OI8-i nchorO.022-inch.Becausewe stri veforasIowaforceaspossibleinorthodonti cmechanotherapy,itispreferableto usetheO.OI8-inchslotsystem,becauseittakesasmallersizewiretofillitsslotand thuslighterforcesareexertedontheteeth.Bracketsarebondedon allteeth exceptthe firstmolars(Figs.D2.5and02.6).Metalbandsarccementedontotheseteeth.Bands provide better bondstrengthonthese teeth. especially if aheadgear applianceis used. 118PartDOrthodontic Ml'ChanotherapJ' 02.2C Figure02.2.A-D.Anelastomericchainisapplyingaforce ontheteethasitpullsallthebracketstogether.Notethe rotationalcontrolofthedeltoidbracket.Withinone month, the anterior spaces were closed. Figure02.1Variouscontemporaryorthodonticbrackets (fromlentoright):singlewi ngbracket(Ormco,CA),del toidbrackets(GAC.NY),andtwinbrackct(Unit ck!3M, MN). 02.20 D2.3A Figure cuspid onth( ti cs,V ( b o d i l ~ the ho 02.4 Figure dehoi(l bracke deltoi ll 11 BPartDOrthodontic Mechanotherapy 02.2A 02.2C Figure02.2.A- O.Anelastomeri cchainisapplyingaforce ont hetccthasitpullsallthebmcketstoget her.Notethe rotationalcont rolofthedeltoidbracket.Withinonc month,the anteri or spaces wereclosed. Figure02.1Variouscontemporaryorthodont icbrackets (fromlefttoright ):singlewi ngbrdcket(Ormco,CAl,del-toidbrackcts(GAC,NY),andtwi nbracket( Unitekj3M, MN). 02.20 02.3; Figul cusp 00( ti cs. (bod thet 02.41 F I g ~ delta brno delta 02.3A Figure02.3.A,B. Close-upview of thedellOid(ontheupper cuspid)andtwinbrackets(ontheincisors).Notethehook onthedeltoidbracketfortheplacementof auxiliaryelas-tics.Withintwom o n t h ~cuspidretractionwascompleted (bodilymovementandcompleterotationalcontroldueto thehorizontalbar of the deltoid bracket). 02.' Figul'e02.4Close-upviewof thesinglewing(left )andthe ddloid(right)brackets.Notet hemuchbulkiersinglewing bracket.Alsonotethe"stretch"ofthe"0"ringonthe deltoidbracket, whichaids in rotationalcontrol. Chapin2Orlhodomic Metal Fixed Appliances119 D2.3B Figure02.5 The slot of thesinglewing bracketistoo narrow andoffersnorotati onalconlrol.Notetherotatedleftlal-eralincisordespitecorrectbracketplacement.Alsonote thatbrackets(insteadofbands)canbebondedonthe molar teethwhennoheadgear istobeused. I 120PartDOrthodofllic /If('('hanOlilcrapy References 02.6 Figure02.6Anorthodonti cband.Notethetripletubes.The upperoneisforinsertionof auxiliarywires(usedinsome techniques);themiddleonereceivesthemainarchwire;the lowerandbiggeronereceivestheinnerbowof aheadgear. Onthelingualside,thesheathreceivestheTPAorTeA appliances (see further), J.GraberLW:Orthodonlics- Slaleof IheArt.Eswnceof IheScience.51.Louis.MO:C.V.MosbyCo.. 1986. 2.GraberTM.andSwainBF:Orthodonlics-CurrefllPrinciplesandTedniqlles.51.Louis,MO:c.v. Mosby Co .1985. 3.AndrewsLF: SiraightWire-Concept and Appliances.SanDiego: L.A.Wells Co.,1989. 4.MclaughlinRP,andBennetTC:Thetransitionfromsiandardedgewise10preadjusledappliance systems.J Oin Ortbod23: 142 - I 53.1989. Es R",< ell Esthetic Brackets Recentadvancesinthefieldof estheticfixedapplianceshaveresultedinthedevelopmentof fixedappliancesmadeofpolycrystallineorsi ngle-crystalaluminumoxide(99.5%), call edceramicbracketsl-24 (Figs.0 3. 1and0 3.2).Themostapparentdifference betweenpolycrystallineandsingJe-crystalbracketsisiOl. theiropti calclarity, 'Polycrys-tallinebracketstcndtobemoretranslucent, Iwhereasbothsi ngle-crystalandpolycrys-tallineappliancesresiststaininganddiscoloration,'Almostallof thecurrentl yavail-ableceramicbracketsarcmadeofpolycrystallinemat'!rial.' - 11Thephysicalproperties of aluminumoxidethatinterestthepracticingclinicianarctensilestrengt h,fracture toughness,material hardness,andfriction.1,4-8,20 Thetensilestrengthof ceramicsisnotasi mplebulkmaterialproperty,asitisfor stainlesssteel;2,I,itisverydependentonthecondition of the surfaceof theceramic.A shallowscratchonthesurfaceof awilldrasti callyreducetheloadrequiredfor fracture,whereasthesamescratchonametal surfacewillhavelittle,if any,effecton fractureunderload.2,uInaddition,theelongationforstainlesssteelisapproximately 20%whenitfinallyfail s, 2 Theelongationfortheceramicatfailureislessthan1%, making these appliancesmore brittle2 (Fig.D3.3). Thefracturetoughnessof materialisthetotalenergyloadingrequiredtocauseits failure.2 Thefracturetoughnessvaluesforceramicsare20to40timeslowerthan thoseof stainlesssteel.It is, therefore, mucheasiertofracturea ceramicbracketthana metalone. Thus,itisimportantfortheorthodontisttoinspectceramicbracketsforcracksat eachpatientvisit.2 Careshouldbetakenduringtreatmentnottoscratchbracket surfaceswiththeinstrumentsoroverstresswhenligatingoractivatingawire.2,1The patientshouldbecautionedagainstchewingonhardsubstances.'Piecesofbracket couldbeingestedorinhaledinadvertentl yif thefractureoccursinthemouthduring function.'Theproblemof bracketfracturemayalsooccurwhenplacingorremoving rectangulararchwires,whichalmostcompletelyfilltheslot.'Placementof additional torqueinthearchwiresmaycauseeitherti e-wingorslotmicrofracturesoninsertion.' Thefractureresistanceof theceramicbrackets appearstobeadequateforclinicaluse inthe range of 8 to10degrees ofInge neral, ceramicbracketsproducemorefrictionthanmetalbrackets.Inreference tothepresenceoffricti onbetweentheceramicbracketandthearchwires,onestudy emphasizedthatitdecreaseswit hincreasedarchwiresizeslO becauselightwiresare pressednotonl yagainsttheedgesofthebracketbutalongtheanterior slotaswell.A morerecentstudyl lshowedthatthereisadecreasedrateoftoothmovementwith ceramicbracketsthatrangesfrom30%to50%whencomparedtometalbrackets,and thattheamountoftoothmovementdecreasedwithanincreaseinwiresize.In general, slotsurfacesandedgesof the ceramic bracketsweremoreporousandrougher thanthoseof themetalbrackct,21 andwiresurfacesareobviouslyscratchedbythe ceramicbmckets,whereasonlysli ghtscratchesareobservedonthewiresuscdwith metalbrackets. 122J>lIIrtDOr/hodonric Mt>chanOlht7apy Figures03.1and03.2Cernmi cbracketsofferpatientsan esthetic smile whileundergoing onhodonti c treatment. 03.2 Figure03.3A fractured, si ngle-crystalceramicbracket(Star. fire, "A" Company,CA),causedby the brittlenatureof the material.(ReproducedfromViazisAD, CavanaughG, and BevisRR:Bondstrengt hof cerami cbracketsundershear stress:Aninvitroreport. AmJOnhodDentofacialOrthop 98:2 14- 221,1990.Withpermissionof Mosby-YearBook, Inc.) FlgU" Ing 3 1 with like s "'". duceo surfa! cialc 518, Chapter 3Esthetic Brackets123 Asaresultofthis, effi ciencyoftoothmovementissignificantlyreducedbyceramic bracketswhencomparedtometalbrackets.Refinementofceramicbrackets,slot edges,andsurfacesinparticularshouldonedayproducemoreefficientanddesi red toothmovement.Stai nlesssteelisthesmoothestwire,followedbySentall oy(GAC).24 Atpresent,thesewiresarethemostsuitableforusewithceramicbracketsinsliding mechanics. Averyimportantphysicalpropertyofceramicbracketsistheextremelyhi gh hardnessvaluesof aluminumoxide.'Thehardnessof ceramicbracketsisalmostnine timesthatofstainlesssteelbracketsorenamel.M Seriousconsiderationshouldbe giventothepossibilityof enamelcontactwithanopposingceramicbracketandthe detrimental effects itmay have on the integrity ofthe enamep6 Ceramicbracketscausesignificantlygreaterenamelabrasionthanstai nlesssteel brackets6 (Figs.D3.4andD3.5).Weshouldrealizethattheconstrai ntsfacedby prosthodontistsinnotopposingnaturalenamelwithporcelainappl yequall ytothe fieldoforthodontics.'Itwouldberat hersimpletostatethataslongasthebrackets arekeptoutof occl usion,thisundesirablesideeffectisnottobeexpected.'Unfortu-nately,duringthecourseof orthodontictreatment onecannotbesureof avoidingthis problem, especiall y in extraction cases inwhich toothretractionisinitiated.' 03.4 FIgures03.4andD3.5Scanningelectronmicrographsshow-iogabrasionof abicuspidcusptipbeforeandafter contact .'imanopposingceramicbrackct.Notcthecatscratch-litesurface.Half of theabradedareahas beendelaminated, revealingtheintactenamelprismsunderneath.( Repro-ducedfromViazisAD,Delong R,BevisRR,ct al:Enamel surfaceabrasionfromceramiconhodonticbrackets:Aspe-rialcasercpon.AmJOnhodDentofacialOnhop96:5 14-518,1989. Withpermissionof Mosby-Ycar Book,Inc.) 03.5 124Part DOr,hodomic MechanOlherapy Avoidplacingceramicbracketsindeep-bitecases.5 Ceramicbracketsusedonthe mandibulartccthshouldbekeptoutof occlusionatalltimesduringtreatment.5.6 Routinecheckofthismatterisadvisedateveryvisit.5.6Crossbitesshouldfirstbe correetedbeforetheapplicationof ceramicbrackets.)Useof ceramicbracketsonthe anteriormaxillaryteethispossiblythebestwaytobenefitfromtheestheticsof porcelainwhileavoidingpotentiallydeleteriousenamelwearof occludingteeth.jItis notanexaggerationtocorrelatethistypeof abrasiontoasawbladeappliedagainsta hardsurfacearea.j Severeenamelabrasionfromceramicbracketsmightoccurduring asi ngl emeal,sometimeswithinafewseconds.''Qinicall y,damageoccursimmedi. atelyontoothcontactwiththeseappliances.!!"(Figs.03.6and03.7).Enamelwear mayoccurfrommetalappliancesaswell,butthiswouldbegradual(weeksor months)andnotasaggressive.'Theuseofelastomericringswithcoversforthe occl usalpan of the ceramic brackets maybe a wayto avoidthis problem. Accordingtotheliterature,theincidenceofenameldamageondebondingof ceramicbracketsrangesfrom0%to40%forclinicallysoundteethandisashighas 50%forcompromisedteeth(enamelcracks,endodontictherapy,largerestorations).7.8 Theincidenceof bracketfailureondebondingisintherangeof6%to80%.1.8The designof thebracket,morespecificallyof thetiewingitself,affectstheperformance of thebracketduringdebonding.7The j uncti onbetweenthebracketbodyandthetie wingisrelativelynarrowandreducesthebulkof ceramicmaterialsupponingthetic FigureD3.6Contactoralowerccmmicappl iancewithan opposingtooth.(ReproducedrromViazisAD,DelongR. BevisRR.etal:Enamel abrasionrromceramicorthodontic bracketsunderanartificial oralenvironment.AmJOrthod DcntoracialOrt hop98: 10] - 109.1990.Withpcnnissionor Mosby YearBook.Inc.) 03.7 FigureD3.7Dramaticdamagedone totheopposingtoot h in FigureD3.6withinsecondsaftercontactwiththeceramic appli ance.( ReproducedrromViazisAD,DelongR,Bevis, RR,etal:Enamelabrasionfromceramicorthodontic bracketsunderanartificialoralenvironment.AmJOrthod DcntofacialOrthop98:10]-109,1990.Withpcnnissionof MosbyYearBook,Inc.) Figure uponI there: Allure: bracke. Ch.pler 3ESlheric Brackets125 wingextension.1 Absenceofadequatebulk,inadditiontocrackpropagation,is contributory to bracketfailureat the site of applicationof the debonding force.1 Themeanshearbondstrengthofthesilanechemicalbondprovidedbysome ceramicbracketsissignificantl yhigherthanthemeanshearbondstrengthofthe groovedmechanicalbondof vari ousotherccramicappliancesandthefoilmeshbase of the stainless steel brackets.' Mechanical bonds,thatis,metalfoilmeshandgrooved-baseceramicbracketbases, undershearstressfai lprimarilywithintheadhesiveitsclf8(Fig .. 03.8).Thisiscalled brittlefailureoftheadhesivefromlocali zedstressareasduetothebracketbase design.' Chemicalbonds,providedbysilane-treatedceramicbracketbases,failmostl y attheadhesive- bracketinterface.'Thisisdefinedaspureadhesivefailurecausedby wider stress distribution over the whole interface.' Themaximumvalueof shearbondstrengthreportedintheliteratureexceeded 100 lbofforce.'Thisoccurredwiththefirst-generationTranscend(Unitek/ 3M) bracket,whichisnolongeravailableandhasbeenwithdrawnfromcirculationBI" .17 (Figs.0 3.9and03. 10).Thehighbondattributedtothisbracketwasduetoa combinati onofmicromechanicalandchemicaladhesionthatwasprovidedbythe coupling effectof thesilanelayer of thebracketbaSt!. givingitashiny,smoothsurface area thatincreasedthe stressdistribution during debonding.11 Itmustbenotedthatthenewbracketbaseof theTranscend2000(Unitek/3M) appearstobemuch"safer"whencomparedtotheoriginalTranscend. L1Notooth failureswerenotedinastudywi ththeTranscend2000YBothFascination(Denta-raum,Germany)andtheorigi nalTranscendcausedenamelfailureinthesame study, whichisinaccordancewiththefindingsofprevi ousinvestigati ons.B,I ... 17Thenew AgureD3.11 Mechanicalbondsfailsafelywithint headhesive upondebonding.Thisisascanningelectronmi crographor theresidualadhesiveonthetoothafterdcbondingor an Allure(GAC)ceramicbracket.NotetheimprintsorIhe bracketbase. 126Part DOrthodontic Mechanotherapy FigureD3.9First-generationTranscend(Unitek/3M)ce-ramicbracketbondedontoabicuspidtoot h.(Reproduced fromViazisAD,CavanaughG,andBevisRR:Bond strengthof ceramicbracketsundershearst ress:aninvitro report .AmJOrthodDentofacialOrthop98:214-221, 1990. Withpermission of Mosby-YearBook,Inc.) FigureD3.10Toothfailureupondebondingof thebracket showninFigureD3.9.Debondingforcelevelsofthese brackets exceeded100lb.These applianceshavebeenwith drawnfromthemarket.(ReproducedfromViazisAD,Ca vanaughG,andBevisRR:Bondstrengthofceramic bracketsundershearstress:aninvitroreport.AmJ OrthodDentofacialOrthop98: 21 4- 221,1990.Withper mission of Mosby-Year Book,Inc.) generation of theStarfirebrackets alsoappearedtohavebeenimproved.17Therewere less cohesivebracketfailuresthanpreviously reported.I.I ... 11 TheAllure(GAC)bracketsdemonstratesafedebonding.11Theirbondstrength appearstobestrongenoughtobondtotheenamelthroughoutthelengthof treat-mentwithoutcompromisingtheintegrityof thetoothondebonding8 (Fig.03.8).As supportedbyvariousstudies,8.9theAllurebracketistheceramicbracketsystemof choiceforbothpredictabilityandbondstrength.Forthosecl iniciansstillusi ngthe originalTranscendortheFascinationbrackets,amorefl exible,lower,fil ledadhesive may bethe answer to lower bond strengthandprevention of enamel fractuTCS.17 Intheeventthatpartof abracketremainsonthetoothondebonding,ahigh-speeddiamondhandpiecewithamplewaterspraymaybeusedtotaketheresidual ceramicmaterialOff.7.1'Sensi tivityof thetoothmaydevelopif thepulpisirritatedby this procedure.7 Theneedforrelativelystrongforcestoobtainbondfailuremayresultinvarious degreesof patientdiscomfort.'Intheclinicalsetting,suchaforcewouldbetransmit-ted10teeththatareoftenmobileandsometimessensitivetopressureattheendof theactivephaseof orthodontictreatment.'Tominimizesuchanepisode,theteeth shouldbewellsupportedduringbracketremovaL7Ithasbeensuggestedthatthe orthodonti sthavethepatientsbitefirml yintoacottonrolltohelpstabilizethese sensitive and relatively mobile teeth.7 Itneedstobepointedouttotheclinicianthatthelikelihoodof bracketfailurecan beminimizedif thedebondinginstrumentisfull yseatedtothebaseof thebracket andtothetoothsurface' (Fig.0 3.11).Thisfirmscatingallowstheforcesusedfor bracketremovaltobetransmittedthroughthestrongestandbulkiestpartofthe bracket;namely,thebracketbase.Failuretoadheretothisrequirementasaresultof hastinessbytheclinicianorthepresenceoflargeamountof compositeflashonthe surfaceofthetoothandaroundthebracketperipherycouldresultinagreater incidenceof bracketfailure.'Becausebracketfailureisusuall y quickandsudden,it couldresultininj urytothepericoronalsoftti ssue,theoralmucosa.,thetooth, or the clinicianif debracketing is performed carelessly.7 en.pler 3ESlhel;cIJrackels127 Figure03.11Specialinstrumentsarerecommendedby variousmanufacturerstodebondceramicappliances.This instf1lment,byUnit ek/3M,shouldbefullyandfinnly scatedbeforethe debonding forceis applied. Wholeorfracturedbracketparticlescanbecomedislodgedintothefieldof opera-tionandingestedoraspiratedbythepatient,creatingasigni ficantmedicalemer-gency.'Furthermore,thefl yingbracketpaniclessubjectboththepatientandthe cliniciantopossibleeyeinjuryif protecti veeyewearisnotavai lableornotwornby bothindividuals.7 Ifthepliersdesignedforremovalofbracketshaveaprotective sheaththatcoverstheworkingendoftheinstrument,theprobabilitythatbracket fragmentswillbecomedislodgedinthepatient'smouthorinthefieldof operationis decreased.Theplierbladesprogressivelylosetheirsharpnessbecauseoftheinterac-tionbetweenthestainlessstcclbladeandthemuchharder andmoreabrasiveceramic materi al.Astheplier blades become dull, debonding effi ciencyisreduced. Ithasbeenadvocatedthattechniquesusedduringdebondingofconventional stainlesssteelbracketsmaybeinappropriateforremovalof ceramicbrackets.Alter-nati vedebonding, suchasultrasonicandelectrothermaldebracketing,techniquesthat minimizethepotentialforbracketfailureaswellasthetraumatotheenamelsurface duringdebonding,havebeeninvestigated.Thesemaybemoretimeconsuming,and thelikelihoodofpulpaldamageneedstobethoroughl yinvesti gated.Prototypede-bracketing instruments are, at present,undergoing clinicaltrials. Alotoftheaforementionedproblemswillbeavoidedif theorthodontistperforms averycarefulcl inicalexaminationof thepatient,withparticularattenti ontocom-promisedteeth,goes overathoroughinformedconsentandtreatment agreementwith thepatient,emphasizestothepatienttheadvantagesanddisadvantagesofceramic brackets,adherestothemanufacturer'sinstructions,andiskeptuptodatewiththe informationthatbecomes available inthe literature. References I.Swanz ML: Ceramic brackets. J Oin Orthod 22:82-88,\988. 2.ScottGE:Fracturetoughnessandsurfacecracks- Thekeytounderstandingceramicbrackets..A n g l ~ Orthodl:3- g,1988. 3.OdegaardT,andSegnesD:Shearbondstrengthofmetalbracketscomparedwithancwceramic bracket.AmJOrthodDcntofacial Orthop 94:201-206,1988. 4.GwinneltAJ:It.comparisonof shearbondstrengthsofmetalandceramicbrackets.AmJOrthod Dentofacial Or1hop 93:346-348,1988. 128PartDOrthodon/ic /I!('chuIIQln.erapy 5.ViazisAD.DelongR.Beri!RR.DouglasWHo andSpeidelTM:Enamelsurfaceabrasi onfrom ceramiconhodonti ebrackets:Aspecialcaserepon.Am1OnhodDenlofaeialOnhop 1989. 6.ViazisAD.DelongR.ScrisRR,RudneyTD.andPintadoMR:Enamelabrasionfromceramic onhodonticbracketsunderanartificialoralenvironment.AmJOnhodDentofacialOrthop 109.1990. 7.Bisl\araSE.and Trulove TS: Comparisonof differentdebonding techniquesforctramicbrackets:Anin vitro study.Am 1 OrthodDentofacialOrthop 1990. 8.VinisAD.Ca\l3naughG.andBerisRR:Bondstrengthof ceramicbracketsundershearstress:Anin vi tro repon. Am J OrthodDentofacial Orthop 1990. 9.BrittonJC,Mcinnesp.Wei nbergR,LedouxWR.andReliefDH:Sh.earbondstrengthof ceramic orthodonticbrackets to eDamel. Am 1 OrthodDentofacialOrtbop 353,1990. 10.Angol karPV,KapiJaS.DuncansonMG,aDdNandaRS:Evaluat ionoffrictionbetweenceramic brackets and orthodontic wires offour alloys. AmJOnhodDentofacialOnhop 1990. [I.KusyRP.andWhitley1Q:Coeffi cientsof frictionforarchwiresinstainlesssteelandpolycrystalline alumina bracket slots.PanI: Thedrystate. Am J Onhod Denlofacial Onhop 312,1990. 12.PrattenDH.PopliK.GennaneN.andGunsollcyJC:Frictionalresistanceof ceramicandstainless steel onhodontic brackets.Am J Onhod Dentofaeial Onhop 1990. 13.HarrisAMP.JosephVP,andRossounE: Comparisonof shearbondstrengthof onhodonti cresins10 cerami c andmetalbrackets. J ain Onhod 24:725 728.[990. 14.EliadesT.ViazisAD,andEliadesG:Bondingof ceramicbrackets10enamel :Morphologicaland struct ural considerations.AmJOrthodDentofacialOrthop 1991. [5.Viazi s AD: Directbonding inorthodontics. Journalof Pedodont icsJ: I[986. 16.GwinneltA1:Acomparisonofshearbondofmetalandcerami cbnlckets.AmJOnhod DentofacialOrthop 1988. 17.EliadesT.ViazisAD,andLekkaM:Fail uremodeanalysis of cerami cbracketsbondedtoenameLAm J Onhod Dentofacial Onhop (inpress) 18.VukovichME.WoodDP,andDaleyTO:Heatgeneratedbygrindingduri ngremovalof cerami c brackets.Am J OrthodDentofacialOrthop 199 I. 19.HoltMH.NandaRS,andDuncansonMG.Jr.:Fractureresistanceofceramicbracketsduringarch wiTttorsion. AmJ Onhod DentofacialOnhop 99:287 1991. 20.BednarJR,GruendemauGW,andSandrikJL:Acomparati vestudyoffrictionalforcesbetween orthodontic braekets and :uchwires.Am J Orthod Dentofaeial Onhop[(1):5 1991. 21.TanneK.MatsubaraS.ShibaguehiT.andSakudaM:Wirerrictionfromceramicbraeketsduring simulated canine retraction. Angle Orthod 1991. 22.AmericanAssociationof Orthodontists:Ceramicbraeketsurvey,memorandumtomembers.Apri l7. 1989. 23.AmericanAssociat ionof Orthodontists:Ceramicbracketsurveyresultsupdate,memorandumtomemo bers.December1989. 24.PrososkiRR.BagbyMD,andEricksonLC:Staticfrictionalrorceandsurfaceroughne:ssofnickel ti tanium arch wires. Am J Onhod Dentofacial Onhop100;341991. Dil Ad Sine: Direct Bonding of Brackets/ Adhesive Systems ella Sincetheintroductionoftheacid-etchingtechniquebyBuonocore, l.2whi chenhancedthe adhesionofresi nstoenamel,rapiddevelopmentshaveledtotheconceptofdirect bondinginorthodontics,whereattachmentsaredirectl ybondedtotheenamel surface}- IINaturall y,theeffectivenessofthebondedappliancesintransferringthe desiredforcestothetccthisdependentonthebondstrengthtothetooth.Thiscanbe accomplishedbyanadhesivesystemthatwillbondthebracketsdirectlytothetooth surfaceandmaintainthemthroughoutthedurationoftreatment(Figs.04. 1 through 04.20). Orthodonticresinsmustideallyhaveadequatestrength,beabletorondtoboth ceramicandmetalbrackets,remainstain-freeandthusbeestheticall ypleasing,have variablesettingtimesformultipleuses,andpossessadequatehardnesstofacilitate debonding.)Theyaredividedintotwosystems:theultraviolet(UV)- andseJf-cured systems.) TheUVcuringsystemsrelyonexternallysupplied,long-wavelength,UVradiation toproduceafree-radical-liberatingcompound,suchasbenzoinmethylether,inthe resin.)'"Theyareone-componentsystemsandthereforeareeasiertousc;themost importantadvantageisthatofunlimitedworkingtime.Ingeneral,thereisnostatistic-allysignificantdifferencebetweenthemeanshearbondstrengthoflight-curedand chemicall ycuredadhesives(twopastesornomix).!Thefactthatvisible,light-cured resinsarebeingusedsuccessfull ywouldseemtoindicatethat,althoughtheirinvitro shearbondstrengthisclinicall ylessthanthatof thechemicall ycuredresi n,visible, light-curedresins canbe usedclinicall y with goodresults.' Bothli ghtl yfilleda ndheavilyfilledresinspredisposetoplaqueformationwithout significantQualitativedifferencesbetwccnthem.)Thereisatrendtowardanincreased bondstrengthwithincreasedfill erconcentration.6 Theremovalof hi ghlyfilledcom-positecementsonaveragecausesmorelossof enamelthanremovalof anunfilled adhesive.1OAlowerfillercontentdecreasestheabrasiveresistanceandsimplifiespol-ishing and finishing of the enamel surface after debonding. Recently,glassionomercementswereintroducedinclinicalorthodontics(Figs. 04.21through04.26).Agreatadvantageofglassionomercementsistheirabilityto actasreservoirsoffluorideions,thusreducingthepossibilityof decalcification.II- 2" Auorideionsarereleasedintheimmediatevici nit yof thecementsoonafterplace-ment, andthisionrelease continues atsignifi cant levels for atleast12months. Glassionomercementswerefoundtoadherewithoutetching;simpleprophylaxis anddryingof theenamelproducedthestrongestbond.Etchingactuallyreducedbond strength,becauseglassionomersformadirectchemicalbondwiththeenamel,unlike themechanicalbondofcomposi teresins.Theyalsobondrelativelybettertothe bracketthanto theenamel;fracturestendedtobecohesivefai lures,withinthecement itself.Theclinicalimplicationisthatlittlecementwillbeleftonthetoot hafter debonding. 130PariDOrthodontic MechanOlh"Tapy ...I' ~" , Figure04.1Afterisolalionwithcheekretractors(forboth arches)orcottonroll s(forsingle-toothprocedures),the teetharepumicedandadequatelyrinsed,followedbyacid etching witha disposable brush for15 seconds. 04.3 Figure04.3Mostadhesivescomewithtwoparts:aliquid formandapasteform. 04.2 Figure04.2 Thoroughrinsinganddryingare absolutelynec-essaryinordertoobtainthechalky-whiteetchedtooth surfacethatallowsforagoodbond.Atthispoint,thetooth isready toreceive thebracket. Figure04.4Theliquidpartis appliedontothetoothsurfact witha brushbythe clinician. Figur, chair 04.7 Figure longE edge. "'.5 Figure04.5 Thepasteispl acedontothebracketbasebythe chairside assistant. Rgur.04.7Thecl inicianthenali gnstbebracketalongthe longaxisof thetoothataspecificdistancefromtheincisal ""'. Chapl,,4Direcl Bonding 0/ BracketsjAdht's;I'e Systems131 Figure04.8Thebracketisthenplacedonthecenterof the tool hwithaspecialholdingplieror evenapairofcotton pliers. FigureD4.8Thisismoreeasily doneforthetwi nanddel-toidbracketswit htheperioprobe.due\0theconvenient shape of theseappl iances. 1321" r1 1)Orthodontic Ml'ChunOlhaapy Figure04.9Att heend.asafi nalcheck,thebracketis checkedwit hamouthmirrortoensurethatitisaligned properly. Figures04.11through04.15TheplacementoftheciastO-mericmodules("0"rings)overthebracketisdonewi tha hemostat.Themoduleishookedaroundonewingand then.withthe"baseballhome-run"twistingmotion.all fourringsof thetwinbracket arcengaged. Figure04.10Wireplacementisdoneintraoratlywiththe Howeplierswhichallowafinngripof thewireandeasy placement inthemolar tubes and the bracket slots. Cbapltr 4DirI'C1 Bonding of BrackelSj Adhesire S}'SlemS133 04.1304.14 134Part DOrthodomic MrxhulI()/herapJ' Figures04.16and04.17Forthehook-upoftheelastic chai ns,theprocedureisquitesimilar:oninsertionof one of theloops..thechainisstretchedandtherestistiedina simi lar manner. Figure04,18Tosecurethearchwireinthebracketslot tightly,aligaturewire-tieisused.Itisplacedbeneathftrst themesialwi ngsofthebracketandthenthedi stalones whi leslidingalongthemainarchwire.Atthispoint,the twolegsarecrossedover,twistedbyhandafewtimes,and thensecurelytightenedwithahemostat.The excessligature iscutoff andtheremainingJ- mmtwi stedpanisplaced beneath themainarch wire. FigureD4.19Whenremovalof aligaturewire-tieisdesired, aligature-cutterpli ermaybeusedtocutthewireand, withoutlettinggoof it,theligatureti eisremovedwiththe same plicr. Figurel placen moveo Figurel 9O-rap,' allyspeaking.t!cbondingandcleanupwithscalersandplierscreatesurfacedefects suchascraters.pits.andporcelainfractureastheresinisremoved.Diamondpolish-ingpasteisbetterinrestoringthesurfacethanarepolishingstones.Irreversible damagetoporcelainmayalsooccur.Becausethebondstrengthstoglazedand deglazedporcelainarenotsignificantlydifferent,itmaybedesirabletobondtoglazed porcelaintominimizesurfacedamage.ll Rougheningofporcelainwithsilanetreat-mentallowsforclinicallyacceptablebondstrengths of orthodonti cbracketstoporce-lain.2IRoughenedsurfacesandsurfaceswithmicrofracturcscanbesatisfactorilyfin-ishedandpolishedwitheither aseriesof gr.ldedceramist's 'points (ShofuDentalCo.) or adiamond-impregnatedpolishingwheel( Meissi nger, JanDentalCo.),followedby a diamondpoli shing paste (Vident).29 References I.BuonOCOf'eMG:Asi mple:methodofilM;reasingthe:tdhesionof acrylicfillingmatcrialstocnamel surfaCC$.JDentRes34:849- 853,1955. 2.ViazisAD:Direct bonding of onhodontic brackcts. JPedodonticsII:], 1986. 3.MaijerR:Ihmdinx S),$/('m$ in Biocfm!ptJlibifil), oJ DenIal Materials.Vol .II.BocaRaton. FL: CRePress.1982, pp.3:51- 76. 4.Lee:HI..OrlowskiJA,andRocm;BJ :Acomparisonofultr.aviokt-curing andsclf-dil' Dmlo/al'iaJe. BaJl'jf "'or!d0l1l('tIfaJN. Paris: JulienPrtlat.1975 . Cltal e r ChinCup Therapy Strongorthopedicforcesintherangeof 400to800gmightbeusedtoreduceamandibular prognathismwiththeuscofthe"chin-nlition279 F4.28 280P. TtFOrthodonti C rfM/fllml Modo/IIIN Figure F4.32 The patient's occlusionI week after debondi ng. FiguresF4.34andF4.35Thisisadentalopenbitewi th significantflaringoftheant eri orteeth.Itisobviousthat theanteri orteethneedtoberetmctedtotheiridealposi. tionoverthebasalbone.Thecrowdingisminor(3mm) andmoderate(6mm)ontheupperandlowerdental arches.respectively. FlgureF4.33Themaxillaryandmandi bularHawleyrt tainersprovideposttreatmentstabil ity.Notetheacryl icto preservethelowerEspaceunt ilthepatienthasprosthetic workdone. F'tgUf.'F4.36andF4.37Exuactionof thefirstbicuspidsfa-cilitatedtheretractionoftheanteriortccthwithupperand lower0.0 16X0.022inch!Neoscntall oy(GACjwiresand elastomeri cchains.NotethenormalOBandOJrelation-shipof 2mmthathasbeenestablishedearlyintreatment (within3months). F4.3S Flgur F4.38andF4.39Thebileiscontinuingtocloseas furtherleveling(especiall yoftheupperarchontheright side)is lak.ing place. ChaplH 4Trf!QlmenlPlanning in fhe Permon/'nl iJenllfion281 282PartFOrthodonlic '''rlOllllt'lII Modufitit's F4.40 FiguresF4.40IndF4.41Finishing!.IainlcsssIL"C1rectangular wires(0.016X0.022inchZ)arcused10place compcns:lIing bends as space closure conli nues wi thelastomeric chains. F4.42 FigureF4.42Towardtheendoftreatmentwithspaceclo-sure almost completed. FU3 FIguresF4.43throughF4.4ePatient'socclusionbeforetreat-ment.NotetheclassImolarrelationship.theopenbi te tendency,andthemesi allytippedbicuspidsandcuspids, whichmakethemappearinaclassIrelationshi pversusa classII50%(end-to-end)if theywereupright.Thecrowd-ing isminor (about3mmfor each arch). F4.45 o.pter"rrealmml Planning in the I'tmUl1I,nl Dentition283 F4.44 F4.46 284r l l 1 ~ 'OflhodUflticTreatment Modafitil'! F4.47 FiguresF4.47andF4.48Althoughthiscasecouldhavebeen treatedwi thTR,thetherapyplanherewaselttmctionof theupperfirstandthelowcrsecondbicuspids.Thisextmc-ti onpatternwasnecessitatedbythepatienl 'slonglower facialpalternwithanopen-bitetendency(seeFig.4.44). Immediatelyafterbracketplllccment ,init ialO.OI75-i nch braidedstai nlesssteelarchwi resareused(anO. 12-inch stainless steel wire couldhave beenused as well). FlSJuresF4,49andF4,5QAfterhaving gonethroughtheusual stainless steel roundarchwiresequencepresentedprevi ously (0.0 14-inch,0.016-inch),0.0 16X0.022inch2 fini shingrec-tangularstainlesssteelarchwireswereused.Themechanics usedforspaceclosureareelastomeri cchainsfrommolar to molarandclassIIelastics(fromIhelowermolartothe uppercuspid),wornfull-timeoratleastalnightOassII elasti cswereused24hoursadayforover3months(from thelowermolartotheuppercuspid),andhaveatendency toextrudethelowermolarswhileflaringthelowerand tippingbacktheupperanteriorteet h.Elasticsshouldbe usedonl ywithrectangulararchwirestominimize t heafore-ment ionedsideeffectsandtomaximizetheiruse,whi chis forbodil ymesialmovementofthelowerposteriorseg-ments and di stal movement of Iheupper anteri or segment. F4.48 f'19uresF .51andF . 52Aftertheposteriorspacesha ....e closedandaclassI cuspidandmolarrelationshiphasbeen achie .... ed,C-chainsfrommolartomolarwillconsolidate toot hcontactsandcloseanyremainingspaces:0.016X 0.022inch1 stainlesssleelarchwireswilhaccentuatt.'dand re\'el"SC.'curveof Speeontheupperandthelowerarches. rtSpttti ....el y.areused.Thesewillcounteractthelinguallip-pingoftheanteriorsegmentsdue10theconstantpullof theelasticchainsoverthemonthsof treatment.If thi sside elfectSlans10occur,theclinicianwillnoticethecreation ofan openbite inthebicuspidareaandexcessiverelroclin-Ilion of the anterior segments. Chaptet"Trrotme"tPlanning inthe Pe"nan(,nIIJentullJf1285 286Plrtt'O"hodtJmk l'reaJmerrlMotialilin F ~ r e sF4.53throughF4.56Patientafterapplianceremoval. Note the2- mm overbiterelationship that has been achieved. F4.54 FIgureF4.57Thispatienldemonstraledapalatallyimpacted cuspidthatwasbroughtinthearchwithaslightmodifica-tionof the" ballistaspringsystem"(JacobyH:The" bal-listaspring"systemforimpaett.'dteeth.AmJOrthod 75: 143- 151.1979).Thedouble-loopspringforinitialacti -vat ionofpalatall yimpactedcuspidsismadeof 0.0 16X 0.022inch!wire.It sposterior endisinsertedintotheauxil -iarybuccaltubeofthemolarband.whileitsmiddle segmentforms a45-degrceanglewiththemainarehwire. F4.59 FigureF4.59Theactivationofthespringhelpsguidethe impactedtoothtoitsfinalpositioninthearch,whereelas-tics may compl ete itsmovement. Chapl""Trt'fJlmelll Pio"'''''R If! Ihf' Pf"fmol'lt'lII Dt'I'Imwn287 FigureF4.58Theanteriorsegmentofthespri ngfom sa 9O-degreeanglewiththerestof theappliance andintersects theocclusalplanetowardthepalate.whereithooksonto tbeloopoftheligat uret iewireoft hebracketthatwas bondedtothe cuspiduponits surgicalunco\'ering. 288PartFOrthodonlic TrOOl menlModaillln F4.60 FiguresF4.60throughF4.63AcasewithclassII50%rela-tionshipwithsevertmaxillary(16mm)andmandibular (8mm)crowding.ThecrowdingC'dn\'eryeasi lybecalcu-latedbyeye-ballingthearches:thecuspidwidthisabout 8mm.whereaseachincisoroverlapisabout2mmof crowding.Withsuchseverelackof space.extractionsare necessaryinbotharches.Thismeansthat,inordertoend up wit haclassI cuspidrelat ionship,wemustsecureaclass Imolar relationshipaswell.Inotherwords,wemustmake surtt hatthemandibularfirstmolarscome3to4mm anteriorly,whilekeepingthemaxillaryoneswheretheyare, sothataclassJ relationshipmaybeachieved.Thecombi-nationofupperfirstbicuspidandlowersecondbicuspid extractionsbringsusclosertoour goals:themaxillarycus-pidscaneasi lybebroughtintothespaceof thef,Tstbicus-pids.andthemandibularmolarscanslipanteriorl ywith slidingmechanics.Asshowninthediagram.ifwehada fullclassII( l ~ )molarrelationship,thenthetotaltooth mo\'ementwouldhavebeenevenmoredifficult.because thelowermolarwouldhavetomoveanteriorl y evenmore and theupper cuspid7mm dista