ORIGINALARTICLE - PDF document

ORIGINALARTICLE Prevalenceofthirdmolarimpactioninorthodonticpatientstreatednonextractionandwithextractionof4premolarsTae-WooKim,DDS,MSD,PhD,JonÅrtun,DDS,DrOdont,FarajBehbehani,DDS,MS,FlaviaArtese,DDS,MScSeoul,Korea;SafatandKuwaitCity,Kuwait;RiodeJaneiro,BrazilThepurposesofthisstudyweretoconÞrmthatpremolarextractiontreatmentisassociatedwithmesial ofextractiontherapyonmaxillarythirdmolarimpactionisverylimited.Thesamplesinseveraloftheabovestudieswereandmightnothaverepresentedthegeneralpopulation.Otherpotentialproblemsincludediffer-encesintheagesofthesubjectsandinthecriteriausedtodiagnoseimpaction.Casestudiessuggestapotentialforthirdmolareruptionduringthenalstagesofrootformation,despiteapparentsignsofdevelopmentofimpaction(Fig1).Theaverageageatthirdmolaremergencerangesfrom17to21years,buttherootsarenotfullyformeduntil18to25yearsofage.Accordingly,thirdmolarimpactioncouldhavebeenoverdiagnosedinstudiesexaminingsubjectslessthan20yearsold.Also,practitionerswhobelievethatthemesialpressureoferuptingthirdmolarsisacantfactorforrelapseofincisoralignmentarelikelytorecommendearlyremoval.Scoringprevioussurgicalremovalofmandibularthirdmolarsasimpac-couldimplyasystematicoverdiagnosisofimpaction,particularlyinnonextractioncases,therebybiasingtheresults.Thepurposesofthisstudyweretoconrmthatpremolarextractiontreatmentisassociatedwithmesialmovementofthemolarsconcomitantwithanincreaseintheeruptionspaceforthethirdmolarsandtotestthehypothesisthatsuchtreatmentreducesthefrequencyofthirdmolarimpaction.MATERIALANDMETHODSLateralcephalograms,panoramicorperiapicalra-diographs,andstudymodelsmadebefore(T1)andafter(T2)treatmentandaminimumof10yearspostretention(T3)ofallpatientswithoutdentofacialdeformities,severefacialasymmetries,ormissingteethotherthan4premolars,andwhohadbeentreatednonextraction(n242)orwiththeextractionof4premolars(n315)byfacultymembersorgraduatestudentsintheDepartmentofOrthodonticsattheUniversityofWashington,Seattle,wereexamined.Atotalof389patientshadradiographicevidenceofatleast1thirdmolaratT1orT2.Thepatientswhosedevelopingthirdmolarshadbeenremovedbeforeevidenceofapicalrootclosureorwhoseradiographsdidnotallowidenticationoftheapicesoftheremain-ingthirdmolarswereexcluded.Thenalsampleconsistedof157patients.Atotalof51weretreatednonextraction(nonex),ofwhom41couldbeevaluatedinthemaxillaand38inthemandible,and106weretreatedwithextractionof4premolars(ex),ofwhom91couldbescoredinthemaxillaand96inthemandible.AngleClassIandIImalocclusionscomprised94.1%percentofthesample.Theextractionprotocoloftheexpatientswas4rstpremolarsin67.9%andacombi-nationofmaxillaryrstandmandibularsecondpremo-larsin22.6%.IndependenttestsdocumentedasmallbutstatisticallysignicantdifferenceinageatT1andT3(.05,TableI),andchi-squaretestsshowednocantdifferenceindistributionofAngleclassicationbetweentheexandthenonexpatients.However,womencomprised39.2%oftheexpatientsand64.2%ofthenonexpatients(.05,chisquaretest).testsshowednosignicantdifferenceinage(.05),andchi-squaretestsshowednocantdifferenceindistributionofAngleclassication(.05)betweentheselectedandtheexcludedpatients.However,womenconstituted56%and67%oftheselectedandexcludedpatients,andextractionwas Fig1.Periapicalradiographsmadeat,15years9months,and29years10monthsofapatientwhohadreceivedorthodontictreatmentwithextractionof4rstpremolars.Noteeruptionofmandibularthirdmolarsduringnalstageofrootformationdespiteapparentimpactionatage15years9months.AmericanJournalofOrthodonticsandDentofacialOrthopedicsKimetal performedin66%and56%oftheselectedandex-cludedextractionpatients,respectively(.05,chi-squaretest).ThirdmolarimpactionwasdenedasincompleteeruptionatT2orT3becauseofinclinedpositionrelativetothesecondmolarortheascendingramus,orlackofspace(Fig2),withradiographicevidenceofapicalclosure.ThirdmolareruptionwasdenedasthepresenceofthethirdmolarsinfullocclusionatT2orUppermolarmovement(U-MM)andlowermolarmovement(L-MM)weremeasuredtothenearest0.5mmalongtheaveragedocclusalplaneonthesuperim-posedimagesoftheT1andT2cephalogramswithadigitalcaliper(FredV.FowlerCo,Newton,Mass).MaxillarysuperimpositionwasperformedaccordingtoDoppeletal,andmandibularsuperimpositionaccordingtoBjoTheupper(U-ES)andlower(L-ES)eruptionspacesweremeasuredontheT2cephalograms(Fig3).U-ESwasdenedasthedistancefromthepterygoidverticaltothedistalsurfaceofthemaxillaryrstmolarcrownalongtheocclusalplane(Fig3).L-ESwasdenedasthedistancefromRickettsXipointorfromtheanteriorborderoftheramus(R)tothedistalsurfaceofthemandibularsecondmolarcrownalongtheocclusalplane(Fig3).Subjectswithincompleteerup-tionofthemandibularsecondmolarswerenotmea-Thereproducibilityofthemeasurementswasas-sessedbystatisticallyanalyzingthedifferencebetweendoublemeasurementstakenatleast1weekaparton10randomlyselectedpatients.Theerrorwascalculatedfromtheequation D2 isthedifferencebetweenduplicatemeasure-mentsandisthenumberofdoublemeasurements.Theerrorswere0.44mmforU-MM,0.50mmforL-MM,0.76mmforU-ES,0.46mmforL-ES(Xi),and1.12mmforL-ES(R).Aproposedtotalimpactionscore,denedasthenumberofimpactedthirdmolarsinbotharchesdividedbythenumberofthirdmolarsevaluated,wasmadeforeachofthe157patientsinthesample.Similarly,proposedmaxillaryimpactionscoresweremadeforthe132patientswhocouldbeevaluatedinthemaxilla,andproposedmandibularimpactionscoresweremadeforthe134patientswhocouldbeevaluatedinthemandi-ble.Separatesamplemeanswerecalculatedfortheexandnonexpatients,andindependenttestswereusedtotestforpossiblesignicances.Inaddition,separatesamplemeansofU-ES,L-ES(Xi),andL-ES(R)atT2andofU-MMandL-MMfromT1toT2werecalcu-latedfortheexandnonexpatients,forthepatientswithimpactionanderuption,andforthesubgroupsofexandnonexpatientswithimpactionanderuption.Fortheseanalyses,patientswithimpactionon1sideanderuptionontheotherwereincludedinthegroupofpatientswithimpaction.Independenttestswereusedtotestforpossiblesignicantdifferences.Thetotalimpactionscore(.01)andtheimpactionscoresforthemaxilla(.01)andthemandible(.05,TableII)werehigherforthenonexthantheexpatients.Similarly,thenonexpatientshadahigherproportionofimpactedmaxillaryandmandibu-larthirdmolars(TableIII).MeanU-MMwas2.2mmmoremesialandmeanL-MMwas1.8mmmoremesialintheexthaninthenonexpatients(.01,TableIV).Also,meanU-MMwas1.8mmmoremesial(.01)inthepatientswitheruptionthaninthosewithimpactionoftherespectivethirdmolars,butnodifferencecouldbedetectedinmeanL-MM(TableIV).Nodifferencesinmolarmovement(MM)werefoundbetweenthesubgroupsofexpatientswithimpactionandthosewitheruption,orbetweenthesubgroupsofnonexpatientswithimpac-tionandthosewitheruption(.05).ThevariationinMMwasconsiderable,withU-MMrangingfromto8.0mmandL-MMfrom1.5to8.3mmintheexpatients;U-MMrangedfrom2.7to5.2mmandL-MMfrom2.9to3.5mminthenonexpatients.MeanU-ESwas3.0mmlargerintheexthaninthenonexpatients(.01)and1.6mmlargerinthepatientswitheruptionthaninthosewithimpactionofthemaxillarythirdmolars(.05,TableV).Ofthe114patientswithU-ESlessthan25mm,79(69.3%)experiencederuption,and2ofthe5patientswithU-ESlessthan14mmexperiencederuption.Atotalof17TableI.Agesbefore(T1)andafter(T2)treatmentandatleast10yearspostretention(T3)atradiographicexaminationsofpatientstreatednonextraction(nonex)andwithextractionoffourpremolars(ex) Nonex(nEx(nSDPT111.81.912.6T215.01.915.41.9NST329.23.630.6notsigniAmericanJournalofOrthodonticsandDentofacialOrthopedicsFebruary2003Kimetal (20.7%)ofthe82patientswithU-ESgreaterthanorequalto18mmexperiencedimpaction.ThesmallestU-ESassociatedwitheruptionwas13.0mm,andthelargestU-ESassociatedwithimpactionwas24.0mm.L-ES(Xi)andL-ES(R)were2.6and1.8mmlargerintheexthaninthenonexpatients,and2.7and1.9mmlargerinthepatientswitheruptionthaninthosewithimpactionofthemandibularthirdmolars(TableV).Atotalof56(64.4%)ofthe87patientswithL-ES(Xi)lessthan23mmand12(42.9%)ofthe28patientswithL-ES(Xi)lessthan19mmexperiencederuptionofthemandibularthirdmolars.Ofthe3patientswithL-ES(Xi)greaterthanorequalto28mm,1experiencedimpaction.Thesmallestvalueassociated Fig2.Periapicalandsectionsofpanoramicradiographsofpatientsinoursample:at33years9months,illustratingmesialimpactionofmaxillarythirdmolar;,at29years2months,illustratingmesialimpactionofmandibularthirdmolar;,at30years1month,illustratingdistalimpactionofmandibularthirdmolar;,at39years5months,illustratingdistalimpactionofmaxillarythirdmolar;at29years6months,illustratingverticalimpactionofmandibularthirdmolar.AmericanJournalofOrthodonticsandDentofacialOrthopedicsKimetal witheruptionwas12.0mm,andthelargestvalueassociatedwithimpactionwas24.5mm.Also,46(60.5%)ofthe76patientswithL-ES(R)lessthanorequalto5.0mmand29(55.8%)ofthe52patientswithL-ES(R)lessthanorequalto3.5mmexperiencederuption.Thesmallestvalueassociatedwitheruption0.5mm,andthelargestvalueassociatedwithimpactionwas9.0mm.WeconrmedthendingsofFaubionthatimpactionofthemandibularthirdmolarsoccursabouttwiceasofteninnonexpatientsthaninexpatients.Cephalometricgrowthstudiessuggest2im-portantmechanismsfordevelopmentoftheretromolarspaceinthemandible:resorptionattheanteriorborderoftheascendingramusandanteriormigrationoftheposteriorteethduringthefunctionalphaseoftoothBothmightdependmoreontheamountanddirectionofcondylargrowththanonthepresenceofthethirdmolars.Theamountofperiostealappositiononthemaxillarytuberositiescouldbemorecompensatory,ectingthesizeandnumberofthemaxillaryposte-riorteeth.Accordingly,mesialmovementofthemolarsduringclosureoftheextractionsitecouldhavealargereffectonthirdmolarimpactioninthemandiblethaninthemaxilla.However,wesuggestthatthismightnotbethecase.Ourdataclearlyindicatethatthedifferenceinimpactionrateofthethirdmolarsbetweenexandnonexpatientsissimilarinbotharches.Afrequentargumentforpremolarextractioninborderlinecaseshasbeenthattheproceduremightbeconsideredasubstitutionforthirdmolarextraction.However,ourresultssuggestthatthisassumptionisfalseineveryfthcase(TablesIIandIII).Itmightbeprudenttoinformpatientsandtheirparentsthatpre-molarextractiontherapyofteninvolvestheremovalof8teeth.Ourresultsindicatethatthirdmolarimpactionmightbeasmallerproblemafternonextractiontherapythanpreviouslysuggested.concludedthatonly15%ofmandibularthirdmolarseruptedingoodpositionafternonextractiontherapy.Similarly,Richardsonfoundthat,innonextractionpatients,asmanyas56%ofthemandibularthirdmolarswereeitherimpactedorhadproblemsthatneededsurgicaltreatment.However,thesamplesintheabovestudieswererathersmallandmightnothaverepresentedthegeneralpopulation.Incontrast,the157subjectsinoursamplerepresentedeverycasefromalargepatientpoolthatallowedaccuratediagnosisofimpactionversuseruptionofthethirdmolars.Inaddition,statisticaltestsensuredthattheselectedcases Fig3.Cephalometrictracingindicatingmeasurementofuppereruptionspace(U-ES)fromprojectionofdistalcontactpointofmaxillaryrstmolaronocclusalplanetointersectionofpterygoidvertical(PTV)andocclusalplane,andlowereruptionspace(L-ES)measuredfromdistalcontactpointofmandibularsecondmolartoXipoint(Xi)andanteriorborderoframus(R)alongocclusalplane.TableII.Totalimpactionscoreandimpactionscoresinmaxillaandmandibleofpatientstreatednonextraction(nonex)andwithextractionoffourpremolars(ex) SD(n)SD(n)SD(n)Nonex0.480.50(41)0.450.49(38)0.480.48(51)Ex0.180.38(91)**0.220.40(96)*0.230.40(106)**.05;**TableIII.Frequencyofimpactedanderuptedthirdmolarsinmaxillaandmandibleof51patientstreatednonextraction(nonex)and106patientstreatedwithextractionof4premolars(ex) MaxillaMandibleN(%)N(%)N(%)N(%)Nonex36(50)36(50)26(40)39(60)Ex26(16)141(84)38(22)138(78)AmericanJournalofOrthodonticsandDentofacialOrthopedicsFebruary2003Kimetal weresimilartothosethatwereexcludedbecauseofcientrecords.Finally,thepatientsinthelargebackgroundpoolwereoriginallyselectedatrandom.Oursamplecanbeconsideredrepresentativeofthegeneralpopulationoforthodonticpatients.Anotherproblemwiththepreviousstudieswasthatsubjectslessthan18yearsoldwereincludedintheandmostwerelessthan20yearsold.Duringthescreeningprocess,wefoundthateruptionduringthenalstagesofrootdevelopmentofthirdmolarsthatappeartobecomeimpacted(Fig1)isbynomeansunusual.Thisndingsuggestsariskofoverdi-agnosisinthepreviousstudies.Theaverageageofoursamplewas30.2yearsatT3,witharangefrom22.2yearsto45.3years(TableI),andallthirdmolarrootsshowedradiographicevidenceofapicalclosureatexamination.Althoughourstudydesignprecludesconclusionsaboutcause-and-effectrelationships,theresultsstronglysuggestthattheincreasedpotentialformesialmolarmovementduringextractionsiteclosure,withconcomitantincreaseinretromolarspace,mightbethemajorreasonfortheintergroupdifferenceinthirdmolarimpaction.However,wecoulddetectnodiffer-enceinL-MMbetweenpatientswitheruptionandimpactionofthemandibularthirdmolars.Also,whenevaluatingthesubgroupsofexandnonexpatientsseparately,wedetectednodifferencesinMMineitherarchbetweenpatientswithandwithoutthirdmolarimpaction.Asimilarndinghasbeenreportedinthemandibulararchinapreviousstudy,suggestingthatothervariablescouldbeequallyimportantforthedevelopmentofsufcienteruptionspaceforthethirdmolars.WealsofoundlargeindividualvariationsintheamountofMMduringactiveappliancetherapy(TableIV)andinthesizeoftheeruptionspacesatapplianceremoval(TableV).Suchvariationiswelldocumentedinthemandible.Inexcases,partoftheexplanationmightbevariationintheamountofcanineretractionbecauseofpretreatmentdifferencesinirreg-ularityandinthelabiolingualpositionoftheincisors,andtomechanicalvariationduringresidualspaceclosure.However,ourresultssuggestthatthevariationisequallylargeinnonexcases,andaslargeinthemaxillaasinthemandible.Severalstudieshavefailedtousestatisticswhenevaluatingtheeffectofpremolarextractiononimpac-tionofthemandibularthirdmolars.Also,ithasbeencommontocomparethenumberofquadrantswithimpactionversuseruptionbetweengroupsofexandnonexpatients.However,theseanalysesmightbebiasedifthetendencyforeruptionontherightandleftsidesineachpatientiscorrelated.Toovercomethatpotentialproblem,wehaveproposedtheuseofanimpactionscorewhentestingforpossibleintergroupIthasbeensuggestedthatthesizeofthemaxillaryeruptionspaceatapplianceremovalisavalidpredictorforwhetherthethirdmolarswillerupt.Onearticlestatesthatatleast18mmisrequiredfromthedistalofrstmolarstothepterygoidverticalwhenmeasuredalongtheocclusalplane,andthattheprognosisforeruptionisverypoorifthedistanceislessthan14However,about20%ofthepatientsinourTableIV.Upper(U-MM)andlower(L-MM)molarmovementofpatientstreatednonextraction(nonex)andwithextractionof4premolars(ex)andwithimpactionanderuptionofthirdmolars SD(n)SD(n)SD(n)SD(n)U-MM2.13.3(41)4.32.5(91)*2.33.0(37)4.12.8(95)*L-MM2.33.2(38)4.12.2(96)*3.12.8(42)3.82.6(92)NS.01;NS,notsigniTableV.Upper(U-ES)andlower(L-ES)eruptionspaceofpatientstreatednonextraction(nonex)andwithextractionof4premolars(ex)andwithimpactionanderuptionofthethirdmolars SD(n)SD(n)SD(n)SD(n)U-ES16.23.5(41)19.23.9(91)**17.13.6(37)18.74.2(95)*L-ES(Xi)18.44.8(38)21.04.3(96)**18.44.3(42)21.14.5(92)**L-ES(R)3.73.3(38)5.53.0(96)**3.63.1(42)5.53.0(92)**.05;**Xipoint;R,anteriorborderoframus.AmericanJournalofOrthodonticsandDentofacialOrthopedicsKimetal sampleexperiencedimpactiondespiteadistanceequaltoorgreaterthan18mm,andthethirdmolarseruptedsuccessfullyin2ofthe5patientswithadistancelessthan14mm,callingintoquestiontheclinicalsignicanceofthosedimensionsaspredictorsforeruptionandimpaction.Wealsofoundthatabout70%ofthemaxillarythirdmolarseruptedinsubjectswitheruptionspacessmallerthan25mm,incontrasttoonly10%asdocumentedinapreviousstudy.Partofthediscrepancycanbeexplainedbecausewemeasurederuptionspaceatanaverageageofabout15years(TableI)ratherthaninadults,withoutadjustingforpossiblegrowthincrements.Anotherexplanationmightbethatthesamplewassmallintheotherstudyanddidnotnecessarilyrepresentthegeneralpopulation.Morethan60%ofthepatientsinoursamplewithadistanceof23mmorlessfromthedistalofthemandibularsecondmolartoRickettspointXiattheendofactivetreatmentexperiencederuptionofthemandibularthirdmolars.Themandibularretromolarspacecanincreaseabout2mmfromage15toAssumingthattheincreaseinretromolarspaceimpliesasimilarincreasetopointXi,wecouldnotconrmthatthechanceoferuptionisnilwhenthepredictedadultdistanceislessthan25mm.couldweconrmthatthechanceofmandibularthirdmolarimpactionisabout85%whenthepredictedadultdistanceislessthan21mm,becausemorethan40%ofthepatientsinoursamplewithlessthan19mmfromthedistalofthemandibularsecondmolartoXiattheendofactivetreatmentexperiencederuptionofthemandibularthirdmolars.Previousresearchsuggeststhattheprobabilityofmandibularthirdmolareruptionisdirectlyrelatedtotheproportionofthethirdmolarinfrontoftheanteriorborderoftheramusbeforeeruption.Theaveragewidthofthemandibularthirdmolaris10.5mm,whichprobablycorrespondstoabout11mmonthelateralcephalometricimage.Ourthatasmanyas60%ofthesubjectswithadistancefromtheanteriorborderoftheramustothedistalofthesecondmolarsof5mmorlessandasmanyas55%ofthosewithadistanceof3.5mmorlessexperiencederup-contradictthoseresults.Ourndingssuggestthatthesizeofthethirdmolareruptionspaceassociatedwithahighriskofimpactionmightbesmallerthanpreviouslysuggested.Ourresultssuggestaclinicallysignicantreductionintherateofimpactionofmaxillaryandmandibularthirdmolarsinexpatientscomparedwithnonexpatients.Themechanismmightbethatpremolarex-tractiontherapyisassociatedwithanincreaseintheamountofmesialmovementofthemaxillaryandmandibularmolarsandanincreaseintheeruptionspaceforthethirdmolars.Ourndingsalsosuggestthatthesizeofthethirdmolareruptionspaceassociatedwithahighriskofimpactionmightbesmallerthanpreviouslysuggested.1.DachiSF,HowellFV.Asurveyof3874routinefull-mouthradiographs.II.Astudyofimpactedteeth.OralSurgOralMedOralPathol1961;14:1165-9.2.BisharaSE,AndreasenG.Thirdmolars:areview.AmJOrthod3.GroverPS,LortonL.Theincidenceofuneruptedpermanentteethandrelatedclinicalcases.OralSurgOralMedOralPathol4.BjorkA,JensenE,PallingM.Mandibulargrowthandthirdmolarimpaction.ActaOdontScand1956;14:231-71.5.BjorkA.Variationsinthegrowthpatternofthehumanmandible:longitudinalradiographicstudybytheimplantmethod.JDentRes(Suppl1)1963;42:400-11.6.AllingCCIII,AllingRD.Indicationsformanagementofimpactedteeth.In:AllingCCIII,HelfrickJF,AllingRD,editors.Impactedteeth.Philadelphia:W.B.Saunders;1993.p.46-9.7.SillingG.Developmentanderuptionofthemandibularthirdmolaranditsresponsetoorthodontictherapy.AngleOrthod8.BeggPR.StoneAgemansdentition.AmJOrthod1954;40:298-312,373-83,517-31.9.MurphyTR.Reductionofthedentalarchbyapproximalattri-tion.BrDentJ1964;116:483-8.10.CavanaughJJ.Thirdmolarchangesfollowingsecondmolarextractions.AngleOrthod1985;55:70-6.11.GoorisCGM,rtunJ,JoondephDR.Eruptionofmandibularthirdmolarsaftersecondmolarextractions:aradiographicstudy.AmJOrthodDentofacialOrthop1990;98:161-7.12.DierkesDD.Aninvestigationofthemandibularthirdmolarsinorthodonticcases.AngleOrthod1975;45:207-12.13.GraberTM,KainegTF.Themandibularthirdmolar:itspredic-tivestatusandroleinlowerincisorcrowding.ProcFinnDentSoc1981;77:37-44.14.RichardsonME.Theeffectofmandibularrstpremolarextrac-tiononthirdmolarspace.AngleOrthod1989;59:291-4.15.RickettsRM.Aprincipleofarcialgrowthofthemandible.AngleOrthod1972;42:368-86.16.FaubionBH.Effectofextractionofpremolarsoneruptionofmandibularthirdmolars.JAmDentAssoc1968;76:316-20.17.KaplanRG.Somefactorsrelatedtomandibularthirdmolarimpaction.AngleOrthod1975;45:153-8.18.RichardsonME.Thedevelopmentofthirdmolarimpaction.BrJOrthod1975;2:231-4.19.RichardsonME.Therelativeeffectsoftheextractionofvariousteethonthedevelopmentofmandibularthirdmolars.TransEurOrthodSoc1976;79-85.20.HaavikkoK,AltonenM,MattilaK.Predictingangulationaldevelopmentanderuptionofthelowerthirdmolar.AngleOrthod21.ProftWR,FieldsHW.Earlystagesofdevelopment.In:ProfWR,FieldsHW,editors.Contemporaryorthodontics.2nded.St.Louis:MosbyYearBook;1993.p.56-86.AmericanJournalofOrthodonticsandDentofacialOrthopedicsFebruary2003Kimetal 22.AshMMJr.Developmentanderuptionoftheteeth.In:AshMMJr,editor.Wheelersdentalanatomy,physiologyandocclusion.7thed.Philadelphia:WBSaunders;1993.p.24-45.23.DoppelDM,DamonWM,JoondephDR,LittleRM.Aninves-tigationofmaxillarysuperimpositiontechniquesusingmetallicimplants.AmJOrthodDentofacialOrthop1994;105:161-8.24.BjorkA.Predictionofmandibulargrowthrotation.AmJOrthod25.SchulhofRJ.Thirdmolarsandorthodonticdiagnosis.JClinOrthod1976;10:272-81.26.RickettsRM,TurleyP,ChaconasS,SchulhofRJ.Thirdmolarenucleation:diagnosisandtechnique.JCalifDentAssoc1976;27.RickettsRM.Studiesleadingtothepracticeofabortionoflowerthirdmolars.DentClinNorthAm1979;23:393-411.28.DahlbergG.Statisticalmethodsformedicalandbiologicalstudents.London:GeorgeAllenandUnwinLtd;1940.p.122-32.29.GanssC,HochbanW,KielbassaAM,UmstadtBE.Prognosisofthirdmolareruption.OralSurgOralMedOralPathol1993;76:30.LedyardBC.Astudyofthemandibularthirdmolararea.AmJOrthod1953;39:366-73.31.AshMMJr.Mandibularsecondmolar.In:AshMMJr,editor.sdentalanatomy,physiologyandocclusion.7thed.Philadelphia:W.B.Saunders;1993.p.291-9.32.OliveR,BasfordK.Reliabilityandvalidityoflowerthirdmolarspace-assessmenttechniques.AmJOrthod1981;79:45-53.33.ForsbergCM,VingrenB,Wessle`nU.Mandibularthirdmolareruptioninrelationtoavailablespaceasassessedonlateralcephalograms.SwedDentJ1989;13:23-31.BOUNDVOLUMESAVAILABLETOSUBSCRIBERSBoundvolumesoftheAmericanJournalofOrthodonticsandDentofacialOrthopedicsavailabletosubscribers(only)forthe2003issuesfromthePublisher,atacostof$96.00($115.56Canadaand$108.00international)forVol.123(January-June)andVol.124(July-December).Shippingchargesareincluded.Eachboundvolumecontainssubjectandauthorindexes,andalladvertisingisremoved.Thebindingisdurablebuckram,withthejournalname,volumenumber,andyearstampedingoldonthespine.Paymentmustaccompanyallorders.ContactMosby,SubscriptionCustomerService,6277SeaHarborDr,Orlando,FL32887;phone800-654-2452or407-345-4000.Subscriptionsmustbeinforcetoqualify.BoundvolumesarenotavailableinplaceofaregularJournalsubscription. AmericanJournalofOrthodonticsandDentofacialOrthopedicsKimetal