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IsaacPost,DDS,MSDGeorgeLanger,DDS,MSD
GNATHOLOGYINORTHODONTICS
DefinitionofGnathology:
Whyrelategnathologytoorthodontics?Whyshouldweconsidergnathologicalconcepts(generallyprosthodonticconcepts)inanorthodonticpractice? "ThemostconspicuouslapseoflogicisperhapsthestatementthatthemajorityofstudiesshownoassociationbetweenocclusalfactorsandTMD;thereforetheyarenotcausallylin ed.Thereiterationofsuchanobviouserroronlyservestomisdirectresearchefforts.Absenceofevidenceisnotevidenceofabsence."(Kirves ari,J.Cranio.Bio.,1999)
GnathologicalSocietyfoundedin1926byDr.McCollum,aprosthodontist Inthe1970's,Dr.RonaldRothintroducedtheuseofgnathologicalprinciplesiorthodonticdiagnosisandtreatmentplanning
Centraltognathologicalprinciplesshouldbe:1. EstablishcentricRelation Roth'sdefinition:Positionofthemandiblewhenthecondyleisseatedinitsmstsuperioranteriorpositionagainsttheposteriorslopeoftheeminencewitht
hethin,central,avascularportionofthediscinterposedandcentered2. Coordinationofcentricrelation(CR)andmaximalintercuspation(MI) Whentheteethareinmaximalclosure,theyshouldmeshina"normal"relationsipandshouldnotcausethecondyleorcondylestobepulledforwardordownoutofthefossae3. Aharmoniousfunctionalscheme Theteethshouldnotinterferewiththefullextentofmovementthatthemandibeiscapableofma inginalldirections
Recognizingocclusaldisharmonyandinterferences-signsandsymptoms Excessiveocclusalwear Excessivetoothmobility Limitationsofmouthopening
Inabilitytoexecutesmooth,fulllateralandprotrusiveexcursions Myofascialpain TMJsounds Excessivecontractureofmusculature Tongueposition Mandibularshiftuponclosure
Ifanyofthesesignsorsymptomsarepresent,itmaybewisetofabricateasplintforthepatient
Toalleviateorlessensymptoms Toallowthemusclestodeprogramsothemandiblecanrepositionitself Mostofourpatientsareyoung
IsCR-MIcoincidencetrulypossible?Rothinitiallythoughtthatitwaspossibleinalmostallcases PerfectcoincidenceofCR-MIisourgoalbutprobablyrarelyattainable Equilibrationshouldbelimitedtominordiscrepancies-majoronesneedprosthdontichelpororthodonticretreatment
Howcloseisacceptable? Roth(AO,1973)saysmaximalacceptabledifferencebetweenMI(maximalintercusation)andCR(centricrelation)is1mmvertically,1mmanterioposteriorlyand.
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5mmtransversely
Techniquesfordeterminingcentricrelationhaslongbeendebatedbypractitioners:
Roth'sPowerCentricbiteregistration Patientsitsforminimumof5minuteswithcottonrollorleafgaugebetweeninisors Twopiecebiteregistration Anteriorsegment Posteriorsegment Technique:
ForpatientsthatareseverelymuscularlyadaptedandprogrammedorhaveTMDsymptomology,useagnathologicalsplint-Unmas struerelationshipofmaxillaandmandiblethatishiddenbyexcessivemuscularcontracture
Otheritemstobeawareoftomaintaincentricocclusion1.Overcorrectionmustbebuiltintotheappliance2.Secondmolarsaremostcommonteethtoexhibitocclusalinterference3.AdheretoAndrew'sSixKeysofOcclusion4. Bewareofcreatingamolarfulcrum
Evidenceagainstthegnathologicalapproach Eventhegnathologistsagreethatthegreatmajorityofcasescanbesuccessfulytreatedwithoutthegnathologicalapproach RothhimselfsaysthatinmostcasesCR-MIisanunrealisticgoaloftreatmen Johnson,J.ProsthDent,1988-CR-MIdiscrepanciesoftenincrease Sadows iet.al.,AJO,1980-CR-MIdiscrepenciesandnon-functionalcontacts Klaret.al.,SeminOrtho,2003-200orthocasestreatedwithgnathologicaltehniquesandguidelines Nohardexperimentalevidenceshownlin ingocclusalfactorstoTMD(althoughtegnathologistscallthesestudies"unclear") Many(Phillips,J.Prosth.Dent.,1986)arguethatthereisgreaterthan.5mmpoceduralerrorinmeasuringCRandMIsothesenormsaremeaningless CPIreadingsmaynotalwaysbereproducible(Lavine,et.al.,SeminarsinOrtho
,June2003)
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