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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)
