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Langer Topics GNATHOLOGY and ORTHODONTIC outline

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Langer Topics GNATHOLOGY and ORTHODONTIC outline Powered By Docstoc
					                                               Isaac Post, DDS, MSD
                                              George Langer, DDS, MSD

                   GNATHOLOGY IN ORTHODONTICS

Definition of Gnathology:

Why relate gnathology to orthodontics? Why should we consider gnathological
concepts (generally prosthodontic concepts) in an orthodontic practice?
    "The most conspicuous lapse of logic is perhaps the statement that the
      majority of studies show no association between occlusal factors and
      TMD; therefore they are not causally linked. The reiteration of such an
      obvious error only serves to misdirect research efforts. Absence of
      evidence is not evidence of absence." (Kirveskari, J. Cranio. Bio., 1999)

Gnathological Society founded in 1926 by Dr. McCollum, a prosthodontist
 In the 1970's, Dr. Ronald Roth introduced the use of gnathological principles
  in orthodontic diagnosis and treatment planning

Central to gnathological principles should be:
1. Establish centric Relation
    Roth's definition: Position of the mandible when the condyle is seated in its
       most superior anterior position against the posterior slope of the eminence
       with the thin, central, avascular portion of the disc interposed and centered
2. Coordination of centric relation (CR) and maximal intercuspation (MI)
 When the teeth are in maximal closure, they should mesh in a "normal"
   relationship and should not cause the condyle or condyles to be pulled
   forward or down out of the fossae
3. A harmonious functional scheme
 The teeth should not interfere with the full extent of movement that the
   mandible is capable of making in all directions

Recognizing occlusal disharmony and interferences - signs and symptoms
 Excessive occlusal wear
 Excessive tooth mobility
 Limitations of mouth opening
 Inability to execute smooth, full lateral and protrusive excursions
 Myofascial pain
 TMJ sounds
 Excessive contracture of musculature
 Tongue position
 Mandibular shift upon closure

If any of these signs or symptoms are present, it may be wise to fabricate a splint
for the patient
   To alleviate or lessen symptoms
   To allow the muscles to deprogram so the mandible can reposition itself
   Most of our patients are young

Is CR - MI coincidence truly possible?
Roth initially thought that it was possible in almost all cases
 Perfect coincidence of CR - MI is our goal but probably rarely attainable
        Equilibration should be limited to minor discrepancies - major ones
           need prosthodontic help or orthodontic retreatment

How close is acceptable?
 Roth (AO, 1973) says maximal acceptable difference between MI (maximal
  intercuspation) and CR (centric relation) is 1mm vertically, 1mm
  anterioposteriorly and .5 mm transversely

Techniques for determining centric relation has long been debated by
practitioners:

Roth's Power Centric bite registration
 Patient sits for minimum of 5 minutes with cotton roll or leaf gauge between
   incisors
 Two piece bite registration
        Anterior segment
        Posterior segment
 Technique:

For patients that are severely muscularly adapted and programmed or have TMD
symptomology, use a gnathological splint
-Unmasks true relationship of maxilla and mandible that is hidden by excessive
muscular contracture

Other items to be aware of to maintain centric occlusion
1. Overcorrection must be built into the appliance
2. Second molars are most common teeth to exhibit occlusal interference
3. Adhere to Andrew's Six Keys of Occlusion
4. Beware of creating a molar fulcrum

Evidence against the gnathological approach
 Even the gnathologists agree that the great majority of cases can be
   successfully treated without the gnathological approach
 Roth himself says that in most cases CR - MI is an unrealistic goal of
   treatment
 Johnson, J. Prosth Dent, 1988 - CR-MI discrepancies often increase
 Sadowski et. al., AJO, 1980 - CR-MI discrepencies and non-functional
   contacts
   Klar et. al., Semin Ortho, 2003 - 200 ortho cases treated with gnathological
    techniques and guidelines
   No hard experimental evidence shown linking occlusal factors to TMD
    (although the gnathologists call these studies "unclear")
   Many (Phillips, J. Prosth. Dent., 1986) argue that there is greater than .5mm
    procedural error in measuring CR and MI so these norms are meaningless
   CPI readings may not always be reproducible (Lavine, et. al., Seminars in
    Ortho., June 2003)

				
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posted:7/20/2011
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