title: The effect of the physiological rest position of the mandible on cerebral blood flow and physical balance: an observational study.
abstract: OBJECTIVE
  There has been much published evidence that balance can improve by changing the mandible's position relative to the maxilla as it comes together with the teeth (or oral device) as the endpoint. To help with the complexity of this topic, a definitions table* (in Appendix) has been included at the end of the manuscript for reference as needed. The aim of the current study is to evaluate whether the physiologic rest position of the jaw* (oral device overtop of the teeth as endpoint where the muscles of mastication are optimized) can have an effect on cerebral blood flow and physical balance using measurable data relative to the person's natural, or habitual bite (teeth as endpoint) in both healthy and diseased volunteers.
  
  
  METHODS
  Seven healthy male professional football athletes and two females with multiple sclerosis were included in this observational study, which tested the subjects in both jaw positions. Cerebral blood flow was measured non-invasively by ultrasound over the temporal region of the skull using mean flow velocity (MFV)* and pulsatility index (PI)* of the right and left middle cerebral arteries while the subject clenched the teeth together in both jaw positions. The MFV is the average speed of the blood flow in a given region of a blood vessel. The PI measures cerebral intravascular resistance. Physiologic balance of the whole body was also tested while the subjects were in both jaw positions using the y-excursion balance test* and by videotape.
  
  
  RESULTS
  (i) Cerebral blood flow. On the natural teeth, the MFV dropped from baseline to clenching position (mean drop -2.6±7.7 cm/second, whereas, the MFV was slightly enhanced with the physiologic rest position (PRP) [mean enhancement is 0.82±3.7 cm/second (P=0.07)]. At baseline on natural teeth, the PI dropped slightly from baseline to clenching (mean drop 0.015±0.19). Whereas with PRP, the PI dropped by mean of 0.059±0.072 (P=0.15). (ii) Balance. The mean balance measurement while using the PRP was 119.54±12.56 cm (P=0.001), whereas the mean balance measurement on natural teeth was 110.72±9.47 cm. Balance improved subjectively in both MS patients on videotape.
  
  
  CONCLUSIONS
  The physiologic rest position of the mandible might have an effect on balance by showing a trend (demonstrating a tendency) in enhancing cerebral blood flow as measured by transcranial Doppler. Further studies are needed to confirm this study's finding.
authors.forename: Tammarie
authors.initials: T
authors.lastname: Heit
authors.forename: Carol
authors.initials: C
authors.lastname: Derkson
authors.forename: Jordan
authors.initials: J
authors.lastname: Bierkos
authors.forename: Maher
authors.initials: M
authors.lastname: Saqqur
mesh_terms: D000328:Adult; D001783:Blood Flow Velocity / Q000502:physiology*; D002560:Cerebrovascular Circulation / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008334:Mandible / Q000502:physiology*; D009064:Mouth Protectors; D009103:Multiple Sclerosis / Q000503:physiopathology; D011673:Pulsatile Flow; D017585:Ultrasonography, Doppler, Transcranial; D014655:Vascular Resistance; D014743:Videotape Recording
keywords: Balance,; Cerebral blood flow,; Headache,; Migraine,; Multiple sclerosis,; TMJ,; Transcranial Doppler