Journal of Dental Research, Vol 69, 470-472, Copyright © 1990 by International & American Associations for Dental Research Online Journals
Hysteresis in jaw positioning following lateral stretches
J. D. Rugh, R. R. Lemke and F. B. Dal Santo
Department of Oral and Maxillofacial Surgery, University of Texas Health Science Center, San Antonio 78284.
The purpose of this study was to examine hysteresis of the masticatory
system following brief, voluntary lateral positioning of the mandible.
Hysteresis was studied in ten healthy subjects, as a function of both time
and distance that the mandible was held laterally off the midline. So that
the effects of distance of lateral stretch on hysteresis could be studied,
subjects positioned their jaws to the left or right of the midline
distances of 2, 4, 6, 8, and 10 mm for ten s. So that the effects of time
could be studied, the distance of lateral stretch was held a constant 8 mm
for durations of two, four, six, 12, 16, and 20 s. Following each voluntary
lateral stretch, subjects relaxed the muscles using EMG biofeedback and
allowed the mandible to reposition itself passively. Hysteresis was defined
as the difference in the mandibular resting position between pre- and
post-stretch recordings. Mean hysteresis effects ranged from 0.7 mm to 1.8
mm. Hysteresis effects were found to increase with both distance and time;
after eight s, however, no additional effect of time was noted.
