Mandibular postural tremor during relaxation and during volitional innervation of the jaw muscles.

Jaw tremor was recorded as the changes in the vertical distance between mandible and maxilla. Two states of motor performance of the jaw muscles were chosen: relaxed and actively positioning of the mandible close to toothcontact, referred to as respectively rest- and activity tremor. Rest tremor contained a strong ballistocardiac component (bc power = 50%) and was of small amplitude (9.4 micron rms). Activity tremor revealed increased amplitudes (19.2 micron rms) with a predominant neuromuscular component (nm power = 75%). Bc tremor patterns differed significantly from nm tremor patterns. A negative linear relationship, which apparently was similar for rest and for activity tremor (P greater than 0.10), existed between the estimated bc contribution and tremor amplitude. As tremor amplitude increased neuromuscular activity appeared increasingly time locked to bc activity, which should be attributed to synchronization of spindle activity, either through the stretch reflex or through vascular pulsation. The average bc contribution to tremor amplitude remained of almost constant magnitude (7.0 micron rms), with no differences between rest and activity for the group as a whole. During resting conditions, complete relaxation of the jaw muscles was not attained by the majority of the subjects. The latter revealed a heart rate arrhythmia that was strongly correlated with motor (nm) activity (P less than 0.001). During activity conditions no such correlation was present. The present results demonstrate that for the understanding and the interpretation of the underlying mechanisms of jaw tremor genesis, both the recording technique, i.e., differential jaw displacements, and the signal analysis procedure, i.e., autocorrelograms and power spectra over extended record length, were of crucial importance.(ABSTRACT TRUNCATED AT 250 WORDS)