Frequency-dependent modulation of rhythmic human jaw movements.

Modulation of jaw movement patterns by alteration of the chewing rhythm was analyzed in nine subjects. Jaw movements were monitored by an electronic transducer system. The subjects were asked to chew gum either at voluntarily determined rates or at rates guided by a light flash that varied from 2 to 7 Hz at 1-Hz intervals. The results can be summarized as follows: Chewing was generally conducted at rates below 3 Hz when the rhythm was voluntarily determined. When the rhythm was guided, however, the maximum chewing rate could occasionally be raised up to 6 Hz; the duration of the chewing cycle was more closely related to changes in the duration of the opening and occlusion phases than to that of the closing phase; at chewing rates below 3 Hz, the maximum gape did not appreciably change with the chewing rhythm, while it decreased linearly at rates above 3 Hz; and at chewing rates below 3 Hz, the jaw opening velocity increased with speed of chewing, whereas it decreased or sometimes fluctuated over a wide range at rates above 3 Hz. It is concluded that, during normal mastication at rates below 3 Hz, chewing rhythm is altered by changing both the velocity of jaw opening and the duration of the occlusion phase.