Abstract
Purpose: In order to clarify the functional role of head movements associated with the jaw movement during stomatognathic functions, the relationship between the amount of head movement during chewing of raw rice and the abilities of chewing or biting was analyzed.
Methods: Twenty-eight adult volunteers (25 males, 3 females, mean age 21.2 years) participated in this study. The head movement was monitored by a head-tracking sensor positioned near the forehead of the subject. The masticatory performance (MP) was measured by using the sieving method of raw rice used in many studies. The maximum bite force (BF) produced by the incisors of both jaws was measured by a strain-gauge transducer attached to a U-shaped bite stick. To inhibit the anteroposterior flexion of the head during chewing or biting, the head of the subject was held by an experimenter.
Results: 1. The degrees of head flexion during chewing varied among subjects. The degree of head flexion divided the subjects into two groups, the Small group and the Large group. 2. In the Small group, the MP was not changed by holding the head, but the BF was increased by about 20% by it. 3. In the Large group, the BF was not changed by holding the head, but the MP was decreased by about 10% by it.
Conclusions: In the subjects who moved their heads largely during chewing, the dynamic control system of head position served to increase chewing ability. Furthermore, from the data observed in the subjects who did not move their heads at all during chewing, it was suggested that the BF was limited by the static control system of head position.
