The effects of chewing rates on mandibular kinematics

The purpose of this study is to provide basic understanding of how the spee d of chewing affects masticatory jaw kinematics. Twenty-six healthy subject s (23.6 +/- 2.5 years of age) chewed a standardized bolus of gum at fast (1 00 cycles s(-1)), habitual and slow (50 cycles s(-1)) rates. The rates were controlled with a metronome and the order of rates was randomized for each subject. An optoelectrical system independently recorded head and jaw move ment. Special computer programs identified representative cycles for each s ubject and computed various aspects of jaw movement. Multilevel statistical procedures were used to compare cycle variables among the three rates, est imate variability and model jaw movements. Maximum ranges of anteroposterio r (AP), vertical and lateral jaw excursions were significantly less for the fast than the habitual or slow rates. While the shape of 3-D pathway was s imilar for the three rates, the perimeter of the pathway was significantly shorter for fast chewing cycles. Maximum AP, vertical, lateral and total 3- D jaw velocities were significantly different among the three rates. Betwee n cycle variation in cycle duration and jaw excursion were least during fas t chewing and the greatest during slow chewing; variability in maximum velo city was similar for the three rates.