The effects of chewing rates on mandibular kinematics.

The purpose of this study is to provide basic understanding of how the speed of chewing affects masticatory jaw kinematics. Twenty-six healthy subjects (23.6 +/- 2.5 years of age) chewed a standardized bolus of gum at fast (100 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 movement. Special computer programs identified representative cycles for each subject and computed various aspects of jaw movement. Multilevel statistical procedures were used to compare cycle variables among the three rates, estimate variability and model jaw movements. Maximum ranges of anteroposterior (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 similar 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. Between cycle variation in cycle duration and jaw excursion were least during fast chewing and the greatest during slow chewing; variability in maximum velocity was similar for the three rates.