Journal of Dental Research, Vol 78, 1662-1668, Copyright © 1999 by International & American Associations for Dental Research Online Journals
Smoothness of human jaw movement during chewing
K. Yashiro, T. Yamauchi, M. Fujii and K. Takada
Department of Orthodontics, Faculty of Dentistry, Osaka University, Suita, Japan.
Human limb movements are successfully modeled based on the assumption that
the central nervous system controls the movements by maximizing movement
smoothness. Movement smoothness is quantified by means of a time integral
of squared jerk (jerk-cost), where jerk is defined as the rate of change in
acceleration. This study was performed to investigate whether the control
of human masticatory vertical jaw movements can also be explained by a
minimum-jerk (maximum-smoothness) model. Based on the assumption that
minimum-jerk models account for vertical jaw-opening and -closing movements
during chewing, the actual time profile of the movement trajectory was
simulated by the model. The simulated jerk-costs and peak velocities were
compared with those obtained by actual measurements of jaw movements during
chewing. Jerk-costs and peak velocities of the jaw movements during chewing
were significantly correlated with those predicted by minimum-jerk models
(P < 0.0001, r between 0.596 and 0.799). The minimum-jerk models
predicted closing movement trajectories more accurately than opening
movement trajectories (jaw opening, root-mean-square error = 1.19 mm; jaw
closing, 0.52 mm, t = 4.375, P < 0.0001). The results indicated that the
vertical jaw movement control during chewing was represented by the
minimum-jerk control model and that the vertical jaw-closing movement is
smoother than the opening movement during gum-chewing.
