Smoothness of masticatory jaw movements before and after orthodontic treatment

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First, we investigated whether the minimum-jerk model predict the 3D jaw movement trajectories during chewing. The two types of test foods were used : gum and gummy jelly. The jaw movements were recorded from children and adults groups with good occlusions. For adults and children groups, the model precisely explained the jaw movement kinematics. Hence, it is suggested that the subjects with normal occlusions may control the jaw movement so as to maximize their smoothness during chewing. However, the jerk-costs of the jaw closing motion for the children were significantly higher than those determined for the adults. In addition, the jerk-cost variation was greater in children than adults. The greater variances of jerk-cost for the children may be the results of variety of the motor adaptation process to the dental developmental changes during childhood with mixed-dentition.Second, the jaw motor adaptation process to the experimentally produced acute occlusal interference was investigated. The unilateral chewing jaw motion with occlusal interference set at the molar site on the contra- lateral side was recorded for adults' volunteers. The jerk-cost showed significant decrease in association with the progress of the motor adaptation. Accordingly, it is confirmed that the jerk-cost may be the useful parameter of evaluating quantitatively the changes in jaw kinematic characteristics during chewing efforts.Finally, the masticatory jaw movements were recorded from the patients with severe skeletal 3 antero-posterior jaw deviations. The results showed significantly higher jerk-costed jaw movements in patients with deviated jaw relationships. Thus, it is suggested that the masticatory jaw motion in subjects with good occlusion may optimize the jaw motion to be more economical than that for the patients with sever malocclusion.