Smoothness of masticatory jaw movements before and after orthodontic treatment

首先，我们研究了最小抽搐模型是否能预测咀嚼过程中颌骨的三维运动轨迹。使用了两种测试食物：口香糖和软糖果冻。记录咬合良好的儿童组和成人组的下颌运动。对于成人和儿童群体，该模型精确地解释了颌骨运动的运动学。因此，建议咬合正常的受试者在咀嚼时控制下颌运动，以最大限度地提高咀嚼的流畅性。然而，儿童闭合下巴动作的抽搐成本明显高于成人。此外，痉挛成本的变化在儿童中比成人更大。儿童的抽动成本差异较大可能是混合牙列儿童对牙齿发育变化的运动适应过程变化的结果。其次，研究了颌运动对实验产生的急性咬合干扰的适应过程。记录了成人志愿者在对侧磨牙位置设置咬合干扰的单侧咀嚼颌运动。随着运动适应的进展，抽动成本显著降低。由此证实，猛咬代价可能是定量评价咀嚼过程中颌骨运动特性变化的有用参数。最后，记录严重前、后颌骨骨偏差患者的咀嚼颌运动。结果显示，下颌关系偏离的患者的下颌运动明显更高的抽搐成本。因此，我们认为，咬合良好的受试者的咀嚼颌运动可能比严重错颌患者的咀嚼颌运动更经济。

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.