Regulation of occlusal force due to hardness-change of the bite object

首先，我们研究了咬合力对咬合垂直尺寸意外变化的调节。8名健康受试者使用一种改变下颌垂直闭合位置的装置，指导他们在恒定的咬合力下进行重复的下颌开合运动。垂直颌闭合位置增加后，第一次试验的峰值咬合力大于第二次或第三次试验，而垂直颌闭合位置减少后，第一次试验的峰值咬合力小于第二次试验。结果表明，在改变垂直颌闭合位置后的前两到三次试验中，这种调节似乎几乎完成了（Tanaka et al. 2006）。接下来，我们通过实验再现咀嚼过程中食物硬度不可预测变化的情况，分析了咬合力的控制。7名健康受试者被要求在整个试验过程中进行重复的下颌开合运动并保持恒定的咬合力。硬度的变化对峰值咬合力和冲量有显著影响，硬度的增加会引起对指令的峰值咬合力和冲量的增加，之后这些值保持不变，而被试咬合的硬度水平不变。这些结果表明，所产生的咬合力水平是根据咀嚼食物的硬度自动调节的。我们得出结论，当食物的硬度发生不可预测的变化时，通过咬合力可以有效咀嚼（Shimada et al. in press）。

First, we investigated the modulation of occlusal force to unexpected changes in the occlusal vertical dimension. Using a device to change the vertical jaw closing position, eight healthy subjects were instructed to perform repetitive jaw open-close movements with constant occlusal force. The peak occlusal force was greater in the first trial than that in the second or third trial after increase in the vertical jaw closing position, but it was smaller in the first trial than in the second trial after a decrease in the vertical jaw closing position. The results indicate that this modulation appears to be almost completed in first two or three trials after change in the vertical jaw closing position (Tanaka et al. 2006).Next, we analyzed the control of occlusal force by experimentally reproducing situations in which the hardness of food changed unpredictably during mastication. Seven healthy subjects were instructed to perform repetitive jaw open-close movements and to maintain constant occlusal force throughout the trial. Peak occlusal force and impulse were significantly affected by the change in hardness, while an increase in hardness caused increase in the values for peak occlusal force and impulse against the instruction, after which those values remained constant while the subjects occlude the same level of hardness. These results indicate that the level of the resulting occlusal force is regulated automatically according to the hardness of the chewed food. We concluded that occlusal force was adopted for efficient mastication when the hardness the hardness of food changes unpredictably (Shimada et al. in press).