Analysis of the intersurface relation between opposing first molars in the gliding phase of chewing cycle

为了分析下颌运动过程中对牙之间的咬合关系，开发了一种结合颌骨运动测量和三维形状测量的计算机辅助分析系统。然后，研究侧移时第一磨牙的咬合关系。采用这种运动代替咀嚼的原因是：1)它的记录容易，重复性好；2)它的路径与咀嚼周期的滑动阶段几乎一致。利用先前开发的LED和PSD相机光电系统和三维激光扫描仪分别测量颌骨移动和牙齿形状。通过以下方式定量评估咬合关系：1)对于上表面上的每个点，求出其到相对下表面的最小距离，2)计算了上地表距离为*0.3 mm和1 mm的上地表面积，分别记为S(0.3)和S(1.0)，S(1.0)在工作侧横向偏移时的下降率小于非工作侧，符合预期。至于S(0.3分)，出乎意料的是，其下降的速度在双方几乎相同。这揭示了这样一个事实，即两侧接触部分或近接触部分的暴露几乎相同，这表明即使在非工作侧，相对的第一磨牙在侧移过程中也彼此接近。

In order to analyze occlusal relation between opposing teeth during mandibular movements, a computer-aided analyzing system was developed, combining jaw movement measurement and three-dimensional shape measurement. Then, the occlusal relationships on the first molars during lateral excursion were investigated. Employment of this movement, instead of chewing, came from the the following reasons: 1) it can be recorded easily with high reproducibility and 2) its path almost coincides with that in the gliding phase of chewing cycle.A photo-electronic system using LEDs and PSD cameras and a three-dimensional laser scanner, both of which were developed previously, were employed, to measure jaw movements and tooth shape, respectively.The occlusal relationship was evaluated quantitatively in the following manner: 1) for every point on the upper surface, its minimum distance from the opposing lower surface was obtained, and 2) the area of the upper surface region with that distance being * 0.3mm or 1.0mm was calculated, which was denoted by S(0.3) or S(1.0), respectively.Decreasing rate of S(1.0) during lateral excursion on the working side is smaller than that on the non-working side, as was expected. As for S(0.3), however, its decreasing rate was almost the same on the both sides, unexpectedly. This revealed the fact that the disclosion in the contact or near contact portions was almost the same on the both sides, suggesting that the opposing first molars are close to each other during lateral excursion even on the non-working side.