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

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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.