[Estimation of occlusal force based on tooth displacement during mastication].
The objective of this study was to clarify the relation between the occlusal force and the tooth displacement path just after unloading, and to estimate the occlusal force during mastication with healthy natural teeth. Three-dimensional occlusal force was calculated from the magnitude of the occlusal force measured by pressure-sensitive film, and from normal vectors of the occlusal contact areas recorded on the study model. The tooth displacement paths were measured using the three-dimensional tooth displacement transducer type M-3. Three male subjects aged 27, 38, and 46 were selected. The subject teeth were their upper left molars. There are two phases of tooth displacement just after unloading: instantaneous recovery, and the subsequent slow recovery. If the maximum tooth displaced position is R, the critical tooth position at the beginning of slow recovery is C, and the original tooth position is O, then re represents the vector RC-->, and rv represents the vector CO-->. The values of re and rv calculated for each unloading tooth displacement path just after clenching the pressure-sensitive film showed different physical properties. The dominant direction of re was to the buccal side, and that of rv was to the coronal side. The coefficient of correlation between the magnitude of occlusal force and re was 0.81-0.87, and that between the magnitude of occlusal force and rv was 0.20-0.63. Based on these physical properties, it was considered that re depends on the recovery of the distortion of alveolar bone, and rv depends on that of periodontal membrane. As described above, the occlusal force during mastication, which is fast movement, can be estimated from re.