[Condylar displacement and mandibular bending deformation due to bite force].

The purpose of this study was to investigate the influence of the difference of the biting pivot positions, vertical dimensions and mandibular positions on the condylar displacement during clenching. The condylar displacement was measured by the Pantograph using the point of condyle on the Kinematic Axis as the representative and the Path of the Kinematic Axis (PKA) as the standard for the judgement of the displacement. The bending deformation of the mandible was also measured by a multi-vision and image analyzing system in order to correct its influence on the condylar displacement measured. The results were as follows: 1. The direction and magnitude of the condylar displacement changed with the biting pivot position. The bilateral condyles moved upwards deviating from the PKA when clenching on the bilateral 2nd-molar or the bi-or unilateral canine teeth; Whereas the biting-side condyle moved downwards and the idling condyle either moved upwards deviating from the PKA or backwards along the PKA when clenching on the unilateral 2nd-molar. 2. The displacement of the idling condyle was multi-directional when clenching on the habitual closure whereas it was unidirectional and of a smaller magnitude when clenching on the most retruded closure. 3. When clenching on the unilateral 2nd-molar, the mandible on the non-pivot side had an inward and upward bending deformation and the arch width decreased. It can be inferred that the actual idling condylar displacement was more inward and upward than that measured by the Pantograph.