Although the mechanical compression of the temporomandibular joint (TMJ), which could be caused by bruxism, would probably result in a slight change of the occlusal relationship, the effect of clenching in the eccentric mandibular position on the occlusal contact has not yet been clarified. This study aimed to investigate the effect of eccentric clenching on bilateral condylar position and thus to estimate any change of occlusal contact. Before and after voluntary clenching, with one third of the maximal voluntary clenching force, for 3 min at the canine edge-to-edge position, vertical deviation of the bilateral condyles was measured at the 1 mm open mandibular position. This was regulated by the three-dimensional position of the anterior reference point which stands for the incisor point. The mean vertical displacement of the highly deviated side of the condyle was 141 ± 55 μm, and the calculated mean displacement of the mandibular first molar region of the highly deviated side was 65 ± 27 μm. From the results of this study, it was revealed that the eccentric clenching gave rise to three-dimensional deviation of the mandible even when the mandible was in the vicinity of the rest position.
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