Does Minimum Opening Position during Chewing Coincide with Intercuspal Position?

Objectives: Occlusal contact area (OCA) is most important during the occlusal phase when food particles are being pulverized. However, OCA is most easily measured statically at maximum intercuspal position (ICP). The purpose of this study was to estimate the differences in mandibular position and OCA between the ICP and the minimum opening position (MOP) during chewing. Methods: In thirteen healthy Japanese females, OCA was estimated with a measurement system combining 3-D tracking of mandibular movements with 3-D digitization of tooth shape. The three-dimensional straight-line distance traveled by the lower incisal point was defined as the ″IP Distance″. The IP Distance for both the closing and opening strokes were divided into 0.1 mm intervals. At each of these positions, distances from all points on the mandibular model to all points on the maxillary model were calculated, and the minimum distance for each point on the mandibular model was identified. The OCA of each tooth on the mandible was calculated using the sum of distances less than 0.2mm. Multilevel statistical model analysis was used to evaluate the OCA. Results: The three-dimensional distance between the two positions was 0.129 mm. At the MOP the maximum OCA was 98.5 % (68.42 mm²) of that at the ICP (69.46 mm²). Moreover, the least between-subject and within-subject variation was observed at the same position. Conclusion: These results justify using OCA measurements at ICP to predict maximum OCA during chewing. Figure: The red area indicates OCA (A) at 0.5 mm IP Distance on the closing stroke, (B) at the MOP, and (C) at 0.5 mm and (D) 1.0 mm IP Distance on the opening stroke.