Abstract
The purpose of this study was to investigate the relationship between the occlusal condition and the patterns of masticatory movement during the final stage of occlusion by means of evaluating the efficiency in food breakdown.
The methods and the results were as follows:
1. Two subjects with Angle's Class II and one subject with normal occlusion were selected. On the basis of the occlusal condition and the relationship of the maxillary and mandibular teeth, the mastication, and the occlusal force of the subjects, the efficiency in food breakdown was evaluated by finite element non-linear dynamic analysis. The results showed that there was only little characteristic difference in the timing of the masticatory efficiency among the subjects.
2. In each subject, according to the subjects' records of mastication, the movement direction of their mandibular first molars during the final stage of occlusion was observed. The results showed that the amount of the movement of mandibular first molars in the subjects with Angle's Class II, compared with that in the subject with normal occlusion, was large in antero-posterior direction.
3. During the final stage of occlusion, the movement direction of mandibular first molars in the subjects with Angle's Class II was replaced by that of the subject with normal occlusion, and the efficiency in food breakdown was evaluated. The results showed the conspicuous declination in the timing of the masticatory efficiency.
The obtained results imply that the masticatory movement direction compensates for the difference in the position and the occlusal surface morphology of the maxillary and mandibular teeth; consequently, the efficiency in food breakdown is made to be higher.
