[Study on grinding movements in chewing. 1. A comparison between grinding movement in chewing-like empty jaw movement...

The purpose of this study is to clarify the relationship between grinding movements during chewing, and lateral excursions starting from the intercuspal position. For this purpose, I measured two different types of three-dimensional mandibular movement; lateral excursions and empty-jaw movement like chewing in 10 subjects, and compared these paths with each other in the lateral occlusal position, when the incisal point is 2.0 mm distant from the intercuspal position. The results can be summarized as follows: 1. The two positions of the incisal point were statistically coincident. 2. The position of both working and non-working side molars during chewing tended to be inferior to that during lateral excursion. 3. The moved distance of the working side condyle during chewing was significantly less than that during lateral excursion. 4. The position of the non-working side condyle during chewing tended to be medial to that during lateral excursion. 5. The difference in the condylar position was deeply related to that in the molar position. The differences mentioned above were considered to be originated from the difference in the masticatory muscle activity and the occlusal contact.