[Study on grinding movements in chewing. 2. Relationship between grinding movement in chewing-like empty jaw movement...

The purpose of this study is to clarify the relationship between the occlusal form of a molar and mandibular movement. For this purpose I measured the occlusal form of the upper first molar, and the 3-dimensional movement of the lower first molar during the grinding movement in chewing-similar to empty jaw movement. In this study the following three parameters were analyzed.; (1) the distance between the upper and lower first molars in the lateral occlusal position, (2) the inclination of the cusp-slope, (3) the inclination of the lower first molar path. Results were follows: 1) On the working side, the inclination of the cusp-slope is closely connected to that of the path, 2) On the non-working side, the correlation between the inclination of the cusp-slope, and that of the path was so weak, as to be statistically insignificant. 3) The distance between the molars tended to increase as the inclination of the path steepened. This tendency was marked on the non-working side. The results mentioned above proved that, in cases with steeper anterior guidance, the upper and lower first molars disclude more on both the working and non-working sides. On the working side, however, the steeper cusp-slope prevents excessive disclusion of molars.