Maximal mandibular opening and closing movement is performed by a combination of condylar rotation and anterior translation. The purpose of this study is to clarify the timing of these two factors of this movement. The timing of the movement obtained by means of Kyushu University 3-D movement analyzing system was studied in 30 normal subjects. We plotted the condylar rotation vs. the anterior translation with the sagittal condylar path to evaluate the timing, and named this locus “timing curve”.
The following results were obtained:
1. We classified the timing curves of all subjects into 3 patterns.
2. By comparing the timing curves of both sides of condyles in each subject, it was clarified that one side can not be independent of the other side, and it is necessary to estimate the timing in consideration of the one on the other side.
3. The antero-postero length and shape of the condylar path affects the patterns of the timing curve.
4. There is a close relationship between the pattern of the timing curve and the pattern of the sagittal incisal path.