Abstract
Purpose: The purpose of this research was to develop the standard morphology of the ideal dental occlusion. In this study, the kinetic role of each occlusal facet on upper and lower molars was evaluated by analysis of occlusal contacts during the end phase of jaw closing stroke.
Methods: Masticatory movements of fourteen adult volunteers with chewing gum were measured by a six-degree-of-freedom jaw tracking device. Cast stone models of these subjects were scanned with 3-D digitizer to obtain three-dimensional shape of occlusal surface. These configuration data were linked with jaw movement data to analyze relative position of upper and lower dentition during mastication. Occlusal facets on main occlusing area were classified into six different types (AM, AD, BM, BD, CM, CD) according to the direction of its normal vector and its position. A, B and C represents medio-lateral position of each facet and direction of the normal vector there of, and M and D represents antero-posterior direction of the normal vector. Transition pattern of occlusal contacts during the end phase of closing stroke was studied.
Results: When jaw closing, occlusal contacts was begun with AM or CM type occlusal facet. This finding suggests that AM and CM type occlusal facets work as the functional guidance of masticatory movement. This property was clearer with the occlusal facets on the functional cusp. Incident angle of the terminal jaw closing movement was 30° to BD type occlusal facet, and 40° to BM type facet.
These data suggest that BD type facet meets at a right angle to the occlusal surface, and works for the compression of food during mastication.
Conclusion: Occlusal facets of molar surface were classified into six different types, and the kinetic role of each occlusal facet was revealed.
