Cusp height, cusp form and cusp inclination are considered to be the most important elements for the occlusion of natural dentition and artificial denture. Inclination angle of the occlusal facets which was defined by the author as small surfaces of occlusal wear, was measured on 100 young adults with complete dentition, and functional meanings of facets were studied. Measurements were taken by means of the new optical protoractor, which has been deviced and reported recently by the author.
Results are as follows:
1) In accordance with occlusal form, occlusal pattern of upper dentition was classi-fied into 52 facets and lower dentition into 56 facets, and frequency of their appearance was investigated statistically.
2) The greatest number of facets was found on upper and lower 1 st molers, and the least was lower 1 st bicuspid.
3) Working facets in frontal section show the maximum inclination at cuspid, and decrease their steepness from anterior to posterior. On the contrary, bal lancing facets are steepest at 2 nd moler and decrease their inclination from posterior to anterior.
4) These rules are found to be correct in all cases of 100 subjects without exception, and mathematical formulations were determined for the purpose of generalization.
5) Three-dimensional inclination of occlusal facets and lateral mandibular movements, which were recorded by means of intraoral registration, are closely related with each other.
