[Investigation of occlusal force on lower first molar in function].

The purpose of this investigation is to detect vertically and buccolingually the occlusal force on the lower first molar in function and to make a two-dimensional vector analysis concerning the occlusal force. The subminiature occlusal force measuring apparatus, which makes use of two-dimension load cell, is developed with the apparatus equipped in the corona on the natural root of the tooth, each occlusal force on the single tooth is detected, when three subjects clench and masticate four kinds of test-foods. Conclusions are as follows: 1. Average occlusal force exerts 3.6 kgf during light clenching and 25.7 kgf during heavy clenching. The average direction of occlusal force against the tooth axis exerts 21.2 degrees during light clenching and 19.5 degrees during heavy clenching. 2. The masticatory force intensity exerts the differences in the phases of mastication and the properties of the test-foods. The maximal masticatory force is 33.1-7.9 kgf during the initial phase and 9.6-5.1 kgf during the last phase of mastication. 3. Average direction of masticatory force against the tooth axis is 19.9 degrees during the initial phase and 27.8 degrees during the last phase of mastication. 4. The operating period of masticatory force per cycle is 0.331 second on the average during the process of mastication. The longest period is in the initial phase of mastication, and as the mastication proceed it gradually decreases.