Studies on Masticating and Biting Forces in Upper First Molars of Complete Dentures

Abstract

Researching for the mastication, the digestion in mouth, that is physical and chemical, comes into a question. The masticating movement is to be regarded as the former. By way of its stueies, the determination of masticatory area, the distributive observation of crushed foods, the measurement of masticating forces, the electromyographic investigation of masticatory muscle, the electric analysis in jaw movement and radiographic method have been carried out.
The personally developed apparatuses for measurement of biting and masticating forces using the semi-conductor are put in the upper first molars on complete dentures wearers (10 males) from 50 to 60 in age. The biting forces, the masticating forces and the forces in swallowing period are recorded at the same time as the electrimyography of masseter and temporalis of left and right.
As the result of these efforts, the following conclusions are obtained.
1. The biting forces in upper first molars are 14.7-15.1 kg in the intercuspal position, 13.6-14.1kg in the working side of lateral position, 7.7-8.2kg in ballancing side and 5.1-5.5kg in the protrusive occlusion.
2. When the muscle activity is observed at each jaw position, the masseters and temporalis in the intercuspal position, the masseter of the working side in lateral occlusion and the masseter in the protrusive occlusion are marked active. Furthe-rmore, the muscle activities begin than the biting forces.
3. The masticating forces in upper first molar are 9.2-12.9kg by peanut, 7.3-12.2kg by ham and 9.5-12.5kg by pickled radish. The masticating forces in first period are differed from other periods, then the scond, third and fourth period are larger values. Regarding the duralation of masticating forces, the first period is largest value (0.33-0.39 sec) and the fourth period is smallest value (0.27-0.29 sec). As for the term, the fifth period is largest (0.73-0.76 sec). As regards the forces of the upper first molars in swallowing period of all foods, each period is smallest (6.4-7.2 kg).
4. When the electromyography in masticatory movement of peanut, ham and pickled radish are observed by means of the masticatory rhythm, the following finding are obtained.
As for the duration, the first period in all foods is largest (0.35-0.41 sec) and the fifth period is smallest (0.28-0.31 sec). Among foods, the peanut is largest. In order next comes ham and pickled radish. Regarding the interval, the fifth period is largest (0.41-0.47 sec) and the second period is smallest (0.29-0.34 sec). Among foods the ham is largest, then the peanut and pickled radish is smallest. As for the term, the first and fifth period are largest (0.68-0.77 sec) and the second, third and fourth period are smaller (0.58-0.70 sec) in all foods. Among foods the ham is largest, furthermore, in order next comes the peanut and pickled radish. As regards the ratio of the term to the duration, the first period is largest (0.51-0.55) and the fifth period is smallest (0.30-0.43) in all foods. Among foods the peanut is largest, in order next comes ham and pickled radish. The pattern in the swallowing period is largest, then it is differed from the masticatory rhythm in the duration, interval and term.
5. The masticatory rhythm of masticating for ces and electromyography and the pattern of the swallowing period are almost alike in all periods of peanut, ham and pickled radish. The muscle activitis begin and finish earlier than the masticating forces in all periods. It is tendency that the masseters begin and finish earlier than the temporalis.