There are a lot of studies on the abutment teeth of the full cast crown, and its reasonable forms were investigated with the photoelastic studies from a dynamic point of view. The two-dimensional studies have mainly been found, but the three-dimensional photoelastic ones have been researched little.
So as to analyze the stress concentration at the inner part of abutment on the axis, occlusal face and marginal form, the author carried out the three-dimensional photoelastic studies applied to the anatomical solid specimen.
To insure uniformity of the specimens tested, the basic plaster model is the simplified form of the maxillary second premolar enlarged three times. The epoxy specimens were made of the master model.The abutment models consist of three groups and nine kinds, that is A group (cusp angle: 0°, marginal form knife-edge, axial angle: 5°, 10° and 20°), the B group (axial angle: 10°, marginal form: knife-edge, cusp angle: 10°, 20° and 30°) and the C group (axial angle: 10°, cusp angle: 0°, marginal form: bevel-edge, chamfer-edge and shoulder-edge).
The photoelastic and stress freezing apparatus, product of Riken-Keiki Co., are used for these studies. The load direction was applied to the long axis of the specimens, and the resulting isochromatic fringe patterns of each section in the specimens were recorded photoelastically. The circumferential stress distribution of each specimen was analyzed and the following conclusions were obtained.
1. In all of the specimens, the highest concentration of stress was observed at the cervical area, but the stress was not concentrated in the area of the pulp horns.
2. The stress in the cervical marginal area with the buccolingual section of axialangle 20° and the mesio-distal section of axial angle 10° showed the least concentration.
3. The stress concentration in the cervical marginal area is decreased, when the cusp angle is increased. And it exhibits very little stress at the cusp angle of 30°.
4. The marginal form of the chamfer-edge developed a tendency to have the same degree stress as did the bevel-edge is best mechanically. The end of the marginal ledge with the shoulder-edge showed very higher stress concentration. The knife-edge showed much higher stress concentration at the end of the marginel ledge.

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As the analysis of the masticating movement, the studies on the masticating forces and the electromyographic investication have been mainly reported. But, as for the masticating function on the complete denture, there are something yet to study its analysis on the masticating forces, the biting forces and the EMG in only upper first molars.
Then, the author uses the semi-conductor apparatus developed by Moriya and Fukamizu, and leaves on the records of these forces and the EMG of the masseter and temporalis on the upper second premolar of complete denture wearers (10 males) from 50 to 60 in age at variuos occlusal positions.
As the results of these efforts, the following conclusions are obtained.
1. The biting forces in upper second premolars are 7.3-7.9 kg at the intercuspal position, 6.3-7.6 kg at the working side of the lateral position, 3.1-3.5 kg at the ballancing side and 3.0-3.2 kg at the protrusive position.
2. The masseter and temporalis of both side at the intercuspal position, its muscles of woking side at the lateral position and the masseters of both side at the protrusive positionare marked active. And the muscle activities begin earlier than the biting forces.
3. The masticating forces in upper second premorals are 2.4-4.9 kg by peanut, 2.0-5.3 kg by ham and 2.2-4.8 kg by pickled radish. Its forces are largest values in the fourth and fifth period, and are smallest value in the first period.
The duration is largest value (0.33-0.53 sec) in the first period and smallest value (0.25-0.34 sec) in the second period. The interval (I) and term (T) are largest values (I: 0.79-0.90 sec, T:1.17-1.36 sec) in the fifth period and smallest values (I: 0.48-0.66 sec, T: 0.76-1.02 sec) in the third period. The forces in the swallowing period have a tendency to be smallest value every foods.
4. When the masticating movement of peanut, ham and pickled radish are obtained by means of the masticatory rhythm, the following finding are obtained.
As for the duration, the first period in all foods is largest (0.42-0.67 sec) and the second period is smallest (0.35-0.52 sec). Among foods, the ham is largest, in order next comes peanut and pickled radish.
Regarding the interval, the fifth period in all is largest (0.70-0.92 sec) and the second period is smallest (0.31-0.62 sec). Among them the peanut is largest, then ham and pickled radish is smallest.
As for the term, the fifth period in all is largest (1.10-144 sec) and the second period is smallest(0.68-1.04 sec). Among them the ham is largest, in order next comes peanut and pickled radish.
As regards the ratio of the term to the duration, the first period in all is largest (0.45-0.59) and the Fifth period is smallest (0.35-0.39). Among them the ham is largest, in order next comes peanut 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.

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