Abstract
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.
