Photoelastic stress analysis of supporting alveolar bone as modified by nonrigid connectors.

A two-dimensional photoelastic model was constructed to represent the mandible with a missing first premolar and first molar. The model contained a canine, second premolar, and second molar as abutment teeth supported by simulated periodontal ligament and photoelastic bone. Six FPDs were constructed, one of rigid design and five of nonrigid design with varying location and orientation of the nonrigid connector. Each of the six prostheses was subjected to six different loading conditions. Patterns of stress for each loading condition were recorded photographically and evaluated. This study indicated that the rigid FPD distributed stresses vertically and evenly. The nonrigid D of canine and nonrigid M of molar designs distributed stresses almost as well as the rigid FPD. They also resisted rotational movements and resultant horizontal stress better than other nonrigid designs. Compared with the other designs, prostheses with nonrigid connectors at the pier exhibited greater apical and horizontal stress particularly with one-point loading on the pier. Considering the limitations of this study, the following conclusions were drawn: 1. The pattern of stress is dependent on incorporation and location of a nonrigid connector. 2. The pattern of stress reflected the condition of loading. 3. The pattern of stress is independent of the orientation of the nonrigid connector at the distal aspect of the pier abutment. 4. The placement of a nonrigid connector at the mesial surface of the pier is least desirable.