Stresses created by occlusal prematurities in a new photoelastic model system.

A new photoelastic model system incorporating a simulated periodontal ligament sleeve around an experimental first molar has been developed. The system was used to visualize internal compressive stresses created by various premature occlusal incline relationships in both buccolingual and mesiodistal dimensions. When prematurities were applied singly and observed buccolingually, both class 1 and and class 2 prematurities produced stresses along the lingual aspect of the root, whereas the class 3 prematurity produced stresses along the buccal aspect of the root. When viewed buccolingually, combinations of class 1 and class 2 prematurities resulted in stresses along the lingual aspect of the root. The stress pattern was similar to those created by the single class 1 or class 2 prematurities. A combination of class 2 and class 3 prematurities did not produce a well-defined indication of stress distribution. There was slightly more stress along the buccal aspect of the root. Comparison of this combination with individual class 2 and class 3 prematurities indicates that such a combination tended to diminish tipping of the tooth in any one direction. A combination of class 1 and class 3 prematurities showed slightly greater stress along the buccal aspect of the root surface. Again, the combination produced less tipping of the tooth in any one direction when compared with tipping caused by the individual prematurities. When all three prematurities were tested at the same time, the stress pattern was almost coincident with that achieved in the absence of prematurities. When prematurities were observed mesiodistally, the location of stresses was dependent on the mesial or distal placement of the prematurity, irrespective of its position buccolingually.