Photoelastic Analysis of the Effects of Tooth Position on Apical Stress

The anatomical form of the teeth and the density of the base bone differ greatly at different tooth positions. Thus, it is necessary to investigate the effect of tooth position variation on the apical occlusal stress because it would be helpful to understand the mechanism of occusal force transduction along the mandible. Epoxy resin models of seven different occlusal types set up with identical plastic teeth were employed to determine the stress directions and magnitudes in the apical area under 2.0 Kg of vertical load. Both the values and directions of the main stress were measured. Our results indicated that variation of the tooth position had no effect on the directions of principle stress around the apex area in the symmetrical occlusal type. For the asymmetrical occlusal type, the mesio-distal and the lingual-buccal directions of anterior teeth were found to be affected by variations in tooth position. The magnitude of the apical main stress was also apparently altered with changes of tooth position, but the differences were insignificant with occlusal types. Therefore, we conclude that variation in the tooth position could affect the direction of the main apical stress when the symmetry of the occlusion type was also involved. In contrast, the apical stress magnitude was much more related to tooth position than to occlusal symmetry.