Biomechanical Study of the Stress Transfer Characteristics of Primary Tooth Dilacerations

Objective: The replacement of an organ, such as the change from a primary tooth to a permanent tooth, is a particular and dynamic phenomenon. Primary teeth have cervical concentrations and dilacerations that differ from those of permanent teeth. However, few studies have been conducted on the biomechanical significance of these differences. The purpose of this invstigation was to examine the stress effects of occlusal loads on primary teeth dilacerations on the supporting alveolar bone. Methods: Three-dimensional complex models of the first primary molar, the second primary molar, and first permanent molar were made to apply quasi-three-dimensional photoelastic analysis. Photoelastic materials representating the modulus of teeth (PLM-1, Photolastic Division) and supporting alveolar bone (PL-2). Vertical loads simulating occlusal loads were applied to the models in a bath of mineral oil. The resulting stress patterns in the alveolar bone were observed and recorded in the field of a circular polariscope. Results: In the first and second primary molar, a lack of stress was observed in the permanent tooth germ. On the other hand, stress patterns were concentrated at and around the root in the permanent molar. Stress patterns also differed in the supporting alveolar bone between the primary molar and the first permanent molar. Conclusions: The results indicate that concentrations of internal stresses caused by occlusal forces in primary molars were not near the permanent tooth germ but in the supporting alveolar bone. This suggests that the dilacerations of primary teeth protect the permanent tooth germ by dispersing occlusal load induced internal stresses.