Abstract
To study how the shape of the cavity formed in a tooth affects the tooth's mechanical resistance, we produced a test tooth by preparing a box-like or plate-like cavity with a base or tunnel penetrating through the enamel, enamel/dentin, and dentin of the tooth, and then filling the cavity with a light curable composite resin.Next, we applied a load corresponding in force to that estimated to be present during mastication repetitively onto the test tooth to evaluate its mechanical resistance.Through this test, we examined the fatigue strength and sealing stability at the cavity margins of the tooth.In addition, we observed the boundary between the internal surface of the tooth forms and the resin by SEM.The following results were obtained.Among cavities of a given shape, those that formed in the enamel showed the largest fatigue strength, followed by those formed in the enamel/dentin, and those in the dentin.Regardless of the shape of the cavities, as the repetitively applied load increased in intensity or the number of cycles increased, the sealing stability at the margins was impaired more severely, and cracks were observed at the boundary more frequently.These factors may account for the reduced resistance of the test tooth when exposed to a repetitively applied load.The plate-shaped cavity demonstrated a sealing stability superior to that of the box-shaped cavity.I boundaries were less affected by cracks.The plate-shaped cavity's lower consumption of tooth substance for formation suggests that such cavities formed in teeth can be more effectively treated.
