RGO: Revista Gaúcha de Odontologia ()
Biomechanical analysis of teeth restored with cast intra-radicular retainer, with or without ferrule
Abstract
Objective: To evaluate the influence of variations in ferrule shape given by the core placed, on stresses developed in the root.Methods: Six 3D models of a maxillary second premolar were made according to the mean dimensions obtained in the literature. A masticatory load (291.36N) was simulated with result parallel to the long axis of the tooth. In four models, the size of the plate (E) was varied: 1/3 of the root wall thickness (E1) or 2/3 (E2). The height (A) of the bevel was equivalent to E1 (A1) or E2 (A2), that is: ferrule E1A1 and E2A2 with an inclination of 45º. One model represented a healthy tooth, another model simulated the core only, with plate, without ferrule (E2A0). All the cases had the same coronal restoration. All the structures were considered homogenous, isotropic and linear elastic. The increase in the height of the recess (from E2A1 to E2A2 or from E1A1 to E1A2) caused changes in the compressive sheer stresses in the root dentin over the recess.Results: The best results were obtained by model E1A2, which minimized the sheer/ stresses in the cervical root dentin and in the root dentin close to the periodontal ligament, followed by models E1A1, E2A1 and E2A2. Conclusion: To distribute the stress on the root dentin on the plate in the best possible manner, it is imperative to have the ferrule. The ferrule protects the root dentin under the plate (the higher the better) and the inclination of 45o results in a more efficient protective effect for the dentin over plate.
