Effect ferrule on the strength of anterior teeth with FRC posts
Journal Title: Prosthodontics - Year 2012, Vol 62, Issue 4
Abstract
Background. The decision of cutting or preserving cervical tissues is important during teeth preparation for posts. The supragingival structures can be clamped by a prosthetic crown that exerts the „ferrule effect”.Aim of the study. To estimate the influence of ferrule effect on the strength of anterior teeth with FRC posts.Material and methods. The investigation was conducted by means of finite element analysis with the application of contact elements. Four 3D models of maxillary first incisors were generated: 1) intact tooth; 2) tooth with ceramic crown; 3) tooth with the FRC post and ferruled supragingival structures; 4) tooth without “ferrule effect” restored with the FRC post. Each model was subjected to a load with a total force of 100N uniformly distributed over the lingual cusp with an angle of 130°. To evaluate the strength of tooth tissues, ceramics, core composites and cement, the modified von Mises failure criterion was used and for FRC the Tsai-Wu criterion was applied. The equivalent stresses occurring in the tested models were compared with the tensile strength of the materials. Contact stresses in the cement-tissue adhesive interface around the posts were calculated. Results. The mvM stresses in model 4 (tooth without ferrule) were considerably higher than those in models 2 and 3 (with ferrule). These stresses in the dentin of models 2 and 3 were reduced by 10%, and in the dentin of model 4 were increased by 25% as compared with stresses in the intact tooth (model 1). The equivalent stresses in ceramic crown in tooth without ferrule were 23% higher than those in the incisor with ferrule. In the core of model 4 the stresses were 3 times higher and in the cement around the post stresses they were 4 times higher than in the core composite of model 3. The value of the Tsai-Wu index of the FRC post was 2 times higher in an unferruled tooth than that in the ferruled tooth. Contact tensile stresses around the post of model 4 increased by 10 times and on bearing area by 5 times as compared with model 3. Conclusion. The ferrule effect in tooth restored by the FRC post reduced considerably the stresses generated in dentin, post, composite core, ceramic crown and resin luting cement during physiological loading. The ferrule effect provides higher strength of the restored teeth. This effect decreased contact stresses in the tooth-post interfaces area by several times and improved the marginal adaptation of post restoration.
Authors and Affiliations
Beata Dejak
Keywords
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