CERAMIC BRACKET DESIGN - AN ANALYSIS USING THE FINITE-ELEMENT METHOD

This investigation was designed to generate finite element models for selected ceramic brackets and graphically display the stress distribut ion in the brackets when subjected to arch wire torsion and tipping fo rces. Six commercially available ceramic brackets, one monocrystalline and five polycrystalline alumina, of twin bracket design for the perm anent maxillary left central incisor were studied. Three-dimensional c omputer models of the brackets were constructed and loading forces, si milar to those applied by a full-size (0.0215 x 0.028 inch) stainless steel arch wire in torsion and tipping necessary to fracture ceramic b rackets, were applied to the models. Stress levels were recorded at re levant points common among the various brackets. High stress levels we re observed at areas of abrupt change in geometry and shape. The desig n of the wire slot and wings for the Contour bracket (Class One Orthod ontic Products, Lubbock, Texas) and of the outer edges of the wire slo t for the Allure bracket (GAG, Central Islip, N.Y.) were found to be g ood in terms of even stress distribution. The brackets with an isthmus connecting the wings seemed to resist stresses better than the one br acket that did not have this feature. The design of the isthmus for th e Transcend (Unitek/3M, Monrovia, Calif.) and Lumina (Ormco, Glendora, Calif.) brackets were found to be acceptable as well. The Starfire br acket (''A'' Company, San Diego, Calif.) showed high stresses and irre gular stress distribution, because it had sharp angles, no rounded cor ners, and no isthmus. The finite element method proved to be a useful tool in the stress analysis of ceramic orthodontic brackets subjected to various forces. This analysis provides key information to the devel opment of an optimum bracket design.