Mandibular anterior intrusion using miniscrews for skeletal anchorage: A 3-dimensional finite element analysis.

INTRODUCTION: Deepbites can be corrected by intrusion of mandibular anterior teeth. Direct anchorage with miniscrews simplifies complex tooth movements; however, few studies have reported their use for mandibular anterior intrusion. The purpose of this study was to evaluate, by means of the finite element method, initial tooth displacement and periodontal stress distribution using various mandibular anterior intrusion mechanics. Miniscrews were used as skeletal anchorage devices. METHODS: Cone-beam computed tomography scans were used for 3-dimensional reconstruction of the mandible and the mandibular anterior dentition. Models included the 4 incisors with or without the canines. After all surrounding periodontal and bony structures were determined brackets, segmental archwires, and miniscrews were added. Finite element studies were performed to assess initial tooth displacement and periodontal stress distribution with multiple intrusion force vectors. Changes in the location of the miniscrews and loading points on the archwire created 14 scenarios. RESULTS: Minimum buccolingual displacements, a uniform distribution of periodontal stress, and overall group intrusion for both 4-tooth and 6-tooth scenarios were best achieved when applying distointrusive vectors. The highest peaks of periodontal stress were observed when the force was directed at the corners of the segmental archwire. It was found that, in addition to distointrusive vectors, 4 loading points on the archwire were necessary for pure intrusion and uniform distribution of periodontal stress in the 6-tooth scenarios. CONCLUSIONS: The simulations in this study suggest that group intrusion of all 6 mandibular anterior teeth might be achieved by applying distointrusive vectors. Inserting a pair of miniscrews distal to the canine roots, 1 screw per side, and directing 4 loading points on the archwire generates uniform periodontal stress distribution and minimum buccolingual displacements. Local conditions, such as narrow bone width and attached gingiva level, play significant roles in the clinical viability of the proposed virtual scenarios.

Evaluation of the Loading, Unloading, and Permanent Deformation of Newly Available Epoxy Resin Coated Ni-Ti Wires Using Self-Ligating Brackets.

AIM: The purpose of this study was to evaluate the load and unload deflection and permanent deformation of round 0.016'' and rectangular 0.016'' × 0.022'' regular and coated Ni-Ti wires. MATERIALS AND METHODS: Ni-Ti archwires produced by two manufacturers were evaluated. Both regular and coated round and rectangular Ni-Ti wire segments (n = 15) from each group were submitted to a three-point bending test. Both types of wires were evaluated for permanent deformation at the end of a recovery cycle. RESULTS: The coated round 0.016'' Ni-Ti wires produced a significantly lower force in loading (p < 0.01) and unloading (p < 0.01) than regular wires of the same manufacturer and size. There was no significant difference in permanent deformation between coated and regular round Ni-Ti wires from the same company. For rectangular 0.016 × 0.022'' Ni-Ti wires, there was a significant difference in the loading evaluation, but the unloading test presented no significant differences. The permanent deformation of the rectangular wires revealed no significant difference between them. CONCLUSION: The addition of an esthetic coating to these new Ni-Ti wires produced changes in their mechanical properties, manifested as a reduction in the applied force, which should be considered in clinical management.