Biomechanical Characteristics Of Customized Lingual Bracket System During Retracting Maxillary Anterior Teeth With Micro-implants And Sliding Method

Objective:To analyze the biomechanical characteristics of the customized lingual bracket system during retracting maxillary anterior teeth with micro-implants and sliding method, study CT characteristics of the alveolar bones in the maxillary posterior regions with micro-implants, and provide anatomical guidance for safe micro-implant operations.Methods:To construct an entire3-D finite element(FEM) model including dentition, periodontal ligament(PDL), alveolar bone, e-Brace brackets, lingual wire and micro-implants according to the design principles of the customized lingual bracket system. By using the3-D FEM model, at different micro-implant loading positions between the second premolar and the first molar or the first molar and the second molar, including2mm,6mm and10mm from the alveolar ridge crest, the dentition movement tendency and the stress distribution in PDL were analyzed by sliding closing space mechanic. Thirty healthy adults with individual normal occlusion were selected from the people examined with256slices Computer Tomography (CT). The alveolar width and thickness were measured at2mm,4mm,6mm,8mm and10mm from the alveolar ridge crest and analyzed by Paired T test.Results:1. An entire3-D FEM model was constructed including dentition, PDL, alveolar bone, eBrace brackets, lingual wire and micro-implants.2. As micro-implants began to close the extraction space at different positions, the main side effect was the extrusion of the maxillary anterior teeth accompanied with corresponding rotation and lingual inclination. The posterior teeth were generally stable in saggital direction and the bowling effect was basically eliminated at horizontal direction and vertical direction. The stress distribution in the PDL for the space closure stage in the eBrace customized lingual system mainly focused on lateral cervix and canine cervix.3. With the distance between micro-implants and the alveolar ridge crests changing from10mm to6mm and then to2mm, UYmax, UZmin and USUM all increased, whereas UXmax decreased, whether they are located between the second premolar and the first molar or between the first molar and the second molar. Likewise, UYmax, UZmin and USUM all increased, whereas UXmax basically decreased, with the micro-implants located at the same height (10mm,6mm or2mm, relative to the alveolar ridge crests), changing from the position between the second premolar and the first molar to the position between the first molar and the second molar.4. At the same height relative to the alveolar ridge crests,the width between mesio and distal of maxillary bone:the biggest region was between the second premolar and the first molar on the palatal side, and the second biggest was between the second molar and the first molar on the palatal side. The widest position was (6.15±1.72mm) at8mm plane from the alveolar ridge crest. The buccal-lingual alveolar thickness:the one between the second molar and the first molar was thicker than the one between the first molar and the second premolar, which is thicker than the one between the second premolar and the first premolar. The thickest position was (15.33±1.50mm) at6mm plane from the alveolar ridge crest between the second molar and the first molar. Conclusions:1. The originated eBrace customized lingual3-D FEM model has high geometrical similarity, and is hence reasonable, reliable and practical.2. The micro-implants provided stable and effective anchorages.3. While closing the extraction space on the conditions of normal anterior inclination and overbite, the micro-implant works better at2mm from the alveolar ridge crest than at6mm where it works better than at10mm, no matter it is between the second premolar and the first molar or between the first molar and the second molar. The implanting position between the first molar and the second molar is preferred to that between the second premolar and the first molar at the same height, whether at10mm or6mm or2mm from the alveolar ridge crest. Considering maxillary anterior teeth rotation,lingual inclination and torque loss, effective ligature, or torque control, gable bend or additional torque, has to be operated to resist side effects.4. The usual micro-implant operation at6mm plane from the alveolar ridge crest of all the alveolar bones of the maxillary posterior regions is safe, comfortable and convenient in healthy adults. The palatal region is better than the buccal region for easy micro-implant operations.256slices CT is much helpful for complicated micro-implant operations.