Abstract:

Objective To investigate the biomechanical effects of implant-anchored retraction and intrusion of maxillary anterior teeth under different force systems using three-dimensional finite element analysis (3D-FEA), by constructing models simulating both normal periodontium and mild alveolar bone resorption. Methods Cone-beam computed tomography (CBCT) data from a patient with skeletal protrusion and gummy smile was utilized. 3D finite element models integrating micro-implants anchorage(MIA) and a straight-wire appliance for en-mass retraction of maxillary anterior teeth were established using Mimics, Geomagic, SolidWorks, and Ansys software. Six experimental groups were designed based on alveolar bone height and vertical positioning of posterior MIA. Groups A1, A2, A3:Normal alveolar bone height. Groups B1, B2, B3: Mild alveolar bone resorption. Posterior MIA were placed between the first molar and second premolar at vertical heights of 4, 6, and 8 mm (relative to the cementoenamel junction), respectively, each loaded with 200 g retraction force. Anterior MIA between the central and lateral incisors delivered 50 g intrusion force. Stress distribution, anterior tooth displacement patterns, and torque changes were analyzed and compared across all groups. Results Under varying force conditions, greater torque loss was observed in the anterior teeth of the mild alveolar bone resorption group compared to the periodontally healthy group. Differential displacement patterns emerged among central incisors, lateral incisors, and canines when posterior MIA were placed at different vertical heights. The center of resistance in the resorption group shifted apically, resulting in undesirable extrusion and compromised torque control during intrusion-retraction of maxillary anterior teeth. Conclusion Anterior torque control is more challenging in the alveolar bone resorption group than in the periodontally normal group. Elevating posterior MIA height promotes bodily movement of central incisors, thereby mitigating the "bowing effect" to a clinically relevant extent.

Key words: finite element analysis(FEA), micro-implant anchorage(MIA), alveolar bone resorption, biomechanics