Abstract: PURPOSE: To evaluate the biomechanical effect of arch wire deformation, height of micro-implant and lever-arm on movement of the maxillary anterior teeth in the lingual retraction force system. METHODS: Nonlinear 3-D finite element model of lingual orthodontic force system with micro-implant was constructed. When the arch-wire was set to be flexible body and rigid body, lingual retraction force system using sliding mechanism, the height of micro-implant and lever-arm was 0, 3, 5, 7 mm to alveolar ridge crest of the middle point of maxillary second premolars and maxillary first molars. The initial movement and hydrostatic pressure of anterior teeth were calculated. RESULTS: In the lingual retraction force system with micro-implant using sliding mechanism, when the wire was set to be flexible body, retroclination primary displacements of maxillary anterior teeth were found because of wire deformation. The maxillary lateral incisor's primary displacement became larger with the height of micro-implant increased. When the wire was set to be rigid body, the teeth tended to be slightly tipping, and with the increase of height of micro-implant, the change of movement tendency was not obvious. High value of periodontal ligament hydrostatic pressure was observed in the lingual retraction force system of maxillary anterior teeth with micro-implant when the wire was flexible, exceeding the capillary pressure. When the wire was rigid, the value of periodontal ligament hydrostatic pressure was small within the upper limit value of capillary pressure. CONCLUSIONS: Deformation of wire has a great influence on initial teeth movement and periodontal hydrostatic pressure. In clinic, using more rigid wire and reducing the initial force may reduce the risk of orthodontic root absorption.

Key words: Lingual orthodontic treatment, The Arch wire deformation, 3-D finite element analysis