Biomechanical Analysis of Micro-implants Lingual Straight Wire Appliance during Retracting Maxillary Anterior Teeth

This study aimed to establish three-dimensional finite element models of micro-implants-lingual straight wire appliance and to investigate the effects of different wire patterns on the initial displacement of the maxillary anterior teeth and the stress of the periodontal ligament and tooth root during retracting maxillary anterior teeth in lingual orthodontics.A three-dimensional geometric models of maxilla with maxillary dentition was established using Cone-beam CT scan .Three types of maxilla models including microimplants and Duet-Slot Lingual Bracket appliance with three different arch wires ( model A: 0.016 inch × 0.022 inch stainless steel square wire; modelB: 0.016 inch stainless steel round wire; model C: double wire of 0.016 inch × 0.022 inch stainless steel square wire + anterior teeth 0.016 inch stainless steel round wire) were assembled by Unigraphics NX 8.5 software.The labial intrusion force and lingual retraction force were simulatively loaded to obtain initial displacement of the anterior teeth and the stresses of each tooth root and periodontal ligament, using three-dimensional finite element calculation software Ansys Workbench 15.The initial displacement of the lateral incisors was close to the bodily movement; and central incisors and lateral incisors slightly extruded.Compared with group A and group C, canine teeth appeared obviously horizontal "arched effect" by crown labial tipping in group B. The stress distribution of the tooth root and periodontal ligament was minimal and uniform in the group C. The 0.016 × 0.022-in stainless steel rectangular wire combined with 0.016-in stainless steel round wire used in the anterior teeth can better control the torque of the maxillary anterior teeth for space close in lingual orthodontics.Moreover, the stress distribution of tooth root and periodontal ligament is even, which is difficult to damage the periodontal ligament or result in external resorption of tooth root.