3-D Finite Element Analysis Of Maxillary Anterior Teeth Lingual Retraction Force System Using Micro-Implant Anchorage

ObjectiveResearch the influence of labial and lingual orthodontic system and the position of brackets to center of resistance. To evaluate the effect of height of micro-implant and lever-arm、retraction pattern and the material properties of arch wire to biomechanical properties of maxillary anterior teeth lingual retraction force system.MethodThe 3D geometrical model of maxillary bone and teeth was constructed from the data of spiral CT with high resolution,and the model of lingual appliance and micro-implant were constructed in the Solidworks CAD software. The parameter of periodontal membranes was set as nonlinear and the maxilla bone as non-homogeneous and anisotropic. ANSYS were used to mesh the model and construct the nonlinear 3-D finite element model of maxillary anterior teeth lingual retraction force system with micro-implant.Construct the segment retraction force system of labial brackets with different height and lingual brackets, arch wire is set to be rigid. A retraction force was applied to the anterior teeth parallel to the arch wire. The force height levels begin on arch wire and o.5mm increased every time. When the ratio of displacement of maxillary incisor edge’s middle point and apex is close to 1, we consider the anterior teeth occurred to bodily movement and record the perpendicular distance of CR. Determine the anteroposterior position of CR in the same way.Construct the maxillary anterior teeth lingual retraction force system with sliding method and segment method. Siding mechanism contains flexible and rigid arch wire respectively and in segment technique, the wire is rigid. The distance of micro-implant and lever-arm is Omm,3mm> 5mm> 7mm to alveolar ridge crest of the middle point of maxillary second premolars and maxillary first molars. Force vector is applied to micro-implant and lever-arm by spring. Calculate the initial movement and hydrostatic pressure of anterior teeth.Result1. The nonlinear 3-D finite element model of maxillary anterior teeth lingual retraction force system with micro-implant was constructed with good similarity in geometric and mechanical aspect.2. In labial orthodontics, when the distance of maxillary anterior teeth’s brackets to incisor edge is 5mm, the location of center of resistance is 16.5mm apical and posterior 13mm to the incisor edge. When the distance is 6mm, the location of center of resistance is 17.5mm apical and posterior 12mm to the incisor edge. When the distance is 4mm, the location of center of resistance is 18.5mm apical and posterior 13mm to the incisor edge. In lingual orthodontics, the location of center of resistance is 16mm apical and posterior 11.5mm to the incisor edge.3. In maxillary anterior teeth lingual retraction force system with micro-implant using sliding mechanism, when the arch wire is set flexible, retroclination initial displacements of maxillary anterior teeth were found because of wire deformation. The maxillary lateral incisor’s initial displacement become larger with the height of micro-implant increased. When the wire is set to be rigid body, the teeth trend to be slightly tipping, and with the increase of height of micro implant, the change of movement tendency is not obviously. Use Segment and arch wire is rigid, with the increase of height of micro implant, tipping movement trend of anterior teeth is reduced. When the micro-implants apical to alveolar ridge crest about 7 mm (i.e., through center of resistance), the anterior teeth trend to be bodily movement approximately.4. High value of periodontal ligament hydrostatic pressure is observed in maxillary anterior teeth lingual retraction force system with micro-implant when the wire is flexible, exceed the capillary pressure. When the wire is rigid, the value of periodontal ligament hydrostatic pressure is small within the upper limit value of capillary pressure.Conclusion1. The position of center of resistance of labial and lingual orthodontic system and different position of labial bracket is close.2. The height of micro-implant and lever-arm influence the pattern of teeth movement in maxillary anterior teeth lingual retraction force system with micro-implant.3. Different retraction way influence the pattern of teeth movement. Using segment technique combined with micro-implant, when the force across the center of resistance, the anterior trend to bodily movement.4. The deformation of wire has a great influence on initial teeth movement and hydrostatic pressure. In clinic, using more rigid wire and reduce the beginning force may reduce the risk of orthodontic root absorption.