Biomechanical Study On Torque Control Of Anterior Teeth In Lingual Orthodontics With Different Arch Wires

Objective:Three-dimensional finite element models and typodonts were established to study the movement and stress of maxillary anterior teeth caused by different arch wires in the lingual orthodontics system in extraction space sliding closure.Explored which type of arch wire could control the torque of anterior teeth well and provided the theoretical basis for torque control of anterior teeth treated by lingual orthodontics in clinic.Methods:This study was divided into two parts.1.A three-dimensional finite element model of lingual orthodontics including maxilla,maxillary dentition,micro implants and straight wire-double slots brackets was established.Three different arch wire types,0.016 inch ×0.022 inch stainless steel square wire,0.016 inch stainless steel round wire,0.016 inch ×0.022 inch stainless steel square wire and 0.016 inch stainless steel round segment wire of anterior teeth,were loaded simultaneously with labial and lingual force applied on the models in the 3D finite element calculation software.The absolute value of sagittal initial displacement difference between edge and apical of each anterior teeth,stress of anterior root and periodontal ligament were observed.2.The second part of this study was to apply same experimental conditions to the typodonts.The absolute value of sagittal displacement difference was measured and calculated by using three-dimensional digital overlapped image.Finally,the results of two parts were combined to obtain the type of arch wire which could control the torque of anterior teeth well.Results:1.The first part of the experiment showed that the anterior teeth of square-wire group and double-wire group were moved bodily than that of round-wire group.The stress of root and periodontal ligament was much smaller.2.The second part showed that the absolute value of double-wire group was much smaller than that of other two groups,and there was no significant statistical difference between square-wire group and round-wire group.Conclusion:The torque of anterior teeth can be controlled better by using 0.016 inch × 0.022 inch stainless steel square wire and 0.016 inch stainless steel round segment wire into different slots of double-slot brackets in lingual orthodontics in extraction space sliding closure.The stress distribution of root and periodontal ligament is more uniform,and the periodontal tissue is not easy to be damaged.