Tooth Movement Tendency With Different Traction Position In Lingual Orthodontics: A 3-dimensional Finite Element Analysis

Lingual orthodontics is not only esthetic but also has many superiorities, such as strong anchorage, deep bite being opened easily. But both horizontal and vertical “bowing effect” appeared in the dental arch during space closure sliding mechanics in the customized lingual appliance, which affect the normal sliding of archwire, and reduce treatment efficiency. So the aim of this research is to analyze the teeth movement tendency during retraction of maxillary anterior teeth with micro-implants and sliding method.Objective: To analyse the tooth movement tendency during anterior retraction with micro implant and sliding method in the customized lingual appliance, when traction position is different. And lay biomechanical foundation for effective clinical use of lingual orthodontic appliance.Methods: Set up the finite element models of maxilla, maxillary dentition in MIMICS 10.2 and Geomagic Studio 12.0 software by volunteers’ CBCT scanning.Set up the finite element models of customized lingual brackets in Solidworks by measurements in vitro. Assembly is finished in Abaqus. By using the 3-D FEM model, at different traction positions, mesial or distal to the canine,the dentition movement tendency during space closure was analyzed.Results:1. An entire 3-D FEM model was constructed including dentition, PDL, alveolar bone, STb brackets, and customized lingual wire.2. During retraction of maxillary anterior teeth with micro-implants and sliding method:In the horizontal direction, when the lingual anterior retraction hooks(LARHs) were placed at mesial to the canine, horizontal “bowing effect” appeared in the dental arch evidently. When the LARHs were placed at distal to the canine, canine turned inward, the width in second premolar area decreased, no width change happened in first molar area, which decrease horizontal “bowing effect” in dental arch during en masse retraction effectively.In the sagittal direction, no matter theLARHs were placed at mesial or distal to the canine, the movement tendency of incisors was controlled tipping with crown tippinglingually and extruding and apex hardly moving. When the LARHs were placed at distal to the canine, the retraction of six anterior teeth was more evenly. And posterior teeth rotated distally slightly.In vertical direction, no matter the LARHs were placed at mesial or distal to the canine, the dental arch movement tendency was similar.About arch wire deformation, compared to the condition with LARHs placed at mesial to the canine, When the LARHs were placed at distal to the canine, the arch wire in anterior teeth area retracted evenly and kept original radian unchanged; however, the deformation of archwire in vertical direction was great.Conclusions: 1. The customized lingual 3-D FEM model has high geometrical similarity, and is hence reasonable, reliable and practical.2.During space closure by customized lingual appliance, it is better to locate LARHs distal to the canine. In this way, dental arch width hardly changed, the retraction of six anterior teeth was more evenly.Considering maxillary anterior teeth lingual inclination and torque loss, effective ligature, torque control or additional torque, has to be operated to resist sideeffects.Due to the obvious archwire deformation in vertical, reverse curve arch wire is necessary to counteract the side effect.