Three-Dimensional Finite Element Analysis Of Buccal Movement Of Mandibular Molars In Invisible Orthodontics

Objectives In order to explore the movement mode and force characteristics of the mandibular molars in the process of invisible orthodontics without brackets,a threedimensional finite element model of the mandibular dentition-periodontal ligamentalveolar bone-bracketless invisible appliance was created.Experiments were carried out on the design of attachments and preset torque angles at different positions of the left first molar,and the results of displacement trend and stress distribution during the buccal movement of the molars were obtained.The biomechanical characteristics of the invisible orthodontic molar buccal movement were studied,and the influence on the molars was analyzed.The factors of the overall buccal movement process provide a theoretical basis for the design of more reasonable attachment positions and torques for the overall buccal movement molars in invisible correction,and provide theoretical guidance for clinicians to formulate more reasonable correction plans.Methods Three-dimensional scan of volunteers’ cranial and face using CBCT.The three-dimensional finite element model of mandibular dentition-periodontal ligamentalveolar bone-invisible appliance was obtained through Mimics medical 21.0,Geomagic Studio 13.0,and UG NX10.0 software.According to the purpose of the experiment,the models with different designs of the left mandibular first molar are grouped: Group A is a blank control group,no attachments and preset torque are designed;Group B is the attachment group,and B1 is designed with a horizontal rectangular attachment on the buccal side of the molars.B2 is designed with horizontal rectangular attachments on the lingual side of the molars,and B3 is designed with horizontal rectangular attachments on the cheek and lingual sides of the molars.Each attachment is located in the center of the clinical crown;Group C is the preset torque group,and C1 presets the appliance with0.5° root buccal torque,C2 presets the appliance with 1° root buccal torque,C3 presets the appliance 1.5° root buccal torque,C4 presets the appliance 2° root cheek ahead torque.Each group forced the appliance to move 0.3mm to the buccal side.The threedimensional model was imported into Ansys software for analysis and solution,and the displacement trend and stress distribution of the left mandibular first molar and periodontal tissue were obtained.Results 1 The molars of different groups moved in the buccal direction,and the movement mode was the crown-buccal inclined movement,and the amount of crown movement was greater than that of the root.2 the displacement of molar,von-Mises stress of periodontal ligament and alveolar bone,and the maximum principal stress of molar and periodontal ligament in groups A and B were compared and analyzed.The results showed that the displacement,molar movement efficiency,stress value and stress distribution uniformity were as follows: no attachment < buccal attachment < lingual attachment <bilateral attachment.When the attachment was bonded on both sides,the stress distribution on the buccal and lingual side of the molar was the most uniform,and there was no obvious stress concentration point.3 In group C,the rotation axis of the teeth was basically horizontal,and the mesial and distal movement of the crown was equal.A comparative analysis of groups A and C shows that with the increase of the preset torque angle,the maximum displacement and maximum principal stress of the molar first decrease and then increase.Although the statistical values of the displacement of the molar,the von-Mises stress of the periodontal ligament and alveolar bone,the maximum principal stress of the molar and the periodontal ligament had certain changes,the total difference was not significant.With the increase of the preset angle of invisible appliance,the stress distribution of periodontal ligament and alveolar bone is more uniform.When the angle is2 °,there is no obvious stress concentration point in periodontal ligament and alveolar bone.Conclusions 1 When the invisible appliance pushes the molars on the buccal side,the movement mode is oblique movement.2 Adding attachments can improve the efficiency of cheek movement of molars;Add attachments to the cheek and lingual sides of the molars at the same time,which is closer to the overall movement than the teeth without attachment or unilateral attachment.3 Setting the root buccal torque for the molar in advance can improve the buccal movement of the molar and make it closer to the whole movement;When the preset root buccal torque is 2°,the molars basically move as a whole.Figure22;Table14;Reference 81...