Three-dimensional Finite Element Analysis Of The Effect Of Different Retraction Methods On The Torque Of Maxillary Central Incisor With Clear Aligner

Objective: A three-dimensional finite element model was established to simulate the orthodontic process of retraction of maxillary centeral incisors,and the stress distribution and tooth displacement trend of maxillary central incisors under different loading modes were analyzed and discussed.The results provide a biomechanical basis for the application of clear aligner technique in torque control of maxillary anterior teeth.Methods: Cone beam CT was used to scan the head of the volunteers who met the experimental conditions.The data of the maxillary and teeth were obtained and saved in DICOM file format.The maxillary,dentition,periodontal ligament and clear aligner were established using Mimics,Geomagic software and ANSYS finite element software.The finite element model of the retraction maxillary incisor was simulated in three different ways by the clear aligner.The group A applied the palatal load of the maxillary central incisor,and the force was evenly distributed throughout the whole crown.It was achieved by deforming the appliance by 0.2 mm;the group B was based on the group A,and the pressure point was applied vertically to the 1/3 labial cervical maxillary central incisor,and the deformation was 0.1 mm through the appliance;the C group was on the basis of group B,a pressure point was applied to the the 1/3palatal tip of the maxillary central incisor,and it was achieved by deforming the appliance by 0.1 mm.In the central axis of the maxillary central incisor,six nodes are selected from the crown to the root of the tooth,which are the midpoint of the margin,the midpoint of the labial surface,the midpoint of the cervical of the labial side,the1/3 of cervical of the root,and the 1/3 of central of root,and apical point,the displacement and direction of each marker point in the three directions of X,Y and Z were observed.The displacement trend of the maxillary central incisor and the stressdistribution of the periodontal ligamnet were analyzed.Results: 1.The Von-Mises stress concentration zone of the periodontal ligament of group A is mainly located in the 1/3 of palatal-cervical the periodontal ligament.In the group B,the Von-Mises stress concentration zone of the periodontal ligament is distributed in the 1/3 of cervical labial and lingual side.The perimembranous stress gradually decreased from the cervical to the apical root,and.The stress distribution of the periodontal ligament was more dispersed than that of the group A.The Von-Mises stress concentration zone of the periodontal ligament of the group C was located at the1/3 of labial-cervical the periodontal ligament and the distal-palatal midsection.The stress distribution of the periodontal ligament was more uniform than that of the A group and the B group.2.The maximum stress value of Von-Mises in periodontal ligament is the largest in group A,the smallest in group C,and the middle in group B.3.Crown displacement A group is greater than group B,group C is the smallest,and root displacement is higher than group B,group A is the smallest;4.During the process of retraction maxillary central incisor,crown is extruded in the group A and the group B,the group A had higher extrusion than group B,crown was intruded in the group C.Conclusion: Retracting the maxillary incisors with clear aligner,Under different loading modes,the teeth move types was varied.When the appliance directly retracting the maxillary incisors,the teeth appear to move lingual inclination,and the crown moves more than the root of the tooth,and the crown has a extruded trend,suggesting that retracting the maxillary anterior teeth will be overbite deepen;the pressure point can be increased at the labial cervical and the lingual margin of the appliance,and the controling root movement of the teeth can be achieved and can prevent the overbite from deepening.