Three-dimensional Finite Element Analysis Of The Effect Of Different Designs Of Expansion Method On The Torque Of Maxillary First Molar With Clear Aligner

Objective: To study the maxillary first molars with five different forces during maxillary expansion with clear aligner,analyze the stress distribution and tooth displacement trend of the maxillary first molar.The results provide corresponding theoretical guidance for clinician program design.Methods: Scan for oral data from volunteers.Using Mimics,Geomagic,and Abaqus/CAE software to create 3D stereoscopic models of the oral cavity of volunteers,including 3D models of maxillary teeth,alveolar bone and matching invisible appliance,and then simulate the maxillary first molar of the invisible appliance when expanding the arch the maxillary first molar loading with force.Observe the initial displacement,displacement trend and stress distribution of teeth and periodontal ligament in the five groups of maxillary first molars.Divided into five groups to simulate the force loading of maxillary first molars by the clear aligner: Group 1 is a group without attachment.This group is a control group.The maxillary first molars are not designed with any attachments.The crown and cheeks of the maxillary first molars are loaded horizontally;Group 2 is a buccal horizontal rectangular attachment group.A horizontal rectangular attachment is designed in the center of the buccal clinical crown of the maxillary first molar.The loading of force is the same as that of group 1;Group 3 is the horizontal rectangular attachment group of the palatal side.The horizontal rectangular attachment of the clinical crown center of the maxillary first molar crown is designed with the same load as the first group;Group 4 is a pressure point group.Based on group 1,the pressure point is applied vertically on the 1/3 of the lateral neck of the crown.Group 5 is a pair of pressure points group.It is based on group one,and at the same time,the pressure poinst are applied vertically on the crown buccal occlusal 1/3 and palatal neck 1/3.Results:1.Stress concentration areas are visible around horizontal rectangular attachments andpressure points,And no roots of stress concentration appeared in the roots of the first molars in the five groups of models.It indicates that the presence of attachments and pressure points can transmit the correction force,and the correction force of the clear aligner is beneficial to the health of periodontal tissue.2.The clear aligner performs maxillary expansion,and the first molars move differently under different force loading conditions.The movement trends of the no-attachment group,buccal horizontal rectangular attachment group,and lingual horizontal rectangular attachment group are all tilted movements of the cheek to the remote side accompanied by obvious palatal cusp droop;The buccal and palatal pressure points of the group of teeth moved in the direction of root lip,crown,and buccal movement of the root is greater than the root control movement of the crown movement.The buccal cusp has a small amount of depression,and the palatal cusp with little elongation.The tooth movement mode of a pressure point group on the buccal side is between group 1and group 5,and it tends to move the cheek to a distant whole.It can not obvious palatal cusp droop.Conclusion: Whether the molar is placed with a horizontal rectangular attachment and the placement of the attachment has no significant difference in the torque control of the tooth after expansion.Both are tilted movements in the remote cheeks with obvious palatal cusp droop.The presence of the attachment can increase the retention force of the clear aligner and has no effect on the torque of the molar;the design pressure point of the molar can be used to effectively control the torque of the molar when expanding the arch.