Three-dimensional Finite Element Analysis Of The Design Of Invisible Orthodontic Attachment On Maxillary Molar Distalization

Objective: To establish a three dimensional finite element model about the distal movement of maxillary first molar treated by invisible appliance in different attachment positions and attachment angles,and calculate the periodontal membrane stress distribution and the displacement trend of the maxillary first molar,so as to provide a theoretical basis for the attachment design of the distal maxillary first molar treated by invisible appliance.Methods: The DICOM data of the patient’s maxilla was obtained by CBCT scanning,and the A,B,C and D finite element models were established by using Mimics,Geomagic wrap and other software according to the different locations of the attachments.Model A—no attachments;Model B—The vertical rectangular attachment was located in the center of the clinical crown;Model C/Model D— The midpoint of the vertical rectangular attachment was located 2 mm proximal/distal to the center of the clinical crown.The E,F,G and H finite element models were established according to the different angles of the attachments.Model E/Model F—The middle point of the rectangular attachment passed through the center of the clinical crown and was at an Angle of 15°/30° mesially to the positive direction of the Z axis.Model G/Model H—the middle point of the rectangular attachment was through the center of the clinical crown and was 15° /30° distally to the positive direction of the Z axis.The positive direction of Z axis is the direction from crown to root.The designed movement was the distal movement of the maxillary first molar by0.25 mm.To analyze the periodontal membrane stress and the movement trend of maxillary first molar.Results: 1.Attachment position results:(1)The displacement trend from the crown to the root was decreased in all four groups A,B,C and D,which indicated that the distal movement of molars was tipping movement.The displacement of the group without attachments(group A)is smaller than that of the group with attachments(groups B,C,D),which indicates that the addition of attachments is beneficial to the overall distal movement of molars.For the attachment groups in different positions,group C has the largest distal displacement and the maximum displacement,0.12321 mm,indicating that the attachment in the mesial position is beneficial to the distal movement of molars.(2)In the four groups of models,the periodontal ligament stress of the maxillary first molar presented the trend of inclined movement with the gradual reduction of the cervical to root periodontal ligament stress,and compared with the group A,the periodontal ligament stresses with the addition of vertical rectangular attachments(groups B,C,and D)showed an increase.In the group C(the attachments were located in the proximal part),the periodontal ligament stress from the cervical to the root in the distal part was stronger than that in other groups,and the equivalent stress was the largest,0.20038 MPa.2.Attachment angle results: The displacement trend and periodontal membrane stress distribution were similar in groups E,F,G and H,and the maximum displacement and maximum equivalent stress were similar,of which,the maximum displacement in group G was 0.12051 mm,and the maximum periodontal ligament equivalent stress in group E was 0.18134 MPa.Conclusions: The design of rectangular attachments can increase the efficiency of tooth movement when the molar is moved distally,and for the rectangular attachments in different positions,the effect of distal molar movement is better when the attachments are located in the mesial position,but the angle of attachment had little effect on the distal movement of molars,and the effect was mainly in buccallingual direction.