Three-dimensional Finite Element Analysis On Canine Distalization By Different Attachments Of Invisalign Orthodontic Treatment

Objective: By establishing a FE model,comparing when canine distalization the force system and displacement patterns produced by three types of aligner attachments: Vertical rectangular attachment(1 mm thick,2mm width,4mm high),power arm(6mm high)and composite attachment.Intending to provide basis for invisible orthodontic treatment.Methods: CBCT scanning image of a patient with individual normal occlusion was adopted,Mimics,Geomagic and Pro/E software were used for establishing three-dimensional models of maxilla,maxillary dentition,periodontal ligament,invisible appliance and attachments.Ansys workbench was utilized as finite element analysis tool for analyzing stress distribution and movement pattern of canine and parodontium when canine was equipped with vertical rectangular attachment,power arm and composite attachment.Without attachment design group was regarded as a control.In this FE simulation of a clinical event,a displacement of 0.25 mm in the distal direction was imposed on the simulated thermoplastic aligner segment that was previously incorporated passively on the tooth crown.Results: All four groups have distalization canine effect.The maximum principal stress of the without attachment group is mainly distributed on the distal-labial and mesial-lingual side.The movement pattern is distal-inclination,and the crown lingual constriction and extrusion.There are Von-Mises concentration around the attachment of the vertical rectangular attachment group and the maximum principal stress is mainly located on the cervical and apical root.The maximum principal stress distribution of the teeth in the mesial-distal side of power arm group was uniform,and the canine was bodily movement.The maximum principal stress of the composite attachment group was distributed in the cervical and root tip,and the mesial-distal displacement pattern was root controlling movement.The vertical rectangular attachment group,Power arm group and the composite attachment group were all the moving trend of the lingual direction and intrusion.Conclusion: The canine of the Power arm group is the bodily movement.the composite attachment group is the root controlling movement.the vertical rectangle group is the inclination movement,accompanying a certain root controlling effect.without attachment group are inclination movement with a counterclockwise rotation(occlusal surface view).The retention force of the vertical rectangular attachment is larger than that of the half elliptic attachment and the correction efficiency is higher.