Three Dimensional Finite Element Analysis Of Rotation Of Conical Premolars With Invisible Orthodontic Appliance

Objective: To analyze the biomechanical effects of different attachments and different rotation quantities on conical torsional premolars corrected by invisible orthodontic appliance.Methods: A three-dimensional finite element model of the mandibular denture-periodontal membrane-alveolar bone-attachments-invisible orthodontic appliance was established.The second premolar on the right side of the jaw was designed no attachment,a single vertical rectangular attachment,optimized torsion attachment,buccal-lingual vertical rectangular attachments,and constructed eight different groups of three-dimensional finite element models with different rotation quantities of 1°and 2°.After loading with finite element analysis software,the periodontal membrane stress and initial tooth displacement of the second premolar were analyzed and compared.Results: The stress and displacement of the attachment groups were significantly higher than the without attachment groups.The Von-Mises stress and maximum stress of the optimized torsion attachment group and the buccal-lingual vertical rectangular attachments group were significantly higher than the other two groups.The Von-Mises stress distribution was the most uniform of the buccal-lingual vertical rectangular attachment group was rotated 1°.The teeth showed inclination and intrusion tendency when rotation movement occurred,and there was extrusion tendency in the optimized torsion attachment group.The displacement was as follows: the optimized torsion attachment group > the buccal-lingual vertical rectangular attachments group > the single vertical rectangular attachment group > the without attachment group.The stress of the group with rotation of 2° was greater than that of the group with rotation of 1°,and the displacement of the former was about 1.5 times that of the latter.Conclusion: Adding attachments and increasing the amount of rotation in each step of the invisible orthodontic appliance can improve the expression of the orthodontic effect.It is suggested that in clinical operation,the tooth rotation effect is better for the conical torsional teeth that do not need strong retention to design the optimized torsion attachment;for the teeth that need to be strengthened,the buccal-lingual vertical rectangular attachments are added to enhance the retention,which is beneficial to the expression of stress.The design of 2°rotation of each appliance is more conducive to the improvement of the efficiency of the rectification than that of 1°.