Influence Of The Shape And Position Of The Attachments On The Treatment Of Torsional Canines In Clear Aligners

Objective To compare the influence of the shape and position of the attachments on the treatment of torsional canines in clear aligners by three-dimensional finite element analysis.Methods The finite element models of the clear aligner-attachment-maxillary canine-periodontal ligament-spongy bone-cortical bone(attachment groups)and(nonattachment group)were established according to the scanning data of in vitro maxillary canine.The models with attachments were divided into three groups based on different kind of attachment,namely vertical rectangular attachment、vertical wedge-shaped attachment、optimized torsion attachment groups.The placement positions were divided into buccal middle 1/3,distal 1/3 and buccal-lingual middle 1/3.2°clockwise rotation of the tooth long axis was applied to the clear aligner.The action of the appliance and the canine were simulated and calculated by Abaqus software.Then,the nephograms of stress and displacement,and the maximum stress and displacement values were collected.Results 1.The maximum initial displacement value of the canine and the stress value of periodontal ligament in the attachment group are higher than that in the non-attachment group.2.When the same attachment was selected,there was no significant difference in the stress value and maximum initial displacement between the buccal 1/3 and buccal-lingual middle 1/3,but the stress and displacement expression of buccal-lingual middle 1/3 was more efficient,and the effect of the distal 1/3 was relatively poor.3.In the same position,the stress value and maximum initial displacement of the vertical wedge-shaped attachment are the highest,followed by the vertical rectangular attachment,and the optimized torsion attachment is relatively poor.Conclusion 1.Position of attachment:buccal-lingual middle 1/3 is better than buccal middle 1/3 better than buccal distal 1/3.There was no significant difference in the stress values and the maximum initial displacement between buccal middle 1/3 and buccal-lingual,but buccal-lingual is more effective,and eliminate unnecessary tipping and vertical changes.2.Shape of attachment:vertical wedge-shaped attachment with the inclined plane in the torsional direction is better than vertical rectangle better than optimized torsion attachment.Due to the limitation of research method and design,the actual effect of optimized torsion attachment needs further clinical verification.3.In a word,the buccal-lingual vertical wedge-shaped attachment works best.But in clinical treatment design,the shape and position of the attachment should be customized according to the patient’s condition.