Influence of attachment position and torque overcorrection on arch expansion in clear aligner treatment: a three-dimensional finite element analysis

To investigate the influence of attachment position and torque overcorrection on stress distribution and tooth displacement trends during arch expansion in clear aligner therapy (CAT). Dental and skeletal models were obtained from an adult volunteer with angle Class I and mild crowding. Attachments were designed on the buccal, lingual, and buccolingual surfaces of the first molar. Different overcorrection torques were designed on the first molar. The displacement and stress of the whole arch were analyzed using a three-dimensional finite element analysis model. Crown buccal tipping was observed during arch expansion, while the lingual attachment showed more buccal crown and lingual root movement. Based on the trend of displacement, 1.5° of buccal root torque overcorrection without attachments could lead to bodily movement, 1.8° with a lingual attachment, 0.5° with a buccal attachment, and 0.9° with a buccolingual attachment. Arch expansion is primarily achieved by teeth tipping despite attachments placed on the buccal or lingual side of teeth in CAT. Appropriate overcorrection of buccal root torque could contribute to the achievement of bodily movement.