Quantifying external root resorption associated with various orthodontic tooth movements in clear aligner treatment: a retrospective clinical study

This study investigated associations between tooth movements and external root resorption (ERR) during clear aligner (CA) orthodontic treatment (OT). Forty-eight patients who underwent non-extraction OT using ClearCorrect aligners were included. Maxillary and mandibular incisors and canines were assessed, comprising 576 teeth. Pre- and post-OT digital models were superimposed to quantify intrusion, extrusion, crown tipping, crown torque, rotation, buccolingual translation, and mesiodistal translation. Root length, projected root surface area (PRSA), and ERR were measured on pre- and post-OT panoramic radiographs. Associations between tooth movements and root length, PRSA, and ERR were evaluated using correlation and multivariable linear regression analyses, with correction for multiple comparisons where appropriate. Significant movement-specific associations were observed in the maxillary lateral incisors and canines, with crown torque associated with root length and ERR changes and crown tipping associated with ERR in the lateral incisors, while extrusion was associated with PRSA changes in the canines. No significant movement–resorption associations were observed in the mandibular teeth. The magnitude of the observed resorptive changes was generally limited. Overall, the findings suggest that root responses during CA treatment may vary according to both the type of tooth movement and tooth group; however, the observed movement-specific associations should be interpreted cautiously.