Predictors of refinement in clear aligner therapy: a retrospective tooth-level study of maxillary anterior teeth

This study evaluated the association between planned anterior tooth movements, attachment use, and the need for refinement in clear aligner (CA) therapy using logistic regression. A retrospective analysis was conducted on 116 patients and 696 anterior teeth treated with Invisalign^®. For each tooth, planned movement magnitudes (extrusion, intrusion, rotation, angulation, inclination) and the presence of attachments were recorded. Refinement was defined as a binary outcome. Multivariable logistic regression and independent t-tests were used to assess associations and compare movement magnitudes between refined and non-refined teeth. In tooth 11, greater planned rotation was associated with a modest but statistically significant reduction in refinement likelihood (OR = 0.92, p < .05). Attachment use emerged as a significant factor for teeth 12 and 21, decreasing refinement risk in tooth 21 (OR = 0.05, p < .01), yet increasing it in tooth 12 (OR = 4.95, p < .05). For tooth 22, increased planned extrusion reduced the probability of refinement (OR = 0.34, p < .05), whereas higher degrees of rotation and inclination were associated with increased refinement rates (OR = 1.13 and OR = 1.52, respectively; p < .05). No statistically significant predictors were identified for canines (teeth 13 and 23). These findings underscore the heterogeneity in biomechanical response among maxillary anterior teeth during CA. Specifically, lateral incisors demonstrated a greater susceptibility to refinement needs in the presence of complex movements such as rotation and inclination. These results support the adoption of individualized, tooth-specific treatment planning strategies to enhance predictability and minimize the need for refinement in CA therapy.