Factors Associated With Maxillary Incisor Crown Torque Expression in Non-Extraction Clear Aligner Treatment

To quantitatively assess the accuracy of maxillary incisor torque expression and identify its influencing factors in non-extraction cases treated with Invisalign aligners.

Records of 50 adult patients treated with Invisalign aligners at a single tertiary stomatology center between June 2019 and December 2024 were retrospectively analysed. A total of 144 maxillary incisors were included. Digital models from pretreatment (T0), after staged treatment (T1), and predicted posttreatment (T2) were obtained from ClinCheck. Torque values were measured on all models using Geomagic Control X software to calculate the torque expression rate (TER). Predicted and achieved torque changes were compared using paired t-tests. Multiple linear regression was employed to identify significant predictors of TER.

The overall TER for maxillary incisors was 48.1%. On average, the achieved torque change was significantly less than predicted, with a mean difference of 4.25° (95% CI, 3.21°-5.30°; p < 0.05). Under-expression of the planned torque was observed in 111 incisors (77.1%). Regression analysis identified planned crown torque and vertical skeletal pattern as independent predictors of TER (p < 0.05). For each 1° increase in planned torque, TER increased by 5.92%. A high-angle vertical pattern was associated with an 18.45% reduction in TER compared with other vertical patterns.

Torque expression of maxillary incisors with clear aligners was limited. Planned crown torque and vertical skeletal pattern were significant influencing factors.