Reliability of torque expression by the Invisalign® appliance: A retrospective study

Introduction: Incisal torque in orthodontics has always been important due to its relationship with smile aesthetics and the stability of a final treatment outcome. The aim of this study was to quantify the accuracy of torque expression predicted by ClinCheck (R) planning associated with Invisalign (R) treatment, compared to clinical outcomes. Methodology: Forty adult patients consecutively treated using the Invisalign appliance were selected. Torque and the interincisal angle (IIA) were measured at T0 (pretreatment), T1 (predicted post-treatment), and R (end of initial aligner sequence) stages on STL files using metrology software (Geomagic Control X). Results: The difference between the predicted and achieved torque (torque differential) was statistically significant (P < 0.001) in the labial crown torque group with a mean of 6.43 degrees (SD = 7.09) for the upper central incisor, 5.06 degrees (SD = 7.32) for the upper lateral incisor and 2.75 degrees (SD = 5.7) for the lower incisor sub-groups. In contrast, the corresponding lingual/palatal crown torque sub-groups did not show a statistically significant torque differential (P >0.05). Similar observations were made for the IIA differential (difference between predicted and achieved IIA) with a mean IIA differential of 9 degrees (SD = 10.73; P < 0.001) and-3.4 degrees (SD = 7.9; P > 0.05) in the labial and lingual/palatal crown torque IIA groups, respectively. Conclusions: Torque was under-expressed when the teeth were moving labially, and fully-or over-expressed when moved lingually, indicating Invisalign's inefficiency in torqueing incisors in the labial direction.

Automated summary

This study quantified the accuracy of torque expression predicted by Invisalign's ClinCheck planning compared to clinical outcomes. The results showed that torque was under-expressed when teeth were moved labially, and fully or over-expressed when moved lingually, indicating inefficiency in torqueing incisors in the labial direction.