Influence of lower anterior crowding on the predictability of mandibular tooth movement in Invisalign therapy: a retrospective cohort analysis

Introduction: Invisalign® can resolve up to 91.4% of mandibular incisor crowding. However, there is insufficient evidence to support clear aligner therapys effectiveness for various tooth movements. While the accuracy of Invisalign® has been evaluated, few studies have evaluated its efficacy in alleviating lower arch crowding. Hence, we aimed to identify significant differences between predicted and achieved linear, vertical, and rotational tooth movements in Class I mild-to-severe crowding cases. We also examined the association between lower anterior crowding and discrepancies in predicted vs. achieved movements. Methods: This retrospective cohort study, conducted in Saudi Arabia, included 44 participants collected between May and September 2023. The treatment protocol involved proclination followed by interproximal reduction for lower mandibular crowding. Results: The sample comprised 63% female patients (mean age: 32). All anterior lower teeth showed significant discrepancies between predicted and achieved movement (3.64 ± 3.25). A significant positive relationship was observed between crowding and lower right canine linear/rotational movements, as well as lower left central/lateral linear movements,lower left lateral vertical and lower right lateral linear movement. Clinically, a one unit increase in crowding correlated with a 0.49 increase in lower right canine rotational difference, while a one unit increase in crowding corresponded to a 0.405 increase in lower right lateral rotational difference. Conclusion: Dental crowding reduces the accuracy of clear aligner therapy. Clinically, overcorrection should be routine, and additional tools should be used to improve predictability in cases with significant crowding.