Evaluation of planned and achieved root angulation changes in teeth adjacent to mandibular premolar extraction sites in patients treated with Invisalign: A retrospective study

INTRODUCTION: This study aimed to determine the efficacy of Invisalign (Align Technology, Santa Clara, Calif) in achieving planned root angulation of molars, premolars, and canines adjacent to mandibular premolar extraction sites. METHODS: Digital models of adult patients treated with Invisalign aligners and extraction of at least 1 mandibular first (L4) or second (L5) premolar between 2013 and 2019 were evaluated after import into the Geomagic Control X (3D Systems, Rock Hill, SC) metrology platform. RESULTS: Thirty-one patients, comprising 30 L4 and 25 L5 extractions, were assessed. The accuracy of the planned root angular changes ranged from -119.05% to 162.75%. Similar patterns of expression were observed across the L4 and L5 extraction sites. When root tipping away from the extraction site was planned, the overexpression of root movement was likely in the canines and first molars. Underexpression of planned root angulation change was likely in the premolar adjacent to the L4 extraction site, whereas overexpression was more common in a premolar adjacent to a L5 extraction site. No differences in root angulation outcomes related to patient sex, number of prescribed aligners, or attachment type (P >0.05) were observed. A 2-week wear protocol resulted in a significant (P = 0.005) shortfall of 4.52° of root angulation compared with the 1-week wear protocol when crown tipping away from the L5 extraction sites was planned. CONCLUSIONS: The root angulation changes in teeth near the mandibular premolar extraction sites did not match those planned. The use of optimized attachments appeared not to improve root angulation outcomes compared with conventional attachments.