Efficiency of upper arch expansion with the Invisalign system

Objectives: To investigate the efficiency and movement pattern of upper arch expansion using Invisalign aligners. The correlation between the amount of designed expansion and the efficiency of bodily expansion was evaluated, as were the initial molar torque and efficiency of bodily expansion. Materials and Methods: Twenty Chinese adult patients who underwent arch expansion with Invisalign aligners were included in this study. Records of pretreatment (T0 stage) and immediately after completing the expansion phase (T1 stage) were collected, including digital models and cone-beam computed tomography. Dolphin 3D, Geomagic Studio 12.0, and Meazure software were employed to measure data and calculate differences between the expected and actual outcomes. Results: There were significant differences between the expected and actual expansion amounts (P<.05). The average expansion efficiencies of the upper canine crown, first premolar crown, second premolar crown, and first molar crown were 79.75 +/- 15.23%, 76.1 +/- 18.32%, 73.27 +/- 19.91%, and 68.31 +/- 24.41%, respectively. The average efficiency of bodily expansion movement for the maxillary first molar was 36.35 +/- 29.32%. Negative correlations were found between preset expansion amounts and the efficiency of bodily expansion movement (P<.05), and between initial maxillary first molar torque and efficiency of bodily expansion movement (P<.05). Conclusions: Aligners could increase the arch width, but expansion was achieved by tipping movement. The evaluation of initial position and preset of sufficient root-buccal torque of posterior teeth were necessary due to the lower efficiency of bodily buccal expansion by the Invisalign system.