Morphometric analysis of dental arch form changes in class II patients treated with clear aligners

Purpose: The purpose of this study was to evaluate the arch form changes in class II Caucasian patients treated with Invisalign® (Align Technology, San José, CA, USA). Methods: A total of 27 class II patients, for whom a maximum of 4 mm arch expansion was planned, were selected. Both maxillary and mandibular digital casts were compared at three different times: pretreatment (T0), accepted set-up (T1), and retention phase (T2). Each digital model was imported into GOM Inspect© software (GOM GmbH, Braunschweig, Germany) to identify teeth crown facial axis (FA) and cusp points to create a coordinate system. In each model the origin of the coordinates was located at the contact point of central incisors and a system of Cartesian axes was constructed. Using the FA points, an average arch form was obtained for each clinical step and then the following comparisons were performed for each class group: T0–T1, T0–T2, and T1–T2. Results: T1 showed wider maxillary and mandibular dental arches compared to T0 with maximum movements observed in the premolar regions (maximum movement 1.94 mm for tooth 15; P < 0.0001). In the T1–T2 comparison, a more buccal position of tooth 22, tooth 23, and tooth 24 (maximum movement 0.56 mm; P < 0.05) and a more lingual position of tooth 37 (maximum movement 0.81 mm; P < 0.01), tooth 36, and tooth 47 were observed at T1 with respect to T2. Conclusions: Although Invisalign® treatment resulted in a significant increase in arch width according to the prescription, some of the outcomes were different than those planned especially in relation to the final position of the lower molars.