Estimation of centers of rotation of the maxillary incisors during nonextraction space closure using the Invisalign appliance.

Abstract

Introduction: The primary objective was to establish the center of rotation of maxillary incisors during nonextraction space closure with a series of Invisalign aligners (Align Technology, Santa Clara, Calif) and to determine the accuracy of planned orthodontic tooth movement (OTM). The secondary objective was to investigate the efficacy of achieving labiolingual incisor angulation changes planned before the commencement of treatment.

Methods: Digital models representing the pretreatment (T0), planned treatment (T1), and achieved treatment occlusion (T2) were superimposed and analyzed using the Geomagic Control X (version 2022.0; 3D Systems, Rock Hill, NC) software platform. Three-dimensional vector analogs for the long axes of the teeth were generated, and their intersection determined the center of rotation at T1 and T2. The angle formed by the vectors to the y-axis Cartesian plane represented the incisors' labiolingual angulations at the 3-time points.

Results: A total of 240 maxillary incisors in 60 patients were assessed. The mean (standard deviation) accuracy of achieving the planned OTM for maxillary incisors ranged from 33.2% (31.8) to 35.4% (25.2). Uncontrolled tipping was the most accurate OTM, achieving 76% accuracy for central and 60% for lateral incisors. During the labiolingual incisor change, the planned incisor retroclination was overexpressed by 169% for central and 126% for lateral incisors. Planned incisor proclination was inefficacious, with 10.7% of central and 43.5% of lateral incisors proclining as planned.

Conclusions: Approximately one-third of the planned OTM for maxillary incisors after nonextraction space closure was achieved. Planned maxillary incisor retroclination was overexpressed, and most incisors retroclined during planned proclination.