Analysis of predicted and achieved root angulation changes in teeth adjacent to maxillary premolar extraction sites in patients treated with the Invisalign appliance.

Introduction: This study aimed to investigate the expression of root angulation in canine, premolar, and first molar teeth adjacent to first and second premolar extraction sites in the maxilla after treatment with an initial series of Invisalign aligners (Align Technology, Santa Clara, Calif).
Methods: Adult patients (aged ≥18 years) with at least 1 first and/or second premolar extraction in the maxilla and satisfying strict selection criteria were evaluated. Digital models representing pretreatment, predicted, and posttreatment were obtained from Align Technology's digital interface, ClinCheck. The Geomagic Control X (version 2017.0.3; 3D systems, Rock Hill, NC) software facility was used to determine and compare the root angulation of adjacent canine, premolar, and first molar teeth at different time points.
Results: The predicted angulation of teeth was significantly different (P <0.02) than that achieved in most patients. When adjacent teeth roots were planned to tip away from the extraction site, there was an overexpression of the movement. When teeth roots were planned to tip into the extraction site, underexpression occurred, and movement was in the opposite direction in some instances. There was no difference in root angulation outcomes according to the prescribed number of aligners, 1- or 2-week wear protocols, and sex (P >0.05). Attachments were influential in controlling angulation in first-premolar extractions (P = 0.05), but optimized attachments were not any more effective than conventional attachments (P >0.05).
Conclusions: The achieved root angulation in teeth adjacent to premolar extraction sites in the maxilla after treatment with an initial series of Invisalign aligners differed significantly from that predicted. Attachments play a minor role in the predictability of root angulation outcomes.
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