Investigation Into the Significance of Daily Invisalign Tray Wear Duration

Objectives: Clear aligner orthodontic therapy is an alternative to fixed-appliance therapy, however tooth movement achieved by removable aligners is dependent upon patient tray wear adherence. Invisalign recommends 22 hours per day of aligner wear, however there is a lack of evidence to support this recommendation. The aim of this project was to determine incisor facial/lingual tip, bodily movement and rotation change differences when aligners are worn 12, 17, and 22 hours per day for the first 8 weeks of treatment.
Methods: 45 subjects were recruited and randomly assigned to wear aligners either 12, 17, or 22 hours per day. Subjects were to wear each aligner for one week and track wear time. Intraoral scans (3 Shape, Trios) were taken at baseline and 8 weeks. Tooth movements produced by separate wear times were quantified (ToothMeasure, Align Co), and analyzed for significant differences (ANOVA, p<0.05).
Results: Data are presented for 5 subjects in each group. Wear times of 17 and 22 hours were significantly different from 12 hours when comparing buccal inclination of maxillary and mandibular incisors between all groups by multiple Wilcoxon tests using the Dwass, Steel, Critchlow-Fligner Method (12 vs 17: p=0.0083; 12 vs 22: p=0.0011).
Conclusions: Quantity of tooth movement is dependent on aligner wear time in hours per day. Achievement of buccal inclination of incisors may be reduced when aligners are worn for 12 hours compared to 17 or 22 hours. 17 and 22 hour aligner wear may be equally effective in achieving desired buccal inclination. However, caution is indicated because of the preliminary nature of the data. More definitive results will be presented when data collection and analysis is complete.