Clinical expression of programmed mandibular canine rotation using various attachment protocols and 1- vs 2-week wear protocols with Invisalign SmartTrack aligners: A retrospective cohort study

Am J Orthod Dentofacial Orthop. 2022 Sep;162(3):e103-e115. doi: 10.1016/j.ajodo.2022.06.015. Epub 2022 Jul 12.


Introduction: Rotation of rounded teeth, particularly canines, is reported as one of the most difficult and inaccurate tooth movements with aligners. This retrospective study aimed to assess the accuracy and reliability of prescribed mandibular canine rotation with Invisalign aligners and the influence of attachment type and wear schedule on accuracy.

Methods: A sample of 75 subjects with mandibular canines requiring rotation was collected from an existing database. The initial, predicted finish, and achieved finish, were measured using metrology software, and the differences between predicted and achieved mandibular canine rotations were calculated. The sample was divided into 3 groups: optimized rotation attachments using 1-week wear, optimized rotation attachments using 2-week wear, and conventional rectangular attachments using 2-week wear.

Results: Rotation was an underexpressed movement, with an overall median sample efficiency of 75.4%. For all groups, predicted rotation was not equivalent to achieved rotation at a ± 5° equivalence margin. This indicates that none of the Invisalign SmartTrack aligner attachment configurations display clinical accuracy in their predicted rotation. By attachment type, median efficiencies of 81.5%, 76.5%, and 63.1% were found for groups 1-week wear, 2-week wear, and 2-week wear, respectively. By wear schedule, there was no significant difference in efficiency for optimized rotation attachments.

Conclusions: The clinical expression of canine rotation with SmartTrack aligners is less than the prescribed rotation for all attachment configurations. Vertical rectangular attachments were associated with the least accurate expression of prescribed movement. There was no difference in rotation efficiency between 1- or 2-week aligner wear.

MeSH terms

  • Cuspid
  • Humans
  • Orthodontic Appliance Design*
  • Orthodontic Appliances, Removable*
  • Reproducibility of Results
  • Retrospective Studies
  • Tooth Movement Techniques