Abstract
Objective
The discrepancy between an anticipated digital configuration and the realised results poses a continual challenge during clear aligner therapy. The present study aims to examine the generated tooth movement achieved when upper molars are moved distally using clear aligners and Class II elastics.
Materials and methods
Thirty adult patients (13 males and 17 females) aged between 18 and 35 years-old were analysed. CBCT scans taken before and at the end of a distalisation phase were superimposed using a voxel-based registration. Molar distalisation efficiency, tipping and rotation angles, and changes in arch width were quantified to assess the achieved tooth movement. Pearson’s correlation coefficients and multiple linear regression models were applied to examine the tooth changes, and how gender, attachments, and initial crowding affected the results.
Results
The study determined that the effectiveness of moving upper molars distally using clear aligners along with Class II elastics was 60% ± 7% of the designed movement. Due to a counterforce, the upper incisors experienced labial tipping of 3.84° ± 1.1°, the lower molar was mesialised by 0.64 mm ± 0.27 mm, and the lower incisors underwent labial tipping of 2.61° ± 1.13°. The upper archwidth displayed a non-significant increase, whereas the width of the lower arch exhibited a non-significant reduction. Furthermore, molars with attachments exhibited reduced distal tipping and rotation. The initial crowding was inversely related to the amount of upper molar distalisation and positively related to tipping.
Conclusion
This is the first CBCT superimposition study to reveal the achieved tooth movements during upper molar distalisation. The results suggest that multiple factors impact tooth movement.