Researchers from the University of Minnesota, Minneapolis, found that orthodontic treatment with clear aligners tends to increase the mandibular intercanine distance with little change in inclination in contrast to treatment with fixed appliances, which leaves the intercanine distance unchanged but leads to more upright mandibular canines. The study, which set out to compare the changes in buccolingual inclination of mandibular canines and intercanine distance in patients treated with clear aligners to those treated with readjusted edgewise appliances, appears in The Angle Orthodontist.

The study looked at 30 patients who had been treated with clear aligners and 30 patients treated with fixed readjusted edgewise appliances. Pre- and post-treatment CBCTs were used to measure the buccolingual inclination of mandibular canines and the intercanine distance. The researchers tested the differences between the aligner and fixed appliance groups and between pre- and post-treatment measurements for statistical significance.

In both groups, the researchers found that most of the mandibular canines had positive buccolingual inclinations—i.e. participants’ crowns were positioned lateral to their roots—both before and after treatment. While no difference was noted between the groups pretreatment, the post-treatment buccolingual inclination was significantly greater in the aligner group. In the fixed appliance group, the canines became more upright with treatment, while the buccolingual inclination did not change significantly in the clear aligner group. The intercanine distance did not differ between the groups either before or after treatment. However, the researchers found that it increased significantly over the course of treatment in the aligner group, whereas it did not change significantly in the fixed appliance group.