Three-dimensional orientation changes of unerupted maxillary canines and second premolars treated with facemask therapy: a retrospective study

Tooth-borne facemask therapy for skeletal Class III malocclusion is often performed during the mixed dentition, when the maxillary canines and second premolars are still developing. Although the appliance advances the maxilla, it also produces dentoalveolar side effects that could theoretically reorient these developing germs into potentially less favourable positions. This study therefore quantified, in three dimensions, the short-term changes in the orientation of unerupted maxillary canines and second premolars following maxillary protraction.

In this retrospective study, baseline and follow-up cone-beam computed tomography records from 30 patients who received tooth-borne maxillary protraction and 30 untreated controls were analysed. A maxilla-specific coordinate system was used to quantify three-dimensional changes in the long-axis orientation of unerupted maxillary permanent canines and second premolars. Between-group differences were assessed using linear mixed-effects models with a participant-level random intercept to account for bilateral observations. Sensitivity analyses adjusted for observation interval, baseline age, Nolla stage, initial tooth-germ orientation and available baseline cusp coordinates.

Compared with controls, canine tooth germs in the facemask group showed greater labial inclination (between-group β = 8.5°, 95% CI 5.0 to 12.0; P < 0.001), without a significant mesiodistal component (P = 0.231). Second premolar tooth germs showed greater mesial inclination (β = 8.0°; P < 0.001), palatal inclination (β = -2.7°; P < 0.001) and anterior rotation of the buccal cusp (β = -6.0°; P < 0.001). These between-group differences remained significant in sensitivity analyses; canine mesiodistal angulation showed no significant between-group difference in either the primary or the sensitivity analyses. Greater angular changes were associated with lower baseline cusp height for both canines (P = 0.001) and second premolars (P = 0.007).

Tooth-borne maxillary protraction was associated with short-term changes in the orientation of unerupted maxillary tooth germs-labial inclination of canines and mesial, palatal and rotational components in second premolars. Because the link between these orientation changes and eruption outcome remains to be established, monitoring of unerupted germs during treatment may be prudent. Longitudinal follow-up is needed to determine whether these changes affect eventual eruption, impaction or arch-space conditions.