Short-term impact of rapid maxillary expansion on ectopically and normally erupting canines

The purpose of this study was to evaluate the short-term impact of rapid maxillary expansion (RME) on the eruption paths of ectopically and normally erupting maxillary canines in the mixed dentition.

Thirty-two patients with 49 ectopically erupting canines (EEC group; age, 9.53 ± 1.10 years) and 18 patients with 27 normally erupting canines (NEC group; age, 9.25 ± 1.06 years) underwent RME. Thirty-six subjects with 54 normally erupting canines composed the untreated control group (UC group; age, 9.03 ± 0.72 years). Horizontal, vertical, and angular positions of canines and adjacent teeth were evaluated in the expanded (EEC and NEC groups) and unexpanded (UC group) patients using panoramic radiographs taken at 2 times with a 1-year interval. The radiographic evaluation methods included score ranking and proportional measurements to minimize panoramic radiograph limitations. Statistical comparisons were performed among the groups (P <0.05).

Before expansion, the EEC group's canines were significantly closer to the midline, more distant from the occlusal plane, and more mesially angulated than those in the UC group. After expansion, the canine positions in the EEC and UC groups were similar, whereas the NEC group had a more favorable canine position for eruption. The EEC and NEC groups showed similar canine positional changes, whereas the UC group had the smallest changes. The positions of teeth adjacent to the canine were also significantly affected by RME, and these changes may be associated with improvement of the ectopic canine position.

The changes produced by RME reduced the percentage of ectopic eruption paths and maintained the nonectopic eruption percentage.