Short-Term Impact of Slow Maxillary Expansion on Labial Ectopic Canine Eruption Pathway in Children: A Retrospective Study

<b>Objectives:</b> This retrospective study evaluated the short-term effects of removable slow maxillary expansion (SME) on eruption patterns of labially ectopic canines in a Chinese pediatric population, comparing treated patients with untreated controls. <b>Methods:</b> Seventy-six patients (mean age 8.38 ± 0.88 years) underwent SME treatment for 11.04 ± 4.44 months. Canine positions were categorized as labial ectopic (TE: <i>n</i> = 40) or normally positioned (TN: <i>n =</i> 112). The TE group was stratified vertically: superior (TES; <i>n =</i> 15, canines above lateral incisors' roots or adjacent to unerupted incisors) and inferior (TEI; <i>n =</i> 25, canines adjacent to erupted lateral incisors' roots). Untreated controls (<i>n =</i> 58; mean age 8.46 ± 0.78 years) included labial ectopic (CE group; <i>n =</i> 32) and normal canines (CN group; <i>n =</i> 84), with CE further divided vertically into CES (<i>n =</i> 24) and CEI (<i>n =</i> 8). Panoramic radiographs at baseline (T0) and follow-up (T1) evaluated sector distribution, midline proximity (3c-ML: canine cusp to midline distance), vertical position (3c-OP: cusp to occlusal plane distance), and angular (3^ML: canine-midline angle). <b>Results:</b> SME significantly improved midline proximity (3c-ML increased) while reducing vertical height (3c-OP decreased) and angulation (3^ML reduced) in the TE group. Notably, TE patients revealed a significantly greater increase in 3c-ML compared to CE. Subgroup analysis showed that TEI canines exhibited significant improvements in all three parameters (3c-OP, 3c-ML, and 3^ML), whereas TES canines displayed minimal changes. The shifts in sector distribution were similar between the treatment and control groups. <b>Conclusions:</b> SME demonstrated short-term efficacy in guiding labially ectopic canines toward more favorable eruption trajectories, particularly when erupted beyond the roots of the lateral incisor. The observed positional improvements underscore SME's potential to optimize eruption outcomes during early orthodontic intervention.