Skeletal effects to the maxilla after rapid maxillary expansion assessed with cone-beam computed tomography

The purpose of this study was to use cone-beam computed tomography to quantitatively evaluate skeletal expansion and alveolar tipping of the maxilla at the maxillary canine (C1), first premolar (P1), second premolar (P2), and first molar (M1) after rapid maxillary expansion (RME). The transverse effects to the maxillary suture, nasal width, and maxillary sinus were also assessed.

Thirty consecutive patients (17 boys, 13 girls; mean age, 13.8 +/- 1.7 years) who required RME with Hyrax appliances as part of their comprehensive orthodontic treatment were studied. Measurements before and after RME of palatal and buccal maxillary widths, palatal alveolar angle, nasal width, nasal floor width, and maxillary sinus width at C1, P1, P2, and M1 were compared by using Wilcoxon signed rank, Kruskal-Wallis, and Wilcoxon rank sum tests. Pearson correlation analyses were also performed (* = .05).

Skeletal expansion of the maxilla had a triangular pattern with a wider base in the anterior region, accounting for 55% of total expansion at P1, 45% at P2, and 38% at M1. Alveolar bending or tipping accounted for 6% of total expansion at P1, 9% at P2, and 13% at M1. The remaining orthodontic (dental tipping) portions of total expansion were 39% at P1, 46% at P2, and 49% at M1. RME produces a statistically significant increase in nasal width and a decrease in maxillary sinus width (P <0.0001). Retention time showed a significant negative correlation to the change in palatal maxillary width at C1, P2, and M1 (P <0.05), the rate of appliance expansion had a significant correlation with palatal maxillary expansion at P1 and P2 (P <0.05), and age had no statistically significant association with any parameter (P >0.05).