Maxillary and upper airway changes immediately after mini-screw assisted rapid maxillary expansion in class Ⅲ patients

Abstract

Objective: To assess maxillary sagittal and vertical as well as upper airway changes immediately after mini-screw assisted rapid maxillary expansion (MARME) in class Ⅲ patients. Method: A consecutive sample of 48 class Ⅲ patients with maxillary transverse deficiency who visited the Department of Orthodontics, School & Hospital of Stomatology, Wuhan University between January 2013 and March 2023 was retrospectively collected. The sample was comprised of 24 growing patients (cervical vertebra maturation, CVM 1-4) and 24 nongrowing patients (CVM 5-6). Cone-beam CT scans before (T0) and immediately after MARME (T1) were imported into Dolphin Imaging software, and then voxel-based superimposition was conducted on the basis of the anterior cranial base. Sagittal and vertical changes of the maxillary landmarks (A, ANS, PNS, UI and Spr), as well as upper airway changes after MARME were measured on multiplanar reconstruction views. Wilcoxon signed-rank test was employed to analyze the changes after MARME. Mann-Whitney U test was employed to compare the changes between growing and non-growing patients. Results: Some class Ⅲ patients exhibited significant maxillary sagittal and vertical changes immediately after MARME. The amount of changes in midpalatal suture was 4.03 (2.99, 4.87) mm in growing patients, significantly larger than that in non-growing patients [2.27 (1.49, 3.64) mm] (U=3.18, P=0.001). In growing class Ⅲ patients, the forward changes of A, ANS, PNS, UI and Spr were 0.35 (0.06, 0.80), 0.48 (0.11, 0.88), 0.48 (0.13, 0.99), 0.53 (-0.33, 1.04) and 0.40 (0.03, 0.69) mm, respectively. Vertically, the downward changes of A, ANS, PNS, UI and Spr were 1.45 (0.99, 2.13), 1.18 (0.61, 1.95), 1.30 (0.91, 1.96), 1.20 (0.71, 1.83) and 1.30 (0.81, 1.73) mm, respectively. All changes were significantly different from 0 after treatment (P<0.05). In nongrowing patients, PNS moved forward by 0.18 (-0.08, 0.39) mm while other sagittal changes were statistically insignificant (P>0.05); vertically, the downward changes of A, ANS, PNS, UI and Spr were 0.90 (0.51, 1.39), 0.73 (0.41, 1.21), 0.70 (0.55, 1.08), 0.60 (0.36, 1.19) and 0.70 (0.55, 1.23) mm, respectively. Significant immediate increase of the nasopharynx volume and nasal width was obtained in both groups (P<0.05), and the changes of oropharynx volume and minimum cross-sectional area (MCA) presented as statistically insignificant (P>0.05). Conclusions: For growing class Ⅲ patients, besides transverse expansion, significant forward and downward changes of maxilla were obtained immediately after MARME. For non-growing patients, significant downward changes were observed, while sagittal changes were negligible. The nasopharynx volume increased in both growing and nongrowing class Ⅲ patients immediately after MARME, whereas, the changes of oropharynx volume and MCA presented as statistically insignificant.