CBCT Evaluation of Upper Airway Volumetric Changes in Patients Treated with Hyrax-Type and McNamara-Type Rapid Maxillary Expanders

Abstract

The Rapid Maxillary Expander (RME) is an orthodontic-orthopedic appliance used to correct transverse maxillary deficiencies, often associated with chronic nasal airway obstruction. The aim of this study is to evaluate volumetric changes in the upper airway using CBCT and to compare any differences between the Hyrax and McNamara Rapid Maxillary Expanders. The study included 21 subjects (mean age: 9.71 years), 11 of whom were treated with the McNamara expander and 10 with the Hyrax expander. CBCT scans were performed before treatment (T0) and after device removal (T1). For each CBCT scan, Total Volume (TV), Retro-Palatal Volume (RPV), and Retro-Glossal Volume (RGV) were measured using ITK-Snap software. The data were statistically analyzed using the paired Student's t-test, while the unpaired Student's t-test was used to compare the two devices. A statistically significant increase was observed in Retro-Palatal Volume (1106 mm³, p = 0.0008) and Total Volume (3396 mm³, p = 0.013). No statistically significant changes were found in Retro-Glossal Volume (279 mm³, p = 0.08). Additionally, no significant differences emerged from the volumetric comparison between the two groups of expanders. CBCT has proven to be a valid and precise method for calculating airway volume. The statistically significant increases in Retro-Palatal Volume (RPV) and Total Volume (TV) suggest a potential reduction in upper airway resistance, which may benefit patients with oral respiratory issues. The lack of significant volumetric differences between the two devices indicates that both expanders have similar effects on the upper airways. Further studies are needed to assess the long-term stability of these airway changes.