Introduction: Functional appliances (FA) have a positive effect on the upper airway volume and minimal cross-sectional area (MCA) in children. An association between morphologic deviations of the upper spine (MDUS) and reduced treatment response was found in appliances used to treat adults with obstructive sleep apnea. This study aimed to: (1) compare airway changes after FA treatment in children with and without MDUS and controls; (2) identify if MDUS causes a smaller upper airway.

Methods: Pretreatment and posttreatment cone-beam computed tomography scans were included from 21 children with MDUS and 42 without MDUS treated with a fixed FA, along with a pair-matched control group (matched for chronological age, skeletal age, gender, and mandibular inclination) who received orthodontic treatment for minor malocclusions without an FA. The influence of MDUS on changes in upper airway volume and MCA were evaluated with 3-dimensional cone-beam computed tomography scans using standardized, previously validated methods and mixed-effects linear regression.

Results: There was a significantly increased volume and MCA in the FA groups with and without MDUS compared with control (P = 0.003 and P = 0.049) and in the FA group without MDUS compared with the MDUS group (P = 0.008 and P = 0.011) after treatment. There was no significant pretreatment difference in airway dimensions between the MDUS and non-MDUS FA groups.

Conclusions: The airway response with fixed FA is significantly reduced in MDUS children. MDUS caused no significant pretreatment airway differences in children. However, MDUS may be important in predicting airway changes in FA treatment.