This study aimed to assess the changes in the pharyngeal airway morphology after premolar extraction and maximum anchorage retraction of the anterior segments in adult bimaxillary protrusion patients by using CBCT.

Twenty-one subjects (mean age 23.8±4.6 years) requiring extraction of four first premolars and en masse retraction of the anterior segments using maximum anchorage participated in the study from July 2022 to May 2024 with an average treatment duration of 19.9 months. CBCT scans were taken before treatment (pre) and after en masse retraction (post). Airway volume was measured by using Relu software. The pre- and post-CBCT scans were superimposed by using Romexis 1 software. The cross-sectional area (CSA) was measured at the level of the hard palate, soft palate, and epiglottis. The most constricted area (MCA) was recorded. The hyoid bone position was evaluated by using 5 linear measurements. The upper and lower incisor angulations to the Frankfort horizontal plane (FH) were measured before and after retraction. Paired t-test was used to analyse the measurements and correlation analyses were made using Spearman's rank-order correlation coefficient (rs). The significance level was set at P<0.05 within all tests.

Twenty-one participants (16 females, 5 males) followed the inclusion criteria and enrolled in the analysis. There were no significant differences in airway volume, cross-sectional areas, or hyoid bone position between before treatment and after en masse retraction (P>0.05). There was a significant retraction of the incisors after treatment (P<0.001). The change in the most constricted area had a large positive correlation with the change in the airway volume (rs=0.509*) and the area of the soft palate (rs=0.653*).

Maximum anchorage retraction had no significant effect on airway volume, cross-sectional area, or hyoid bone position.