Comparative evaluation of upper airway dimensions following isolated mandibular setback versus bimaxillary surgery in the surgery-first approach: A 1-year follow-up study

This study aimed to quantitatively compare alterations in upper airway dimensions-specifically volume and cross-sectional area-following isolated mandibular setback versus bimaxillary surgery using the surgery-first approach (SFA) in patients with skeletal Class III malocclusion. To the best of our knowledge, this is the first study to directly compare these two surgical protocols exclusively under the SFA paradigm with acoustic pharyngometry and per-millimetre analysis over a 1-year follow-up.

A retrospective cohort investigation was conducted on 40 skeletally mature Class III adults, equally allocated into two cohorts: Group 1 underwent isolated mandibular setback via bilateral sagittal split osteotomy (BSSO, n=20), while Group 2 received bimaxillary orthognathic surgery (maxillary advancement combined with mandibular setback, n=20). Upper airway parameters were objectively assessed using acoustic pharyngometry at three distinct intervals: one week preoperatively (T0), one month postoperatively (T1), and one year postoperatively (T2). Spatial airway variations were quantified as percentage changes, with the magnitude of airway reduction and subsequent recovery calculated per millimetre (mm) of surgical mandibular setback.

At T1, both surgical interventions resulted in a statistically significant reduction in airway dimensions. Nevertheless, the extent of airway constriction was markedly more severe in Group 1 compared to Group 2, affecting both volume (-22.84% vs. -7.96%; p < 0.01) and cross-sectional area (-21.45% vs. -6.79%; p < 0.01). The volumetric reduction per millimetre of mandibular setback in Group 1 was -1.168 cc/mm, which was substantially greater than the -0.458 cc/mm observed in Group 2 (p < 0.01). By T2, a distinct airway recovery (relapse) was documented; Group 1 exhibited a higher volumetric recovery rate (+15.83%) than Group 2 (+4.63%). Despite this rebound, the overall airway dimensions at the one-year follow-up (T2) remained significantly larger and better preserved in the bimaxillary cohort than in the isolated setback group (p < 0.05).

Performing an isolated mandibular setback under the SFA protocol induces considerable upper airway constriction. Conversely, incorporating maxillary advancement via bimaxillary orthognathic surgery significantly preserves airway dimensions. Consequently, bimaxillary intervention should be considered a safer surgical indication to proactively mitigate the risk of respiratory impairment, particularly in Class III patients requiring substantial mandibular retropositioning. This study provides new evidence that bimaxillary surgery better preserves airway dimensions in SFA compared with isolated mandibular setback.