Results

This study quantitatively evaluated dimensional alterations of the upper airway—mean volume and cross-sectional area—between two SFA cohorts: Group 1 (isolated mandibular setback) and Group 2 (bimaxillary orthognathic surgery). Data were acquired one week preoperatively (T0), one month postoperatively (T1), and one year postoperatively (T2).

Table 1 summarises the baseline demographic data, preoperative cephalometric parameters, and the magnitude of surgical movements for both cohorts. The population was matched for gender (10 males and 10 females per group). There were no significant differences in mean age (23.45 ± 3.12 vs. 24.10 ± 2.85 years; p = 0.49) or BMI (21.56 ± 1.80 vs. 22.09 ± 2.14 kg/m²; p = 0.32). Both groups exhibited severe skeletal Class III discrepancy preoperatively, with comparable ANB angles (p = 0.06).

Variables | Group 1 (n=20) | Group 2 (n=20) | p-value
Demographics
Age (years),Mean ± SD | 23.45 ± 3.12 | 24.10 ± 2.85 | 0.49(a)
Gender (Male/Female),n | 10 / 10 | 10 / 10 | 1.00(b)
BMI (kg/m2),Mean ± SD | 21.56 ± 1.80 | 22.09 ± 2.14 | 0.32(a)
Preoperative Skeletal Baseline
SNA (o),Mean ± SD | 81.26 ± 3.10 | 79.80 ± 2.91 | 0.13(a)
SNB (o),Mean ± SD | 86.10 ± 2.85 | 85.45 ± 3.20 | 0.49(a)
ANB (o),Mean ± SD | -4.85 ± 1.20 | -5.65 ± 1.45 | 0.06(a)
Surgical Movements (T1-T0)
Maxilla (Point A) |  |  | 
Sagittal advancement (mm) | - | 4.32 ± 1.15 | < 0.001(c)
Vertical impaction/extrusion (mm) | - | 1.20 ± 0.85 | < 0.001(c)
Mandible (Point B) |  |  | 
Sagittal setback (mm) | -5.92 ± 1.45 | -5.10 ± 1.30 | 0.07(a)
Vertical movement (mm) | 0.85 ± 0.61 | 1.04 ± 0.75 | 0.35(a)
Rotational Changes |  |  | 
Δ SN-MP (o) | 2.15 ± 1.43 | 1.50 ±1.22 | 0.13(a)

Group 2 underwent a mean maxillary sagittal advancement of 4.32 ± 1.15 mm. The mandibular sagittal setback at Point B was slightly greater in the single-jaw group (−5.92 ± 1.45 mm) than in the bimaxillary group (−5.10 ± 1.37 mm), though this difference marginally missed statistical significance (p = 0.07). Both protocols required a postoperative clockwise mandibular rotation to establish an interim transitional occlusion, reflected by an increase in the SN-MP angle (+2.15 ± 1.43° for Group 1 and +1.50 ± 1.22° for Group 2; p = 0.13) (Tables 2 and 3).

Volume (cc) | Group 1 (n-20) | Group 2 (n-20) | P-value (Inter-group)
T0 (Mean ± SD) | 29.87 ± 4.59 cc | 31.00 ± 4.54 cc | 0.4386
T1 (Mean ± SD) | 22.78 ± 4.73 cc | 28.10 ± 3.82 cc | 0.0004⁎⁎
T2 (Mean ± SD) | 25.66 ± 4.52 cc | 29.05 ± 4.11 cc | 0.0176*
% Change at T1 from T0 | -22.84% | -7.96% | 0.0046⁎⁎
% Change at T2 from T1 (Relapse) | +15.83% | +4.63% | 0.1082
Airway change per mm setback at T1 from T0 | -1.168 cc/mm | -0.458 cc/mm | 0.0067⁎⁎
Airway change (relapse) per mm setback at T2 from T1 | +0.453 cc/mm | +0.156 cc/mm | 0.2623
P-value (Intra-group) |  |  | 
T0 versus T1 | < 0.0001⁎⁎ | 0.0112* | 
T1 versus T2 | 0.0296* | 0.3771 | 

Mean Cross-Sectional Area (cm²) | Group 1 (n-20) | Group 2 (n-20) | P-value (Inter-group)
T0(Mean ± SD) | 3.08 ± 0.50 cm² | 3.10 ± 0.48 cm² | 0.8980
T1(Mean ± SD) | 2.38 ± 0.47 cm² | 2.85 ± 0.40 cm² | 0.0016⁎⁎
T2(Mean ± SD) | 2.59 ± 0.49 cm² | 2.95 ± 0.42 cm² | 0.0171*
% Change at T1 from T0 | -21.45% | -6.79% | 0.0060⁎⁎
% Change at T2 from T1 (Relapse) | +12.08% | +4.92% | 0.3291
Δ T1-T0 Airway change per mm setback | -0.109 cm²/mm | -0.038 cm²/mm | 0.0075⁎⁎
Δ T2-T1 Airway change (relapse) per mm setback | +0.030 cm²/mm | +0.016 cm²/mm | 0.5822
P-value (Intra-group) |  |  | 
T0 versus T1 | < 0.0001⁎⁎ | 0.0331* | 
T1 versus T2 | 0.1148 | 0.3684 | 

Alterations in mean airway volume

At baseline (T0), mean airway volumes showed no significant intergroup difference (Group 1: 29.87 ± 4.59 cc; Group 2: 31.00 ± 4.54 cc; p > 0.05). Intragroup analyses at T1 revealed substantial volumetric reduction in both groups (p < 0.0001 for Group 1; p = 0.0112 for Group 2).

Intergroup comparison showed that this postoperative decline was significantly more profound in Group 1 (T1: 22.78 ± 4.73 cc vs. 28.10 ± 3.82 cc; p = 0.0004). Group 1 experienced a volume reduction of 22.84%, markedly higher than the 7.96% in Group 2 (p = 0.0046). The discrepancy was even more pronounced when standardised by surgical movement: 1.168 cc/mm of mandibular setback in Group 1 versus 0.458 cc/mm in Group 2 (p = 0.0067).

At T2, a general trajectory of airway recovery was observed. Intragroup evaluation indicated a statistically significant volumetric increase from T1 to T2 within Group 1 (p < 0.05), whereas the corresponding anatomical rebound in Group 2 lacked statistical significance (p > 0.05). Group 1 demonstrated a volumetric recovery (relapse) rate of +15.83% (equivalent to +0.453 cc/mm of setback), exceeding the +4.63% (+0.156 cc/mm of setback) noted in Group 2. Nonetheless, the intergroup variance in the magnitude of this recovery did not reach statistical significance (p > 0.05). Ultimately, at the T2 interval the mean airway volume in Group 2 (29.05 ± 4.11 cc) remained significantly larger and better preserved than that of Group 1 (25.66 ± 4.52 cc).

Alterations in mean cross-sectional area

Mirroring the volumetric trends, baseline (T0) mean cross-sectional areas were comparable between groups (Group 1: 3.08 ± 0.50 cm²; Group 2: 3.10 ± 0.48 cm²).

At T1, both groups showed a significant reduction in airway area (p < 0.0001 for Group 1; p = 0.0331 for Group 2). The cross-sectional area at T1 was significantly larger in Group 2 (2.85 ± 0.40 cm²) than in Group 1 (2.38 ± 0.47 cm²). The proportional area constriction reached 21.45% in Group 1 versus 6.79% in Group 2. Standardised per millimetre of mandibular setback, the decrement was −0.109 cm²/mm in Group 1 and −0.038 cm²/mm in Group 2 (p < 0.05).

At T2, both cohorts exhibited a marginal rebound that did not reach statistical significance. Relative recovery was +12.08% (+0.030 cm²/mm) in Group 1 and +4.92% (+0.016 cm²/mm) in Group 2; the intergroup difference was not significant (p > 0.05). At T2, the mean cross-sectional area in the bimaxillary cohort (2.95 ± 0.42 cm²) remained significantly greater than in the isolated setback cohort (2.59 ± 0.49 cm²; p = 0.0171).