Discussion

The primary objective of this study was to quantitatively compare alterations in upper airway dimensions (volume and cross-sectional area) following isolated mandibular setback versus bimaxillary surgery managed under the SFA protocol. Both modalities precipitated a significant constriction in airway volume and area immediately postoperatively (T1); however, the magnitude was markedly greater in the single-jaw cohort. At the 1-year follow-up (T2), although the isolated setback group showed greater anatomical recovery (relapse), overall airway dimensions were ultimately better preserved by the bimaxillary intervention.

The proportional recovery of airway dimensions at the one-year postoperative mark (T2) in our cohort occurred at a higher rate than has been reported for COA cohorts. These findings may be interpreted within the specific biomechanical context of the SFA, which differs from the COA. In COA, presurgical orthodontic decompensation facilitates a stable postoperative occlusion and limits the magnitude of the required surgical setback.4,26 Conversely, SFA bypasses presurgical orthodontic decompensation; it frequently requires larger surgical setbacks and complex rotational movements to achieve an interim transitional occlusion (ITO). This ITO, combined with the regional acceleratory phenomenon (RAP), contributes to accelerated skeletal remodelling and subsequent neuromuscular adaptation.1,4,27 Consequently, SFA patients exhibit distinct patterns of airway rebound and skeletal relapse compared with those undergoing COA. Kongsong et al. (2025) corroborated this by demonstrating that SFA patients typically undergo more extensive mandibular retropositioning and rotation than COA patients, leading to distinct physiological differences in airway rebound: SFA leads to postoperative elongation of the mCSA of 0.034 cc/mm of setback, whereas COA presents 0.016 cc/mm at the one-year mark.15 Consistent with a previous CBCT-based study (Hussain et al., 2025), isolated single-jaw surgery decreases both total pharyngeal volume and minimum cross-sectional area, whereas bimaxillary surgery mitigates this decrease.7,15,18 This is attributed to the posterior repositioning of the mandible, which retrodisplaces the tongue base and hyoid bone into the pharyngeal space. Conversely, the maxillary advancement in bimaxillary surgery translates the soft palate and pharyngeal musculature anteriorly, generating compensatory tension that counteracts the soft-tissue compression induced by the mandibular setback.28, 29, 30

The initial postoperative trend of airway constriction in both cohorts aligns with global findings; however, the quantitative magnitude differs from studies relying on 2D lateral cephalometry, such as Kori et al. (2022),6 Sahoo et al. (2020),7 and Thapa et al. (2023),17 because 2D cephalometry is limited by anatomical superimposition.31 Tsolakis et al. (2016) demonstrated a remarkably strong correlation between AP and CBCT pharyngeal measurements, with a discrepancy of less than 4% in mCSA and approximately 758 mm³ in pharyngeal volume—clinically insignificant.22 Similarly, D'Urzo et al. reported that mCSA measured by acoustic reflection and CT exhibited a very low discrepancy (<4.3%) with an excellent correlation coefficient (r = 0.92).21 Although CBCT and MRI remain reference modalities for high-resolution 3D anatomical mapping, they provide only a static representation of a dynamic physiological structure; cumulative radiation exposure and cost restrict their use for repeated short-interval monitoring.4 AP offers a dynamic, radiation-free, cost-effective alternative for assessing airway collapsibility; its derived mCSA is an established predictor of OSA severity and demonstrates high test-retest reliability (intra-class correlation r > 0.77).4,20,22

In terms of airway evaluation modalities, although acoustic pharyngometry (AP) is utilized for its non-invasive capabilities, it cannot provide direct anatomical mapping or localize specific soft-tissue impingements. It cannot precisely pinpoint whether airway narrowing is caused by specific soft-tissue factors (e.g., enlarged tonsils, altered tongue posture, hyoid bone displacement) or by neuromuscular compensation.4,20 Therefore, it is important to acknowledge the emerging role of Magnetic Resonance Imaging (MRI), particularly dynamic MRI. Unlike AP, which provides a one-dimensional acoustic reflection profile of the cross-sectional area and volume, dynamic MRI allows for a comprehensive, real-time, three-dimensional visualization of soft-tissue dynamics during the respiratory cycle.7 Recent literature highlights the superiority of dynamic MRI in assessing precise anatomical adaptations, such as tongue deformation patterns and pharyngeal wall collapsibility, thereby identifying specific anatomic risk factors for sleep-disordered breathing without exposing the patient to ionizing radiation .7,20 However, the routine clinical application of dynamic MRI for post-orthognathic follow-up is currently hindered by its high cost, time-consuming nature, limited accessibility, and potential patient intolerance to the supine position due to claustrophobia. AP, therefore, remains a highly practical and reliable alternative for longitudinal volumetric screening in the outpatient orthognathic setting. Future studies integrating the dynamic functional information provided by MRI, the high-resolution three-dimensional anatomical detail offered by CBCT (which is more affordable and remains indispensable for precise presurgical planning and postoperative assessment), and the accessibility of AP to provide a more comprehensive understanding of post-surgical airway adaptations.

Regarding the correlation between morphology and function, the observed physical constriction of the airway space does not necessarily translate into the onset of obstructive sleep apnea syndrome (OSAS).15 Ronchi et al. (2023) concluded that there is no direct causal relationship between mandibular setback surgery (particularly with displacements < 8 mm) and the genesis of OSAS, provided the patient does not possess underlying risk factors such as obesity (high BMI).32 Parameters such as the Apnea–Hypopnea Index (AHI) and Oxygen Desaturation Index (ODI) may exhibit transient elevations during the first postoperative month secondary to soft-tissue oedema, but generally improve and normalise after 6 months. This divergence between morphological parameters (dimensional narrowing) and physiological function (absence of OSAS) is rationalised by the adaptive capacity of the pharyngeal neuromuscular system, which increases resting muscle tone to maintain airway patency during sleep.33, 34, 35

By standardising volumetric airway decrement per millimetre of setback, this study provides a metric with comparable clinical predictive value across surgical interventions. For skeletal Class III patients presenting with a preoperatively narrow airway or requiring substantial mandibular retropositioning under the SFA, bimaxillary surgery represents a safer surgical indication, proactively maintaining airway volume and preventing structural alterations from exceeding the patient's physiological compensatory threshold.

Although AP does not provide intuitive three-dimensional anatomical visualisation equivalent to CBCT, it is anticipated that future prospective studies strictly isolating variables specific to the SFA protocol—such as completion of postoperative orthodontic treatment at T2, and postoperative changes in BMI and skeletal stability—and integrating 3D imaging (CBCT/MRI) with functional polysomnographic metrics over long-term follow-up will establish a more comprehensive assessment of both the static anatomical characteristics and the dynamic functional behaviour of the upper airway in skeletal Class III patients and other dentofacial deformities undergoing SFA orthognathic surgery.