Introduction
Bimaxillary surgery is increasingly used for Class III malocclusion, but concerns about potential airway narrowing and its role in obstructive sleep apnea (OSA) remain. This study aimed to evaluate the long-term effects of bimaxillary surgery on the upper airway and soft tissues and the risk of OSA development in patients with skeletal Class III malocclusion using cone-beam computed tomography (CBCT) and the STOP-BANG (snoring, tiredness, observed apnea, high blood pressure, body mass index, age, neck circumference, and gender) questionnaire.
Methods
In this retrospective descriptive-analytical study, 50 female patients with Class III malocclusion were treated with LeFort I advancement and bilateral sagittal split osteotomy. They all scored 0-2 on the STOP-BANG questionnaire. CBCTs were performed preoperatively and 5 years postoperatively with standardized head and neck positioning. They filled out the questionnaire in the follow-up. Confounding factors were minimized as much as possible. CBCTs were evaluated using OnDemand 3D software (version 10.0.1; Cybermed, Seoul, South Korea). Data were analyzed using an independent-samples t test, Pearson correlation, and chi-square test.
Results
In the long-term, bimaxillary surgery statistically significantly increased the nasopharyngeal volume by 14.06% ( P = 0.015) and decreased hypopharyngeal and upper airway volumes by 20.13% ( P <0.001) and 7.71% ( P = 0.015), respectively. Although there was a decrease in the oropharynx and the position of the soft palate, the changes were not statistically significant. The tongue moved backward ( P = 0.005). No significant differences in STOP-BANG scores were observed ( P >0.05).
Conclusions
Although bimaxillary surgery with the studied method significantly alters airway volume parameters, it may not increase the risk of OSA in healthy individuals. Our results can aid orthodontists and surgeons in selecting the proper treatment plans.
Graphical abstract
Highlights
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5-year follow-up: surgery increased nasopharyngeal volume, reduced others.
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Hypopharyngeal and total airway volumes significantly decreased.
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Airway changes did not increase long-term OSA risk.
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Oropharyngeal volume and soft palate position decreased, not significant.
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Findings support evidence-based surgical-orthodontic planning.
Class III skeletal deformity, caused by mandibular prognathism or maxillary deficiency, leads to functional, esthetic, and occlusal issues. Orthognathic surgery is one of the best treatments for moderate to severe Class III malocclusion. Over the past decade, the frequency of mandibular setback (MS) surgery has decreased to less than 10% of patients with Class III malocclusion, whereas bimaxillary orthognathic surgery (BOS) is now performed in approximately 40% of these cases. BOS causes changes in the pharyngeal airway space (PAS) by causing skeletal and soft tissue changes, and an important consideration is the risk of obstructive sleep apnea (OSA) after this surgery. OSA is a common sleep disorder characterized by frequent collapse of the airway at different planes, which can lead to snoring, hypertension, stroke, myocardial infarction, and even death.
Nonsuperimposed and nonmagnified 3-dimensional (3D) images are more accurate and reliable than 2-dimensional images for upper airway (UA) assessment. , As the airway is a region of no attenuation, its boundaries are accurately detected in cone-beam computed tomography (CBCT). CBCT provides a comprehensive 3D assessment of the UA while offering lower radiation and shorter scan times compared with multidetector computed tomography. ,
The STOP-BANG questionnaire is a validated screening tool for OSA, which was first developed in 2008. Because of its simplicity, ease of use, and high sensitivity, it has been widely used in preoperative clinics, sleep clinics, and the surgical population to detect the risk of OSA among patients.
Determining the exact effect of BOS on the airway is crucial for an effective orthodontic treatment plan and optimal surgical approach. However, the impact of orthognathic procedures on the PAS in patients with Class III malocclusion remains debated. ,, Although some studies report an increase, , others exhibit a decrease , or maintenance ,, of PAS after a combination of maxillary advancement (MA) and MS surgeries. In addition, the studies predominantly assessed short-term effects ,, ; however, the long-term outcomes of surgical procedures should be given significant consideration because of the potential for relapse over time and postoperative edema, which initially obscure changes in PAS but become apparent later as the edema subsides. Thus, we aimed to evaluate the long-term effects of BOS on PAS and soft tissues and the risk of OSA development in patients with skeletal Class III malocclusion using CBCT and the STOP-BANG (snoring, tiredness, observed apnea, high blood pressure, body mass index, age, neck circumference, and gender) questionnaire.
Material and methods
This retrospective descriptive-analytical study was performed in line with the principles of the Declaration of Helsinki. The study protocol was approved by the ethics committee of the university (IR.KHUISF.REC.1401.106).
The study included 50 adult patients with skeletal Class III malocclusion who underwent BOS at the Department of Oral and Maxillofacial Surgery, School of Dentistry, Azad University of Isfahan (Khorasgan), Isfahan, Iran. Both CBCT scans were requested by the clinicians for diagnostic purposes (and not for research purposes). No additional radiation dose was imposed on any patients during the process.
The inclusion criteria were as follows , : (1) dentate female patients aged 18-55 years; (2) confirmed diagnosis of skeletal Class III (angle formed by the sella, nasion, and A point [SNA] ≤78.0; angle formed by the sella, nasion, and B point [SNB] ≥82.0; angle formed by the A point, nasion, and B point [ANB] ≤0; maxillary hypoplasia and mandibular prognathism); (3) submitted to BOS with 1 identical technique (Lefort I osteotomy and bilateral sagittal split osteotomy [BSSO] with the Obwegeser-Dal Pont method with 1 surgical team); (4) no history of previous orthognathic surgery; (5) no tooth extraction during orthodontic treatment; (6) no respiratory indication with surgery; (7) preoperative and postoperative CBCT scans taken with the same machine and same operator; and (8) STOP-BANG questionnaire scores ≤2.
The exclusion criteria were as follows ,, : (1) patients with craniofacial anomalies, maxillary and mandibular transverse asymmetry, cleft lip and palate, and head and neck lesions; (2) patients with syndromes; (3) history of paranasal surgeries; (4) obesity (body mass index >24.9 kg/m 2); (5) temporomandibular joint degenerations, chin augmentation, evident airway pathology, and mandibular transverse asymmetry; (6) serious life-threatening diseases, such as chronic obstructive pulmonary disease, symptomatic ischemic heart disease, congestive heart failure, cerebrovascular accident, chronic renal failure, and hypothyroidism; (7) history of asthma or sinusitis and diseases associated with airway inflammation, such as the common cold and influenza; (8) pregnancy and nursing; and (9) rheumatological diseases.
Surgical treatment of all patients was performed by the same surgeon and team using a single specific method. All patients underwent LeFort I advancement osteotomy with impaction and BSSO with the Obwegeser-Dal Pont method after approximately 2 weeks of surgical splint fabrication. Routine orthodontic treatment was administered, and efforts were made to select a homogeneous group. The amount of advancement was planned using the mean anterior advancement at the anterior nasal spine and the mean posterior mandibular movement at the pogonion. Orthodontic and surgical details are summarized in Table I .
Table I
Descriptive statistics of orthodontic and surgical procedures
| Gender | Mean age, y | Surgical technique | MA | MS | Maxillary impaction | Surgical Splint | Preoperative orthodontic treatment | Postoperative orthodontic treatment |
|---|---|---|---|---|---|---|---|---|
| Female | 35.17 ± 9.16 | LeFort I advancement + BSSO | 4.5 ± 0.5 mm | 6.5 ± 0.9 mm | 2.1 ± 0.3 mm | 2 wk | 14.6 mo | 9.6 mo |
Each patient underwent 2 CBCT scans by the same operator, using the same CBCT scanner (NewTom VGi, Verona, Italy) and consistent exposure settings, including a 300-μm voxel size, 15 × 15 field of view, variable tube current (mA), and 110 kVp. CBCT images were acquired at the end of presurgical orthodontic treatment (preoperative) and during the follow-up visit, at a mean of 60.7 months after surgery (postoperative).
For standardized airway assessment, CBCT scans were acquired with patients in an upright position and the head in natural head posture, with the horizontal visual axis aligned according to Solow and Tallgren. The median plane aligned with the scanner’s midface laser, minimizing tilt and rotation via laser lights and bilateral ear rods. The axial plane was adjusted according to the Frankfurt horizontal plane. Before scanning, patients were instructed to swallow to clear the oral cavity and pharynx and then lightly close their mouths with the maxillary and mandibular teeth in contact. All examinations were obtained at the end of expiration, without swallowing and in centric occlusion to minimize variability in mandibular and soft tissue measurements. The lips were in a resting position, and the tongue was positioned against the palate. ,
The images were saved in the Digital Imaging and Communications in Medicine format and analyzed blindly by an experienced oral and maxillofacial radiologist (S.M.A.) via OnDemand 3D Application (version 10.0.1; Cybermed, Seoul, South Korea). CBCT data were evaluated in axial, coronal, and sagittal planes, and the voxels were isotropic. The UA was defined as 3 parts, as described in Table II and Figure 1 , A – D , and the volume of each part was measured separately. The shifts in the positions of the soft palate (SP) and tongue were measured using a plane parallel to the Frankfurt horizontal plane and perpendicular to the midsagittal plane, passing through the most posterior part of the SP ( Fig 2 , A ) and the tongue base ( Fig 2 , B ), respectively.
Table II
Definitions of boundaries and limits used for UA measurements
| Region | Limits | Anatomic | Technical |
|---|---|---|---|
| Nasopharynx | Anterior | Frontal plane perpendicular to the FH plane, passing through PNS | Same as anatomic |
| Posterior | Soft tissue contour of the pharyngeal wall | Frontal plane perpendicular to the FH plane, passing through C2sp | |
| Upper | Soft tissue contour of the pharyngeal wall | Top of the UA: a plane parallel to the FH plane, passing through the last axial slice before the nasal septum fused with the posterior pharyngeal wall | |
| Lower | A plane parallel to the FH plane, passing through PNS and extended to the posterior wall of the pharynx | Same as anatomic | |
| Lateral | Soft tissue contour of the pharyngeal wall | The sagittal plane perpendicular to the FH plane, passing through the lateral walls of the maxillary sinus | |
| Oropharynx | Anterior | Frontal plane perpendicular to the FH plane, passing through PNS | Same as anatomic |
| Posterior | Soft tissue contour of the pharyngeal wall | Frontal plane perpendicular to the FH plane, passing through C2sp | |
| Upper | Lower limit of the nasopharynx | Same as anatomic | |
| Lower | A plane parallel to the FH plane, passing through C3ai | Same as anatomic | |
| Lateral | Soft tissue contour of the pharyngeal wall | The sagittal plane perpendicular to the FH plane, passing through the lateral walls of the maxillary sinus | |
| Hypopharynx | Anterior | Frontal plane perpendicular to the FH plane, passing through PNS | Same as anatomic |
| Posterior | Soft tissue contour of the pharyngeal wall | Frontal plane perpendicular to the FH plane, passing through C2sp | |
| Upper | Lower limit of the oropharynx | Same as anatomic | |
| Lower | A plane parallel to the FH plane, connecting the base of the epiglottis to the entrance to the esophagus | A plane parallel to the FH plane, connecting the base of the epiglottis to C4ai | |
| Lateral | Soft tissue contour of the pharyngeal wall | The sagittal plane perpendicular to the FH plane, passing through the lateral walls of the maxillary sinus | |
| UA | Anterior | Frontal plane perpendicular to the FH plane, passing through PNS | Same as anatomic |
| Posterior | Soft tissue contour of the pharyngeal wall | Frontal plane perpendicular to the FH plane, passing through C2sp | |
| Upper | Soft tissue contour of the pharyngeal wall | Top of the UA: a plane parallel to the FH plane, passing through the last axial slice before the nasal septum fused with the posterior pharyngeal wall | |
| Lower | A plane parallel to the FH plane, connecting the base of the epiglottis to the entrance to the esophagus | A plane parallel to the FH plane, connecting the base of the epiglottis to C4ai | |
| Lateral | Soft tissue contour of the pharyngeal wall | The sagittal plane perpendicular to the FH plane, passing through the lateral walls of the maxillary sinus |
FH , Frankfort horizontal; PNS , posterior nasal spine; C2sp , the superior-posterior extremity of the odontoid process of C2; C3ai , the most anterior-inferior point of the body of the third cervical vertebra; C4ai , the most anterior-inferior point of the body of the fourth cervical vertebra.
Sagittal view showing the landmarks used to define the UA boundaries for measurement: A, Posterior nasal spine (PNS); B, The most anterior-inferior point of the body of third cervical vertebra (C3ai); C, The most anterior-inferior point of the body of fourth cervical vertebra (C4ai), marking the inferior boundary of the UA; D, 3D volumetric reconstruction of the UA in sagittal and coronal views, using OnDemand 3D software (version 10.0.1; Cybermed, Seoul, South Korea). PNS , posterior nasal spine; C3ai , the most anterior-inferior point of the body of the third cervical vertebra; C4ai , the most anterior-inferior point of the body of the fourth cervical vertebra.
Midsagittal CBCT view showing the measurements of the soft tissues: A, SP; B, Tongue.
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