Evaluation of pharyngeal airway volume and soft tissue changes after bimaxillary orthognathic surgery in skeletal class III patients using CBCT: Long-term Study

doi:10.21203/rs.3.rs-4930469/v1

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Evaluation of pharyngeal airway volume and soft tissue changes after bimaxillary orthognathic surgery in skeletal class III patients using CBCT: Long-term Study

https://doi.org/10.21203/rs.3.rs-4930469/v1

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Background

Bimaxillary surgery is increasingly used to correct 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 posterior soft tissues in skeletal Class III patients using Cone Beam Computed Tomography (CBCT).

Methods

In this retrospective descriptive-analytical study, fifty female patients (mean age, 35.17 ± 9.16 years) with mandibular prognathism were treated with LeFort I advancement nad bilateral sagittal split osteotomy. They all had under two score of STOP-BANG questionnaire. CBCT were performed before surgery and 5 years after surgery with standardized head and neck positioning. Airway volume and posterior soft tissue were analyzed using OnDemand 3D software version 10.0.1. Data were analyzed using independent t-tests, Pearson's correlation, and chi-square.

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% and 7.71% (P = 0.000, 0.015), respectively. Although there was a decrease in the oropharyngeal volume and the position of the soft palate, the changes were not statistically significant. The tongue moved backward by undergoing bimaxillary surgery (P = 0.005). No significant differences in STOP-BANG scores were observed.

Conclusions

Although bimaxillary surgery significantly reduces airway volume parameters, it does not elevate the risk of OSA in normal subjects. Our results can aid orthodontists and oral surgeons in selecting the proper surgical method.

Class III malocclusion

Obstructive sleep apnea

pharyngeal airways

Bimaxillary orthognathic surgery

Class III skeletal deformity is the result of mandibular prognathism or maxillary deficiency [1], which causes functional, aesthetic, and occlusal problems. Today, orthognathic surgery is regarded as the best treatment option for patients with moderate to severe class III malocclusion. With advancements in knowledge and techniques, corrective surgery has evolved to include bimaxillary procedures that adjust the positions of facial bony structures, the hyoid bone, and soft tissues such as the tongue, epiglottis, and soft palate [2, 3]. Over the past decade, the frequency of mandibular setback surgery has decreased to less than 10% of Class III patients, while bimaxillary surgery is now performed in about 40% of these cases [4].

Studies have shown that bimaxillary orthognathic surgery causes changes in the pharyngeal airways by causing skeletal and soft tissue changes. An important point is the risk of obstructive sleep apnea syndrome (OSAHS) and obstructive sleep apnea (OSA) following this surgery [5, 6]. 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 [7, 8].

Various radiological modalities have been introduced for the upper airway assessment including 2D and 3D. non-superimposed and non-magnified 3D images are more accurate and reliable than 2D images (Lateral Cephalograms) [9–11]. Since the airway is a region of no attenuation, its boundaries are accurately detected in Cone-Beam Computed Tomography (CBCT). Using a large field of view (FOV) protocol, CBCT offers a comprehensive three-dimensional examination of the upper airway at various sections, making it an essential tool for airway assessment. It also has a lower radiation dose and a shorter scanning time, compared to MDCT [9].

Determining the exact effect of bimaxillary surgery on the airway is crucial for formulating an effective treatment plan, determining the optimal surgical approach, and assessing prognosis protocols. Numerous studies investigated the impact of orthognathic procedures on the pharyngeal airway space in patients with class III abnormality but they are controversial [12–17]. While some studies report an increase [14, 16], others exhibit a decrease [18–20] or maintenance [17, 21–23] of airway volume following a combination of maxillary advancement and mandibular setback surgery. Additionally, the studies predominantly assessed short-term effects; however, the long-term outcomes of surgical procedures should be given significant consideration. This is due to the potential for relapse over the years and factors such as postoperative edema, which initially presents after surgery but resolves over time. Thus, we aimed to evaluate the long-term effects of bimaxillary orthognathic surgery on pharyngeal airway and soft tissue in skeletal Class III patients using CBCT.

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 institution’s policy includes patients’ consent to participate in any trial and approvals of using their data with full clarification of the benefits and risks of any procedure.

This retrospective analytical study included 50 adult patients with class III skeletal malocclusion who underwent bimaxillary orthognathic surgery at the Department of Oral and Maxillofacial Surgery of Isfahan. Both CBCT scans were requested by the clinicians for diagnostic process (and not for research purposes). No additional radiation dose was imposed on any subjects during the process.

The inclusion criteria were as follows

(15)

Dentate female patients over 18 years, confirmed diagnosis of skeletal class III, submitted to bimaxillary advancement surgery with one identical technique (Lefort 1 without impaction and bilateral sagittal split osteotomy (BSSO) with the Obwegeser-Dal Pont method) with one surgical team, no history of previous orthognathic surgery, no respiratory indication with surgery, preoperative and postoperative CBCT scans taken with the same machine and same operator, score under two of STOP-BANG questionnaire.

The exclusion criteria were as follows:

(1) Patients with craniofacial anomalies, important maxillary and mandibular transverse asymmetry, cleft lip, and palate, head and neck lesions, (2) syndromic patients, (3) history of paranasal surgeries, (4) obesity (BMI above 30), and patients younger than 18 years old (due to lack of full development of craniofacial structures), (5) TMJ degenerations, chin augmentation, and evident airway pathology, 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, diseases associated with airway inflammation such as the common cold and influenza, (8) Pregnancy and nursing (9) Rheumatological diseases, (10) Patients using intraoral appliances.

Surgical treatment of all patients was performed by the same surgeon and his team using a single specific method. For all patients, LeFort I advancement osteotomy without impaction combined with bilateral sagittal split osteotomy (BSSO) with the Obwegeser-Dal Pont method was performed to reposition the mandible backward following the fabrication of surgical splints for approximately two weeks. Routine orthodontic treatment was administered to all patients, and efforts were made to select a homogeneous group. The average lengths of orthodontic treatment were 14.6 months (preoperative) and 9.6 months (postoperative). The amount of advancement was planned using Arnett’s soft tissue cephalometric analysis [24]. The maxillary and mandibular displacement range was 4–10 and 5–10 mm, respectively with a mean advancement of 6.5 ± 3.0 and 6.5 ± 2.1. The mean total discrepancy was 7.80 mm.

CBCT scanning:

Each patient underwent two 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]: A preoperative CBCT at the end of presurgical orthodontic treatment and a postoperative CBCT at the follow-up visit, with a mean of 60.7 months after surgery.

The patients' head position was standardized for consistent airway assessment. The scans were taken with the patients upright, the head in a natural position, and the horizontal visual axis, as per Solow and Tallgren [25]. The median plane aligned with the scanner's midface laser, minimizing tilt and rotation via laser lights and bilateral ear rods [26]. The axial plane was adjusted according to the Frankfurt plane. The vomer bone, soft palate, tongue base, and pharynx's anterior wall were considered the pharyngeal airway's anterior limits. Patients were instructed to breathe quietly and not to swallow during the scan. The images were saved in DICOM format and analyzed blindly by an experienced Oral and Maxillofacial Radiologist via OnDemand 3D Application version 10.0.1 (Cybermed, Seoul, Korea) in axial, coronal, and sagittal sections.

The upper airway was defined as three parts: nasopharynx, oropharynx, and hypopharynx and the volume of each part was measured separately. The limits of the airway are described in Table 1 and Fig. 1[27]. The shift in the position of the soft palate was measured using a plane (plane B) parallel to the Frankfurt plane and perpendicular to the midsagittal plane, passing through the soft palate's most posterior part. Similarly, the position of tongue shift was measured using a plane (plane C) parallel to the Frankfurt plane and perpendicular to the midsagittal plane, passing through the most posterior part of the tongue's base.

Table 1

Definitions of boundaries and limits used for airway measurements
Region	limits	Anatomical	Technical
Nasopharynx	Anterior	Frontal plane perpendicular to FH passing through PNS	=
	Posterior	Soft tissue contour of the pharyngeal wall	Frontal plane perpendicular to FH passing through C2sp
	Upper	Soft tissue contour of the pharyngeal wall	Top of the upper airway: Plane parallel to FH passing through the last axial slice before the nasal septum fused with the posterior pharyngeal wall
	Lower	Plane parallel to FH passing through PNS and extended to the posterior wall of the pharynx	=
	Lateral	Soft tissue contour of the pharyngeal wall	Sagittal plane perpendicular to FH passing through the lateral walls of the maxillary sinus
Oropharynx	Anterior	Frontal plane perpendicular to FH passing through PNS	=
	Posterior	Soft tissue contour of the pharyngeal wall	Frontal plane perpendicular to FH passing through C2sp
	Upper	Lower limit of Nasopharynx	=
	Lower	Plane parallel to FH plane passing through C3ai	=
	Lateral	Soft tissue contour of the pharyngeal wall	Sagittal plane perpendicular to FH passing through the lateral walls of the maxillary sinus
Hypopharynx	Anterior	Frontal plane perpendicular to FH passing through PNS	=
	Posterior	Soft tissue contour of the pharyngeal wall	Frontal plane perpendicular to FH passing through C2sp
	Upper	Lower limit of Oropharynx	=
	Lower	Plane parallel to FH connecting the base of the epiglottis to the entrance to the esophagus	Plane parallel to FH connecting the base of the epiglottis to C4ai
	Lateral	Soft tissue contour of the pharyngeal wall	Sagittal plane perpendicular to FH passing through the lateral walls of the maxillary sinus
Upper airway	Anterior	Frontal plane perpendicular to FH passing through PNS	=
	Posterior	Soft tissue contour of the pharyngeal wall	Frontal plane perpendicular to FH passing through C2sp
	Upper	Soft tissue contour of the pharyngeal wall	Top of the upper airway: Plane parallel to FH passing through the last axial slice before the nasal septum fused with the posterior pharyngeal wall
	Lower	Plane parallel to FH connecting the base of the epiglottis to the entrance to the esophagus	Plane parallel to FH connecting the base of the epiglottis to C4ai
	Lateral	Soft tissue contour of the pharyngeal wall	Sagittal plane perpendicular to FH passing through the lateral walls of the maxillary sinus
FH, Frankfurt Horizontal; C2sp, Cervical 2 superior posterior; C4ai, Cervical anterior inferior.

[insert Table1]

A total of 600 measurements were conducted, including evaluations of the volume (V)of the nasopharynx, oropharynx and hypopharynx, and total airway as well as soft palate (SP) and tongue position (Fig. 2,3). The subjects were asked to fill out the STOP-Bang questionnaire in the follow-up.

Statistical analysis:

The data were analyzed by independent t, paired t-test, Mann-Whitney, and Kruskal-Wallis in SPSS software version 27 (SPSS Inc., IL, USA), and the p-value = 0.05 was considered the significance level.

Intra‑operator Reliability:

Measures for the first and second replicates of 20 patients were recorded and intraclass correlation coefficient (ICC) was established for all measurements. A high level of reliability was observed with ICC values exceeding 0.88–0.96.

Demographics:

Fifty female patients with a mean age of 35.17 ± 9.16 years at the time of the surgery (range 18–65 years) were evaluated. No significant differences in STOP-BANG scores were observed. Table 2 indicates the mean ± SD values of participants with the surgical procedure.

Table 2

Variable changes with performing the surgical procedure
Variable	Stage	Mean	SD	P-value
V-Nasopharynx	before	6010.7	2466.2	0.015
V-Nasopharynx	after	6856.3	2799.0	0.015
V-Oropharynx	before	5158.9	2910.3	0.828
V-Oropharynx	after	4664.3	1791.7	0.828
V-Hypopharynx	before	9760.2	6017.9	0.000
V-Hypopharynx	after	7795.3	3940.1	0.000
V-Upper airway	before	20930.0	9375.8	0.015
V-Upper airway	after	19316.0	6134.2	0.015
Soft palate	before	10.1	2.7	0.277
Soft palate	after	9.6	2.0	0.277
Tongue	before	12.9	5.3	0.005
Tongue	after	11.7	3.8	0.005
Statistically significant at p < 0.05. V: volume.

[insert Table 2]

Our results showed a statistically significant 14.06% increase in the V-nasopharynx (volume of nasopharynx) following bimaxillary surgery (P = 0.015). A statistically significant decrease of 20.13% in the V-hypopharynx (P = 0.000), 7.71% in V-UA (volume of upper airway) (P = 0.015), and 9.30% in the position of the tongue (P = 0.005) was observed. Although there was a decrease in the V-oropharynx and the position of the soft palate (SP) by undergoing the surgical procedure, the changes were not statistically significant, with p-values of 0.828 and 0.277, respectively.

Bimaxillary surgery is increasingly used to correct Class III malocclusion, but concerns about potential airway narrowing and its role in obstructive sleep apnea (OSA) remain. Understanding its impact on the upper airway is essential for clinicians to develop effective treatment plans. This study aimed to evaluate the long-term effects of bimaxillary surgery on the upper airway and posterior soft tissues in skeletal Class III patients using CBCT.

CBCT is the gold standard for angular and linear measurements [28, 29], providing orthodontists and oral surgeons with precise 2D and 3D analysis [30]. Studies show that the soft palate, epiglottis, and esophagus entrance move posteriorly when shifting from upright to supine, reducing oropharyngeal airway volume [31]. To account for this, we assessed parameters in the upright posture. Additionally, we meticulously replicated the specific positioning method described to eliminate postural variation and maintain consistency across scans. Despite the growing number of 3D studies evaluating the airways, the significant variability in chosen airway delimitation landmarks complicates comparisons [12, 27]. To address this, hard tissue landmarks were utilized to define airway boundaries, offering a more precise and consistent form compared to the variable nature of soft tissue landmarks such as the palate and epiglottis, which can change post-surgery. Only women were selected because sex differences in pharyngeal airway changes were evident [21, 32].

The literature about the effects of bimaxillary orthognathic surgery on OSA is still controversial [12–17]. In the present study, by bimaxillary surgery with a mean maxillary advancement and a mandibular setback of 6.5 mm the following statistically significant changes were observed over a 5-year follow-up period: a 14.06% increase in nasopharyngeal volume and decreases of 20.13% and 7.71% in hypopharyngeal and upper airway volumes, respectively. Similar to the results of our study, Kim et al. [15] reported a decrease in the pharyngeal airway volume up to 6 months after bimaxillary surgery. Cakarne et al. [33] found a significant increase in nasopharyngeal airway space after bimaxillary surgery (8 months follow-up), which is in line with our findings. Moreover, recent research on bimaxillary orthognathic surgery with 6–24 months follow-ups has reported a significant linear increase in nasopharyngeal and oropharyngeal volumes, while the hypopharyngeal volume either decreased or showed no change [14, 21, 34, 35]. Samman et al. [36] found statistically significant decreases in oropharyngeal and hypopharyngeal dimensions at a 6-month follow-up. These findings are consistent with our results regarding the nasopharynx and hypopharynx but contradict our findings in the oropharyngeal region which showed no statistically significant difference in the V-oropharynx. Chen et al. [21] indicated an increase at the nasopharyngeal levels and decrease at the oropharyngeal and hypopharyngeal levels only in the short term, with no significant change in the long term (2 years follow-up). Khaghaninejad reported that the airway dimensions were significantly lower than the pretreatment values in subjects who underwent double jaw surgery in a 6-month follow up. This discrepancy in the results can be attributed to different sample sizes, unequal gender distribution and different surgical techniques. Also, different airway limits and the level of classification of these three parts of the pharyngeal airway in different studies can be regarded as factors contributing to these differences [12, 27]. Considering all these, confounding factors were minimized in the study by evaluating one gender with a specific method of surgery and a determined measure of maxillary advancement and mandibular setback.

No significant differences were observed between the groups in terms of STOP-BANG scores. Hence, despite the statistically significant reduction in pharyngeal airway parameters, all patients remained at low risk for OSAHS in the long-term following bimaxillary surgery.

In the immediate postoperative period, a reduction in airway space may occur due to edema, obscuring the actual changes achieved during surgery [37]. Additionally, the potential for surgical relapse must be considered. The posterior soft tissue, which undergoes positional changes as a result of the surgery, may gradually shift and influence the airway over time [13]. Therefore, it is essential to evaluate the long-term effects of bimaxillary surgery on the airway to accurately assess the outcomes, independent of the transient effects of edema or soft tissue relapse.

Studies state that the soft palate morphology changes after bimaxillary surgery, and it causes a decrease in the pharyngeal airway as it is moved backward [32, 38]. It can be due to the fact that the base of the tongue moves backward when the mandible moves backward. This tongue repositioning causes the palatoglossus to be at a lower angle. The results of the present study are consistent with those findings, as the position of the tongue decreased significantly meaning that it moved backward in the long term by undergoing bimaxillary surgery.

The present study has some limitations. First, the small sample size was a result of the strict eligibility criteria. Second, the scarcity of similar studies focusing on long-term effects limited the availability of comparative data. Conducting longitudinal studies with larger sample sizes would be beneficial to elucidate the impact of these surgical-orthodontic treatments on airway and soft tissue. Investigating the long-term changes with other orthognathic surgeries is recommended.

Bimaxillary surgery, involving a mean maxillary advancement and mandibular setback of 6.5 mm, resulted in a statistically significant increase in nasopharyngeal volume and reductions in hypopharyngeal and upper airway volumes over a 5-year follow-up period. Additionally, the base of the tongue moved posteriorly. Although bimaxillary surgery significantly reduces airway volume parameters, it does not elevate the risk of OSA in normal subjects. Our results can aid orthodontists and oral surgeons in selecting the proper surgical method.

Ethics approval and consent to participant: This 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).

Consent for publication: Not applicable

Availability of data and materials: The data that support the findings of this study are available from the corresponding author upon reasonable request.

Competing interests: The authors have no relevant financial or non-financial interest

Funding: The authors declare that no funds, grants, or other support were received during the preparation of this manuscript interests to disclose.

Authors’ contributions: A.T. and R.G. implemented the study idea. S.Z.H. Provided CBCT data. H.M. provided statistical analysis. S.MA. drafted the main manuscript. S.SA. revised the manuscript. All authors read and approved the final manuscript.

Acknowledgments: Not applicable

Statements and Declarations: The authors also confirmed that the manuscript is original and does not contain any unlawful statements and any material, the publication of which would violate any copyright or other personal or proprietary right of any person or entity. They also confirm that they have written permission from copyright owners if their work has been used in this manuscript. The authors declare that the following manuscript has not been published elsewhere (in any format or language) and has not been concomitantly sent to another journal for publication consideration. The authors agree that they are responsible for paying any fees for permissions.

*This manuscript does not contain any studies with human or animal subjects performed by the any of the authors.

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No competing interests reported.

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Evaluation of pharyngeal airway volume and soft tissue changes after bimaxillary orthognathic surgery in skeletal class III patients using CBCT: Long-term Study

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Abstract

Background

Methods

Results

Conclusions

Figures

Background

Methods

The exclusion criteria were as follows:

CBCT scanning:

Statistical analysis:

Results

Intra‑operator Reliability:

Demographics:

Discussion

Conclusion

Declarations

References

Additional Declarations

Status:

Version 1