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Table of Contents
ORIGINAL ARTICLE
Year : 2022  |  Volume : 71  |  Issue : 1  |  Page : 54-60

Evaluation of pharyngeal airway by cone-beam computed tomography after mono- and bimaxillary orthognathic surgery


1 Department of Oral and Maxillofacial Surgery, Tokat Gaziosmanpasa University Faculty of Dentistry, Tokat, Turkey
2 Department of Oral and Maxillofacial Radiology, Faculty of Dentistry, Bolu Abant Izzet Baysal University, Bolu, Turkey
3 Department of Biostatistics, Tokat Gaziosmanpasa University Faculty of Dentistry, Tokat, Turkey

Date of Submission16-Sep-2020
Date of Acceptance31-Oct-2021
Date of Web Publication17-Mar-2022

Correspondence Address:
Dr. Merve Sari
Department of Oral and Maxillofacial Surgery, Tokat Gaziosmanpasa University Faculty of Dentistry, Tokat
Turkey
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jasi.jasi_189_20

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  Abstract 


Introduction: The aim of this study was to evaluate the changes of the pharyngeal airway obtained using mono-and bimaxillary orthognathic surgery in patients with skeletal malocclusion. Material and Methods: The analysis was conducted on cone-beam computed tomography images taken preoperatively and postoperatively of patients undergoing mono-or bimaxillary orthognathic surgery. The pharyngeal airway was divided into four airway volume segments and measured by planimetry. Results: The bimaxillary surgery group showed an increase in nasopharynx and velopharynx volumes and a decrease in glossopharynx and hypopharynx volumes (P < 0.05). The mandibular setback surgery group showed decreases in glossopharynx, hypopharynx, oropharynx, and pharynx volumes (P < 0.05). The mandibular advancement surgery group showed increases in glossopharynx, hypopharynx, oropharynx, and pharynx volumes (P < 0.05). The maxillary advancement surgery group showed increases in nasopharynx, velopharynx, and pharynx volumes (P < 0.05). Discussion and Conclusion: Mandibular setback surgery had a narrowing effect on the pharyngeal airway volume. Maxillary advancement surgery compensated for the constrictive effect of mandibular setback surgery on both the oropharynx and pharynx volumes. Although maxillary and mandibular advancement surgery affected different sites, these were the operations that contributed most to the increase in pharyngeal volume.

Keywords: Cone-beam computed tomography, orthognathic surgery, pharyngeal airway


How to cite this article:
Sari M, Sen E, Akbulut N, Bayrak S, Demir O. Evaluation of pharyngeal airway by cone-beam computed tomography after mono- and bimaxillary orthognathic surgery. J Anat Soc India 2022;71:54-60

How to cite this URL:
Sari M, Sen E, Akbulut N, Bayrak S, Demir O. Evaluation of pharyngeal airway by cone-beam computed tomography after mono- and bimaxillary orthognathic surgery. J Anat Soc India [serial online] 2022 [cited 2022 Jul 3];71:54-60. Available from: https://www.jasi.org.in/text.asp?2022/71/1/54/339876




  Introduction Top


Orthognathic surgery and orthodontics are applied together with the overall aim of correcting dentofacial deformities through both functional and aesthetic changes.[1] Orthognathic surgery provides the ideal dental occlusion and facial esthetics to bring the patients to their desired position both socially and psychologically. Skeletal movements in orthognathic surgery can also cause changes in the pharyngeal airway space by pushing or stretching the soft tissues while changing the positions of the jaw and soft tissues to the required maxillomandibular relationship and esthetics.[2],[3]

In the last 20 years, the pharyngeal airway has been a prominent issue in orthognathic surgery operations.[4],[5],[6],[7],[8],[9] The maxilla and mandible are directly or indirectly connected to the tongue, soft palate, hyoid bone, and many muscles. Therefore, movement in these bones leads to spatial changes in bone-associated structures, while causing tension in the associated soft tissues and muscles. As a result, skeletal movement will result in changes in the nasal and oral cavity and airway volumes.[4],[5],[6],[7],[8],[9] The main cause of concern is the fact that the pharyngeal airway space may narrow after orthognathic surgery, impeding airway during breathing. Orthognathic surgery involves skeletal movements in different directions, so the effects of these operations on the pharyngeal airway will also differ.[10] The aim of this study was to evaluate the effects of mono-or bimaxillary orthognathic surgery operations on the pharyngeal airway using cone-beam computed tomography (CBCT) images in patients with skeletal class II (maxillary hyperplasia and/or mandibular hypoplasia) or class III (maxillary hypoplasia and/or mandibular hyperplasia) and associated malocclusions. This information was also used to inform patients before surgery and to ensure necessary precautions before the operation when risk factors (e.g., septum deviation and obesity) were present that could cause airway narrowing in the patient.


  Material and Methods Top


This study was approved by Tokat Gaziosmanpaşa University Faculty of Medicine Clinical Research Ethics Committee and conformed to the Declaration of Helsinki (approval no: 18-KAEK-100). This retrospective study included images of 42 patients (This retrospective study included images of 42 patients (15 males; 27 females) who had skeletal class II (maxillary hyperplasia and/or mandibular hypoplasia) or class III (maxillary hypoplasia and/or mandibular hyperplasia) with associated malocclusions treated with mono-or bimaxillary orthognathic surgery at Tokat Gaziosmanpaşa University, Faculty of Dentistry, Department of Oral and Maxillofacial Surgery, during the period of 2015-2019. Patients without syndromes, who had skeletal class II (maxillary hyperplasia and/or mandibular hypoplasia) or class III (maxillary hypoplasia and/or mandibular hyperplasia) with associated malocclusions treated with mono-or bimaxillary orthognathic surgery, who had preoperative and postoperative CBCT records were included to the study. Patients with syndromes or craniofacial abnormalities (e.g., cleft lip and palate), who had previously undergone orthognathic or orthodontic treatment, or who had undergone genioplasty or rhinoplasty operations were excluded from the study. All patients provided written informed consent. The sex and age of the patients were recorded.

The patients were divided into the following four different groups according to the orthognathic surgical treatment method:

  • Group 1: Patients with maxillary advancement + mandibular setback
  • Group 2: Patients with mandibular setback alone
  • Group 3: Patients with mandibular advancement alone
  • Group 4: Patients with maxillary advancement alone.


All operations were performed by the same surgical team. Bilateral sagittal split ramus osteotomy and/or Le fort I osteotomy were performed in all patients who underwent mono-or bimaxillary orthognathic surgery. Both jaws were subjected to rigid internal fixation.

Cephalometric films were obtained for all patients 2 weeks before the surgery (T0) and 6 months after the surgery (T1). Cephalometric films were evaluated using a modified analysis method.[11] In this method, the plane with an angle of + 7° to the Sella-Nasion line is the horizontal reference plane, and the strut lowered to this plane from the Nasion point was used as a vertical reference plane. The distances of the hard and soft tissue landmarks to these 2 planes were measured on cephalometric films taken before and 6 months after the operation and the difference between them was recorded as the amount of hard tissue movement.

CBCT images were obtained for all patients to evaluate the three-dimensional changes in the pharyngeal airway 2 weeks before the surgery (T0) and 6 months after the surgery (T1). The CBCT images were obtained with a Galileos device under conditions of 98 kVp, 15–30 mA, 15 mm × 15 mm imaging area, 0.25 mm3 voxel size, 2–5 s irradiation, and 14 s scanning time. While the images were being obtained, the patient was adjusted in a standing position so that the Frankfurt horizontal plane was parallel to the floor and the sagittal plane was perpendicular to the floor. Preoperative (T0) and postoperative 6th month (T1) images were obtained with the same devices for each patient.

The Cavalieri Principle was applied to calculate the airway volume on the CBCT images. DICOM files of these images were transferred to the 3D-DOCTOR (3D-DOCTOR Able Software Corp., Lexington, USA) image analysis program. Measurements were performed on sagittal sections. The image was divided into 0.3 mm sequential sections. No gap was left between the sections. Airway volume measurements were performed in four sections: Nasopharynx, velopharynx, glossopharynx, and hypopharynx.

Planes drawn from the following anatomical points were used when separating these sections[12] [Figure 1]:
Figure 1: The pharyngeal airway volume was divided into four sections: (a) Nasopharynx; (b) Velopharynx; (c) Glossopharynx; (d) Hypopharynx

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  1. Nasopharynx: The region between the top of the upper airway and the hard palate plane (the plane between anterior nasal spine and posterior nasal spine). The line passing between posterior nasal spine and ala of vomer is its anterior border
  2. Velopharynx: The region between the hard palate plane and the tip of the uvula
  3. Glossopharynx: The region between the tip of the uvula and the upper part of the epiglottis
  4. Hypopharynx: The region between the upper end and lower end of the epiglottis.


The oropharynx volume was obtained as the total of the velopharynx and glossopharynx volumes. The pharynx volume was obtained as the total of the nasopharynx, velopharynx, glossopharynx, and hypopharynx volumes. Thus, six-volume parameters were created from four airway volume segments.

The volume was calculated with the current program by determining the surface area of the related region on each section using a planimetry method. The boundaries of the related area on each section were manually drawn using a computer mouse [Figure 2]. Upon completion of the drawing, the program automatically multiplied the total surface area by the section thickness and calculated the total volume in mm3. This procedure was performed for the nasopharynx, velopharynx, glossopharynx, and hypopharynx on pre- and postoperative images for all patients. The preoperative and postoperative images of each patient were measured twice by the same maxillofacial radiologist and their mean values were calculated.
Figure 2: The 3D image of pharyngeal airway volume

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Statistical analysis

Student's t-test and one-way ANOVA were used when comparing the means of quantitative variables between groups. A paired samples test was used for dependent groups. P < 0.05 was considered statistically significant. Ready Statistics software was used for the calculations (IBM SPSS Statistics 19, SPSS inc., an IBM Co., Somers, NY).


  Results Top


In total, images of 42 treated patients were included in the study. The included patients were aged 15–34 years and had a mean age of 21.29 ± 4.45 years. The sex and age distributions of the subjects according to orthognathic surgical treatment method are shown in [Table 1]. No statistically significant difference was noted between the groups in terms of age (P > 0.05). Amounts of surgical movement in orthognathic surgical treatment groups are summarized in [Table 2]. No statistically significant difference was evident between the groups in terms of the extent of surgical movement (P > 0.05).
Table 1: The sex and age distributions of the subjects according to orthognathic surgical treatment method

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Table 2: Amounts of surgical movement in orthognathic surgical treatment groups

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The volumetric changes in the pharyngeal airway volume segments are summarized in [Table 3]. In the bimaxillary group, the nasopharynx and velopharynx volumes increased and the glossopharynx and hypopharynx volumes decreased (P < 0.05). In the mandibular setback group, the glossopharynx, hypopharynx, oropharynx, and pharynx volumes all decreased (P < 0.05). In the mandibular advancement group, the glossopharynx, hypopharynx, oropharynx, and pharynx volumes all increased (P < 0.05). In the maxillary advancement group, the nasopharynx, velopharynx, and pharynx volumes increased (P < 0.05).
Table 3: The volumetric changes in the pharyngeal airway volume segments

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  Discussion Top


Orthognathic surgery is widely applied for the correction of dentofacial deformities as well as for aesthetic improvement.[13] The effects of these operations on airway dimensions have been the subject of research for the past 30 years. In particular, studies focusing on mandibular setback operations have reported narrowing of the airway area.[7],[14],[15] Orthognathic surgery may cause changes in the surrounding structures and pharyngeal airway space by pulling forward or pushing backward the soft tissues as the positions of the jaws are altered to achieve the required maxillomandibular aesthetic and functional relationships.[2],[3],[16] A positional change in the maxilla affects the nasopharyngeal space, the posterior part of the nose, and the superior part of the soft palate. A change in the mandible position may affect hard and soft tissues in the oral and maxillofacial regions, including the upper respiratory tract.[13]

In the present study, the airway volume was evaluated at four levels - the nasopharynx, velopharynx, glossopharynx, and hypopharynx - and six-volume parameters were established. The volume measurements of the pharyngeal airway were the measurements used in airway determination referenced in the study by Chen et al.[12] As in the study of Tepecik et al.,[16] the authors used reference points on soft tissue instead of vertebral reference points when separating airway segments. This was because the use of vertebral points for reference points does not provide an exact match of the boundaries of the velopharyngeal and glossopharyngeal regions that are most responsible for obstructive sleep apnea (OSA).[16] In addition, the vertebral lengths, upper or lower limits, and the locations do not correspond to the same site in each patient, so different regions are compared as a result. Therefore, the velopharyngeal and glossopharyngeal regions are more appropriately measured using points determined from the anatomical structures that form the boundaries or are adjacent to these structures.[16]

The literature shows two main trends regarding the changes in the pharyngeal airway as a result of bimaxillary surgery, but one trend is that the pharyngeal airway decreases[10],[17],[18] and then in the second trend, the oropharyngeal airway remains unchanged.[15],[19],[20],[21],[22] In the present study, the authors noted a significant decrease in pharyngeal volume in the mandibular setback group but no significant change in the bimaxillary group. Uesugi et al.[22] reported a reduction in the pharyngeal airway volume in the monomaxillary group of 40 class III patients undergoing mono-and bimaxillary surgery, whereas the change in the bimaxillary group was not significant. Park et al.[21] reported no significant decrease in pharyngeal airway space after mandibular setback surgery and found no physiological adaptation to maintain airway capacity in the pharyngeal airway. Some studies have suggested that bimaxillary surgery compensates for the pharyngeal airway narrowing caused by mandibular setback surgery.[9],[21] This probably reflects a balancing of the airway contraction after mandibular setback with the forward movement of the velopharyngeal muscular system due to maxillary advancement.[23]

In the present study, a significant increase was observed in the pharynx volume in the mandibular advancement and maxillary advancement groups. Hernández-Alfaro et al.[24] evaluated the effect of mono-and bimaxillary advancement on the pharyngeal airway with CBCT. They reported an average increase in pharyngeal airway volume of 69.8% in the bimaxillary advancement group, 78.3% in the mandibular advancement group, and 37.7% in the maxillary advancement group. In that study, a greater effect on the pharyngeal airway volume was suggested for mandibular advancement than for maxillary advancement.[24] Achilleos et al.[5] and Alves et al.[25] also reported an increased pharyngeal airway volume after mandibular advancement.

The nasopharyngeal airway was not included in previous assessments of the effect of only mandibular operations on airway sizes, as it was considered to be unaffected by movement of the mandible.[7],[8],[15],[26] Present study revealed no significant change in the nasopharynx volume in the mandibular setback and advancement groups, which included only surgery on the mandible. A few studies have evaluated the changes in the nasopharynx after mandibular setback surgery but reported no significant change.[14],[21]

In the present study, the authors observed a significant increase in the nasopharynx volume in the bimaxillary and maxillary advancement groups. Progression of the maxilla and subsequent forward movement of the soft palate has been previously reported to increase the volume of the nasopharynx.[27] In most studies, although the nasopharynx volume tends to increase, no significant changes have been reported after bimaxillary surgery.[16],[18],[21],[22] Li et al.[18] reported an increase in the nasopharyngeal volume from 6.07 cm3 to 6.10 cm3 at 6 months after bimaxillary surgery. However, despite the forward movement of the maxilla, the volume of the nasopharynx remained almost the same, in contradiction to present findings.[18] Li et al.[18] reported a mean forward motion of the maxilla of 3.5 ± 0.8 mm, whereas the authors found a mean movement of 5.33 ± 1.3 mm. This difference in findings may reflect the amount of forward movement of the maxilla and increase in the airway. Becker et al.[23] reported an increase in nasopharynx volume after bimaxillary surgery.

Many studies have reported that mandibular setback surgery decreases the pharyngeal airway space.[9],[20],[22],[23] A posteroinferior displacement of the hyoid bone, which moves the tongue in a similar direction, is observed after mandibular setback surgery.[4],[13],[26] An increase in the angle of contact between the posteriorly displaced tongue and the soft palate may narrow the glossopharyngeal area, thereby decreasing the volume of the oropharynx.[4],[26] Enacar et al.[4] emphasized a need for careful monitoring of the decrease in the oropharyngeal airway space after mandibular setback. Several studies have shown a decrease in the size of glossopharyngeal and hypopharyngeal airways after mandibular setback surgery.[2],[6],[9],[13] In the present study, the decrease in the glossopharynx, oropharynx, and hypopharynx volumes in the mandibular setback group was statistically significant, but no significant change was evident in the velopharynx volume. The glossopharynx and hypopharynx probably undergo narrowing due to the contraction of the hyoglossus and consequent retroposition of the tongue corpus. Yang et al.[28] reported a decrease in the velopharynx, glossopharynx, oropharynx, and hypopharynx volumes after mandibular setback. In that study, a velopharyngeal constriction was reported as a result of soft palate lengthening and elevation caused by posterior movement of the tongue when the mandible was moved backward. Similar to the present study, other studies also have reported a decrease in oropharynx and hypopharynx volumes after mandibular setback surgery during short and long follow-up periods.[21],[26]

In the present study, in the maxillary advancement group, the velopharynx and oropharynx volumes increased, but only the increase in the velopharynx volume was statistically significant. An increase in these regions is expected due to the anterior movement of the supporting structures. The increase in velopharynx volume and decrease in glossopharynx and hypopharynx volumes were significant in the bimaxillary group, whereas the change in oropharynx volume was not significant. Hatab et al.[3] and Tepecik et al.[16] reported no change in velopharyngeal airway volume after bimaxillary surgery. However, other studies have reported significant constriction of the velopharyngeal airway volume after surgery.[10],[21] Some studies report no change in the glossopharyngeal volume after bimaxillary surgery[3],[16],[21] while others report a significant decrease.[10] In the present study, the absence of any significant change in the oropharynx volume in the bimaxillary group was consistent with the findings of some studies,[22] although Tepecik et al.,[16] Li et al.,[18] and Lee et al.[20] reported a decrease in the volume of oropharynx after bimaxillary surgery. By contrast, Jakobsone et al.[19] reported a significant increase in oropharynx and hypopharynx volumes after bimaxillary surgery. In the present study, the authors observed that maxillary advancement in the bimaxillary group increased the velopharynx volume, while mandibular setback decreased the glossopharynx volume, to produce a balancing effect on oropharynx volume obtained by summing velopharynx and glossopharynx volumes. This indicates that maxillary advancement decreases the constructive effect of a mandibular setback on the oropharynx volume.

In the present study, the bimaxillary group showed a significant increase in velopharynx volume compared to the mandibular setback group. In their meta-analysis, Christovam et al.[29] reported a decrease in velopharyngeal and glossopharyngeal airway volumes after mandibular setback surgery, whereas the velopharyngeal airway volume decreased and glossopharyngeal airway volume increased after bimaxillary surgery. This appears contradictory and is exactly the opposite of the expected result. Brunetto et al.[17] suggested that surgeries in which both jaws move in the same direction tend to have more predictable results. In addition, when the base of the tongue moves backward, the soft palate may be pushed in the same direction, resulting in a decrease in the velopharyngeal volume.[17] In addition, the decrease in the hypopharynx volume in the mandibular setback and bimaxillary groups is expected, due to the posteroinferior movement of the hyoid bone in response to the posterior movement of the mandible. Becker et al.[23] reported a decrease in the volume of the hypopharynx after bimaxillary surgery.

A significant increase was detected in the glossopharynx, oropharynx, and hypopharynx volumes in the mandibular advancement group. Mandibular advancement has been previously reported to increase the glossopharyngeal airway volume.[29] Jiang et al.[30] and Sahoo et al.[31] reported a significant increase in the oropharyngeal and hypopharyngeal airway space as a result of mandibular advancement.


  Conclusion Top


Mandibular setback had a constrictive effect on the pharyngeal airway volume. Therefore, extensive surgical movements should be avoided in the presence of a mandibular setback indications, unless airway dimension is greater than normal prior to surgery. Although maxillary advancement and mandibular advancement affect different sites, they are operations that contribute to increased pharyngeal volume. Therefore, these surgeries should be the first choice, especially in patients at risk for OSA. Maxillary advancement compensated for the constrictive effect of mandibular setback on both the oropharynx and pharynx volumes, even if bimaxillary operations included mandibular setback surgery. If the patient has predisposing factors for the development of OSA, such as obesity, macroglossia, short neck, and large uvula, then bimaxillary surgery should be preferred over mandibular setback, or, if possible, only maxillary advancement should be performed.

However, this study had some limitations. The number of samples was not homogeneous, and the postoperative period could not be evaluated for longer than 6 months. Sample sizes for mandibular setback, mandibular advancement, and maxillary advancement groups are too small to make conclusive evidence of airway changes. Therefore, future studies should be conducted on larger and more homogenous patient groups for longer periods and should include a minimum of three axial area parameters. However, to the best of our knowledge, this study is the first to use Cavalieri Principle to calculate the volume of pharyngeal airway.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest



 
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