Correlation between hyoid bone position and airway dimensions in Chinese adolescents by cone beam computed tomography analysis

Abstract

This study aimed to investigate the correlation between upper airway dimensions and hyoid bone position in Chinese adolescents based on cone beam computed tomography (CBCT) images. CBCT images from a total of 254 study subjects were included. The upper airway and hyoid bone parameters were measured by Materialism’s interactive medical image control system (MIMICS) v.16.01 (Materialise, Leuven, Belgium). The airway dimensions were evaluated in terms of volume, cross-sectional area (CSA), mean CSA, length, anteroposterior dimension of the cross-section (AP), lateral dimension of the cross-section (LAT), and LAT/AP ratio. The hyoid bone position was evaluated using eight linear parameters and two angular parameters. Facial characteristics were evaluated using three linear parameters and three angular parameters. Most hyoid bone position parameters (especially the distance between the hyoid bone and hard palate) were significantly associated with most airway dimension parameters. Significant correlations were also observed between the different facial characteristic parameters and hyoid bone position parameters. Most airway dimension parameters showed significant correlations with linear facial parameters, but they displayed significant correlations with only a few angular facial parameters. These findings provide an understanding of the static relationship between the hyoid bone position and airway dimensions, which may serve as a reference for surgeons before orthodontic or orthognathic surgery.

The upper airway is a tube-shaped structure that plays an important role in respiration and deglutition. Anatomical anomalies of the upper airway, such as micrognathia, retrognathia, hyperdivergent growth patterns, reduced cranial base length, and steep mandibular plane angles, may lead to a narrow airway space, small volume, and even obstructive sleep apnoea. The hyoid bone is the only bone that is not articulated to any other bone in the body, and is connected to the pharynx, mandible, and cranium through muscles and ligaments; this is necessary for talking, chewing, swallowing, and airway patency.

Orthognathic surgery, as performed nowadays, can alter the pharyngeal airway dimension, and this is an interesting topic for orthodontists. Mandibular setback surgery can narrow the airway and cause a significant posterior movement of the hyoid bone. Mandibular advancement surgery can increase the airway space volume and thus significantly widen the narrower sites. Certain functional orthopaedic treatments have also been shown to change the pharyngeal airway dimensions and hyoid bone position in teenagers. However, other functional orthopaedic treatments such as rapid maxillary expansion and modified bionator treatment are believed to have no influence on the pharyngeal airway and hyoid bone position. Furthermore, the hyoid bone will move posteriorly and the airway dimension will become smaller or narrower in the case of the mandibular bone being moved backwards. Therefore, the correlations between airway dimensions and hyoid bone position should be considered carefully during orthodontic diagnosis and treatment. However, an analysis of the correlation between upper airway dimensions and the hyoid bone position in teenagers with normal maxillofacial characteristics has not yet been reported.

Cephalometric analysis has been used previously to study the correlations between airway and hyoid bone positions. However, lateral cephalograms only display the sagittal plane, while related information on axial width, cross-sectional area, and volume are missing when assessing the morphology of the upper airway. Cone beam computed tomography (CBCT) provides a reliable and accurate method to analyze the airway dimensions, soft tissue, and surrounding airway space. As reported previously, the CBCT scan obtained before orthodontic diagnosis and treatment can help in gaining a clear clinical judgement of the upper airway space and hyoid bone position in patients. Therefore, CBCT is a standard method adopted in otolaryngology for early diagnosis and evaluation, and assessment of the upper airway by CBCT has become a necessary step before orthodontic or orthognathic surgery. However, CBCT scans have rarely been used to investigate the relationships between the upper airway and hyoid bone position in healthy teenagers.

In this study, the correlations between upper airway dimensions and hyoid bone position were investigated in Chinese adolescents based on CBCT images, with the goal of highlighting the need to pay greater attention to the adverse effects of orthodontic or orthognathic treatments, and also to provide more references for appropriate treatment planning.

Materials and methods

Subjects

CBCT images were obtained from the CBCT image library of the Stomatology Hospital of Shandong University. Only images of patients of Han Chinese ethnicity, aged 6–18 years, taken between December 2010 and December 2012, were included. Strict inclusion criteria were applied while examining the medical history and CBCT images of the study subjects.

With regard to the CBCT images, only those for subjects meeting the following criteria were included: (1) clinically symmetric; (2) class I molar relationship, normal overjet and overbite; (3) no discrepancy in centric relation/centric occlusion; (4) no history of previous orthodontic treatment; (5) reasonably aligned upper and lower incisors without severe crowding; (6) no missing permanent teeth; (7) acceptable oral hygiene without obvious periodontal disease. CBCT images in which the airway structure was not seen clearly or was not complete were excluded, as well as airways containing artefacts.

In terms of the medical history, the selection criteria included no history of any craniofacial surgery or anomaly, no congenital anomalies (such as cleft lip and palate), no dysfunction of the masticatory system, no respiratory pathology or pharyngeal pathology (such as adenoid hypertrophy, tonsillitis and adenoidectomy, or history of tonsillectomy), no history of breathing problems, and no mouth breathing habit, complaint of airway restriction, nasal obstruction, snoring, or obstructive sleep apnoea. This study was approved by the necessary research ethics committee. Finally, 254 CBCT images from 119 males and 135 females were included in this study.

CBCT process

For CBCT scanning, each patient was seated in an upright position and asked to keep their jaws in maximum intercuspation, with the lips and tongue in a resting position. The Frankfort horizontal plane (FH plane) of the patients was kept parallel to the floor. Patients were instructed to breathe normally through the nose, avoiding swallowing and moving their head or tongue during the scanning process. All of the images were acquired using a Galileos CBCT scanner (Sirona, Bensheim, Germany) at 85 kV, 7 mA, and 14 s per rotation (resolution accuracy <0.15 mm). CBCT images were then saved as DICOM (digital imaging and communications in medicine) files.

Segmentation and measurement

The DICOM files were imported into Materialism’s interactive medical image control system (MIMICS) (v.16.01; Materialise, Leuven, Belgium) to visualize the images in the axial, coronal, and sagittal planes by volume-rendering.

Once the DICOM files were imported, the three-dimensional (3D) reconstruction of the patient’s head was oriented so that the FH plane was parallel to the axial plane and the midsagittal plane was oriented to the subject’s midline. The patient’s midsagittal plane was defined as a vertical plane passing through both the anterior nasal spine (ANS) and the posterior midpoint of the spine (centrum) ( Fig. 1 A) . Thirteen landmarks were labelled in the midsagittal view: sella (S), nasion (N), basion (Ba), deepest anterior point in the concavity of the upper labial alveolar process (A), deepest anterior point in the concavity of the lower labial alveolar process (B), menton (Me), anterior nasal spine (ANS), posterior nasal spine (PNS), the tip of uvula (UT), the base of epiglottis (EB), the highest point of hyoid bone (H), the most antero-inferior point on the corpus of the third cervical vertebra (C3), and the roof of the nasopharynx (Roof) ( Fig. 1 B). The hyoid bone position was evaluated using eight linear parameters C3–Me, C3–H, H–EB, H–PNS, H–Me, H–X, H–Y, and H–(C3–Me), as well as two angular parameters, H–S–Ba and H–N–S. Facial characteristics were evaluated using three linear parameters N–Me, N–ANS, and ANS–Me, as well as three angular parameters SNA, SNB, and ANB ( Fig. 1 C).

Fig. 1
(A) Midsagittal orientation (in the axial plane) defined by the anterior midpoint between the centre of the anterior nasal spine (ANS) and the posterior midpoint of the centrum of the cervical vertebrae (centrum). (B) Thirteen landmarks were identified in the midsagittal view: S, sella; N, nasion; Ba, basion; A, deepest anterior point in the concavity of the upper labial alveolar process; B, deepest anterior point in the concavity of the lower labial alveolar process; Me, menton; ANS, anterior nasal spine; PNS, posterior nasal spine; UT, the tip of the uvula; EB, the base of the epiglottis; H, the highest point of the hyoid bone; C3, the most inferior and anterior point on the corpus of the third cervical vertebra; Roof, roof of nasopharynx. (C) Definitions of the measurement parameters in the midsagittal view. Parameters of hyoid bone position: (1) H–EB; (2) H–Me; (3) C3–H; (4) C3–Me; (5) H–(C3–Me) (H to C3–Me line); (6) H–PNS; (7) H–X (perpendicular distance from the hyoid bone to the vertical line passing through point S); (8) H–Y (perpendicular distance from H to the horizontal line passing through S); (9) H–N–S (angle formed by H–N line and N–S line); (10) H–S–Ba (angle formed by H–S line and S–Ba line). Facial characteristic parameters: (I) N–ANS; (II) ANS–Me; (III) N–Me; (IV) SNA; (V) SNB; (VI) ANB.

To isolate the desired airway from the CBCT images, the threshold value was set to a range of −1024 to −300 Hounsfield units (HU). The layers of the airway structures were defined and colour-coded based on the minimum and maximum threshold values. Finally, the upper airway in the midsagittal plane was divided into six planes, including plane 1: the horizontal plane passing through Roof (superior border); plane 2: the vertical plane passing through PNS (anterior border); EB plane (inferior border); PNS plane: the boundary of nasopharynx (NP) and oropharynx (OP); UT plane: the boundary of palatopharynx (PP) and glossopharynx (GP); H plane: the highest point was selected as the marker point for the hyoid bone, which varied with EB ( Fig. 2 A, B ). The lateral and posterior boundaries consisted of the pharyngeal walls and the anterior boundary, the anterior wall of the pharynx, the base of the tongue, and the soft palate. Meanwhile, corresponding 3D models were also reconstructed ( Fig. 2 A′, B′, A″, B″).

Fig. 2
Airway segmentation and reference planes. Reference planes were viewed in the midsagittal plane (A, B) and 3D model (A′, B′, A‴, B″). Plane 1: the axial plane passing through the Roof point. Plane 2: the coronal plane passing through the PNS point. PNS plane: the axial plane passing through the PNS point. UT plane: the axial plane passing through the UT point. EB plane: the axial plane passing through the EB point. H plane: the axial plane passing through the H point. NP, nasopharynx; OP, oropharynx; PP, palatopharynx; GP, glossopharynx; Hyp, the top part of the hypopharynx.

The airway dimensions were evaluated in terms of multiple parameters, including volume (VOL), length (L), cross-sectional area (CSA, the ratio of VOL/L), mean CSA, anteroposterior dimension of the cross-section (AP), lateral dimension of the cross-section (LAT), and LAT/AP ( Table 1 , Fig. 3 ).

Table 1
Definitions of airway dimension parameters.
Description Parameter Symbol Unit Definition
Volume VOL VOL1 cm 3 Volume of NP
VOL2 Volume of PP
VOL3 Volume of GP
VOL4 Volume of Hyp
VOL5 Volume of OP
VOL6 Volume of total airway
Mean cross-sectional area Mean CSA Mean CSA1 mm 2 Mean CSA of NP
Mean CSA2 Mean CSA of PP
Mean CSA3 Mean CSA of GP
Mean CSA4 Mean CSA of Hyp
Mean CSA5 Mean CSA of OP
Mean CSA6 Mean CSA of total airway
Length L L1 mm Length of NP
L2 Length of PP
L3 Length of GP
L4 Length of Hyp
L5 Length of OP
L6 Length of total airway
Cross-sectional area CSA CSA I mm 2 CSA of the airway in PNS plane
CSA II CSA of the airway in UT plane
CSA III CSA of the airway in EB plane
CSA IV CSA of the airway in H plane
Anteroposterior dimension of the cross-sections AP AP I mm AP of the airway in PNS plane
AP II AP of the airway in UT plane
AP III AP of the airway in EB plane
AP IV AP of the airway in H plane
Lateral dimension of the cross-sections LAT LAT I mm LAT of the airway in PNS plane
LAT II LAT of the airway in UT plane
LAT III LAT of the airway in EB plane
LAT IV LAT of the airway in H plane
Shape of the cross-sectional area LAT/AP LAT I/AP I LAT/AP in PNS plane
LAT II/AP II LAT/AP in UT plane
LAT III/AP III LAT/AP in EB plane
LAT IV/AP IV LAT/AP in H plane

NP, nasopharynx; PP, palatopharynx; GP, glossopharynx; Hyp, hypopharynx; OP, oropharynx; CSA, cross-sectional area; PNS, posterior nasal spine; UT, the tip of uvula; EB, the base of epiglottis; H, the highest point of hyoid bone; AP, anteroposterior.

Fig. 3
Axial slice images of the pharyngeal airway in four defined planes: (A) PNS plane; (B) UT plane; (C) EB plane; (D) H plane. AP, anteroposterior width; LAT, lateral width.

Statistical analysis

All of the parameters were measured twice by the same investigator. Among the 254 CBCT images from the study subjects, 20 were selected randomly to assess the intra-examiner concordance by intra-class correlation test (ICC) before the correlation analysis. The average value for each parameter from the two measurement times was used for Pearson correlation analysis to detect the correlation between hyoid bone position and airway dimensions. A P -value of <0.05 was considered to be statistically significant. All analyses were performed using SPSS version 13.0 software (SPSS Inc., Chicago, IL, USA).

Results

Assessment of intra-examiner concordance

According to the ICC test, the concordance index was greater than 0.98, indicating high intra-examiner concordance.

Correlations between airway dimensions and hyoid bone position

The length, width, area, and volume were positively correlated with C3–Me, H–Y, H–(C3–Me), C3–H, H–Me, and H–PNS, while they were negatively correlated with H–EB and H–S–Ba. Additionally, H–X and H–EB were negatively correlated with the volume, mean CSA, CSA, LAT, and AP. Of note, H–PNS had a significantly higher correlation with most of the airway dimension parameters ( Table 2 ).

Table 2
Correlations between airway dimensions and hyoid bone position ( N = 254).
Measurements C3–Me H–X H–Y H–(C3–Me) C3–H H–EB H–PNS H–Me H–S–Ba H–N–S
L1 0.182 ** −0.069 0.414 ** 0.187 ** 0.169 ** −0.112 0.317 ** 0.118 −0.132 0.213 **
L2 0.296 ** 0.298 ** 0.519 ** 0.333 ** 0.187 ** −0.054 0.635 ** 0.217 ** −0.177 ** 0.047
L3 0.295 ** 0.015 0.759 ** 0.502 ** 0.232 ** −0.208 ** 0.808 ** 0.239 ** −0.286 ** 0.261 **
L4 −0.142 * 0.048 −0.112 0.092 0.008 0.332 ** −0.125 * −0.210 ** 0.135 * 0.078
L5 0.355 ** 0.159 * 0.807 ** 0.525 ** 0.260 ** −0.179 ** 0.899 ** 0.275 ** −0.294 ** 0.218 **
L6 0.359 ** 0.109 0.812 ** 0.501 ** 0.274 ** −0.188 ** 0.858 ** 0.271 ** −0.291 ** 0.252 **
VOL1 0.256 ** −0.169 ** 0.434 ** 0.132 * 0.206 ** −0.171 ** 0.344 ** 0.254 ** 0.006 0.124 *
VOL2 0.560 ** −0.082 0.528 ** 0.261 ** 0.366 ** −0.258 ** 0.591 ** 0.508 ** −0.101 0.005
VOL3 0.568 ** −0.197 ** 0.530 ** 0.301 ** 0.371 ** −0.389 ** 0.594 ** 0.525 ** −0.312 ** 0.014
VOL4 −0.149 * 0.055 −0.129 * 0.058 −0.033 0.236 ** −0.129 * −0.193 ** 0.123 * 0.055
VOL5 0.588 ** −0.152 * 0.545 ** 0.282 ** 0.378 ** −0.352 ** 0.613 ** 0.544 ** −0.227 ** 0.004
VOL6 0.542 ** −0.172 ** 0.560 ** 0.259 ** 0.357 ** −0.331 ** 0.587 ** 0.507 ** −0.179 ** 0.038
Mean CSA1 0.230 ** −0.172 ** 0.324 ** 0.042 0.184 ** −0.185 ** 0.274 ** 0.278 ** 0.062 0.028
Mean CSA2 0.539 ** −0.209 ** 0.433 ** 0.178 ** 0.348 ** −0.286 ** 0.454 ** 0.516 ** −0.055 −0.018
Mean CSA3 0.587 ** −0.257 ** 0.366 ** 0.161 * 0.356 ** −0.404 ** 0.412 ** 0.566 ** −0.273 ** −0.087
Mean CSA4 0.376 ** −0.236 ** 0.309 ** 0.095 0.233 ** −0.290 ** 0.343 ** 0.377 ** −0.285 ** −0.085
Mean CSA5 0.589 ** −0.240 ** 0.389 ** 0.152 * 0.357 ** −0.366 ** 0.427 ** 0.570 ** −0.177 ** −0.070
Mean CSA6 0.536 ** −0.255 ** 0.393 ** 0.118 0.336 ** −0.342 ** 0.399 ** 0.535 ** −0.122 −0.047
CSA I 0.368 ** −0.096 0.401 ** 0.091 0.277 ** −0.190 ** 0.380 ** 0.356 ** 0.007 0.017
CSA II 0.569 ** −0.332 ** 0.307 ** 0.082 0.340 ** −0.276 ** 0.319 ** 0.562 ** −0.137 * −0.072
CSA III 0.534 ** −0.324 ** 0.486 ** 0.207 ** 0.376 ** −0.367 ** 0.522 ** 0.466 ** −0.319 ** −0.034
CSA IV 0.527 ** −0.312 ** 0.434 ** 0.190 ** 0.364 ** −0.369 ** 0.471 ** 0.472 ** −0.331 ** −0.046
LAT I 0.390 ** −0.092 0.445 ** 0.128 * 0.263 ** −0.241 ** 0.463 ** 0.352 ** −0.162 * 0.010
AP I 0.428 ** −0.009 0.358 ** 0.062 0.318 ** −0.169 ** 0.402 ** 0.384 ** −0.036 −0.065
LAT II 0.570 ** −0.206 ** 0.492 ** 0.217 ** 0.312 ** −0.324 ** 0.531 ** 0.535 ** −0.205 ** −0.024
AP II 0.654 ** −0.306 ** 0.203 ** 0.025 0.424 ** −0.273 ** 0.240 ** 0.647 ** −0.162 * −0.150 *
LAT III 0.356 ** −0.171 ** 0.585 ** 0.319 ** 0.211 ** −0.278 ** 0.623 ** 0.329 ** −0.260 ** 0.085
AP III 0.637 ** −0.266 ** 0.318 ** 0.055 0.414 ** −0.288 ** 0.362 ** 0.551 ** −0.253 ** −0.125 *
LAT IV 0.345 ** −0.212 ** 0.538 ** 0.292 ** 0.211 ** −0.221 ** 0.553 ** 0.319 ** −0.262 ** 0.035
AP IV 0.516 ** −0.209 ** 0.230 ** 0.039 0.307 ** −0.316 ** 0.288 ** 0.479 ** −0.184 ** −0.112
LAT I/AP I −0.120 −0.056 0.031 0.064 −0.124 * −0.078 −0.008 −0.105 −0.179 ** 0.114
LAT II/AP II −0.035 0.076 0.377 ** 0.245 ** −0.064 −0.088 0.381 ** −0.074 −0.069 0.149 *
LAT III/AP III −0.447 ** 0.186 ** 0.028 0.141 * −0.307 ** 0.139 * 0.004 −0.382 ** 0.115 0.188 **
LAT IV/AP IV −0.313 ** 0.103 0.110 0.129 * −0.188 ** 0.162 * 0.047 −0.274 ** 0.020 0.162 *
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Jan 16, 2018 | Posted by in Oral and Maxillofacial Surgery | Comments Off on Correlation between hyoid bone position and airway dimensions in Chinese adolescents by cone beam computed tomography analysis
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