Evaluation of pharyngeal airway space amongst different skeletal patterns

Abstract

The aim of the present study was to evaluate the dimensions of the pharyngeal airway space (PAS) in awake, upright children with different anteroposterior skeletal patterns using cone beam computed tomography (CBCT). The volume, area, minimum axial area and seven linear measurements of PAS were obtained from the CBCT images of 50 children (mean age 9.16 years). The patients were divided in two groups according to the ANB angle (group I 2° ≤ ANB ≤ 5°; group II ANB > 5°). Means and standard deviations of each variable were compared and correlated using independent t -test and Pearson’s correlation test. There were statistically significant differences in the following parameters: angle formed by the intersection between NA and NB lines ( p < 0.001), angle formed by the intersection between SN and NB lines ( p < 0.05), Minimal pharyngeal airway space between the uvula and the posterior pharyngeal wall ( p < 0.05), airway volume ( p < 0.01), airway area ( p < 0.01) and minimum axial area ( p < 0.05). The anteroposterior cephalometric variable SNB had positive correlation with the variables PAS-UP ( p < 0.01), Minimal pharyngeal airway space between the uvula tip and the posterior pharyngeal wall ( p < 0.05), Pharyngeal airway space on mandibular line ( p < 0.05), Minimal pharyngeal airway space between the back of the tongue and the posterior pharyngeal wall ( p < 0.05), volume airway ( p < 0.05), airway area ( p < 0.05) and minimum axial area ( p < 0.05). The vertical cephalometric variables angle formed by the intersection between SN and GoGn lines ( p < 0.05) and angle formed by the intersection between FH and mandible plane ( p < 0.05) showed negative correlation with PAS-UT. These results showed that PAS was statistically larger in group I than group II, indicating that the dimensions of the PAS are affected by different anteroposterior skeletal patterns.

Since Angle showed that Class II Division 1 malocclusion is associated with obstruction of the pharyngeal airway space (PAS) and mouth-breathing subjects, several studies have evaluated the upper airway in patients with different skeletal patterns.

Much attention has been paid to the relationship between respiratory function and facial morphology. Some articles have analysed the dimensions of the upper airway in patients with different sagittal and vertical skeletal facial morphologies using lateral cephalograms. Class II patients have a narrower anteroposterior pharyngeal dimension, and this narrowing is specifically noted in the nasopharynx area at the hard palate level and in the oropharynx at the level of the tip of the soft palate and the mandible.

Upper airway dimensions have been considered contributing factors to obstructive sleep apnoea (OSA). Nongrowing patients with such condition have been treated with continuous positive airway pressure (CPAP), soft-tissue surgery, removable oral appliances directed at mandibular protrusion or orthognathic surgical advancement of the mandible. This aspect is very important, especially in growing patients with skeletal discrepancies and clinical signs of adenoid faces. Early diagnosis, evidence-based explanations of aetiology, and assessment of the functional factors might be vital for the restoration of the normal craniofacial growth and the stability of the treatment results.

Traditionally, the PAS has been evaluated using cephalometric radiographs, but this method results in superimposition of all bilateral structures of the craniofacial complex and only provides a two-dimensional (2D) anteroposterior linear dimension. With the advent of cone beam computed tomography (CBCT), airway evaluation became more accurate and reliable, generating more comprehensive information than the 2D radiographs. Their compact size and relatively low radiation dosage makes CBCT scanning an imaging modality that helps address the previous challenges effectively and efficiently. The resulting volume of digital data can be manipulated and allows the production of three-dimensional (3D) images that can be rotated in the three axes, selectively contrasted, emphasized, and reduced to visualize certain anatomical structures, such as the airway.

The aim of the present study was to evaluate the PAS dimensions in awake, upright children with different anteroposterior skeletal patterns using CBCT.

Material and methods

From the records of an oral radiology clinic in Rio de Janeiro, Brazil, 50 healthy Brazilian Caucasian children with a mean age of 9.16 ± 0.64 years (range 8–10 years) who had CBCT scans of the head for orthodontic records were selected from a group of 68 children for this study. This study was revised and approved by the Institute of Collective Health Studies Research Ethics Committee of Rio de Janeiro Federal University. The parents were questioned about their children’s medical history to exclude any children with obvious hyperplasia of tonsils and adenoids, tonsillectomy or adenoidectomy and those with OSA. Eighteen patients with symptoms of upper respiratory infection, pharyngeal pathology or a history of adenoidectomy or tonsillectomy were excluded.

The patients were divided into two groups according to their ANB angles: 25 (14 boys, 11 girls) with ANB angles ranging from 2° to 5° were allocated to group I, and 25 (13 boys, 12 girls) who had ANB angles greater than 5° were allocated to group II ( Fig. 1 ).

Fig. 1
Facial morphology reflecting the underlying anteroposterior skeletal pattern. (A) Group I, with ANB angles ranged from 2° to 5°. (B) Group II, with ANB greater than 5°.

All CBCT scans were taken with the same cone beam machine (i-CAT, Imaging Sciences International, Hatfield, PA, USA), according to a standard protocol (120 kV, 5 mA, 13 cm × 17 cm FOV, 0.4 mm voxel and scan time of 20 s) used for orthodontic records by the oral radiology clinic.

Data were imported in DICOM (Digital Imaging and Communications in Medicine) format and handled by Dolphin Imaging ® software, version 11.0 (Dolphin Imaging, Chatsworth, California, USA). The head 3D reconstructions of each patient were re-oriented based on three reference planes: axial plane, passing through the right and left orbital points (the most inferior point of the lower contour of right and left orbits, respectively) and right porion (the most superior point of the right external acoustic meatus); coronal plane, passing through the left and right porion and being perpendicular to the axial plane; sagittal plane, passing through the nasion point (the intersection of frontal-nasal and inter-nasal suture) and perpendicular to axial and coronal planes ( Fig. 2 ).

Fig. 2
Three-dimensional digital image of the head after the orientation by the references planes axial, coronal and sagittal ( Dolphin Imaging ® software, version 11.0 /Orientation function).

The volume of the airway is influenced by head posture so the craniocervical inclinations of all subjects were examined to ensure that their inclinations were within the normal range (90–110°). The patients were instructed not to breathe deeply, not to swallow, to maintain the teeth in maximum intercuspation, and not to move the head and tongue during scanning. Once the image was oriented, the software was used to create a 2D simulated lateral cephalometric image with the use of a ray-sum technique. The options were set to an orthogonal projection type and a 100 mm ruler was placed in the cephalometric image. Landmark identifications and physical measurements were performed by the same investigator (M.A.J.). For the cephalometric analysis, nine conventional hard-tissue cephalometric landmarks were identified, and three anteroposterior and two vertical measurements were calculated ( Table 1 and Fig. 3 ).

Table 1
Description of the cephalometric variables used in this study.
Variable Definition
Anteroposterior skeletal pattern
SNA Anteroposterior position of the maxilla in relation to cranial base represented by the angle formed by the intersection between SN and NA lines
SNB Anteroposterior position of mandible in relation to the cranial base represented by the angle formed by the intersection between SN and NB lines
ANB The difference between SNA and SNB angles
Vertical skeletal pattern
SN-GoGn Mandible inclination in relation to SN plane represented by the angle formed by the intersection between SN and GoGn lines
FMA Mandible inclination in relation to FH plane represented by the angle formed by the intersection between FH and mandible plane

Fig. 3
Two-dimensional lateral cephalometric image with the landmarks, anteroposterior measurements, and vertical measurements used in the study ( Dolphin Imaging ® software, version 11.0 /Orientation function).

The airway analysis tool in Dolphin 3D Imaging software was used to define the portion of airway of interest. The superior border was defined by the edge of the hard palate to the posterior of the pharynx (parallel to Frankfort Horizontal (FH)) and the inferior border the tip of the epiglottis on a plane parallel to FH. The update volume was generated and the airway volume, airway area and minimum axial area obtained ( Fig. 4 ).

Fig. 4
(A) Pink area defining airway portion of interest. (B and C) Obtaining airway volume, airway area and minimum axial area ( Dolphin Imaging ® software, version 11.0 /Orientation function). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of the article.)

Lateral cephalometric images were printed by HP colorjet (HP Color LaserJet 2600n, Hewlett-Packard Company, Palo Alto, Califórnia, USA) and linear measurements were made in different levels of the PAS ( Fig. 5 and Table 2 ) as previously described by Pracharktam et al. and Hochban and Brandenburg.

Fig. 5
Two-dimensional lateral cephalometric image with the linear distances: (1) PAS-NL; (2) PAS-UP; (3) PAS-OccL; (4) PAS-UT; (5) PAS-Bgo; (6) PAS-ML; (7) PAS-TP ( Dolphin Imaging ® software, version 11.0 /Orientation function).

Table 2
Cephalometric distances (mm).
PAS-NL Pharyngeal airway space on nasal line
PAS-UP Minimal pharyngeal airway space between the uvula and the posterior pharyngeal wall
PAS-OccL Pharyngeal airway space on occlusal line
PAS-UT Minimal pharyngeal airway space between the uvula tip and the posterior pharyngeal wall
PAS-BGo Pharyngeal airway space on B-Go line
PAS-ML Pharyngeal airway space on mandibular line
PAS-TP Minimal pharyngeal airway space between the back of the tongue and the posterior pharyngeal wall

The linear measurements were hand-traced and calculated by the same author. The intra-class correlation test (ICC) was applied to assess the intraexaminer concordance (95% confidence interval) for all lateral cephalometric variables and airway dimensions using 12 CBCTs that were randomly selected; all measurements were repeated within 1 week. Descriptive statistical analysis (mean and standard deviation) was carried out for all variables. Differences between sexes were tested by using an independent t -test. Kolmogorov–Smirnov’s test confirmed normal sample distribution and an independent t -test was used to compare the airway volume, airway area, minimum axial area and the linear distance between groups I and II. p < 0.05 was considered statistically significant. Pearson’s correlation coefficient test was used to detect any relationship between the measurements of the upper airway (linear measurements and airway dimensions) and 2D cephalometric variables that represent anteroposterior and vertical growth standards. All statistical analyses were performed using SPSS software (17.0 version).

Results

Means and standard deviations for all upper airway variables were compared between sexes, which showed no statistically significant differences ( p > 0.05) so the subjects were combined for subsequent analysis. The concordance index was greater than 0.98 for all variables analysed, except for minimum axial area (0.91) and PAS-UP (0.92).

Table 3 shows that there were statistically significant differences in the following parameters: ANB ( p < 0.001), SNB ( p < 0.05), PAS-UP ( p < 0.05), airway volume ( p < 0.01), airway area ( p < 0.01) and minimum axial area ( p < 0.05). According to the cephalometric analysis, group II showed greater skeletal anteroposterior discrepancy and mandibular retrusion, as evidenced by the ANB and SNB, respectively. In relation to linear measurements, only PAS-UP showed a statistically significant difference between the two groups. The airway dimensions, which include airway volume, airway area and minimum axial area showed statistically significant differences between the groups.

Table 3
Descriptive analysis (mean and standard deviation) to groups I and II.
Variable Group I ( n = 20) Group II ( n = 17) p
Mean SD Mean SD
Cephalometric analysis ANB 3.46 1.19 6.72 1.56 0.000 ***
SNA 80.81 4.04 82.20 2.67 0.253
SNB 77.85 3.46 75.48 2.52 0.029 *
SN-GoGn 34.81 5.69 37.34 4.80 0.168
FMA 26.75 4.89 28.73 5.62 0.262
Linear measurements PAS-NL 12.79 4.38 12.26 7.48 0.790
PAS-UP 7.06 2.29 5.46 2.34 0.047 *
PAS-OccL 9.06 3.38 7.66 2.44 0.179
PAS-UT 9.58 2.67 8.26 2.76 0.161
PAS-BGo 10.42 3.50 9.46 2.18 0.353
PAS-ML 10.83 3.37 9.47 3.30 0.230
PAS-TP 9.81 2.94 8.20 2.87 0.110
Volume measurements Airway volume 7588.82 1892.75 5561.92 1778.13 0.002 **
Airway area 422.51 65.01 348.26 97.39 0.009 **
Minimum axial area 124.16 46.53 92.82 48.15 0.055 *
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Jan 26, 2018 | Posted by in Oral and Maxillofacial Surgery | Comments Off on Evaluation of pharyngeal airway space amongst different skeletal patterns
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