Material and methods

The research ethics committee of Piracicaba Dental School–UNICAMP approved this study under protocol number 071/2013.

Data of patients who had CBCT head scans and facial profile photographs taken were obtained from the records of the oral radiology clinic. Six hundred eighty images with different fields of view were acquired from March 2011 to February 2014. One hundred three images with extended fields of view were selected. Those with signs of orthognathic surgery, radiographic signs of upper airway pathology, cervical spine that was not upright, and CBCT images without nasion or the base of the third cervical vertebra region were excluded. Therefore, 74 subjects (38 men, 36 women) from 18 to 56 years old (mean ± SD, 32.8 ± 1.8 years) were selected as the convenience sample.

CBCT images were acquired with an i-CAT unit (Imaging Sciences, Hatfield, Pa) with the following settings: 80 kVp, 4.8 mA, acquisition time of 40 seconds, reconstruction time of 62 seconds, voxel size of 0.4 mm, and field of view of 23 × 17 cm. The facial profile photographs were taken with the patients facing laterally away from the camera in natural head position, at maximal intercuspation and with the lips at rest.

The sample was classified according to vertical facial patterns (brachyfacial, mesofacial, and dolichofacial) and anteroposterior facial skeletal types (Class II and Class III) by cephalometric analysis. A study of the facial profile was performed for each subject.

Lateral cephalograms from images acquired with the CBCT scans were used for the analysis, which was performed using Nemotec software (Nemotec, Madrid, Spain). For all patients, the vertical facial patterns were labeled according to the VERT index in Ricketts’ analysis. Moreover, Steiner’s and Jacobson’s measurements were used to determine the anteroposterior facial skeletal type ( Fig 1 ). The corresponding medians and interquartile deviations to the measurements obtained with Ricketts’, Steiner’s, and Jacobson’s analyses are shown in the Supplementary Table .

Cephalometric analysis: 1 , facial axis angle; 2 , facial depth; 3, mandibular plane angle; 4 , lower facial height; 5 , mandibular arch angle; 6 , ANB; 7 , AO-BO.

Facial analysis was performed using facial profile photographs analyzed with the Facial Analysis Sideview (photo) functionality feature of the Cef X software (CDT Software, Bauru, São Paulo, Brazil). Facial thirds were measured according to the following reference points.

• 1.

  The proportion of the upper facial third (trichion to soft tissue glabella) in relation to facial height (trichion to soft tissue menton).

• 2.

  The proportion of the midfacial third (soft tissue glabella to subnasale) in relation to facial height.

• 3.

  To the lower facial third: the proportion of stomion to soft tissue menton (Stm-Me′) and subnasale to stomion (Sn-Stm) in relation to lower facial third (subnasale to soft tissue menton). Moreover, the proportion of lower facial third in relation to facial height.

To assess the pharyngeal dimensions, 3D reconstructions were created from the CBCT data with Insight ITK-SNAP version 2.4.0 ( www.itksnap.org ). One examiner (D.M.B.), who has solid experience with reconstruction software, performed all measurements. For the initial calibration, the examiner assessed 10 pictures repeatedly until consistent measurement replications were achieved. After that, all images were assessed, and measurements were taken. To determine intraexaminer agreement, 15% of the sample was reassessed a second time.

The 3D pharyngeal reconstruction was achieved with semiautomatic segmentation software. Limits for the area of interest are shown in Figure 2 . Values for total pharyngeal, nasopharyngeal, and oropharyngeal volume calculations were obtained ( Fig 3 ).

Limits of the area of interest: anterior, vertical plane passing through PNS, perpendicular to the sagittal plane; posterior, posterior pharyngeal wall; lateral, lateral pharyngeal walls, including the entire pharyngeal lateral projections; inferior, the tangential plane to the medial caudal projection of the third cervical vertebra, perpendicular to the sagittal plane; superior, highest point of the nasopharynx.

Separation between the nasopharynx and the oropharynx: A, reference point PNS in a sagittal reconstruction; B, most inferior point of the atlas in a sagittal reconstruction; C, distinction between nasopharynx and oropharynx in the sagittal plane, and D, in a 3D reconstruction.

To determine the cross-sectional pharyngeal areas, 5 spatial planes were set and identified with different colors in the 3D model. The areas were calculated using the manual segmentation tool of the Insight ITK-SNAP software, as shown in Table I and Figure 4 .

References of cross-sectional areas in the sagittal plane: A, PNS point in the coronal plane ( pink vertical line ); anterior pharyngeal wall extending from the PNS ( yellow vertical line ); PNS point in the axial plane ( blue horizontal line ); lowest point of the soft palate ( purple horizontal line ); epiglottis base ( orange horizontal plane ). B, PNS-coronal area in pink ; C, PNS-posterior area in yellow ; D, PNS-axial area in blue ; E, soft palate area in purple ; F, epiglottis area in orange .

Results

Distributions regarding anteroposterior facial skeletal types and vertical facial patterns were evaluated with the Fisher exact test. There were no statistically significant differences between the Class II and the Class III distributions ( Table II ).

The results of the reproducibility were considered excellent, with intraclass correlation coefficients greater than 0.9 and P <0.001.

Among the anteroposterior facial skeletal types, the soft palate cross-sectional area ( P <0.05) was greater for the Class III subjects. There was no statistically significant difference between this group and the others for pharynx measures ( Table III ).

No significant differences among the vertical facial patterns concerning the pharyngeal dimensions were detected ( Table IV ).

No statistically significant sex differences were found for the pharyngeal volume and cross-sectional areas, except for postnasal spine (PNS)-coronal ( P <0.01) and PNS-posterior ( P <0.01), which were significantly greater for the men ( Table V ).

A positive correlation between the midfacial third and the soft palate cross-sectional area of the oropharynx was found, as well as negative correlations between the upper facial third and total pharyngeal volume, oropharyngeal volume, and soft palate cross-sectional area ( Table VI ).

Moreover, correlations seemed more frequent in the Class II subjects when compared with the Class III group, and in the brachyfacial and dolichofacial subjects compared with the mesofacial group. There were correlations between pharynx volumes and soft palate cross-sectional areas of the oropharynx in the anteroposterior facial skeletal patterns and vertical patterns ( Tables VII and VIII ).

Table VII

Correlations (Spearman C [ P value]) between pharyngeal volumes and pharyngeal cross-sectional areas in anteroposterior skeletal facial types

Anteroposterior skeletal facial types	Pharyngeal volumes			Pharyngeal cross-sectional areas
	Total pharynx	Nasopharynx	Oropharynx	PNS-coronal	PNS-posterior	PNS-axial	SP
Class II (n = 50)
Nasopharynx	0.831 † (0)
Oropharynx	0.927 † (0)	0.624 † (0)
PNS-coronal	0.317 ∗ (0.025)	0.394 † (0.005)	0.255 (0.073)
PNS-posterior	0.112 (0.438)	0.269 ∗ (0.036)	0.046 (0.753)	0.797 † (0)
PNS-axial	0.695 † (0)	0.751 † (0)	0.585 † (0)	0.500 † (0)	0.353 ∗ (0.012)
SP	0.744 † (0)	0.436 † (0.001)	0.815 † (0)	0.287 ∗ (0.043)	0.126 (0.383)	0.504 † (0)
EP	0.526 † (0)	0.273 ∗ (0.021)	0.546 † (0)	0.262 (0.066)	0.177 (0.218)	0.370 ∗ (0.008)	0.642 † (0)
Class III (n = 24)
Nasopharynx	0.583 † (0.003)
Oropharynx	0.820 † (0)	0.214 (0.315)
PNS-coronal	0.396 † (0.003)	0.575 † (0.003)	0.096 (0.657)
PNS-posterior	0.199 (0.351)	0.341 (0.103)	−0.003 (0.990)	0.807 † (0)
PNS-axial	0.561 † (0.004)	0.657 † (0)	0.311 (0.139)	0.605 † (0.002)	0.361 (0.083)
SP	0.789 † (0)	0.227 (0.286)	0.752 † (0)	0.122 (0.571)	−0.001 (0.997)	0.393 (0.057)
EP	0.709 † (0)	0.172 (0.421)	0.664 † (0)	0.170 (0.426)	0.176 (0.412)	0.326 (0.120)	0.587 † (0.003)

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