Pharyngeal airway volume and shape from cone-beam computed tomography: relationship to facial morphology

Abstract

Introduction: The aim of this study was to assess the differences in airway shape and volume among subjects with various facial patterns.

Methods: Cone-beam computed tomography records of 62 nongrowing patients were used to evaluate the pharyngeal airway volume (superior and inferior compartments) and shape. This was done by using 3-dimensional virtual surface models to calculate airway volumes instead of estimates based on linear measurements. Subgroups of the sample were determined by anteroposterior jaw relationships and vertical proportions.

Results: There was a statistically significant relationship between the volume of the inferior component of the airway and the anteroposterior jaw relationship (P = 0.02), and between airway volume and both size of the face and sex (P = 0.02, P = 0.01). No differences in airway volumes related to vertical facial proportions were found. Skeletal Class II patients often had forward inclination of the airway (P <0.001), whereas skeletal Class III patients had a more vertically oriented airway (P = 0.002).

Conclusions: Airway volume and shape vary among patients with different anteroposterior jaw relationships; airway shape but not volume differs with various vertical jaw relationships. The methods developed in this study make it possible to determine the relationship of 3-dimensional pharyngeal airway surface models to facial morphology, while controlling for variability in facial size.

Fig 1

Facial morphology reflects the underlying skeletal configuration and internal soft tissues. The sample was divided into 3 groups according to 2 criteria: A, the AP relationship of the jaws, and B, the vertical pattern of the face.

Fig 2

The size of face was established by creating a prism (A) with edges as (B) the bizygomatic width, which is parallel to the true horizontal and does not need to be projected, (C) the Na-Me distance projected on the y-axis and (D) the Ba-ANS distance projected on the z-axis.

Fig 3

Segmentation by user-initialized 3D surface evolution (A). Limits for airway analysis are: (B, C) anterior, a vertical plane through posterior nasal spine perpendicular to the sagittal plane at the lowest border of the vomer; posterior, the posterior wall of the pharynx; lateral, the lateral walls of the pharynx, including the full extensions of the lateral projections; lower, a plane tangent to the most caudal medial projection of the third cervical vertebra perpendicular to the sagittal plane; (C, D) upper, the highest point of the nasopharynx, coinciding with the posterior choanae and consistent with the anterior limit.

Fig 4

The orientation of the bisecting plane for the superior and inferior airway compartments was different between A and B, skeletal Class II, and C and D, skeletal Class III; the latter was more horizontal, and the former was more oblique, reflecting an anatomic difference between these groups.

Fig 5

Different airway shapes of skeletal Class II and Class III subjects, depicting a more vertical orientation of the airway in Class III subjects. A and C, This finding was statistically significant, P <0.001. B and D, The differences between subjects in the vertical groups are less apparent, with no statistically differences found.

Fig 6

Registration techniques for 3D data adapted for airway study use: A, pre- and postmandibular advancement 3D models of the airway registered on the cranial base (semiautomatic registration); B, interpatient manual airway registration shows a skeletal Class II subject and a skeletal Class I subject.