Can we predict the success of dental appliance therapy for the treatment of obstructive sleep apnea based on anatomic considerations?

Traditional cephalometrics (1-3), though having the limitation of any two-dimensional (2D) method, has several advantages, including low cost, easy access and reduced invasiveness. Although computerized tomography (CT) has many advantages as a measuring tool for three-dimensional (3D) airway size (4-8), it is time consuming and expensive for· routine clinical use. However, 3D color reconstructions ofthe tongue, oropharynx and hypopharynx (9,10) provide more realistic views of each of the tissues under study and are ideal for detailed interpretations of the interaction between tongue, airway and soft palate size (Fig. 1). There appears to be a strong linear relationship between 2D cephalometric and 3D CT reconstructions for the tongue, soft palate and nasopharynx, but not for the oropharynx and hypopharynx (10). Approximately 40% of the variation of tongue volume can be explained by tongue cross-sectional area. The oropharynx and hy. po pharynx have no direct hard tissue support and the configuration of these structures appears to be less consistent. The posture of the head and neck, swallowing and glottic closure (11,12) may also affect cephalometric and CT measurements. Furthermore, CTs are taken in supine position, whereas traditional lateral cephalograms are obtained in the standing position. Different body postures may be a crucial factor affecting these measurements. To solve this problem, cephalograms should be obtained from OSA patients in a supine position identical to that used for CT evaluations (2). We believe that 2D cephalograms can be used to estimate the volume of the tongue, soft palate and nasopharynx but not the volume of the oropharynx or hypopharynx (10). Because the airway obstruction is most commonly seen in the collapsible oropharynx, CT or magnetic resonance imaging (MRI) techniques appear superior to 2D cephalometry fqr this structure. Three-dimensional evaluations of tongue, soft palate and airway as shown in Fig. 1 may be of significant clinical usefulness in the differential diagnosis of patients with OSA.