Changes in airway and hyoid position in response to mandibular protrusion in subjects with obstructive sleep apnoea (OSA)

This prospective clinical study examined the alterations in airway and hyoid position in response to mandibular advancement in subjects with mild and moderate obstructive sleep apnoea (OSA). Pairs of supine lateral skull radiographs were obtained for 13 female and 45 male, dentate Caucasians. In the first film, the teeth were in maximal intercuspation, while in the second the mandible was postured forwards into a position of maximum comfortable protrusion. Radiographs were traced and digitized, and the alterations in the pharyngeal airway and position of the hyoid were examined. Males and females were analysed separately. In males only, correlations were sought between the changes in hyoid and airway parameters, and the initial and differential radiographic measurements. In males, mean mandibular protrusion at the, tip of the lower incisor was 5.3 mm, increasing its distance from the posterior pharyngeal wall by 6.9 mm (or 9 per cent). Movement of the hyoid showed extreme inter-subject variability, both in the amount and direction. In relation to the protruded lower jaw, the hyoid became closer to the gonion by 6.9 mm and to the mandibular plane by 4.3 mm. With respect to the upper face, a 1.3-mm upward and 1.1-mm forward repositioning was seen. The percentage alterations in airway dimensions matched or bettered the mandibular advancement. The minimum distances behind the soft palate and tongue improved by 1.0 and 0.8 mm, respectively. Despite their smaller faces, females frequently showed greater responses to mandibular protrusion than males. No cephalometric features could be identified which might indicate a favourable response of the airway to mandibular protrusion. Larger increments of hyoid movement were associated with an improved airway response, but the strength of the correlations was generally low.