Effects of a Titratable Oral Appliance on Supine Airway Size in Awake Non-Apneic Individuals SLEEP-RELATED BREATHING DISORDERS

RESPIRATORY-RELATED ACTIVATION OF THE UPPERAIRWAY-DILATING AND TONGUE-PROTRUDING MUSCLES IS WIDELY KNOWN to be effective in reducing the tendency of the upper airway and tongue to collapse during sleep. The electromyographic (EMG) activity of the genioglossus (GG) muscle increases in the head-up and/or supine position and thereby acts to maintain upper airway patency.1-4 However, sleeprelated reduction of the upper airway-dilating EMG activity may cause respiratory disturbances which include snoring and/or obstructive sleep apnea (OSA).5 Anterior displacement of the mandible accompanied by a forward migration of the tongue enlarges the upper airway and counteracts partial or complete obstruction.6,7 Mandibular advancement oral appliances have been established as one treatment modality for primary snoring and/or mild OSA7-15 and the usefulness of oral appliances for the treatment of such sleeprelated disorders is no longer in question. In addition, oral appliances have been recommended for moderate to severe OSA patients who cannot tolerate or refuse nasal continuous positive airway pressure (nCPAP) or for subjects who are not suitable surgical candidates.7 However, the precise relationship between the degree of mandibular advancement and the morphological changes in the upper airway has not been well evaluated except for the maximum mandibular protrusion. It was reported that the upper airway in OSA patients was significantly enlarged at the most protrusive mandibular position while awake10,16 and under general anesthesia.6 If we could determine a less protruded mandibular position that provided the same effect as the maximum protrusion in terms of enlargement of the upper airway, therapy using oral appliances would be simplified. Furthermore, it could provide less discomfort or strain to the jaw muscles and/or the temporomandibular joint, leading to increased patient compliance. The purpose of this study was to define the precise relationship between the degree of mandibular advancement and changes in upper airway structures using a titratable oral appliance. Morphological changes in the upper airway and its ambient structures were evaluated in healthy males using awake supine lateral cephalograms.