An investigation of therapeutic effectiveness and the mechanism of oral appliance therapy on obstructive sleep apnea syndrome]

In order to investigate the effectiveness and the mechanism of action of oral appliances (OA) on obstructive sleep apnea syndrome (OSAS), a series of studies including overnight polysomnography, both ultrafast MRI and measurement of intraesophageal pressure during daytime naps and cephalometric analysis while awakening were performed on 19 OSAS patients before and during the treatment. In all cases, a significantly decreased apnea hypopnea index (AHI), shortened apnea duration, and a significant elevation in the lowest value of nocturnal arterial oxygen saturation, in comparison with the pretreatment values, were recognized during treatment with OA. The number of patients who responded to OA treatment, i.e., those whose AHI decreased by more than 50% of the pretreatment value, was 13 (68.4%). In cases with an AHI of 30 per hour of sleep or more before treatment, the number of arousals decreased and the percentage in stage 3 + 4 increased significantly during the use of OA. Cephalometric analysis revealed the anteroinferior advancement of the mandible, the anterosuperior movement of the hyoid bone and increase of upper airway area with OA in the cases studied. An MRI of the upper airway during sleep showed that glossopharyngeal obstruction disappeared with the use of OA in all cases, and velopharyngeal obstruction disappeared in nearly half of the cases. Moreover, the fluctuation of the intraesophageal pressure during sleep decreased significantly with OA. There were no differences in clinical background (e.g., age, body mass index, pretreatment value of AHI, and upper airway characteristics) in patients who AHI had decreased to less than 50% and those in whom it remained over 50%. These results confirmed the effectiveness of the treatment with OA. OA can be recommended for OSAS patients with not only glossopharyngeal obstruction, but also velopharyngeal obstruction, which is the most common cause of OSAS.