Effect of mandibular advancement oral appliances in patients with obstructive sleep apnea/hypopnea syndrome

The aim of this study was to investigate the radiographic changes that occur in the pharynx and the positions of hyoid bone in response to use of a mandibular advancement oral appliance (MAOA) in patients with obstructive sleep apnea/hypopnea syndrome (OSAHS). Nine patients in whom OSAHS was diagnosed on polysomnography who had no change in head posture between lateral cephalograms with and without the MAOA were studied. After MAOA insertion, the mean apnea/hypopnea index (AHI) decreased from 50.3 to 16.9, and the mean improvement rate of AHI was 65.2 %. Six of the subjects showed an increase in the anteroposterior diameter of the upper pharynx. The remaining three subjects did not show an increase in this variable, but their AHI decreased. Use of a MAOA apparently caused lateral patency of the upper airway. The position of the hyoid bone in all subjects moved upward, almost perpendicular to the palatal plane. The mean displacement distance in the remaining three subjects was larger than that in the other six subjects. The results of this study suggested that use of a MAOA moves the hyoid bone upward, there by contributing to not only anteroposterior, but also lateral airway patency.