Patients and Methods: Two groups of 30 male patients (25-65 years, body mass index < 35 kg/m2) will be selected: the first group with an apnea-hypopnea index (AHI) between 5 and 15 events per hour of sleep and the second one with an AHI between 15 and 30 events per hour of sleep. Each patient will undergo three polysomnographic recordings (baseline, CPAP titration, after two months of treatment with oral appliance). Subjective (sleep disorders questionnaire, the Epworth Sleepiness Scale, and sleep diaries) and objective (polysomnography) parameters of sleep will be evaluated, besides the quality of life (SF-36), mood (POMS), and anthropometric measurements (neck circumference and craniofacial characteristic). Good response to treatment with the AIO will be considered as a 50% reduction in the baseline AHI index or AHI after treatment less than 5 events per hour of sleep.