The aim of the study was to compare the effects of a mandibular advancement device (MAD) with those of nasal continuous positive airway pressure(nCPAP) and of an intra-oral placebo device in obstructive sleep apnea (OSA) patients. The hypothesis for this study was that both MAD therapy and nCPAP therapy have similar, better treatment effects than placebo therapy in OSA. The study was performed according to the CONSORT (consolidated standards of reporting trials) statement (Altman et al., 2001), employing a parallel-group, randomized, placebo-controlled trial design.