Obstructive sleep apnea (OSA) is a major health problem affecting over 1,000,000 Canadians. It is the cause of significant healthcare costs with increased morbidity and mortality. The two most common and effective therapies used to treat OSA are: (1) Continuous or Automatic Positive Airway Pressure (PAP), and (2) Mandibular Advancement Splints (MAS). While both therapies reduce upper airway collapse during sleep, they differ in efficacy, acceptance, cost and side-effects, but surprisingly are similar in improving quality of life, sleepiness and blood pressure. PAP is more effective in reducing apneas while MAS is easier to use. Until now, studies have used self-reported adherence data on MAS versus objective adherence on PAP. Many studies have hypothesized that the sub-optimal efficacy with MAS therapy is counterbalanced by the superior adherence relative to PAP, resulting in a similar effectiveness for both treatments. Compliance smart chips are a recent innovation for MAS and could be used to prove this hypothesis and allow a new and complete comparison of effectiveness (efficacy + adherence) between MAS and PAP. Understanding the patient's objective adherence and long-term symptomatic improvement would provide vital information to doctors and dentists in choosing the right treatment for patients. Sixty OSA patients will receive both PAP and MAS in a random sequence. This innovative study lead by two experienced new investigators, and a research team of multidisciplinary experts, will assess objective adherence, treatment efficacy, patient preference, sleepiness and quality of life of each treatment used at home for 1 month per treatment. After this, patients will be able to go back and forth between both treatments during an additional 6-month period. The results of this study will be used by healthcare policy makers as well as clinicians who need to be part of the treatment plan decision for the many Canadians who suffer from sleep apnea.