Obstructive sleep apnea (OSA) is a common chronic sleep disorder that often requires lifelong care. The prevalence in the Netherlands is estimated around 300.000 patients. Due to longer life expectancy and increase in weight in the general population, its prevalence is expected to rise. Patients with mild and moderate OSA are treated primarily with an oral appliance at present time. Different oral appliances are available, but most used is the mandibular advancement device (MAD). This study focuses on two different types of MAD: the classic Herbst appliance, which is attached to the mandible and the maxilla and has an iron bar to regulate the open space; and the Somnodent, which consists of two separate splints, fixed on the mandible and the maxilla, but has no iron bar attached.

Inclusion Criteria:

• 18 years and older
• Ability to speak, read, and write Dutch.
• Ability to follow-up.
• Ability to use a computer with internet connection for online questionnaires.
• Diagnosis with symptomatic mild or moderate OSA (5 < AHI < 30).
• Expected to maintain current lifestyle (sports, medicine, diet, etc.)

Exclusion Criteria:

• Untreated periodontal problems, dental pain, and a lack of retention possibilities for an MAD.
• Medication used/related to sleeping disorders.
• Evidence of respiratory/sleep disorders other than OSA (eg. central sleep apnea syndrome).
• Systemic disorders (based on medical history and examination; e.g. rheumatoid arthritis)
• Temporomandibular disorders (based on the function examination of the masticatory system).
• Medical history of known causes of tiredness by day, or severe sleep disruption (insomnia, Periodic Limb Movement Disorder, Narcolepsy).
• Known medical history of mental retardation, memory disorders, or psychiatric disorders.
• Reversible morphological upper airway abnormalities (e.g. enlarged tonsils). - Inability to provide informed consent.
• simultaneous use of other modalities to treat OSA.
• Previous treatment with a MAD.