In this open prospective study 40 patients who received Mandibular Replacement Appliance (MRA) Therapy as treatment of Obstructive Sleep Apnea Hypopnea Syndrome (OSAHS) will be included. The patient's sleep will be registered during 2 periods of 2 days: one while the patient does not wear the MRA and, +/- 1 week later, one while the patient wears the MRA. Furthermore, 2 low dose CT scans (one with and one without the MRA device in the mouth) will be taken. These data must allow the investigators to validate the use of functional imaging (segmentation and Computational Fluid Dynamics) as a predictor of the outcome of the MRA therapy in OSAHS patients.

Inclusion Criteria:

1. Patients with documented OSAHS based on the following criteria:

   AHI >= 5 Complaints of extreme daytime sleepiness with no other explanation and/or 2 or more of the following symptoms:

   • choking or gasping during sleep
   • recurrent awakenings from sleep
   • un-refreshing sleep
   • daytime fatigue
   • impaired concentration

2. Patients who received MRA as treatment for OSAHS

3. AHI >= 5 on at least 1 of the screening nights (patient does not wear MRA device)

4. Male or female patients aged ≥ 18 years

5. Patients with a co-operative attitude

6. Written informed consent obtained

Exclusion Criteria:

1. Pregnant or lactating females or females at risk of pregnancy
2. Patients with an uncontrolled disease or any condition that might, in the judgement of the investigator, place the patient at undue risk or potentially compromise the results or interpretation of the study.
3. Cancer or any other chronic disease with poor prognosis and/or affecting patient status
4. History of alcohol or drug abuse in the last 2 years
5. Patients unlikely to comply with the protocol or unable to understand the nature, scope and possible consequences of the study
6. Patients who participate in another clinical study whose investigational plan is judged to interfere or affect any of the measures of this study