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.