The investigators will perform a clinical trial comparing mandibular advancement device (MAD) therapy with sleep positional trainer (SPT) and the combination of MAD and SPT in patients with positional sleep apnea using MAD. Patients are invited for 2 consecutive polysomnographies (PSGs) in randomized order: one PSG with SPT, one PSG with SPT and MAD. PSGs are performed at the Antwerp University Hospital.