The aim of the study was to compare the effects of a mandibular advancement device (MAD) with those of nasal continuous positive airway pressure(nCPAP) and of an intra-oral placebo device in obstructive sleep apnea (OSA) patients. The hypothesis for this study was that both MAD therapy and nCPAP therapy have similar, better treatment effects than placebo therapy in OSA. The study was performed according to the CONSORT (consolidated standards of reporting trials) statement (Altman et al., 2001), employing a parallel-group, randomized, placebo-controlled trial design.

Setting and participants:

Eligible OSA patients, living in the greater Amsterdam area, were referred to the Slotervaart Medical Center by their family physician. All patients underwent a thorough medical examination, including a full polysomnographic (PSG) recording, at the departments of Neurology, Pulmonary Medicine, and ENT, as well as a thorough dental examination at the Department of Oral Kinesiology of ACTA. OSA patients were invited for participation in this study when they fulfilled the inclusion criteria and exclusion criteria.

Randomisation and allocation:

After written informed consent was obtained, the patients were randomly allocated to one of three therapy groups (MAD, nCPAP, or placebo; see below). To ensure that the groups were of approx. the same size, block randomisation was used. Block sizes were 6, 12, and 18; sizes were randomly varied. The allocation sequence was automatically generated and subsequently concealed by an independent co-worker, who kept a paper copy in a lockable drawer. Sealed opaque envelopes were used to conceal the allocation from the principal investigator.

Interventions and blinding:

Three forms of therapy interventions were used in this parallel-group study. First, an individually fabricated MAD with an adjustable protrusive mandibular position at a constant vertical dimension was used. Second, nCPAP of the REMstar Pro system was used (Respironics, Herrsching, Germany). Third, a thin (< 1 mm), hard acrylic-resin palatal splint with only a partial palatal coverage was used as a placebo.

Patients were blinded to the nature of the assigned therapy (placebo or active). After evaluating the therapy, all patients were asked if they were of the opinion that they had received an active or placebo treatment. Blinding of the analyst was ascertained by assigning codes to data sets and by analyzing these sets in random blocks.

Procedure:

From all patients, two full polysomnographic (PSG) recordings were obtained in the sleep laboratory of the Slotervaart Medical Center, using Siesta hardware and Pro-Fusion software (Compumedics, Abbotsford, Australia): one before therapy assignment (baseline PSG) and one after 6 ± 2 months (mean ± SD) of treatment (therapy evaluation PSG). For the MAD and nCPAP groups, the third and fourth PSG recordings for therapy evaluation were performed 6 months and one year after the first therapy evaluation (long-term follow-up). The primary and secondary outcome measures were obtained at baseline and at therapy evaluations.

The MAD and nCPAP were titrated before the start of the treatment. The titration of the nCPAP was performed during a third sleep laboratory examination. The pressure was increased in incremental steps of 1 cm H2O/h, until respiratory disturbances and respiration-related arousals were reduced to ≤ 5/h, and snoring was minimized.

For the titration of the MAD, four ambulatory PSG recordings were obtained at regular intervals, using Monet hardware and Rembrandt Software (Medcare Automation B.V., Amsterdam, The Netherlands). The most effective protrusion position of the MAD (i.e., the mandibular position that yielded the lowest AHI value) was chosen from among four randomly offered positions (viz., 0%, 25%, 50%, and 75% of the maximum protrusion).

For the placebo group, the study procedure was made equally intense as that for the MAD group by making four ambulatory PSG recordings at regular intervals as well.

Inclusion Criteria:

• age > 18 years
• apnea-hypopnea index (AHI) between 5 and 45 events per hour

Exclusion Criteria:

• evidence of respiratory/ sleep disorders other than obstructive sleep apnea
• a body mass index (BMI) > 40
• medication usage that could influence respiration or sleep
• periodic limb movement disorder
• previous treatment with CPAP or MAD
• reversible morphological upper airway abnormalities (e.g., enlarged tonsils)
• temporomandibular disorders (based on a functional examination of the masticatory system)
• untreated periodontal problems
• dental pain
• lack of retention possibilities for a mandibular advancement device or a placebo appliance