Aims: To determine if pressure pain thresholds (PPTs) of masticatory and neck muscles change after the application of a mandibular advancement device (MAD) in patients with obstructive sleep apnea (OSA). Methods: A prospective study was conducted in a sample of 27 OSA patients (24 males and 3 females; mean age ± standard deviation [SD]: 54.8 ± 11.8, mean apnea-hypopnea index ± SD: 23.5 ± 13.3) and 27 age- and sex-matched healthy controls. Exclusion criteria were signs and symptoms of temporomandibular disorders (TMD), metabolic diseases, and use of antidepressants, analgesics, or anti-inflammatory drugs. A calibrated examiner evaluated PPTs of seven head and neck muscles bilaterally by using a Fischer algometer. In the OSA group, PPTs were recorded immediately before the MAD application (T0), after 15 days (T1), and after 6 months (T2) of therapy; in the control group, PPTs were recorded at the same time intervals. PPT differences at baseline and over time within each group and between OSA and control groups were analyzed by Friedman and Mann-Whitney tests. Results: There were no PPT differences between groups at baseline. In the OSA group, PPTs of temporalis and masseter muscles decreased significantly at T1 compared with T0 (P .05), but no differences were found at T2. No significant PPT differences were found in the neck muscles or over time in the control group. Conclusion: MAD application induces a decrease of PPTs of masticatory muscles at the beginning of the therapy, but a physiologic adaptation occurs by 6 months. Keywords: algometer, mandibular advancement device, masticatory muscles, obstructive sleep apnea, pressure pain threshold