Åke Tegelberg,1,4,5 Bo Wilhelmsson,2 Nina Erixon-Lindroth,6 Leif H Lindström3,41Department of Stomatognathic Physiology, 2Department of Otorhinolaryngology, 3Department of Psychiatry, Central Hospital, Västerås, Sweden; 4Centre for Clinical Research, Uppsala University, Central Hospital, Västerås, Sweden; 5Faculty of Odontology, Malmö University, Malmö, Sweden; 6Department of Clinical Neuroscience, Karolinska Institutet, Stockholm, SwedenObjective: The objective of this study was to evaluate the effect of oral appliance (OA) treatment on cognitive functions in patients with obstructive sleep apnea (OSA).Materials and methods: In a prospective study, 50 male patients with verified moderate-to-severe OSA received an OA with mandibular advancement. The cognitive functions assessed included working memory, vigilance, executive functioning, and mental pace, measured before as well as after 6 months of treatment. Somnography was used to measure physiological treatment effects. Forty-three patients completed the 6-month follow-up study.Results: All domains of cognitive functioning measured improved after 6 months of treatment with an OA (P < 0.001). The apnea/hypopnea- and oxygen desaturation-indices decreased significantly after treatment (P < 0.01). An obvious treatment response was reached in 60% of the patients, and 54% of the patients had recovered ie, had normalized breathing during sleep.Conclusion: OA with mandibular advancement is a treatment modality for the physiological symptoms of OSA, and may have a positive impact on cognitive functions, after only 6 months of treatment.Keywords: clinical trial, cognition, oral appliance, sleep apnea, treatment