Purpose: To evaluate the effects of sleeping with or without a maxillary mucosa-supported complete denture (CD) in edentulous patients wearing a mandibular fixed implant-supported CD on sleep quality, sleep bruxism (SB) activity, and signs of obstructive sleep apnea syndrome (OSAS). Materials and Methods: A total of 18 female patients with maxillary mucosa-supported CDs opposing mandibular fixed implant-supported CDs were selected and tested for sleep quality, SB activity, and signs of OSAS during one night while wearing the maxillary CD and another night without wearing it, with a washout period of 7 days in between. The validated Brazilian Portuguese versions of the Pittsburgh Sleep Quality Index (PSQI-BR), Sleep Assessment Questionnaire (SAQ), and Epworth Sleepiness Scale (ESSBR) were used to assess subjective sleep quality. Diagnosis of OSAS followed the American Academy of Sleep Medicine (AASM) guidelines and was confirmed with an objective and validated type 3 portable cardiorespiratory monitor (ApneaLink Plus v.9.00) by measuring the respiratory disturbance index (RDI). SB activity was assessed with a subjective self-report questionnaire and an objective and validated portable electromyographic device (BiteStrip). Results: The objective measurements of SB activity and the RDI showed significant reduction (ie, improvement) when patients did not wear the maxillary CD. The subjective measurements of sleep quality and self-reports of SB activity showed no significant differences between wearing and not wearing a maxillary CD. Conclusion: The present results have shown that not wearing a maxillary CD at night is preferable as far as SB and OSAS are concerned, but larger-scale studies are still needed.