RecruitingDevice studySevere Label Expansion for EVO Products TrialTitle: Severe Label Expansion for EVO Positioner (SLEEP) Study Description: Single-arm study to determine the safety and effectiveness of treating severe obstructive sleep apnea using the EVO Sleep and Snore Device (ProSomnus Sleep Technologies, Pleasanton, CA). Objectives: To determine the safety and effectiveness of the EVO Sleep and Snore Device in individuals with severe obstructive sleep apnea. Endpoints: The primary effectiveness endpoint is the Sher criteria defined as a reduction of Apnea-Hypopnea Index (AHI) of at least 50% from the baseline value and a post-treatment AHI of less than 20 events/hour at 6 months following initiation of Oral Appliance Therapy (OAT) titration. AHI will be collected using HSAT at baseline and 6 months. The primary safety objective is to evaluate safety by summarizing all reported device and/or procedure related adverse events from the time the EVO device is introduced through 6 months. Study Population: A maximum of 49 individuals over the age of 18 years with severe obstructive sleep apnea will be enrolled. Description of Sites/Facilities Enrolling Participants: The study will be conducted at up to four sites, up to two of which could be located outside of the US. Description of Study Device: The study device is the EVO Sleep and Snore Device (ProSomnus Sleep Technologies, Pleasanton, CA). The device is a mandibular repositioning device used to treat obstructive sleep apnea. The device is currently cleared for the treatment of mild and moderate OSA. Study Duration: The time from when the study opens to enrollment until completion of data analyses is estimated to be 15 months.