RecruitingDevice studyReducing Obstructive Sleep Apnea After Hypoglossal Nerve Stimulation Through Mandibular AdvancementThe purpose of this study is to evaluate the effectiveness, feasibility, and safety of mandibular advancement devices (MAD) for treating severe obstructive sleep apnea (OSA) in patients who are CPAP intolerant and have failed hypoglossal nerve stimulation (HGNS).