Oral appliance
A custom-made mouthpiece worn on the teeth during sleep that moves the lower jaw slightly forward to keep the airway in the throat open.
A little more detail
A custom-made, adjustable device fitted by a dentist that widens the pharyngeal airway by moving the mandible forward. The AASM and AADSM 2015 guideline recommends it in primary snoring when treatment is wanted, and in patients with obstructive sleep apnea who cannot tolerate PAP or prefer another treatment.
Source: Ramar K, Dort LC, Katz SG et al. Clinical practice guideline for the treatment of obstructive sleep apnea and snoring with oral appliance therapy: an update for 2015. J Clin Sleep Med. 2015;11(7):773-827. doi:10.5664/jcsm.4858