The goal of Oral Appliance Therapy (OAT) is to open the airway. Oral appliances fall into two basic categories: tongue-retaining devices (TRD) and mandibular advancing devices (MAD). Tongue-retaining devices are small acrylic devices which fit by suction on the tip of the tongue. Mandibular advancing devices are small acrylic devices that fit over your upper and lower teeth and advance the lower jaw. Both move the base of the tongue forward and open the airway. TRDs do not work as well as MADs. They are non- invasive, easy to use and are effective in improving breathing, reducing snoring and reducing mild sleep apnea. They are less effective for treating people with moderate or severe obstructive sleep apnea and people who are obese. Sleep appliances offer several advantages over other therapy. They are not as expensive, easy to travel with, non-invasive, easy to fabricate, and quite well accepted by patients.