A jaw advancement oral appliance is disclosed to be inserted in the mouth of a user to maintain an airway to the user's throat during sleep. The appliance includes an upper tray assembly against which the user's teeth carried by his upper jaw are seated and a lower tray assembly against which the user's teeth carried by his lower jaw are seated. Each tray assembly includes a bite impression tray having a plurality of holes formed therein and arranged in a honeycomb pattern. The bite impression trays are manufactured from a soft material so that a custom impression of the user's teeth is created when the appliance is heated and the user bites into the bite impression trays.
