An oral device for temporary placement in a patient's oral cavity includes upper and lower jaw braces and a tongue-engaging member. The upper and lower jaw braces are connected so that the lower jaw brace is advanced in an anterior direction relative to the upper jaw brace when the upper and lower jaw braces are closed together. A partial vacuum is drawn in the oral cavity and the vacuum and lower jaw displacement together control the position of the tongue in order to clear the patient's airway to reduce sleep apnea or treat other conditions.