Abstract: An oral appliance to prevent further oral injury to comatose patients and the like. This appliance is a flat body of substantially uniform thickness that defines a U-shape. This provides an intra-oral leg for insertion between the occlusal surfaces of the teeth on one side of the patient's mouth. The second leg is extra-oral i.e., for exterior the mouth, with the curved surface between the legs fitting into the corner of the patient's mouth. This construction permits insertion in either side of the mouth, or periodic switching sides to prevent excessive irritation. A tether or lanyard is fastened to the extra-oral leg by providing a perforation near the distal end thereof. In the preferred embodiment, the extra-oral leg is both wider and longer than the intra-oral leg to facilitate manipulation by attending personnel. This appliance does not require impressions or the like, nor does it require extra-sedation of the patient for installation or manipulation.