Abstract: A hollow tubular mouthpiece that is clampable between the front teeth of a patient that is to receive a medical instrument through the mouth and into the esophagus. The mouthpiece has two spaced flanges to fit over the outside of the lips on the proximal end of the mouthpiece and behind the front teeth on the distal end of the mouthpiece with the intermediate space to be clamped between the biting front teeth. A central hollow passageway permits the instrument to be inserted. A lower curved tongue plate extends inwardly and downwardly to depress the patients tongue and to guide the forward end of the instrument.