A mouthpiece having particular suitability for cooling oral tissue of a patient undergoing chemotherapy or other medical treatments in which reducing oral cavity temperature is beneficial. The mouthpiece includes a cooling medium contained within the top element and the bottom element and able to retain a cooling environment within the mouth, preferably sufficient to reduce capillary blood flow to the patient's mouth. In one embodiment, an external chamber extends from the front of the mouthpiece to house a cooling medium. A bladder is positioned inside the external chamber for storing a solution having a freezing temperature above the freezing point temperature of the cooling medium to assist in cooling the cooling medium. At least one breathing tube extends through the external chamber to permit a patient to breathe through the mouth when the mouthpiece is emplaced within the mouth in the operative close-fitting relationship.
