Abstract: A mouthpiece for covering or protecting the upper dentition of patients under medical or surgical treatments involving oral intervention, comprising an arched tray member to be placed on the dentition and a resilient loop member connected with opposed exterior wall portions of the tray member and in its natural position extending rearwardly from the tray member in the general plane of this member. When the loop member is bent downwardly and forwardly against its own resiliency the foremost portion thereof may be placed in the groove between the outside of the lower dentition and the inside of the underlip and lower cheek portions of the patient, whereby the upper tray member will be effectively held in its mounted position with a low degree of discomfort for the patient. The mouthpiece also causes a certain cheek distension for better skin fit of a mask.