The rubber mouth piece is clinically approved . Made in clear rigid plastic to avoid distortion . Available in the following versions: small , medium , large (upper and lower) and partial (upper, right and left). The major advantages that the mouthpiece features are as follows: Very rigid design prevents deformations , Disposable , Adaptable , Autoclave , Perforated design for improved mechanical retention , Reinforced grip with ribbing for easy handling during removal from the mouth . A must have by many physical therapist in their personal effects . Patients and athletes alike may benefit from this innovation .