Mueller Matrix Mouthguards are the world's most advanced self-fit mouthguard. Designed by OPRO, the world's largest supplier of custom mouthguards, all Mueller Matrix models introduce the OPROfin retention system, giving the Mueller Matrix the best fit performance of any self-fit mouthguard in the world. The highly technological cross-sectional profile means maximum protection against front and lower blows while keeping the palate clear for improved breathing and speech.