It due to a badly fitted or too large mouth guard?

Custom-made guard: The store-bought mouth guards that you buy and try to form to the teeth just don't fit very well. The custom-made professional mouth guards fit snugly. They almost 'snap' in. You do not have to keep your teeth together to keep them in. The players can speak and yell to each other and the coaches. Ask your dentist to fit you with a custom made mouth guard

"It": What is "It?" What is the mouth guard interfering with. Are you requesting information about a sports mouthguard to prevent sports injuries, or a "night guard" to treat occlusal problems? In either instance, your Dentist can assure better fit and effectiveness with custom made appliance rather than OtC.