Back in the days of football before mouthguards & facemasks, dental & facial injuries were 40% of football injuries. Requiring the mouthguard & facemask dropped that percentage to 0.5%.
However, tooth loss is still a major injury/consequence of sports in America. A survey from the American Association of Orthodontists discovered that 67% of parents surveyed stated their children do not wear any type of mouthguard during sporting activities. The truly frightening part of that stat is that, according to the National Youth Sports Safety Foundation, "athletes who do not wear mouthguards are sixty times more likely to damage their teeth!!!"
As a dentist who provides sports dentistry services (not to brag, but I am the consulting dentist to Lee's Summit High School Sports Teams), the previous paragraph makes me cringe. Add to the above statistics that the majority of amateur athletes are wearing over the counter "boil and bite" mouthguards which provide little to no protection, and that 67% number is even higher.
Many parents and adult athletes have the perception that a "boil and bite" mouthguard or a flat piece of U-shaped rubber held between the teeth offers the same protection as a custom made professional mouthguard. Nothing could be further from the truth.