http://msn.foxsports.com/nfl/story/Michael-Vick-lack-of-mouthpiece-could-have-led-to-concussion-092011/?GT1=39002

"The impact left Vick with a concussion and lacerated tongue both of which may not have occurred had he been using that piece of protective equipment."

"Vick isn't required to use one. Neither are any other NFL players because of pushback from the NFL Players Association about making them mandatory despite the league's strong anti-concussion efforts."

"In his research of mouth guards, Tufts University professor Dr. Noshir Mehta wrote that there "is evidence the stability of the head and neck is helped by specific jaw posture. A lower guard made by the dentist to hold the jaw in a stable height and position with respect to the upper teeth has been shown to be helpful in reducing the incidence of concussions.""

On a related topic....
-Elite athletes want to attain better performance
-More oxygen/air intake occurs while running with one's mouth open.
-Higher oxygen levels decrease fatigue.
-Mouthguards are required for NCAA football participation

If the above assertions are true, then why in the world would an athlete that
wants to better his performance, choose to limit their oxygen level by wearing a pacifier mouthpiece, the type with the big lip flange.

Water cooled engines run longer when the radiator is unobstructed and free of internal build up. (No Mouthguard)
The same engine's performance is minimally affected if air flow to the radiator has a few bugs in the fins and mild buildup internally. (Custom-Fitted Mouthguard)
However, the engine will fail rapidly if air flow to the radiator is blocked.(Pacifier Mouthguard)

It's just dumb to not wear a mouthguard because of the idea that it impedes communication. I remember reading, years ago, about a former player who was an advocate for mouthguards. He gave a speech in which he advocated the use of mouthguards as a device that could prevent injury and flatly disputed the idea that wearing such a device makes it hard to be understood.

To emphasize his point, at the end of the speech he removed the mouthguard he had worn throughout the speech. No one realized up until that point that he had been wearing a mouthguard.

My sons both play rugby, and they wear a mouthguard. They wouldn't think of stepping onto the pitch, even for practice, without having one.