Clenching teeth during strenuous effort, like lifting weights, can also grind them down.
"You could land the Space Shuttle" on some athletes' teeth, said Piccininni. "Flat as a pancake. They have worn it down so much."
Rowers breathe up to 80 times a minute in competition, and burn through 6,000 calories and eat five times a day, Campbell noted.
"A lot of pressure is going through the mouth," he said. At the Athens Olympics in 2004, "I was grinding my teeth in my sleep and I was waking up with a very sore jaw and sore teeth as well and I had a special gum-shield to wear at night to sleep with."
"That was the stress. It was my first Olympics. I was quite young. I was 21. I think I was feeling the pressure," he said.
The 2016 Rio de Janeiro Olympic clinic will have eight dental chairs, X-ray machines, root canal specialists, surgical facilities. There will be full-time dentists at hockey, rugby, and basketball for any injuries. The clinic will also distribute mouth guards. They handed out 350 in London and 150 at the Sochi Olympics this February, including to four Austrian ice hockey players after a teammate lost a tooth in their first game.
Treatment is free.
Some Olympians "know they've had a dental problem for three weeks or a month or three months, but they know if they can hold off until they get to the games they get it treated for free," Piccininni said. "That's fine. That's one of the reasons that we're there, is because athletes don't have the financial resources."
AP Sports Columnist Jim Litke contributed from Chicago. John Leicester is an international sports columnist for The Associated Press. Write to him at firstname.lastname@example.org or follow him at http://twitter.com/johnleicester
Copyright 2014 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.