When the average kid loses a tooth, he or she expects a nighttime visit from the Tooth Fairy. But for the 20 or so kid actors cast in 2001’s Harry Potter and the Sorcerer's Stone, instead of a couple of coins, they got a fake tooth—molded from their own teeth.
At the start of production, the children cast in the film—including stars Daniel Radcliffe, Rupert Grint, and Emma Watson—had to get their teeth cast and molded. This was so that if one of them lost a tooth, they could put a prop chomper back in and no one would ever know the difference, as Radcliffe recently revealed during an interview with The Hollywood Reporter at the Sundance Film Festival.
The only difference in Watson’s case, however, was that hers were going to be noticeable. In the early stages of filming, director Chris Columbus wanted to stay as true to the Harry Potter books as possible, which describe Hermione as having large teeth. So for one scene, Watson actually had to wear a pair of false teeth to make hers appear bigger. In the end, they only made it to the big screen for one scene, and then were cut out for practical purposes.
After the first couple of movies, however, the then-teenaged actors were of course free to show off their real teeth on camera.