There were many changes made when Harry Potter and the Sorcerer's Stone made the transition from the page to the screen. However, it turns out that one detail was planned to be included until the director realized that it just wasn't going to work after filming the first scene. In the Harry Potter books, Hermione Granger is described as having very large front teeth. For this reason, Emma Watson does wear false teeth in one scene in the film, but after shooting it, the director realized they wouldn't work long term.
The thing we shot on the first day of Sorcerer's Stone was the final train sequence where Harry looks at Hogwarts and Emma, Dan [Radcliffe], and Rupert [Grint] are huddled outside of the train. It was a big thing in the books about [Hermione's] teeth. She sort of had an overbite, so [Emma's] wearing fake teeth in that scene. And I realized that she's never going to be able to perform with these huge fake teeth in her mouth for the rest of the movie. So if you look closely, you can see some fake teeth.
Director Chris Columbus told the Entertainment Weekly Binge Podcast about the decision to scrap the teeth for Hermione. The first two Harry Potter films which Columbus directed were by far the ones that stayed as close as possible to the source material. It turns out that the films had actually tried to stay even closer, with this information about Hermione's teeth and the revelation that the poltergeist Peeves was supposed to be part of the film, but was scrapped due to cost considerations.
It's possible that you don't even notice Emma Watson's teeth in the final scene of the movie. She only has one brief line so otherwise, you don't even see them. However, if you compare the scene to any others in the film, it becomes clear that Emma Watson is wearing prosthetic teeth. Hermione Granger is described as having large front teeth when we first met her in the book. This look persists until Harry Potter and the Goblet of Fire. In that book, Draco Malfoy casts a spell on Hermione that makes her front teeth grow even larger, they're compared to beaver teeth. Following the counter spell to return her teeth to normal, they actually become smaller than they originally had been, giving the character a bit of magical dental surgery.
Comparing Emma Watson's dialogue between this scene and others, now we can hear that she doesn't sound quite as clear in this final scene as she does elsewhere. It was probably a good move to ditch the teeth. Do you agree? What other parts of the novels do you wish the movies hadn't skipped?