[wpietri]

I am glad they did this work, but I don't think it gets at what's behind the joke about British teeth.

For me, the exemplar is the Austin Powers jokes about his teeth. It's not that the average Brit has fewer teeth than the average American. It's that a person who American would expect, for reasons of class and style, to have an engineered smile (very white, very even teeth) instead had a perfectly natural one. Even the movie suggested that the stereotype was somewhat outdated. But to the extent we still have the stereotype, it's about upper- and upper-middle-class use of orthodontia and whitening. Plus the distinctive American emphasis on the big smile, which to a lot of non-Americans can seem mildly deranged.