The whole thing goes beyond the various stages of dental care, evidently.
An article in the Times of London says that you can tell an American from a Brit by the smile:
While we British smile by pulling our lips back and upwards and exposing our lower teeth, Americans are more likely simply to part their lips and stretch the corners of their mouths.
So distinct is the difference that the scientist behind the research was able last week to pick out Britons from Americans from close-cropped pictures of their smiles alone, with an accuracy of more than 90%.
The study by Dacher Keltner, a psychology professor at the University of California in Berkeley, near San Francisco, analysed the 43 facial muscles used by humans to charm, smirk and appease.
He found the British were also more likely to raise their cheeks when they smile, showing the crow’s feet at the corners of the eyes. This produces a more sincere, hard-to-fake smile.
The most common British smile—restrained but dignified—is called the Duchenne smile after Guillaume Duchenne, a 19th century French doctor who analysed facial expressions.
…
By contrast, Keltner found most Americans had the far less expressive “Pan-Am smile”, named after the defunct airline’s gesture of welcome. This depends only on the zygomaticus major corner-tightening muscle and has also been called the “Botox smile” because, like the cosmetic treatment, it leaves the muscles at the corners of the eyes motionless.
I was somewhat frustrated by this story because there were no pictures. (Well, maybe there were with the online edition, instead of the print edition, but you have to register for the online edition.) There’s a bit with analysis of various UK celebrities—”Tim Henman’s grin showed he was ‘genuine, coy and flirtatious’, he said, while David Beckham’s smile and jutting chin indicated he was ‘determined to win at any cost’. The smirking grin of Chris Tarrant, host of Who Wants to be a Millionaire?, suggested a man who ‘felt he was getting away with something'”—that I would love to have compared with actual pictures. Alas. Guess I’ll have to pick up the book.
I’ve heard the bit that you can tell a genuine smile by various factors—such as the skin around the eyes forming crows’ feet before. You have to look at the eyes. I remember walking around San Francisco when David Letterman was coming to town and there were all these giant posters of Dave smiling from various kiosks. “Look at his eyes! That man is terrified!” I said. Not a smiler, that David Letterman.