About one in 10 people have a naturally occurring gap or space between their two top front teeth large enough to see through. This is known as a midline diastema.

  

It's a growth and development problem where the upper lateral fernum, a muscle that attaches from the centre of the upper lip to the gum (the fleshy web you hit with your tongue while running it over your upper gums), fails to recede. Normally, the fernum should recede as the jaw grows, allowing eye teeth, which come in between the ages of nine and eleven, to push the front teeth together and close the gap. There's a hereditary link involved in why this doesn't happen with some people, but it's unknown how prevalent it is.

  

Gaps may not be popular to some people in the real world, but it's almost a trend in celebrity land where Madonna, late night talk show host David Letterman, California governor Arnold Schwarzenegger and Real Madrid soccer star Ronaldo, to name a small few, regularly flash spacey smiles. (Click on the Celebrities link above for names, pictures and biographies for all of them).