What is the origin of the tooth fairy?

Everybody knows the story of the Tooth Fairy. When kids lose their teeth they place them under their pillow, and then during the night a little lady with wings comes fluttering through their bedroom window and replaces the lost tooth with a coin. It's all very cute and we all just sort of take the tradition for granted... But when you think about it, it's a really weird story. So, just how the heck did this tradition get started, anyhow? The Tooth Tips blog investigates.