Most children start to lose their baby teeth between the ages of five and seven, and most cultures acknowledge the loss of those teeth by exchanging them for coins or small presents. How far back does this custom go? Well, even the Vikings presented children with some kind of ‘tooth fee’ for each lost tooth and later used the teeth to make pieces of jewellery they believed would help keep the wearer from harm. In other European countries, the milk teeth of medieval moppets were buried in the ground, like seeds, so that new teeth would grow in their place. This practice was also thought to keep witches from getting hold of them and using them to place curses, as witches were said to do with hair combings or fingernail clippings. (Though what was to stop witches from digging them up, I couldn’t say.) Alternatively, baby teeth could be burned, or fed to rats, which were believed to have good, strong teeth, and might influence the condition of permanent teeth. (Conjures up quite the picture, doesn’t it? “Oh, good, you found a rat. Hello, rat. Nice rat. Come here, rat. Got something for you.”)
The tooth fairy’s a bit more modern, and letters from her can be found at: http://www.toothfairyletter.net/