Around the same time, a professor at nearby Northwestern University Dental School named Rosemary Wells found herself similarly baffled. After all, the ritual of children placing their shed baby teeth under their pillows, in the hopes of finding them replaced with cash in the morning, was already being practiced by millions of young Americans. These kids left notes for the tooth fairy, and believed they shared personal relationships with her that spanned several years (and up to 20 baby teeth). How was it possible, Wells wondered, that nobody knew where she came from?

So Wells decided to take on the project herself. First came a series of magazine articles in which she laid out the first substantive overview of the tooth fairy myth. Then there was her survey, again the first of its kind, conducted among some 2,000 parents in the United States. A decade later, Wells remained so engrossed in her subject that she opened an entire museum dedicated to it, run out of her home in Deerfield, Ill. By then she had become the world’s expert on the tooth fairy, giving countless interviews and talks, and even appearing on “The Oprah Winfrey Show.” Wells’s name became so synonymous with the dental sprite that she had to clarify things to the Chicago Tribune: “I’m not the Tooth Fairy,” she said. “I’m the Tooth Fairy consultant.” It said so on her business card. A spokesperson for the Chicago Dental Society added, “We have no position on the Tooth Fairy. I refer all inquiries to Ms. Wells.”

What Wells discovered in her initial research was striking. Despite the seeming timelessness of the character, the tooth fairy is in fact an extremely recent arrival on the mythological scene. Her first print appearance is an eight-page playlet for children by Esther Watkins Arnold from 1927, and the oldest oral references date her to approximately the turn of the 20th century. By the time Wells started poking around, this supposedly immortal figure was barely even a senior citizen.

Of course, rituals surrounding tooth loss date back much further than that. Every recorded human culture has some kind of tradition surrounding the disposal of a child’s lost baby teeth, and in the 1960s, a researcher named B. R. Townend distilled these rituals down to nine basic forms (as summarized by Wells in her 1991 essay “The Making of an Icon”):

(1) the tooth was thrown into the sun; (2) thrown into the fire; (3) thrown between the legs; (4) thrown onto or over the roof of the house, often with an invocation to some animal or individual; (5) placed in a mouse hole near the stove or hearth or offered to some other animal; (6) buried; (7) hidden where animals could not get it; (8) placed in a tree or on a wall; and (9) swallowed by the mother, child or animal.

The items weren’t mutually exclusive, either. Perhaps the most widely practiced ritual, one that has been documented everywhere from Russia to New Zealand to Mexico, involves offering the lost tooth as a sacrifice to a mouse or rat, in the hopes that the child’s adult teeth will grow in as strong and sturdy as the rodent’s — a wish for transference that anthropologists call “sympathetic magic.” This offering is often accompanied by a specific prayer or song, and, in a pinch, any strong-toothed animal will do. Leo Kanner’s “Folklore of the Teeth,” from 1928, records similar ceremonies involving cats, dogs, squirrels and beavers.