Note: The Tooth fairy that appeared in "Sassette's Tooth" is unrelated to this Tooth Fairy.
Francis the Tooth Fairy (who only appeared in "The Moor's Baby") was an old friend of Papa Smurf, who had been imprisoned behind an Iron Door for 300 years by an ogre who was disappointed at the penny he received for his tooth. The terms of the imprisonment were that she could only get out if someone solved the puzzle on the door.
The Ambassador of Zad, whose daughter Zona Shiba and Baby Smurf were teething at the time, was sharing his knowledge of the newly discovered Algebra which was integral to freeing the tooth fairy. After two of Balthazar's men kidnapped Shiba and held up in her cave as the Smurfs were. Peewit and the Ambassador's men found them when one of the two opened Jokey Smurf's Surprise exploding box. After the two were captured after leaving Shiba in the cave, Baby was able to solve the puzzle himself and free Francis, who was able to help Shiba and Baby finish their teething painlessly.