The film went through five titles ("The Tooth Fairy", "Don't Peek", "Fear of the Dark", "The Tooth Fairy: The Ghost of Matilda Dixon" and "The Tooth Fairy: Every Legend Has Its Dark Side") before it became Darkness Falls (2003).
In a version of the film, the creature only appears in the final act. The studio was not satisfied by this, so they brought Stan Winston in to create a new Tooth Fairy that would be seen throughout the film. The original design (by Steve Wang) bears no resemblance to the new version, although it is the basis for the McFarlane Toys figure released in 2002.
The sound of Matilda Dixon's wailing throughout the film is really the sound of an elderly woman's groaning in bed. The sound was both sped up in the parts where Matilda screams, and slowed down in the places where she gurgles and breathes heavily.
According to FX creator Steve Wang, the original version of 'Tooth Fairy' was an Angel of Death, but when script changes came in, his winged and toothy creation was jettisoned. Actor Doug Jones originally played the Tooth Fairy in Wang's incredible makeup.