The real-life serial killer dentist, Glennon Engleman (1928-'99), was the inspiration for the story of the film. Corbin Bernsen had previously played Engleman in the 1993 telefilm "Beyond Suspicion".
When examining April's radiographs, Dr. Feinstone points out to Karen "There's a shadow here on number 31", which is the lower left central incisor tooth, but then says to April "You have a cavity on one of your lower right molars".