Why does Morrison theorize that the killer may be using dentures to bite his victims in the book, Tooth & Nail: An Inspector Rebus Novel?

Morrison takes impressions of the bites the Wolfman leaves on his victims and studies them so that he can make a comparison when the police find a suspect. Morrison takes the impressions a step further and creates a facial re-creation that represents the way the killer would look based on the bites. The face is badly distorted because the upper and lower jaw do not line up. Morrison also theorizes that the teeth are not the person's natural teeth but might be dentures of some sort.