p(Dentist does this) * p(Dentist gets caught when doing this) = number of police reports on the subject. I'd expect this to be the sort of thing the media would have a ton of fun with, and I don't recall ever seeing a news report on this subject, so I'd assume # of police reports is very low.

Either this is an amazingly easy crime to get away with, or not many dentists do it. By default, I'd favor the latter theory by a wide margin, but I'll concede I'm uneducated on how hard it would be to detect something like this (at a minimum, if another dentist can notice these "starter holes" then simply getting a second opinion would reveal the fraud. The alternate is to assume a national dental conspiracy...)