Well, I have a true life story of a Dentist finding Cancer in someone's mouth:
A guy I know worked at a Zoo in the Minneapolis area and went to the Dentist who examined his mouth during a regular check-up. The Dentist noticed what he saw was a sign of Cancer in the mouth with no extensive testing (he could see it), so the fellow went to his Dr. and sure enough his entire jaw was Cancerous. They had to operate extensively on this guy--and he was in his late 20's then! Yikes!
Anyway, he has gone on to live on disability, but still has a full and happy life now. With some magical work from a Plastic Surgeon, he looks normal, too. I guess they got it all cause he's been Cancer free for 10 years now.
So, it does happen that a Dentist recognizes Cancer in someone's mouth. I, personally, have had a Dentist make a point to me that he was looking for a sign of Cancer (thank heaven nothing was ever found).
The fellow thinks that the strong chemicals they use to wash the urine and feces out of the animal's cages at the zoo is what caused his Cancer, because there has been too high an incidence of his fellow workers at the zoo having Cancer as the years have rolled by.
Guess the moral of this story is to make sure your Dentist checks your mouth for Cancer (I've never heard of a Dentist trying to sell you this check-up), and don't be the guy who washes the urine and feces out of zoo cages.
(Is it just me? I thought all Dentists checked for Cancer in your mouth visually as routine. Any Dentists here to answer that one?)