Dentists just told me I had seven cavities. Was surprised since I'd never had any. They fixed one, then fixed another, then had like a year to wait for the next. I went to Mexico and decided to get them all fixed in one go. She eventually through my weak Spanish, informed me that no, I don't have any cavities.
But hey at least I have permanent pain and sensitivity in the two they 'fixed.'
Actually I think I know the reason. I'd been to that dentist before and they never screwed me. Usually it's some cute girl. This time out to greet me was an ugly old crone who looked like the grinch. She saw my face fall when I saw her. I think she did the cavity scam to get back at me.