If there are only two dentists, and we assume neither travel out of town to get there teeth seen to, and that neither are able to work on their own teeth.

I would have to go for the one with bad teeth, as he's obviously done some good work on the other guy.

The reverse also stands true, unless the guy with bad teeth has a phobia of dentists, as he would surely have had bad treatment from the bad dentist with the good teeth.

Or did I miss something ?