Hi Marilyn,
I had a dentist during treatment who specialized in oral cancer patients. He checked me regularly during treatment to make sure everything was going ok, and started me on flouride trays at the start of radiaion treatment - twice per day.
He advised that even if I get my saliva back, which I have almost completely, that the chemistry of the saliva, due to the radiation damaage, will not protect against tooth decay.
My regular dentist was very good at his job, but (in my opinion) knew nothing about oral cancer patients. I would personally not trust his judgement, or that of other regular dentists, in this area.
Best wishes,
Chris