Do a google on that. Depending upon the kind of x-ray your dentist is using . . . the radiation exposure seems far less, although once a years sounds excessive, at least according to the dentist I work with, but I guess it depends upon each person's condition. There are also ways of protecting the body/brain from the effects of radiation, which a naturopathic consultation is good for.
I'll be looking further into this re: dentistry, as I've got to have some composite fillings done soon.