I agree Notso that mammograms only highlight abnormalities.
What I found worrying about the article was that out of 1000 women tested, there will be one false negative, and 89 false positives. That seems quite a high rate.
As far as dental Xrays go, I think most dentists in practice wouldn't routinely Xray children's teeth to detect decay (as opposed to checking whether all teeth were present, or there were any extra teeth, for example), but it is actually recommended by Dr Edwina Kidd, an eminent academic dentist, as a means of deciding whether decayed teeth should be filled or not.
I don't think it is realistic to expect general practitioners to be able to reel off exact risk levels for brain cancer or thyroid cancer from dental x-rays - with modern film and techniques it is infinitesimally small, anyway. I used to tell patients they got a higher dose of radiation flying to Spain than from routine dental x-rays.