Statistically significant yes. But 90 percent more of 0.00002 is 0.000038. It would be like avoiding conductive jewelry because you're worried about lightning.

You added the word "statistically". I know people tend to kvetch about statistical significance almost reflexively, but that's not being done here. I believe the implication here is that it just plain isn't worth worrying about.

Not to mention, cavities and other dental problems pose a measurable threat to your health and longevity (not to mention quality of life), so I would bet a certain amount of radiation risk can actually be offset by the resulting improved dental health.

That's the wrong question. The question is if the X-rays are actually necessary in order to have good dental health, and apparently the answer is no.

Dentists use them because "what's the harm", but now that a harm is demonstrated they should use them only when actually necessary (when "the benefit outweighs the risks").

Um, a dentist's time isn't infinite, and other methods of examination can be more annoying for the patient than an x-ray. I guarantee you that if we don't use x-rays then in practice people are going to suffer more from dental issues.

If a tumour is only discovered in an autopsy, it's not clinically significant... and the benefits of the x-rays may well outweigh the risk of such a (in this case, usually benign) tumour.

Definition per http://www.ncbi.nlm.nih.gov/books/NBK10468/ :

"Clinically significant: A result that is large enough to affect a patient’s disease state in a manner that is noticeable to the patient and/or caregiver."

But "autopsy" means the person died but not when they died. So an autopsy of a person killed by gunshot in their 20's doesn't alters the average lifetime risk from the xrays.