Radiation and root canals

I know this is a really stupid question, but I have to ask...

I'm 54, and I've never had a root canal in my life (lot's of fillings as a kid, though).

I had radiation for base of the tongue cancer in 2009. Almost immediately after my radiation treatment concluded, I needed a root canal. I didn't have any pain, because I was still really heavily sedated as part of my recovery. They realized I needed it because the abscess showed up on an x-ray. Afterwards, I kept saying to people "What's the deal with root canals? It didn't hurt a BIT". Ah, little did I know.

Now, almost two years later, I've had the SECOND root canal in my life.

When I ask, I've been told that the root canals are coincidental and not related to the radiation. My radiation oncologist snickered when I told him this, but that was as far as he'd go.

Is there any experience or hard evidence that radiation leads to the need for root canals? Or is it really just routine deterioration because of the natural decay process in a mouth with no saliva production?

And, I don't really need to know for any medical reason - at this point, it is what it is.

I just have a certain morbid curiosity.