How likely is needing a root canal or crown if a tooth has never hurt?

Unlikely but: Sometimes I have looked at teeth in the x-ray and found an abscess. It is like a sleeping dog and can come back to "bite" you with a swollen face or intense pain. Those teeth may not have any pain. Your dentist should be able to explian why a tooth needs a root canal.

Depends: If the x-rays are also clear & no swelling or draining infection, you would not expect a rct, however, 1, possitive from any of those makes it very likely.