Tom, I was told very clearly by my oral surgeon that the risk of ORN never goes down after radiation. Anytime the bone is exposed, there is a risk, whether it is two years or twenty years later. He also told me the same thing Joanna said about hyperbaric oxygen --it temporarily protects (usually) against ORN if you need oral surgery but probably doesn't change the longer term risk--you'd need it again for it to help again.

Nelie