Hi littlerosie, I was diagnosed January 2013 - I went to my dentist because of severe pain and infection. I already had periodontal disease and receding gums and in the area of pain the gum had receded so that you can see the tops of the root. He took an ex-ray and saw than a lot of the bone had gone/receded. He also found what he thought was a little bit of bone in the recess (although I wondered whether it was a tiny piece of ground walnut that I had put on my breakfast that morning. He then referred me to the maxilofacial consultant at my nearest hospital. I don't know whether any of the bone was exposed at that time. When I saw a different consultant in December he said that I didn't have ORN because there was no bone exposed. But by that time things had 'settled' anyway and I had had several sessions of HBOT at a MS therapy centre as the HBOT promised by the hospital never happened (although after all this time seems to be going through now).
It's all been confusing and a mess! What I have learned I have found out piecemeal and mostly by having researched and asked questions myself. Very little information has actually been offered and one hospital dentist point blank refused to talk to me about the risks of ORN.