Hello @was123 It is my understanding as well as common sense that when the teeth are failing, the bone is dying or dead. Hyperbaric oxy chamber will not bring that bone back to life. It might help with the blood flow for a while but if osteoradionecrosis has set in, the only thing that works is to have the bone replaced and prosthetic teeth installed.
I don't know where you are located but most cancer centers in the US now offer up excellent surgery for this procedure. An easy way to know if this is the issue is with a jaw or panel xray of your jaw. The bone should show significant reduction from what is considered normal.
I was in the same boat. Local dental surgeons would not touch it. Sadly they don't seem to know what to do as is often the case. The local dentist was not equipped or trained to deal with this. What the local dentist did however at my request was refer me to Mayo Clinic in MN. at my request. That was five years ago. All is well now. I eat what ever I wish without issue.
If your dentist thinks the mandible has been damaged, ask them to refer you to a large cancer center or clinic. The operation is complex but a year from now it will be behind you.
The surgery is called "mandiblectomy with free flap" which means they will take a bone graph (in my case from my fibula) along with good tissue (free flap) with a good blood supply and replace the section of jaw bone that is damaged. The blood supply is connected to the surrounding blood system in your jaw which allows the bone section to live and heal together. The free flap tissue becomes the new gum around the bone.
Any questions just ask. First step is get a referral and forget about all of these non-profit support groups that offer little in actual real support. If your dentist can't do a referral, your local doctor should be able to, even if it is outside their system. Don't get steered to a local small hospital. This is a rare and difficult procedure and should be done only by experience in this specific surgery. Courage.