Dental help for Cancer survivor

My son Zack was diagnosed with cancer located in his sinus cavities at the age of 25. Subsequently he underwent chemo and intense radiation treatments. The cancer was eradicated, but my son was left with many problems. His tongue is permanently locked in one position and all his teeth have crumbled and broke due to the radiation treatment. He can barely eat with his tongue the way it is and now with all the pain he consequently lives with because of his teeth he is getting thinner and thinner. He has gone from a strong 290 to a very thin 150.
We have gone to different dentist and they all have said there is not one tooth worth saving. He also has absesses that they perscribe antibiotics for. He has dental insurance but it only covers  $1000. of dental work. He needs $9000. more before anyone will do any work on him. He is in desperate need of help. He is suffering everyday in pain and as his mom I am helpless to help him that is why I am asking for help.