Several of us have had experience with cats with severe stomatitis and it is awful to watch cats go through it. Sometimes removing the back teeth is enough, though sometimes all the teeth are removed in a more desperate attempt to stop the inflammation, and if that doesn't work the cat is put on depo medrol shots.

What anti-inflammatory is your cat on at present? Metacam?

What is the vet hoping will show up on the specialist x-rays? Is he concerned that some roots were left behind after either his surgery or previous dental surgery? That can be a cause of stomatitis, and better that because it can be cured than the more usual no cause stomatitis.