Hi Sian, it sounds like you could do with a cavitat scan .. My guess is it would show infection around all your root canal teeth + where your had those previous teeth extracted. Dentists never bother removing the periodontal ligaments which hold teeth in, without their removal, especially in the back molars it has a high chance of leaving a cavitation in your jaw. Pretty much what my picture above shows .. If the infection directly effects the nerve in your jaw, you can get pain pretty much all over your face I believe. Sometimes dentists wrongly take out teeth in an effort to cure this pain, when all along the infection is hiding at the back of the mouth somewhere. It is possible to find where the infection is, by using drops of anaesthetic all along the jawline until the pain is turned off. Vets use this technique in animals too, for things like leg pain, when they need to find the exact position of the source of the problem. One of the American cavitation dentists, had some guy with neuralgia facial pain, and basically he killed himself and left his head to this guy to dissect, to find out what was wrong with him. I saw a picture of, basically there was infection in his jaw where the roots of a tooth used to be, but the nerve was in between the roots and was directly effected by the infection, hence his pain. Maybe MRI would have helped these people too ... seeing as how x-ray is so useless.
As for DrMyhill, shes probably the only doctor in the uk worth seeing if you have CFS.