Robinw, sorry for the delay in replying but ds seriously messed up the computer "surfing".
Obviously I can't diagnose without seeing your mouth but from what you have told me I have had the following scattered thoughts which may be of some help. I realise some of this may well be a repeat of what your dentists have told you.
Has the possibility of a problem with a tooth other than your wisdom tooth been ruled out? Is the tooth directly in front of your wisdom tooth heavily filled? Are all the teeth in that quadrant heavilly filled?
Be aware that the pain may have several causes! Tmj dysfunction, wisdom tooth pain,sinusitis, non vital pulp, cyst,periodontal problems....several other things....or a combination of any number.
Wisdom teeth don't really give problems if they are fully through. The teeth themselves are no different from any others. The only reason they get a bad reputation is becaue there is often not enough room for them so they get stuck halfway and may cause recurrent infections around the flap of gum which covers them ( pericoronitis). Wisdom teeth sometimes get blamed for stuff they shouldn't. ( particularly by older teenagers with mouths full of decay)
Assuming part of the problem is TMJ dysfunction, have you had any treatment for this ( been shown exercises or been given a splint to wear)and if so has it helped?
Bear in mind if you do have a TMJ problem, chewing gum is NOT a good idea as it is likely to make it worse.
Of all the possibly diagnoses the wisdom tooth one would be the most simple to exclude by a dentist examining your mouth.It is generally pretty obvious whether a wisdom tooth is a likely source of pain.
Finally, have you been seen by an oral surgeon? They are generally really on the ball with diagnosis.
Having said all that even the best dentist in the world might not be able to identify anything wrong. I hope that if this is the case the pain is not making your life miserable. Do you take painkillers for it and do they help?
Best of luck and if I can think of anything else I'll post later.
Can any of the other dental bods out there add to this?