You have just shared with us the most frustrating problem, next to the pain, about TMJ - the medical specialists themselves (in my opinion). Sometimes I wish that all these "specialists" would experience true TMJ for a few months to understand the complexity and devastation of the symptoms of TMJ.
Did none of them give you self-help techniques? Personally I believe that we can often help ourselves the best by taking supplements like magnesium, etc., life-style changes, posture corrections, watching what and how we eat, getting better sleep at night, etc., not talking so much & fast, using moist heat to relax muscles, and ice to numb the pain and/or reduce any swelling. Going to a good TMJ trained physical therapist can teach us how to do certain exercises and get those muscles to relax with ultrasound, massage, TENS, etc.
Yes, often we do need professional help if there is a structural problem, bite issues and/or trauma. My opinion is that the specialist's first concern should be to reduce pain as much as possible, and then evaluate how to correct the problem, if possible, and preferably without doing anything too major like surgery.
A bite splint tends to be a good, safe treatment option as it is usually reversible. Clenching and/or grinding our teeth while sleeping is a very common problem. Our bodies usually do adjust but we add stress, bad posture, trauma, a dentist who kept our mouth open too wide for too long, and a bad bite - we have problems. A splint can take pressure off of the joints and/or start to correct the bite issues. Once that happens, often the muscles will stop their spasms and pain will reduce.
Of course there are always exceptions, sadly. The disc might not return to a good position in the joint, the body just will not relax as needed, and/or there may be a major structural issue. I still believe it can be "fixed" or managed with conservative methods, which might mean adding medications, regular massage therapy, psycho therapy, etc. Filing one little tooth might resolve the problem also amazingly, but here you have to be careful. This is not reversible and should be done after the pain is controlled. Very little filing also should be the goal. If a lot of filing is needed, then braces or crowns, etc., might be better.
I think that the 4th dentist you consulted might be the better way to start. A bite splint is a known helper. I also hope, tho, that he mentioned other self-help methods, pain medications or physical/massage therapy. If not, ask him. Is relieving your pain (or function problem if that's your major issue) his first step? Do all the research you possibly can and visit Internet health boards/forums/chat rooms/support sites for contact with other TMJ sufferers and the wonderful support they can give.
Sorry for the length of this and I didn't even put everything in that I wanted, but I am truly hoping and praying that something I said will help you figure out what to do. Don't let these "specialists" frustrate you as that will just add stress to you. You fight for the help you need. Please take care and...
God bless you,
Carol