Yes you can. I have been there, thought it would never end, or that I had some nasty disease, but I am fine now (although still seeing the maxillo facial consultant).
I still have a little pain and cannot open my mouth fully, cannot eat a baguette or steak or anything without a lot of pain, but if I steer clear of serious chewing I am fine. Two months ago, I dreaded cleaning my teeth due to the pain. Like you, the consultant said it was 'a muscle in spasm', it really seemed hard to believe. However, I realised that steam made it a lot better, so it made sense. They often prescribe an SSRI, which relaxes the muscles and I took one for 6 months. Sometimes I thought they had just prescribed a placebo, as it seemed to have no effect for several months. I also took a beta blocker, as at the time my GP thought I had Thyroid problems too and he thought it would lessen the symptoms until the blood tests were back. 5 months on, the constant pain, headaches and numbness seem like a distant memory.
You have had an mri and that would pick up most of the nasties. You have a diagnosis and it is certainly treatable. Whilst waiting for my hospital appointment, having been diagnosed by my dentist, I ordered a book on TMJ disorders. You may find something similar comforting to read if you are sceptical about the diagnosis. In fact, my consultant offered me some reading material too.
Have faith that you are now seeing people that can help.