Yeah I had that too, my older and wiser dentist, who sadly retired told me it was inflammation of the T&J muscles in our jaw. I have to be careful what I chew and chewing gum I can't, I haven't chewed gum in years because I pay for it the day after with not being able to open my mouth. Also I have to be careful how I sleep if I sleep on my stomach (facedown) or a lot of weight on my mouth I can't open my jaw or chew the next couple of days... another wonderful symptom of RA :(

My rheumy says TMJ from RA. It is very painful...

Sounds like TMJ. Not necessarily caused by RA. I had it 25 years ago - long before I had RA

Yes, it does have a name, Temporomandibular joint disorder. Sounds big, but like most sufferers, I get it from clenching my jaw without realizing it. I have to do jaw relaxing exercises and a mouth guard at night to stop grinding.

I wear a guard every night, because I grind my teeth when I sleep. My TM joints were damaged by a bad dentist when I was a child, so going to the dentist now is an ordeal because the pain is so bad, but nothing to do with the RA. Strange.