My jaw locked up on my at the dentist. I was getting cap work done in the upper back and it locked. Would only open the slightest bit for the dentist. Not fun at all.
I've never had luck with mouth guards. They made my symptoms much worse in the morning. Had a lot more dizziness, head pressure, just totaly out of it.
I've never understood the night guards. They are there to only protect your teeth.....for me anyways, they did nothing for the muscular pain/stiffness of tmj.
When I did try the nightguards years ago, you could see my teeth marks in them from grinding. And for me, the nightguards put my jaw in an uncomfortable position all night.....hence, the muscular pain/stiffness in the morning.
To me anyways...if you want to save your teeth from the grinding, get a mouth guard. If you want some relief from the pain/stiffness of tmj ....find some kind of med. that relaxes you at night.
This is only my personal opinion. Others may have something else to add.