I mentioned surgery because there are cases that are not due to clenching. Carol Burnett is a classic case. In my case my migraines were not caused by TMJ, years later it was found to be sinus tumor. I actually would do the opposite and not opening my mouth would open the jaw wide like if you sniffed a bad smell. I would agree about soft appliance rather than hard plastic one. The hard one will just from chewing food and talking, wear the teeth down if not properly made.
Speaking of soft guards, what about the teeth guards boxers use?