My friend seems to be having a problem like this. She try and close her mouth but her jaw just shakes like she can't close it. Last night she did it and I opened her mouth and with my thumb put a little pressure on the joints where her jaws connect and that seemed to work. She was able to shut her mouth after I did that.Then i call Davie Orthodontist and they examine the problem and give some medication and now she feels well.