12 year old cocker spaniel mix, chattering jaw

Question
I have a ~12 year old cocker spaniel mix who I rescued a year ago.  She was an abandoned dog, so I know very little about her.  We had her checked by our vet when we got her and he said that, with the exception of her teeth she was very healthy for her age.  She had to have a couple pulled that were rotten, and have the plaque cleaned off of them, and she has been great since!  She adapted very well to me and my husband and we have been a happy little unit.  For the last ten days, however, she has been chattering her jaw, as if she was cold or having a seizure or something.  These episodes last about ten to thirty seconds.  I thought maybe, since her teeth have been bad in the past, that this may have been the issue, and I took her to the vet.  He checked her over and said he did not see any cavities or abscesses.  He ran a full blood panel, just to rule out any abnormalities in her kidneys or liver for cancer or something, and he said everything looked good there.  He sent me home with a anti-inflammatory and a nausea medicine, thinking she may have had pain in her jaw or a stomach ache.  She is not better, and the medicine has not helped.  I am going to call him and take her back in, however I just want to go in with some idea of what to ask him to look for!  Please help!!!!  Thank you!!!

Answer
What else is going on?  Is her body "shivering" or is this limited to the jaw?  Is she eating?
Does this seem to happen at any particular time of day?  How often each day?

I'd certainly want x-rays done but if this were my dog I'd be on the way to the ER to see a neurologist or an Internal Medicine specialist.  Your vet did the bare minimum and I wouldn't waste more time there.  Get a 2nd opinion and get it fast.