My daughters dog grinds his teeth and in all my 40 yrs of dog ownership I have never come across this. He has problems with yeast in his ears on a regular basis and I don't know if this teeth grinding could be related to that problem. Any ideas anyone?

My friends has a girl who would grind her teeth when on the table at shows/class, she didn't enjoy showing so we guessed if was linked to that.

Unhappy about something would be my guess.  It is a sign of anxiety in humans.