This dream metaphor closely resembles the idiom, to have an axe to grind. You may have been dreaming of chewing food and this sent a message to your brain to start chewing in anticipation of food in your mouth.
Grinding teeth, be it an actual movement in your sleep, or just a dream, means you were not getting a restful sleep. Your thoughts, feelings and actions during your day are still being processed in your brain and these disturbances continue into the night.
