gnash teeth, grind teeth

Definition:

To gnash or grind the teeth means to clench the teeth and scrape them back and forth against each other. This often shows extreme pain or anger.

The Bible tells us that gnashing teeth is one thing those in hell will do in their terrible distress.
This term could also be translated as "scraping the teeth against each other" or, if it is not clear what this action means, "grinding the teeth in pain" or "gnashing the teeth in anguish."