Habitual teeth grinding

WordNet Word definitions in WordNet
n. involuntarily or unconsciously clenching or grinding the teeth, typically during sleep

Wiktionary Word definitions in Wiktionary
n. The habit or practice of grinding of the teeth, as while sleeping, or due to stress or certain drugs.

Wikipedia Word definitions in Wikipedia
Bruxism is excessive teeth grinding and jaw clenching. It is an oral parafunctional activity ; i.e., it is unrelated to normal function such as eating or talking. Bruxism is a common problem; reports of prevalence range from 8–31% in the general population. ...

Douglas Harper's Etymology Dictionary Word definitions in Douglas Harper's Etymology Dictionary
"grinding the teeth unconsciously," from Greek ebryxa , aorist root of brykein "to gnash the teeth."