Bruxism is excessive teeth grinding or 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 behavior; reports of prevalence range from 8% to 31% in the general population. Although teeth grinding can be caused by stress and anxiety, it often occurs during sleep and is more likely caused by an abnormal bite or missing or crooked teeth. It can also be caused by a sleep disorder such as sleep apnea.