Bruxism is the grinding of teeth and/or clenching of the jaw. Bruxism is considered a parafunctional habit because it is not a normal healthy function. Prevalence of bruxism has been estimated to be up to 30% of the population. Some of the consequences of bruxism include excessive wear of teeth, sensitivity of teeth, damage to dental work, jaw pain, and headaches. Bruxism can occur during the day or while sleeping. Here is an interesting article relating bruxism to the stresses of living in New York City.