Bruxism is the excessive grinding of the teeth or excessive clenching of the jaw. Bruxism may cause tooth wear and even the damage or breakage of teeth. There are two main types of bruxism: that which occurs during sleep (sleep bruxism) and that which occurs during wakefulness (awake bruxism). Dental damage may be similar in both types. The causes of bruxism are not completely understood, but probably involve multiple factors. Several symptoms are commonly associated with bruxism, including hypersensitive teeth, aching jaw muscles and headaches. Night guard or mouth guard is used to protect the teeth from grinding during sleep.