Bruxism is the excessive grinding of the teeth and/or excessive clenching of the jaw. 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. Bruxism may cause minimal symptoms, and therefore people may not be aware of the condition. Several symptoms are commonly associated with bruxism, including hypersensitive teeth, aching jaw muscles, and headaches. Bruxism may cause tooth wear, and even damage or break teeth and dental restorations such as crowns and fillings. 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, but the symptoms of sleep bruxism tend to be worst on waking and improve during the course of the day, and the symptoms of awake bruxism may not be present at all on waking, and then worsen over the day. The causes of bruxism are not completely understood, but probably involve multiple factors. Awake bruxism is thought to have different causes than sleep bruxism, and is more common in females, whereas males and females are affected in equal proportions by sleep bruxism. Several treatments are in use, although there is little evidence of robust efficacy for any particular treatment.