Society and culture
Clenching the teeth is generally displayed by humans and other animals as a display of anger, hostility or frustration. It is thought that in humans, clenching the teeth may be an evolutionary instinct to display teeth as weapons, thereby threatening a rival or a predator. The phrase "to grit ones teeth" is the grinding or clenching of the teeth in anger, or to accept a difficult or unpleasant situation and deal with it in a determined way.In the Bible there are several references to "gnashing of teeth" in both the Old Testament, and the New Testament, where the phrase "wailing and gnashing of teeth" describes what an imaginary king believes is occurring in the darkness outside of his sons wedding venue. (Matthew  22:13)
A Chinese proverb has linked Bruxism with psychosocial factors. "If a boy clenches, he hates his family for not being prosperous; if a girl clenches, she hates her mother for not being dead. "(男孩咬牙，恨家不起；女孩咬牙，恨妈不死。)In David Lynchs 1977 film Eraserhead, Henry Spencers partner ("Mary X") is shown tossing and turning in her sleep, and snapping her jaws together violently and noisily, depicting sleep bruxism. In Stephen Kings 1988 novel "The Tommyknockers", the sister of central character Bobbi Anderson also had bruxism. In the 2000 film Requiem for a Dream, the character of Sara Goldfarb (Ellen Burstyn) begins taking an amphetamine-based diet pill and develops bruxism.
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. Several symptoms are commonly associated with bruxism, including hypersensitive teeth, aching jaw muscles, headaches, tooth wear, and damage to dental restorations (e.g. crowns and fillings). Symptoms may be minimal, without patient awareness of the condition. If nothing is done, after a while many teeth start wearing down until the whole tooth is gone. There are two main types of bruxism: one occurs during sleep (nocturnal bruxism) and one during wakefulness (awake bruxism). Dental damage may be similar in both types, but the symptoms of sleep bruxism tend to be worse 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 more common in women, whereas men and women are affected in equal proportions by sleep bruxism. Awake bruxism is thought to have different causes from sleep bruxism. Several treatments are in use, although there is little evidence of robust efficacy for any particular treatment. Epidemiology
There is a wide variation in reported epidemiologic data for bruxism, and this is largely due to differences in the definition, diagnosis and research methodologies of these studies. E.g.