Bruxism can be defined as the habitual grinding of teeth when a person is not swallowing or chewing, whether consciously or subconsciously. It usually occurs during sleep at night and is not detected by the person himself, but by the person sleeping next to the person. It is believed to be invoked by stress. Teeth clenching is more common during the day, and is associated with nervousness, stress, or a heightened state of emotion. These habits apply a heavy load onto the teeth over a long period of time causing the teeth to slowly wear down, decrease in height (attrition), and eventually exposing the dentine. Also, these habits have a heavy toll on the temporomandibular joint (TMJ), or the jaw joint, leading to temporomandibular disorders or pain.