Attrition refers to the wearing or breaking down of tooth surfaces brought about by actions such as chewing and grinding food. If attrition is prolonged the front teeth become shorter and the back teeth become flatter; in severe cases it may cause a disfiguring affect on a person's smile. Grinding one's teeth, also known as bruxism, is also a form of attrition. Teeth that have been affected by attrition may also be more sensitive to temperature. Attrition can be treated by applying replacement crowns or onlays, which restore the natural size and strength of the tooth; this will also eliminate the possibility of malocclusion and improve speech. This treatment will also increase the esthetic attractiveness of the patient's smile.