Many people clench their teeth together or grind them during their sleep. This can be caused from stress, or more recently it has been linked to sleep apnea. When the teeth are clenched together they can endure up to 100 pounds of pressure per square cm. That is approximately the size of the surface of one molar enduring 100 pounds of pressure. This can splinter the enamel, crack the dentin or put extra wear and stress on fillings and crowns causing them to fail. The most prudent treatment is prevention when signs of clenching and grinding are seen. A custom night guard can be made to fit the patient. Wearing a night guard at night absorbs the shock of this clenching and grinding distributing these forces into the acrylic and keeping them from hurting the teeth.
Some people grind or clench their teeth even during the day. It is most common to clench your teeth at times that you are in "the zone" and your subconscious takes over. Activities like driving, paperwork, running, weight lifting can all lend to teeth grinding during the day. The design of the day guard is such that it is not so noticeable that you are wearing it. It usually fits the lower teeth and has a cutout for the front teeth.
Many teeth injuries happen during sports. Sports such as football, basketball, hockey, rugby, martial arts, that have high impact contact or could potentially have accidental high impact contact are a high risk for dental trauma. A soft sports guard that covers the teeth and extends up over the gums is best for these type of sports.