A crown completely covers a tooth that may have been weakened by decay, damage, an extensive filling or root canal treatment. It can be made from metal, or porcelain combined with metal, and is fixed neatly over an existing tooth.
To keep your crown in good condition, you need to maintain a high standard of oral hygiene and try to avoid grinding your teeth or chewing on extremely hard foods. The crown itself will not be affected by decay but the area where it meets the underlying tooth, and the tooth itself, need to be kept as clean as possible. If you take good care of your crown, and that includes attending regular check-ups, it can last for ten years or more.