Crowns are full coverage restorations that are used to cover a tooth that is likely to break, or is too damaged to be restored with a filling. They are most commonly done after a root canal procedure, or when a large filling wears out. The larger the hole made by a cavity, the more likely a crown will be needed. Even after a filling is put into a large cavity, a tooth is more likely to break. Keep in mind that the jaw muscles are the strongest in the human body. Teeth are subjected to tremendous pressures. Crowns ride over the weakened tooth, providing strength, stability and protection against tooth fracture. This is critical as a broken or cracked tooth is a serious condition that may lead to loss of the tooth.