Crowns are full coverage restorations that are used to cover a tooth that is likely to break, or is too broken down to be restored with a filling. They are most commonly done after root canal treatment, or when a large filling wears out. The larger the hole made by a cavity that has to be treated, the more likely a crown will be needed. Even after a filling is put in a large cavity, a tooth is more likely to break.
Crowns placed on a weakened tooth, providing strength and protect the tooth against breakage. A broken or cracked tooth is a far more serious matter and much more difficult to treat. Crowns help prevent this, as well as providing a nice smile.
It takes two appointments to restore a tooth with a crown. In the first appointment any decay is removed from the tooth and it is shaped to accept the crown. Then an impression is made of the tooth for use in fabricating a crown.
Between the two visits the crown is made, usually of high-strength porcelain over gold alloy, all ceramic material, or gold. During this time a temporary crown is worn. In the second visit this temporary is removed. Then the permanent crown is adjusted as needed and then cemented in place.