A crown is needed when a filling just will not work.A crown may be made of white porcelain, gold, or porcelain fused to gold. There are many situations that may call for a crown:
If a tooth has decay so deep and large that a filling will not stay, or if the tooth structure is weakened, a crown must be placed on the tooth to save it.
Large old fillings:
When large old fillings break down, or get decay around them, they usually need to be crowned. It is important to crown a tooth that has been structurally weakened to prevent a cracked or broken tooth. Once a tooth breaks, it may not be possible to save it.
When a tooth is cracked, a filling will not seal the crack. A crown has to be placed over the tooth to hold it and the crack together. If a crown is not placed on the tooth, the tooth will become sensitive to chewing pressure, or will eventually break. It is important to crown a cracked tooth before it breaks, because in some cases a broken tooth cannot be crowned and must be extracted.
Broken / Fractured tooth:
A tooth that has broken is usually too weak to hold a filling. A crown will hold the tooth together and prevent it from breaking again. If the fracture involves the nerve, Root Canal Therapy may be required before the tooth is crowned. In some cases, a broken tooth cannot be saved and must be extracted.
This patient chose not to have the cracked tooth above crowned, and it later fractured. This tooth had to be extracted because it cracked all the way to the root.
Teeth that are very sensitive, either from a lot of wear, or from receded gums, sometimes require crowns to seal and protect the teeth from hot and cold sensitivity.
Root Canal Therapy:
A tooth that has undergone Root Canal Therapy will need a crown to properly seal and protect the tooth. A tooth with Root Canal Therapy is more brittle than a tooth with a healthy nerve and blood supply. A crown provides the necessary support to the tooth.
In cosmetic dentistry, crowns (sometimes called caps ) are used less frequently since the advent of veneers, but in some cases a crown may be necessary for a particular tooth. A tooth with a bad fracture or a large filling may be a candidate for a crown instead of a veneer.