A crown fits over the entire top of the tooth above the gum line. Crowns cover, protect, seal and strengthen a tooth. A crown is needed when a filling just will not work. A crown may be made of gold, white porcelain, or porcelain fused to gold. There are many situations that may call for a crown:
Large decay. 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.
Cracked tooth. 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.
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.