When a filling occupies more than 50% or more of the width of a tooth, a crown or onlay restoration is indicated. Crowns surround the tooth and brace it together, while onlays fit down inside the tooth and cover all or some to the cusps of the tooth to provide strength. Teeth with large fillings are prone to breaking and splitting because the large filling acts as a wedge and breaks the tooth. Crowns and onlays provide strength and stability that a large filling cannot provide to the tooth.
Reasons for a crown or onlay:
- The tooth has a large cavity
- The tooth has a broken filling or restoration
- The tooth has had a root canal
- The tooth has a large weak filling
Crowns and onlays can be made out of different materials. Each material is indicated in different situations.
These materials are:
- Porcelain fused to a metal substructure
- All porcelain
- Porcelain fused to a non-metal substructure