A type of "indirect" restoration (made in a lab/mill) that covers one or more cusps (points) of a tooth but not the entire tooth. It is often called a "partial crown."
When a cavity is too big for a regular filling but the tooth is not damaged enough to require a full crown, an onlay is the conservative choice. It preserves more healthy natural tooth structure than a crown.
A custom-made porcelain piece that fits over the biting surface of a damaged tooth.