Inlays and onlays are traditional methods of restoring teeth known as indirect fillings.
When the biting surface of the tooth is damaged and regular fillings are not adequate, inlays and onlays are used to fill crevices or repair extensive damage. An inlay is an indirect restoration (filling) consisting of a solid substance (as gold or porcelain) fitted to a cavity in a tooth and cemented into place. An onlay is the same as an inlay, except that it extends to replace a cusp. Crowns are onlays which completely cover all surfaces of a tooth.