Inlays and overlays are commonly referred to as partial crowns, and are often used to restore a tooth, strengthen it, and prevent further damage. The existing tooth will be used as a base, and the inlay or overlay is placed on it.
An inlay is used when there is no damage to the cusp of the tooth, and the inlay can simply be placed right on the tooth. An overlay is used when the damage is a little more extensive. First, the decay will be removed from the tooth and a mold will be taken of the area and sent to a dental lab. A restoration is then created to perfectly fit your mouth out of porcelain, gold, or composite resin. The restorations usually take between 2-3 weeks to create, during which time you will be fitted with a temporary restoration. As soon as your restoration is finished, it will be cemented onto the existing tooth, giving you a strong and invisible bond and a whole, healthy tooth.