Inlays and onlays are often referred to as partial crowns. They use the existing tooth as a base and fit the inlay or onlay onto the tooth. This is done to strengthen the tooth, restore its shape, and prevent further damage. An inlay is done when there is no damage to the cusps of the tooth and the inlay can be placed right on the tooth. An onlay is used when the damage is a little more extensive.
The decayed area of the tooth is first removed during the procedure. A mold of the tooth is then taken and sent to a dental lab. They create a restoration made from porcelain or a composite resin.