Inlays are similar to fillings and partially cover a tooth. They are custom-made to fit the prepared cavity or breakage, and are then cemented into place.
Onlays are more extensive reconstructions that cover one or more surfaces of a tooth. Onlays are indicated in situations where a substantial reconstruction is required. However, more of the tooth structure can be conserved compared to the placement of a crown.
Inlays and onlays are usually applied in two dental visits. At the first visit, the old filling, or decay, is removed, and the tooth is prepared for the inlay or onlay. The dentist then makes an impression of the tooth and sends this impression to a dental laboratory. The laboratory uses the impression to construct a custom-made porcelain or gold inlay or onlay, which the dentist will seat during the second visit.