In dentistry and oral surgery, an onlay is a method of tooth restoration, which covers, protects or reinforces one or more cusps. Tooth restoration can be achieved either by direct or indirect procedures. Direct restorations include amalgams or esthetic composite, and should be employed in the least invasive way possible. Onlay and inlay are methods for restoring teeth in an indirect way. The most important characteristic is that they compromise more dental tissue than the direct methods (thus are more invasive), where onlays cover one or more cusps and inlays do not cover any cusp: they are limited to the intra-cuspal perimeter. Onlays and inlays are often used when teeth present extensive cavities due to caries, extensive tissue loss due to trauma or caries, as well as when direct restorations lack retention.