Onlay

Additionally, when decay or fracture incorporate areas of a tooth that make amalgam or composite restorations essentially inadequate, such as cuspal fracture or remaining tooth structure that undermines perimeter walls of a tooth, a gold onlay might be indicated. Similar to an inlay, a gold onlay is an indirect restoration which incorporates a cusp or cusps by covering or onlaying the missing cusps.

All of the benefits of a gold inlay are present in the onlay restoration. The onlay allows for conservation of tooth structure when the alternative is to totally eliminate cusps and perimeter walls for restoration with a crown. Because onlays have a very long margin (i.e. the line of tooth-to-restoration contact is much longer than that of a crown because of the many turns and curves that an onlay makes in contacting the tooth), some dentists feel that an onlay is a fundamentally inferior restoration.

This is because it is primarily the marginal adaptation of any dental restoration that will decide whether or not it will successfully remain in the mouth without exhibiting recurrent decay. The increase in marginal length consequently provides a further likelihood of failure.