Introduction
Cast metal restorations are indirect restorations, usually of gold alloy, cast in the laboratory and cemented at a second visit. This note covers the inlay, the onlay and, briefly, the partial veneer crown: when to use them and how the cavity is prepared. Because a casting is held mainly by friction and cement along one path, its cavity has occlusally divergent walls and bevelled margins – nearly the opposite of an amalgam cavity.
Types and material
Material. The classic material is a high-gold casting alloy, graded by hardness into types I–IV: type II (medium) for inlays, type III (hard) for onlays and partial veneer crowns. Gold is biocompatible, does not tarnish or corrode, wears at about the rate of enamel and is ductile, so a thin margin can be burnished onto the tooth. Other cast alloys (palladium–silver, nickel–chromium, cobalt–chromium) are cheaper but harder and less ductile, so their margins cannot be burnished; nickel can cause allergy.