[Amalgam onlay restoration].

The purpose of this article is to describe and discuss a modified amalgam onlay preparation which is a conservative approach to restoring extensively decayed teeth. The cavity preparation for the amalgam restoration appears similar to a preparation for a cast restoration and at the same time the preparation provides a 90 degree cavosurface bevel. The amalgam onlay preparation may be used in any class 1 or class 2 cavity preparation when the cusps are weak and should be protected by the restorative material. The modification of the cavity which is the angulation of the buccal and the lingual walls provides convenience to the clinician during the condensation and carving of the amalgam. In addition to this the natural contours of the tooth are preserved and in cases of upper posterior teeth the buccal surface of the cusps is almost completely preserved and the appearance of the amalgam is not different from that of a gold onlay restoration.