The tensile strength and appearance of solder joints in three base metal alloys made with high- and low-temperature solders

Abstract

N ickel-chrome and cobalt-chrome alloys have been used for nearly 50 years in removable partial dentures. The demand for similar materials for crown restorations and fixed prostheses has been evident because of the elevated cost of gold. Several changes have been made to the original alloys to improve their physical characteristics, and many base alloys are available for single and fixed prosthodontic units. The alloys with a high nickel content are popular. Nickel increases the ductility, making the restoration more amenable to manipulation. Unfortunately, nickel causes allergic contact dermatitis,’ and there are biologic hazards with this element. In Sweden all alloys containing more than 1% nickel are prohibited. Beryllium has been added to some alloys to lower the melting temperature. Unfortunately, inhaling this element can cause berylliosis, a granulomatous lung disorder. Consequently, several alloys that do not contain nickel or beryllium have been developed for restorations. Fixed prostheses, with or without porcelain veneers, are frequently joined with soldered joints. The parts are soldered before or after the porcelain is bonded to the metal, and several studies have been reported on the strength of preceramic versus postceramic solder joints.2-4 The results differ, but there is agreement that preceramic soldering is difficult; porosity and other defects have been associated with base metal hightemperature joints.5 Tests performed with high-temperature solder joints using a Co-Cr-Mo alloy (Vitallium, Howmedica, Inc., Chicago, Ill.) demonstrated that high quality joints can