A comparison of the strength of base metal and gold solder joints

The purpose of this study was to evaluate the procedures involved in forming high- and low-fusing solder joints between two different base metal alloys and to compare the strength of these joints with the strength of those formed between specimens made from a high-gold content alloy. The conclusions of this investigation can be summarized as follows. All but 11 of the 120 specimens failed through the solder joint, which confirms that the solder joint is usually the weakest part of a fixed partial denture. The high-fusing joints formed between the base metal alloys showed higher relative bending strength values than the high-fusing joints formed between the gold alloy specimens. The low-fusing joints formed between the base metal alloys showed higher relative bending strength values than the low-fusing joints formed between the gold alloy specimens, and the low-fusing base metal joints exhibited the highest strength values in this study. The low-fusing joints formed between gold alloy specimens consistently bent before fracturing. Solder joints fail both adhesively (separation of the solder from the parent metal) and cohesively (fracture through the solder, parent metal, or a combination of both). A correctly formed joint between gold components should show cohesive fracture, whereas adhesive fractures are apparently acceptable with base metal alloys since the low-fusing base metal joints failed in this manner but still exhibited high strength values. Voids of different sizes and locations were observed in most of the solder joints, and within each group tested there was usually less strength exhibited by the joints with larger areas of porosity.