The evaluation of the applicability of using gold plating to enhance the predictability and strength of base metal post ceramic gold solder joints when using a flux that does not discolour the porcelain
Waddell, John Neil
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The unpredictability of solder joints in dental base metal alloys constitute a major problem. This study aimed to establish whether gold plating the joint surfaces of a metal ceramic base metal alloy prior to postceramic soldering would enhance the predictability of the soldering method and joint strength. 150 standardised test specimens were prepared from 3 Oegussa dental alloys, viz Resistal P (Nier), Oegulor M (AUPt) and Realor (PdAU). The Resistal P specimens were subjected to 6 porcelain firing cycles and solder joint surfaces of 40 specimens gold plated prior to soldering, using gold plating equipment and solutions found in the jewellery industry. suitable fluxes were used and all soldering was done in a porcelain furnace. First the soldering method was validated by soldering 20 oegulor M specimens and determining the tensile strength of the 10 joints in an Instron testing machine. The data were then compared with the ISO minimum standards. The soldering method proved sound and a control was thus established. secondly, using 3 alloy combinations without gold plating, 30 solder joints were made and their tensile strengths determined. This established the level of predictability and strength and parameters for comparison. Thirdly, the above procedure was repeated, but the Resistal P specimen joint surfaces were gold plated prior to investing for soldering. The levels of predictability and strength were then compared with the parameters set. The fracture sites of broken joints were examined and photographed using a metallurgical microscope. The data were analysed using 4 statistical tests. The Oegulor M control group solder joints were the strongest and the Resistal P joints the weakest. The success rates for the non-plated joints were; oegulor M to oegulor M = 100%, Resistal P to oegulor M = 90%, Resistal P to Realor = 80% and Resistal P to Resistal P = 60%. The success rates for the gold plated joints were; Resistal P to oegulor M = 60%, Resistal P to Realor = 40% and Resistal P to Resistal P = 80%. This study found, under the circumstances of testing, that gold plating of the base metal alloy prior to investing for postceramic soldering did not enhance the strength, solderability and predictability of the solder joints to an extent that a flux that does not discolour porcelain can be used.