The Study Of The Stability Of Ni-Cr Alloy By Surface Electroplating With Gold

Porcelain-fused-to-metal (PFM) has been widely used in clinic now, for lots of advantages, such as beautiful color, vivid configuration and comfort. PFM restorations consist of metal coping and porcelain part outside. There are a lot of metals such as gold alloy, cobalt-chromium alloy, nickel-chromium alloy and pure titanium which were usually used for metal coping. PFM restorations with nickel-chromium alloy base crown represent good mechanical properties and low price, and could also meet basic requirements for prosthesis,so, Ni-Cr alloy was widely used for PFM domestically. But there are few deficiency, for example corrosion resistance and biocompatibility of which may result in some adverse reactions with patients. PFM restorations with precious metal base crown represent both excellent corrosion resistance and biocompatibility. However, the high cost of precious metal restricts its usage in clinic.There are lots of factors in intra-oral environment can cause chemical corrosion and electrochemical corrosion, such as saliva, gingival crevicular fluid, electrolyte solutions, temperature, moisture degree and pH value. Some metal ions which are poisonous to tissue were released during corrosions. Patients with Ni-Cr alloy PFM restorations may suffer some adverse reactions, such as engorgement, inflammation, hypersusceptibility and gray line in gingival. Healthy, appearance and so far could be weakened, under above-mentioned conditions.Corrosions occur initially on the surface of metal, therefore, surface treatment can stop the corrosion and improve biocompatibility of metal. Gold was recognized as the best metal for both chemical and mechanical properties, the color and luster of which are more fit for base crown fabrication. Hence, some researcher use gold-plating technique on Ni-Cr alloy base crown fabrication to improve the surface properties of Ni-Cr alloy.In this study, a new Non-cyanogen gold-plating technique was employed for Ni-Cr alloy surface treatment. The corrosion resistance, chemical stability and biocompatibility of gold-plated Ni-Cr alloy were evaluated by electrochemical constant potential polarization curve, uniformity complete immersion, cytotoxicity test, haemolysis test and mucous membrane irritation test (Hamster's pouch).The results showed that: when pH value of the artificial saliva was 6.8 or 5.0, the positive corrosion potential of Ni-Cr electrodes was fewer than that of gold-coated one, while the corrosion current density of Ni-Cr electrodes was higher than that of gold-coated one, which meant that the corrosion resistance of gold-coated Ni-Cr alloy was improved. The amount of Ni and Cr released from specimens coated with gold was much fewer than those from unplated specimens (P <0.05), which meant the stability of Ni-Cr alloy on the surface was improved. The biocompatibilities of gold-coated Ni-Cr alloy were better than the uncoated alloy, though there was no difference in biological ranking. The further researches of the other aspects of biocompatibilities for non-cyanogen gold-plated Ni-Cr alloy still need to be undertaken..