Section of Restorative Dentistry, and Prosthodontics, College of Dentistry, University of Tanta, Egypt.
J Prosthodont. 2010 Apr;19(3):194-9. doi: 10.1111/j.1532-849X.2009.00565.x. Epub 2010 Feb 19.
The rationale for using gold alloys is based largely upon their alleged ability to resist corrosion, but little information is available to determine the corrosion behavior of recast alloys. This study characterized the elemental composition of as-received and recast type III gold alloy and examined the in vitro corrosion behavior in two media using a potentiodynamic polarization technique.
Seventy-eight disk-shaped specimens were prepared from a type III gold alloy under three casting protocols according to the proportion of as-received and recast gold alloy (n = 26). (1) Group as received (100% as-received metal), (2) group 50% to 50% (50% wt. new metal, 50% wt. once recast metal), and (3) group recast (100% once recast metal). The surface structures of 20 specimens from each group were examined under scanning electron microscopy, and their elemental compositions were determined using X-ray energy-dispersive spectroscopy. Further, the potentiodynamic cyclic polarization between -1000 and +1000 mV (SCE) were performed for six specimens from each casting protocol in 0.09% NaCl solution (n = 3) and Fusayama artificial saliva (n = 3) at 37 degrees C. Zero-current potential and corrosion current density were determined. The data were analyzed with 1-way ANOVA and the Ryan-Einot-Gabriel-Welsch multiple-range test t (alpha= 0.05).
Elemental composition was significantly different among the casting groups (p < 0.001). The mean weight percentage values were 72.4 to 75.7% Au, 4.5 to 7.0% Pd, 10.7 to 11.1% Ag, 7.8 to 8.4% Cu, and 1.0 to 1.4% Zn. The mean values for Zero-current potential and corrosion current density for all casting protocols were not significant (p > 0.05); however, the difference between the electrolytes was significant (p < 0.001). Fusayama artificial saliva seemed to offer the most corrosive environment.
Type III gold alloy in any casting protocol retained passivity under electrochemical conditions similar to the oral environment. Moreover, high-gold type III alloys from reputable manufacturers and recasting protocol tested should produce acceptable corrosion-resistant castings.
使用金合金的基本原理主要基于其据称能够抵抗腐蚀的能力，但很少有信息可用于确定再铸合金的腐蚀行为。本研究通过动电位极化技术在两种介质中对原始和再铸 III 型金合金的元素组成进行了特征描述，并对体外腐蚀行为进行了研究。
根据原始和再铸金合金的比例（n = 26），用三种铸造方案从 III 型金合金中制备了 78 个圆盘状试件。（1）原始组（100%原始金属），（2）50%至 50%组（50%wt.新金属，50%wt.一次再铸金属），（3）再铸组（100%一次再铸金属）。每组 20 个试件的表面结构用扫描电子显微镜进行检查，用 X 射线能谱法测定其元素组成。进一步，在 37°C 下，用 0.09%NaCl 溶液（n = 3）和 Fusayama 人工唾液（n = 3）对每个铸造方案的 6 个试件进行了动电位循环极化，电位范围为-1000 至+1000 mV（SCE）。确定零电流电位和腐蚀电流密度。用单向方差分析和 Ryan-Einot-Gabriel-Welsch 多重范围检验 t（α=0.05）对数据进行分析。
铸造组之间的元素组成有显著差异（p < 0.001）。平均重量百分比值为 72.4%至 75.7% Au、4.5%至 7.0% Pd、10.7%至 11.1% Ag、7.8%至 8.4% Cu 和 1.0%至 1.4% Zn。所有铸造方案的零电流电位和腐蚀电流密度平均值均无显著差异（p > 0.05）；然而，电解质之间的差异具有统计学意义（p < 0.001）。Fusayama 人工唾液似乎提供了腐蚀性最强的环境。
在类似于口腔环境的电化学条件下，任何铸造方案的 III 型金合金都保持钝化。此外，来自知名制造商的高金 III 型合金和测试的再铸方案应能生产出具有可接受耐腐蚀性能的铸件。
