Vermilyea S G, Cai Z, Brantley W A, Mitchell J C
Section of Primary Care, College of Dentistry, Ohio State University, Columbus 43210-1241, USA.
J Prosthodont. 1996 Dec;5(4):288-94. doi: 10.1111/j.1532-849x.1996.tb00513.x.
This investigation compared the Vickers hardness and microstructures of four recently marketed, palladium-based alloys for metal-ceramic restorations.
Wax patterns simulating copings for maxillary central incisors were invested in a fine-grained, carbon-free, phosphate-bonded investment. Following burnout, the palladium alloys were fused with a gas-oxygen torch, centrifugally cast, and bench-cooled. Representative castings were embedded in transparent metallographic resin and sectioned to yield two mirror-image specimens. The specimens were evaluated in either the as-cast condition or following heat treatment simulating the firing cycles for Vita VMK porcelain. Vickers hardness measurements (n = 50) were made using a 1-kg load, and photomicrographs of polished and etched specimens were obtained with a scanning electron microscope.
The measured values of microhardness for the as-cast alloys were in excellent agreement with values reported by the manufacturer. The hardness in the as-cast condition was significantly greater for the Pd-Cu-Ga-In alloy, compared with the other three alloys, which did not contain copper. For the three high-palladium (> or = 75 wt%) alloys, there were small (4%-8%) decreases in hardness following heat treatment, whereas a larger decrease (13%) in hardness occurred for the Pd-Ag-In-Sn alloy after heat treatment. The porcelain firing cycles caused microstructural homogenization for all four alloys, and the relatively thick near-surface oxidation region in the Pd-Cu-Ga-In and Pd-Ag-In-Sn alloys was not observed in the two heat-treated Pd-Ga-Ag-In-Au alloys.
The multiphasic microstructures of these alloys may have some significance for the in vitro and clinical corrosion behavior and the metal-ceramic bond strength. The hardness for the three high-palladium alloys may be controlled by submicroscopic precipitates that remain unaltered by heat treatment. The significantly greater hardness for the Pd-Cu-Ga-In alloy may cause greater difficulty for finishing castings in the dental laboratory compared with the other three alloys studied. The strengthening mechanism for the Pd-Ag-In-Sn alloy has significant temperature dependence, which might be exploited to achieve optimum mechanical properties.
本研究比较了四种近期上市的用于金属烤瓷修复体的钯基合金的维氏硬度和微观结构。
将模拟上颌中切牙全冠的蜡型包埋于细粒度、无碳、磷酸盐粘结的包埋材料中。焙烧后，用气体氧气喷枪将钯合金熔化，离心铸造，并在工作台上冷却。将代表性铸件嵌入透明金相树脂中并切片，得到两个镜像标本。标本在铸态或模拟Vita VMK瓷烧制周期的热处理后进行评估。使用1千克载荷进行维氏硬度测量（n = 50），并用扫描电子显微镜获取抛光和蚀刻标本的显微照片。
铸态合金的显微硬度测量值与制造商报告的值非常一致。与其他三种不含铜的合金相比，Pd-Cu-Ga-In合金在铸态下的硬度明显更高。对于三种高钯（≥75 wt%）合金，热处理后硬度有小幅度（4%-8%）下降，而Pd-Ag-In-Sn合金热处理后硬度下降幅度较大（13%）。瓷烧制周期使所有四种合金的微观结构均匀化，在两种热处理后的Pd-Ga-Ag-In-Au合金中未观察到Pd-Cu-Ga-In和Pd-Ag-In-Sn合金中相对较厚的近表面氧化区域。
这些合金的多相微观结构可能对体外和临床腐蚀行为以及金属烤瓷结合强度具有一定意义。三种高钯合金的硬度可能由热处理后未改变的亚微观沉淀物控制。与其他三种研究合金相比，Pd-Cu-Ga-In合金明显更高的硬度可能会给牙科实验室的铸件精加工带来更大困难。Pd-Ag-In-Sn合金的强化机制具有显著的温度依赖性，可利用这一点来实现最佳机械性能。
