Development of Titanium Alloys for Dental Castings

钛合金具有优异的耐腐蚀性和良好的生物相容性，有望在医疗和牙科领域得到应用。牙科材料对精度和复杂性要求很高，精密铸造是牙科合金不可缺少的技术。然而，钛是一种非常活跃的金属，牙科铸造涉及到一些需要解决的问题，如高温氧化、大气元素的吸收以及与模具材料的反应。国内外对钛合金牙科铸造的研究主要是从模具材料方面进行的。而钛的高熔点(约1670ﾟC)是造成铸件缺陷的主要因素之一。要解决这一问题，合金化的改进被认为是一个重要的作用。合金化不仅可以降低合金的熔化温度，还可以提高合金的力学性能。本研究的目的是开发具有良好力学性能的钛合金，如…发展牙科铸造用新型钛合金的第一个问题是钛材料引起的力学性能的大分散。为此，对影响纯钛铸件力学性能的因素进行了研究。影响因素有钛锭的种类、熔化气氛和铸件中的杂质。获得了所需真空度、钛品位、杂质元素含量等影响因素的基本数据。在此基础上，对钛-锆合金和镍-钛合金进行了研究。钛-锆合金也表现出良好的生物相容性；钛-锆合金表面在人工生物液体中的成分变化与钛表面略有不同。牙科铸造镍钛合金比钛更容易铸造，由于镍钛合金的熔点约为1300ﾟC，比钛低近400ﾟC，所以用常规方法可以在不损失形状记忆效应和超弹性的情况下铸造。较少

Since titanium alloys show excellent corrosion resistance and good biocompatibility, they are expected to be applied in the medical and dental fields. Precision and complication are required in dental materials, therefore, precise casting is an indispensable technique for dental alloys. However, dental casting of titanium, a very active metal, involves some problems to be solved, e.g., oxidation at high temperatures, absorption of atmospheric elements, and reaction with mold materials. Many researches for dental casting of titanium have been performed, mainly from the aspect of mold materials. While high melting point of titanium, about 1670 ﾟC, is one of the main factors of casting defects. To solve this problem, the improvement in alloying is thought to play an important role. Alloying is effective not only to lower the melting temperature but also to improve the mechanical properties. The purpose of this study was to develop the titanium alloys showing good mechanical properties as … More well as suitable for dental casting.The first problem in developing new titanium alloys for dental casting was the large scatter in mechanical properties caused by titanium materials. Therefore, the factors influencing the mechanical properties of pure titanium castings were investigated. The factors were the kinds of titanium ingots, the atmosphere in melting, and the impurities in the castings. As a result, basic data on the influential factors - required vacuum degree, titanium grade, amounts of impurity elements - were attained. Based on the findings, researches on Ti-Zr and Ni-Ti alloys were performed. Ti-Zr alloys also show good biocompatibility; the compositional change of Ti-Zr alloy surface in an artificial bioliquid was somewhat different from titanium surface. Dental casting of Ni-Ti alloy was easier than titanium; it could be cast without losing the special properties of shape memory effect and superelasticity by a conventional method because the melting point of Ni-Ti alloy were about 1300 ﾟC, nearly 400 ﾟC lower than titanium. Less