Properties of titanium–silver alloys for dental application

Abstract

The purpose of this study was to develop titanium–silver alloys with biocompatibility, high corrosion resistance, and low ion-release rate, and to evaluate the electrochemical properties of titanium–silver alloys in artificial saliva. Titanium–silver alloys with silver contents ranging from 0 to 4.5 at % in steps of 0.5 at % were designed. The alloys were arc melted, homogenized at 950°C for 72 h, hot rolled to 2 mm in thickness, and finally solution heat treated at 950°C for 1 h and quenched in water. Chemical compositions, phases, hardnesses, electrochemical properties, and the cytotoxicity of the alloys were investigated. The purity of titanium–silver alloys was maintained above 99.9%, because few impurities were introduced through their manufacture. In the case of alloys containing silver in the range 2.0–4.0 at %, the formation of an acicular α phase was observed inside the β phase. The acicular phase got thinner with increasing amounts of silver. This means that silver is a β-phase stabilizing element in titanium–silver alloys. The hardness value tended to rise with increasing silver content and increased largely over 3.5 at %, and the increase of the hardness value versus pure titanium was about 33%. It is believed that the substantial increases in hardness was due to the effects of solid solution strengthening and of α–β phase transition. Moreover, titanium–silver alloys had higher corrosion resistances than pure titanium. These results mean that silver additions to titanium can improve alloy corrosion resistance. Passive current densities in the potentiodynamic polarization curves were dependent on the chemical compositions of the titanium–silver alloys. However, they did not show a linear relationship with respect to silver contents. Titanium–silver alloys did not show pitting corrosion in artificial saliva. It is believed that silver addition to titanium strengthened the passive film due to titanium dissolution induced by the different electromotive forces of titanium and silver. In the agar overlay test, the cytotoxicity of the titanium–silver alloys and of titanium were none or mild. In summary, titanium–silver alloys had higher mechanical properties and corrosion resistance than titanium, and toxicities that were similar to titanium. Therefore, it is recommended that titanium–silver alloys be adopted cautiously by the biomedical and dental fields.