Influence of temperature and pH on corrosion resistance of Ni–Cr and Co–Cr dental alloys on oral environment

Thesis (MTech (Biomedical Technology))--Cape Peninsula University of Technology, 2015.Dental alloys are widely used in direct contact with oral tissue. In recent years after the price of gold significantly increased, cheaper dental materials were generally considered in the market particularly dental alloys such as cobalt-chromium (Co–Cr), nickel-chromium (Ni–Cr) and titanium alloys. Cobalt– chromium alloys for example, are used in prosthetic for the fabrication of removable partial dentures and also for the fabrication of some fixed prosthetic appliances, due to its excellent properties such as biocompatibility, good mechanical behavior and corrosion resistant. In this work, the corrosion behavior of three different dental alloys, namely PD CASTA H, CERACAST NB Beryllium Free and PD 2000 alloys were studied and tested in Ringers solution (artificial saliva) at different pH values and temperature. The dental alloys were immersed in the Ringers solution for 14 days. The microstructure characterization and composition of selected alloys were done before and after 14 days of corrosion test on artificial saliva, using scanning electron microscopy (SEM). The surface roughness of the alloys was investigated by atomic force microscopy (AFM). The EDS, XRD, and TOF–SIMS were also used in the study. Electrochemical measurement on dental alloys was performed using cyclic voltammetry (CV). A saturated calomel electrode (SCE) was used as reference electrode, platinum was used as counter-electrode and Ni–Cr and Co–Cr alloys were used as working electrode. The polarization curves were plotted in the potential range of -1000 mV/SCE to +1000 mV/SCE at scanning rate of 0.2 mVss-1. It has been shown in the present study that the corrosion behavior of PD CASTA H and PD 2000 alloys, containing Co and a high Cr content, displays the best corrosion resistance compared to CERACAST NB alloy. The influence in the temperature and pH of the solution had effects on the properties of dental alloys. The electrochemical behavior of dental alloys were studied to provide a comprehensive examination of various biomedical materials used in dental application. However, the surface roughness and the surface morphology of the alloys are very important in dental study and application