치과용 Ni-Cr과 Co-Cr 합금의 부식성과 도재와의 접합 특성

Abstract

Using the specimen (L 1.5cm × W 1.0cm × T 0.5cm) of Ni-Cr and Co-Cr alloys which were fabricated by centrifugal casting, composite samples of porcelain fused to metal were prepared to examine the interface between metal and porcelain with the utilization of optical microscope (OM) and scanning electron microscope (SEM). As compared to porcelain fused to Ni-Cr alloy having thick layer (~10㎛) of oxide, relatively thin layer (less than 5㎛) was formed in porcelain fused to Co-Cr alloy indicating that the interface of Co-Cr alloy and porcelain is strong enough, and that it could have a better adhesion strength than that of Ni-Cr alloy and porcelain, to be used as a dental prosthesis. The oxide layer was examined and analyzed to be mainly Al2O3 and Cr2O3 by EDX. The corrosion rates are determined from the polarization curves based on the Tafel extrapolation method. The corrosion rate of Co-Cr alloy (1.61×10-6A/㎠) was three times lower than that of Ni-Cr alloy (4.83×10-6A/㎠) indicating that corrosion resistance of Co-Cr alloy is better. A composite of porcelain fused to Ni-Cr alloy extracted from a patient after about four years of usage was examined to show its resistance to corrosion. The composite was made up with two parts; one being metal covered with porcelain and the other being only bare metal exposed to environment. OM and SEM images for the exposed metal reveal a typical corrosion after the usage of about four years by a patient. The indication of corrosion means that Ni and its compounds could be formed when Ni is released and absorbed in a body. Therefore it is necessary further to do in vivo experiment to evaluate the hazardousness of Ni and its compounds to human body. The aim of this research was to suggest a better replacement of Co-Cr over Ni-Cr alloy as a dental prosthesis for a long term use and to warn the public about the possibility of carcinogenicity of Ni and its compounds when absorbed in a human body.