Microstructure of amalgam surfaces : CHAN K. C., EDIE J. W. and BOYER D. B. J. Prosthet Dent.36 (1976) 644–648

Abstract

the in vitro tarnish resistance of a model amalgam was investigated as a function of finishing technique and age at the time of finishing. One hundred and thirty samples of one alloy were divided into 7 groups and then finished after from 60 min to 8 weeks, either by carving, burnishing, dry clinical polishing, or wet metallographic polishing. The tarnishing treatment consisted of cyclic dipping in a 0.5% sulfide or chloride solution at 37°C for 16 h. Tarnish was evaluated both by subjective visual ranking and by use of a digital reflectometer. Results from the 2 evaluation methods agreed closely, with decreases in reflectance resulting from tarnish ranging from 12.9%–58.9%. In sulfide solutions the best results were obtained from those specimens polished 60 min after condensation. Carved and burnished samples tarnished less than those polished after one week, suggesting that surface roughness was not the most important factor associated with tarnishing. In contrast, in chloride solutions 8-week specimens tarnished less than 60 min specimens, and repolishing corroborated that the chloride attack was restricted to a thinner layer than the sulfide attack. These experiments provide some insight into the mechanisms of corrosion.