Some considerations regarding the degradational interactions between mouth rinses and silver-soldered joints

For immersion tests with mouth rinses of Lavoris, Green Mint, and Cepacol, silver solders and silver-soldered stainless steel joints exhibited corrosive degradational reactions. Exposures to Lavoris resulted in the severest surface attack as followed by optical microscopy, scanning electron microscopy, and energy-dispersive x-ray microanalysis. This was confirmed by measurements of electrochemical potential and polarization. The cyclic voltammograms in Lavoris indicated a highly active corrosion potential of -0.94 v. sce, while potentials in Mint and Cepacol were only about -0.25 v. This activity is attributed to the presence of zinc chloride as the active agent in Lavoris, as well as the high zinc content (up to about 20 percent) and even higher zinc concentrations contained in copper-zinc microstructural phases of the silver solders and the ease for dezincification corrosive attack. Large increases in current above about -0.2 v. are observed with all rinse solutions as well as a prepared saliva substitute solution. The importance of toxicologic considerations of the agents released from silver solders and the interactions of corrosion with stress as factors in causing delayed failures of soldered joints are discussed. The presently available commercial solders without cadmium and zinc contents, but with higher fusion temperatures and decreased flow characteristics, are recommended for dental applications to increase the resistance to corrosion.