Masao Ibaraki

The Corrosion Resistance and Electrochemical Property of Dental Alloys

The corrosion resistace of some dental substitutional alloys now in uses in our country was testedd by dipping them in dil HCl-, lactic acid-, NaCl-, Na2S- solutions, etc. at 37° for 1 week. The results show that Cu-alloys and Acolite were corroded by any of the above solutions, Ni-Cr alloys by only acid solutions, while none of the solutions attacked 18-8 stainless steel and Ag-Pd alloys. The electrolytic potential of the, dental alloys in 1% NaCl and Ringers solution was then measured against N-calomel electrode. 18-8 stainless steel and some Ni-Cr alloys became much nobler with time, and the potential difference between them and 22 K gold was only 0.02-0.08 V after 24 hrs, while other metals and alloys became baser or slightly nobler under the same condition. The galvanic current between each substitutional alloy and 22 K gold in 1% NaCl and lactic acid solutions with electrodes o_??_ 1cm2 and 1cm appart was measured for 3 hrs by a milliammeter, microammeter or a mirror galvanometer in accordance with the amount of current, and the initial current in the instance of short circuiting two electrodes was measured with an oscllograph. The initial current instantaneously-decreases by polarization and alter 1/30-1/10 sec nearly horizontal value is attained and then the current decreases very slowly, taking after several minutes nearly steady-value. The steady galvanic current for several alloys, which is very small compared to the initial value, is as _??_ollows (10-6 A unit; Palladium-s (Ag-Pd alloys)=0.01), 18-8 Stainless steel=0.13, N-Cl (Ni-Cr alloy)=0.06, Ni=3, Cu-9.7 Randolf=14.5, Acolite=35 Amalgam=100 in 1%, NaCl solution.