Masayoshi Tagaya1,2, Masao Ibaraki1,2
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 Ringer's 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.
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