OBJECTIVEThe purpose of this study was to investigate effects of cryotreat on the corrosion resistance of SDA-II medium melting-point castable alloy.

METHODS12 samples were divided into three groups, including the control group, the cryotreated group and the cryotreated & post-cryogenic treated group. The cryotreating process was firstly dropping the temperature from room temperature to -170 degrees C with dropping rate 3 degrees C/min, maintaining -170 degrees C for 2 hrs, and then returning to ambient temperature with an increasing rate of 1 degree C/min. The post-cryogenic process was maintaining the samples in 300 degrees C for 1 hr. Finally, all samples were subjected to the electrochemical potentiodynamic polarization after immersed in the artificial saliva (ISO/TR 10271: 1993 (E), pH 6.8) for 24 hrs at ambient temperature. The exposing area of each sample was 10 mm x 10 mm. The electrochemical tests were carried out in the artificial saliva under 37 degrees C, with the scanning rate of 20 mV/min, starting potential -200 mV below OCP and stopping current 10(-3) A. The corrosion currents (Icorr), the pitting corrosion potentials (Eb) and the potentiodynamic polarization curves were observed using the 283 electrochemical corrosion measuring system automatically.

RESULTSFor SDA-II medium melting-point castable alloy, cryotreat reduced corrosion rate of the alloy, but had no effect on the pitting corrosion potential. As far as the post-cryogenic treatment, it didn't affect the corrosion resistance.

CONCLUSIONThe results suggested that cryotreat was an effective procedure in enhancing the corrosion resistance of SDA-II medium melting-point castable alloy, and it may be applicable in prosthetic dentistry.