Methods: Two groups of cast specimens were used. The first group contained four specimens produced from a Co-Cr base alloy (Octa-C, SAE Dental products IncBramarhaven, Germany) and the second four specimens from cpTi (Biotan, Schutz Dental, Rosbach, Germany). Two specimens of each group were subjected to spark erosion and the other two were conventionally ground and polished. All specimens were embeded with epoxy resin. Two spark eroded and two conventionally finished specimen of each group were used as an electrode in a 1% NaCl solution. In order to obtain the polarization curves a saturated calomel electrode was used as a reference and a platinum wire was used as a counter electrode. The potential scan rate was 10mV/sec and the temperature 37 ïC. The rest two specimens were used for EIS analysis. EIS was mesured at OCP in a frequency range of 106 to 0.01Hz with an applied sinusoidal potential of 15 mV.
Results: Polarization curves showed comparable Ecorr values for Co-Cr alloys (Ecorr=-0.04V) but decreased Epit after EDM procedure (Epit for reference= 0,30V, Epit after EDM = 0.10V). Ti specimens demonstrated decreased Ecorr as well as Epit values compared to conventionally prepared surfaces (Ecorr for reference=-0.30V and Ecorr after EDM= -0.50V, Epit for reference= -0.10V, Epit after EDM= -0.25V). The results of cyclic voltametry and EIS revealed that both alloys showed decreased corrosion resistance after spark erosion treatment.
Conclusion: Spark erosion of Co-Cr and Ti alloys decreases their corrosion resistance in media contains Cl- ions.