Susceptibility to localized corrosion of stainless steel and NiTi endodontic instruments in irrigating solutions.

Abstract

To evaluate the pitting and crevice corrosion characteristics of stainless steel (SS) and NiTi endodontic files in R-EDTA and NaOCl irrigating solutions. The corrosion behaviour of two H-files produced from different SS alloys (Mani, AISI 303 SS, Dentsply Maillefer, AISI 304 SS) and one file produced from NiTi alloy (Maillefer) was determined in R-EDTA and NaOCl irrigating solutions by the cyclic potentiodynamic polarization method. The cutting flutes of 12 files of each material were embedded in an epoxy resin, polished, exposed to the irrigating solutions and used as an electrode. An Ag/AgCl electrode was used as a reference, a platinum plate was used as a counter electrode and polarization curves were obtained for all files in R-EDTA and NaOCl irrigating solutions in 37 degrees C with a potential scan rate of 5 mV min(-1). Corrosion potential (Ecorr), Corrosion current density (Icorr) and Pitting potential (Epit) were calculated from each curve. The results were statistically analysed with two-way anova and Student-Newman-Keuls (SNK) multiple comparison test with materials and irrigating solutions serving as discriminating variables (a = 0.05). Cyclic polarization curves presented negative hysteresis implying that pitting or crevice corrosion are not likely to occur for all the materials examined in both irrigating solutions. In NaOCl all materials showed significantly higher Ecorr (P = 0.011) as well as lower Icorr compared with R-EDTA reagent. Moreover, all materials demonstrated equal Epit in NaOCl, which was to be found significantly lower (P = 0.009) than the value of Epit in R-EDTA. None of the tested materials is susceptible to pitting or crevice corrosion in R-EDTA and NaOCl solutions and from this standpoint are appropriate for the production of endodontic files.