Corrosion in stainless-steel and nickel-titanium files

This study evaluated and compared the corrosion susceptibility of stainless -steel and nickel-titanium (NiTi) endodontic files immersed in sodium hypoc hlorite. For each of the stainless-steel files (Kerr K-Flex, Caulk Flex-O, and Union Broach Flex-R) plus the NiTi files (Union Broach NiTi and Tulsa N iTi), the cutting flutes of 24 ISO size 20 files were immersed into 5.25% s odium hypochlorite. Their open circuit potential (OCP) was recorded for 1 h on a strip chart with high impedance. The strip chart recording for each f ile was classified into a stability score: (i) stable, (ii) unstable, or (i ii) erratic. The CCP was measured by a potentiostat and a standard calomel electrode reference. The OCP classification of unstable and erratic for the files evaluated were as follows: K-Flex (16%), Flex-R (12%), Flex-O (75%), Union Broach NiTi (62%), and Tulsa NiTi (0%). After OCP testing, each of t he 120 files was inspected by light microscopy at x25. The frequencies of v isually observed corrosion were detected as follows: K-Flex (2/24), Flex-R (1/24), Flex-O (6/24), Union Broach NiTi (2/24), and Tulsa NiTi (0/24). The re was a significant difference in corrosion frequency between brands when evaluated by OCP and light microscopy; however, there was no significant di fference between stainless steel and NiTi.