MECHANICAL-PROPERTIES OF NICKEL-TITANIUM ENDODONTIC INSTRUMENTS AND THE EFFECT OF SODIUM-HYPOCHLORITE TREATMENT

The purpose of this study was to assess the mechanical properties-tors ional moment, maximum angular deflection, maximum bending moment, and permanent angular deflection - of four brands of nickel-titanium (NiTi ) endodontic file, and compare them with a conventional stainless-stee l instrument, both in the presence and absence of sodium hypochlorite (NaOCl). NiTi instruments from four manufacturers were randomly select ed and subjected to NaOCl treatment for 12 or 48 h, or not at all. The mechanical properties under test were then measured automatically by a digital torque memocouple. Torsional moment and maximum angular defl ection indicate the resistance to torsional fracture of an instrument, maximum bending moment the stiffness of the instrument, and permanent angular deflection the strength of the base alloy. All instruments ev aluated complied with or exceeded ADA/ANSI Specification No. 28, with the sole exception of the Maillefer ISO size 40 for torsional moment. JS Dental and McSpadden NiTi files were the most resistant to torsiona l fracture, but all NiTi files were inferior when compared with stainl ess-steel files from a previous study. However, NiTi files were superi or in flexibility, and Maillefer and Brasseler instruments were the be st of the instruments tested. NiTi files also had negligible permanent deformation angles. Furthermore, for all properties tested, NaOCl had no statistically significant effect.