Corrosion of NiTi Instruments by Contact with Sodium Hypochlorite in Conditions Similar to the Clinic: TOF-Sims Analisys

Objectives: NiTi endodontic instruments are in contact with solutions of sodium hypochlorite during their clinical use and this can generate corrosion phenomenous of the surface. Aim of this work was to assess, under conditions similar to clinical conditions, signs of corrosion and surface chemical quality changes after immersion in NaOCl solution of Mtwo NiTi endodontic rotary instruments by time of flight – sec- ondary ions mass spectrum (Tof-Sims) analysis.Materials and methods: A total of 75 new Mtwo NiTi rotary files (25.06) were randomly assigned to five different groups (n=15); instruments of groups 1, 2, 3 and 4 were immersed in 5% NaOCl at 37◦C for 16mm (working part). Instruments of Group 1 and 2 were statically immersed in NaOCl solution for 1 and 5min, respectively; instruments of Group 3 and 4 were dynamically (300 rpm/min) immersed in solution for 1 and 5 min, respectively. Group 5 (control group) was composed of new instruments not immersed in solution. All instruments were then tested for quality surface composition recording the chemical elements (Ti, Ni, TiO, Ti(OH)2, Ba) detected on first and last coil from the tip by Tof-Sims. Data were analysed by t-test (P < 0.05) and a quantitative comparison between groups was performed.Results: Surface instruments showed presence of Ti, Ni, TiO, Ti(OH)2 and Ba in all groups. Ni, TiO and Ti(OH)2 had a significantly lower quantity in first and last coil surface from the tip of Group 1, 2, 3 and 4 than in the control group (P < 0.001). Reduction of Ni, TiO and Ti(OH)2 was more signifi- cant for instruments in static immersion (Group 1 and 2) than in dynamic immersion ones (Group 3 and 4). Instruments of Group 2 showed the highest reduction of Ni, TiO and Ti(OH)2 rather than the control group. Conclusions: Immersion of Mtwo NiTi rotary instruments in a NaOCl solution, under conditions similar to clinical con- ditions, produced in all groups molecular signs of corrosion as Ni, TiO and Ti(OH)2 reduction on first and last coil surface from the tip by Tof – Sims evaluation. The Group 2 showed the highest reduction of Ni, TiO and Ti(OH)2 compared with con- trol group. The signs of corrosion increased in instruments immersed for longer time and statically rather than those in motion and for less time.