Effect of irrigation on surface roughness and fatigue resistance of rotary niti files-an atomic force microscopic study

Abstract

Aim: To investigate the effect of irrigation on the surface roughness and fatigue resistance of two rotary systems-ProTaper (Dentsply Sirona Endodontics,York,USA) and M-two (VDW GmBH, Munich,Germany). Materials And Methods: New ProTaper F2 and M-two files of 25mm length (n=30) were investigated under an operating microscope (20×) and files with defects were discarded. Five new files of each group were analysed using AFM as the controls. Twenty-five files from each group were dynamically immersed using an endomotor in 3% NaOCl solution for 15 minutes at 37°C. This was followed by AFM analysis. The roughness average and root mean square values were analysed statistically using a paired sample t-test. Sixty endodontic study models (Nissin,Japan) were used for studying the fatigue resistance of irrigant-soaked instruments. Files from both the groups were inserted into the canal and rotated at 400 rpm using a 16:1 reduction handpiece at a torque of 2.5Ncm. The instruments were rotated freely until fracture occurred and timing was noted. The time was converted into a number of rotations to failure(Nf). The Nf of various groups were analysed using the one-way analysis of variance. Results: For ProTaper files, the Ra and RMS values significantly increased (P<0.05) after the immersion when compared to the M-two files. The resistance to cyclic fatigue of both ProTaper and M-two files significantly decreased (P<0.05) by immersing in 3% NaOCl solution. Conclusion: Under the limits of this study, immersing in NaOCl, the surface roughness of the files increased which in turn reduced the fatigue resistance.