Fractographic Analysis of Separated Heat-Treated Nickel-Titanium Rotary Files-A Scanning Electron Microscopy Study.

AIM: This observational study aims to assess the pattern of failure mode in 40 separated heat-treated nickel-titanium (NiTi) files using scanning electron microscope (SEM).

MATERIALS AND

METHODS

Forty separated endodontic instruments (SEI) from clinical cases were chosen for fractographic analysis. These samples were viewed under SEM at low and high magnifications. The transverse and longitudinal views of fragments were analysed, and the features were tabulated in an Excel sheet. The association between the type of fracture and the canal curvature, length of SEI, level of separation and taper was also assessed. Statistical analysis was carried out using the Statistical Package for Social Sciences software version 26.

RESULTS

Out of the 40 cases analysed under SEM, 21 cases showed a combination of cyclic and torsional fatigue, 13 cases showed cyclic fatigue and 6 cases showed torsional fatigue. The most observed SEM features on the separated fragments in transverse section were circular abrasion marks and fatigue striations, and in longitudinal section were cracks perpendicular to the long axis of the instrument and surface pitting. There was no statistically significant association between the type of fracture and the canal curvature, file length, file taper and level of separation.

CONCLUSION

Within the limitations of this fractographic analysis, heat-treated NiTi rotary instruments undergo a combination of cyclic and torsional fatigue in most cases, followed by cyclic fatigue alone, with no evident association between the type of fracture and canal curvature, file length, level of separation and taper.