Influence of structure on nickel-titanium endodontic instruments failure.

The purpose of this work was to investigate the process history on fracture life of nickel-titanium endodontics files. The results are based on microstructural investigations of nickel-titanium engine-driven rotary instruments based on X-ray diffraction, scanning electron microscopy, and microhardness tests. Endodontic files are very work-hardened, and there is a high density of defects in the alloy that can disturb the phase transformation. The microhardness Vickers confirmed these observations (dislocations and precipitates). The X-rays show that experimental spectrum lines are extended, typical of a distorted lattice. The surface state of the endodontic files (scanning electron microscopy) is an important factor in failure and fracture initiation.