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 micros tructural investigations of nickel-titanium engine-driven rotary instrument s based on X-ray diffraction, scanning electron microscopy, and microhardne ss tests. Endodontic files are very work-hardened, and there is a high dens ity of defects in the alloy that can disturb the phase transformation. The microhardness Vickers confirmed these observations (dislocations and precip itates). The X-rays show that experimental spectrum lines are extended, typ ical of a distorted lattice. The surface state of the endodontic files (sca nning electron microscopy) is an important factor in failure and fracture i nitiation.