Characterization of the nucleus, cutting edge and failure detection in NiTi instruments for endodontic retreatment

OBJECTIVE: To characterize the nucleus, cutting edge and to detect defects in surfaces of nickeltitanium (NiTi) instruments for endodontic retreatment.METHODS: The selected endodontic instruments (D-RaCe, ProTaper retreatment and Mtwo retreatment) were evaluated prior to their use in 30- and 50-fold magnification in scanning electron microscopy (SEM), for linear measurements of lateral cut edge areas and of the nucleus and the ratio between these measures. After use in simulated canals, faults in the active surface were analyzed by SEM with 30 and 50 times magnification, and 200 times magnification when faults were found. The images were examined by three evaluators, whose measurements were previously calibrated. The defects analyzed were crack, blunt and barb, and data were tabulated for analysis.RESULTS: The instruments studied differed in results. The D-RaCe system instruments had the highest nucleus:edge ratio, while ProTaper retreatment instruments yielded the lowest ratio. All instruments presented some defect, with the instruments Mtwo retreatment presenting two instruments with defects.CONCLUSION: All analyzed instruments presented some type of failure after using them for removal of the filling material of simulated root canals. The D-RaCe system presented the highest edge measurements and the smallest nucleus measurements, contrary to the ProTaper retreatment system, which presented the smallest edge measurements and the largest core measurements.