Analysis of defects in ProTaper hand-operated instruments after clinical use

The purpose of this study was to analyze the type and location of defects observed in ProTaper for Hand Use (PHU) instruments after routine clinical use. We analyzed a total of 401 PHUs discarded from an endodontic clinic over a 17-month period. Those failed instruments were examined on the lateral and fractographic surface by scanning electron microscope. Of the 86 PHUs that showed discernible defects, 28 were intact but partially unwound, and 58 were fractured (36 because of shear and 22 from fatigue failure). The primary characteristic of shear failure was the presence of a skewed dimple and/or tear ridge, a typical pattern developed because of a combination of various loads. Nearly 74% of the instruments with defects exhibited shear damage. About three-quarters of the instrument fractures occurred in the apical one-third of the canal, mostly in molars. The results of this study indicated that most PHU instruments fail because of either shear or fatigue.