S Khier, A Al Yahya.
Failure analysis of hand-driven Ni-Ti endodontic instruments.
J Pak Dent Assoc Jan ;11(1):15-8.

OBJECTIVE: To study the effect of heat treatment on torsional properties of Ni-Ti endodontic files. It was also meant to microscopically analyze the failure of the fractured files. MATERIALS AND METHODS: In this study, torsional properties using torque meter assembly were investigated on hand-driven Ni-Ti root canal files in as-received and heat-treated conditions. These files were tested until fracture occurred in both clockwise and counterclockwise directions of torsion. Heat treatment (HT) at 500°C for 10 min. for the tested files was performed. The fracture surfaces of the files were examined utilizing Scanning Electron Microscope (SEM). RESULTS: HT of the files resulted in a slightly large twist angle to fracture compared to those in the asreceived condition. The SEM micrographs of the files broken surfaces as a result of clockwise torsion provided evidence of ductile fracture. A typical brittle fracture occurred when the files underwent counterclockwise torsion. CONCLUSIONS: It is suggested that a 10-minutes heat treatment of root canal files at 500°C would improve both clockwise and counterclockwise torsional characteristics of these files.

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