Properties of endodontic hand instruments used in rotary motion. Part 3. Resistance to bending and fracture.

Bending and torsional properties of 24 different types of nickel-titanium K-files, titanium-aluminium K-files and reamers, conventional stainless steel K-files and reamers, and flexible stainless steel instruments were investigated corresponding to ISO 3630-1 by determination of the bending moment on the one hand and the torque and angular deflection on the other. Numbers 15, 25, and 35 instruments were tested with a sample size of 10 instruments for each type and size. In ascending order of bending moment the instruments ranked: nickel-titanium K-files, titanium-aluminium K-files and reamers, flexible stainless steel instruments, conventional stainless steel K-files, and reamers. Nickel-titanium, titanium aluminium, and flexible stainless steel instruments displayed lower torque values than conventional stainless steel K-files and reamers. The average angular deflection ranged from 380 degrees (#15 reamer) to 2370 degrees (#35 K-file). Overall, the fracture risk of the instruments tested in this study was comparably low.