Bending and torsion properties of endodontic instruments: Fid-Bau Portal

Bending and torsion properties of endodontic instruments

Ph.D. Craig, R.G. / McIlwain, E.D. / D.Sc. Peyton, F.A.

Abstract A torque meter and an improved testing method were used to determine the stiffness in bending, resistance to permanent bend, torsional stiffness, and maximum torsional deflection for conventional and standardized carbon steel and stainless steel root canal files and reamers. The bending and torsional properties showed a gradual increase in stiffness and decrease in resistance to permanent bend as size increased, indicating that a triangular instrument was considerably less stiff and more resistant to permanent bend and torsion than a corresponding square instrument. No differences were found in the stiffness properties of carbon steel and conventional stainless steel instruments, whereas the experimental stainless steel instruments were considerably less stiff because of their greater ductility. Considerable variation was found in torsional behavior of instruments at large angular deflections because of the variations in ductility of the material and the amount of work-hardening in the individual instruments. The greater ductility of the stainless steel files allowed greater maximum angular deflection than the corresponding carbon steel files, but no differences were noted in the reamers. In conclusion, it appears from the general similarity of bending and torsional stiffness and from the general improvement in maximum torsional deflection that the stainless steel instruments would be more advantageous for clinical use.