Comparison of Theoretical and Experimental Bending and Torsional Moments of Endodontic Files and Reamers

¹ School of Dentistry, University of Michigan, Ann Arbor, Michigan

It was shown that for carbon steel files and reamers the ultimate bending and torsional moments could be estimated from experimental values of the yield pointbending and torsional moments, with excellent agreement for the small and good agreement for the large instruments.

The "rupture moduli" in bending and torsion were calculated from the yield point-bending moments and the section moduli at the position on the instrument where it was gripped. The "rupture moduli" of the instruments in bending did not compare well with the tensile strength, but the "rupture moduli" in torsion compared favorably with the shear strength. The lack of agreement resulted from the tapered sections and the degree of twisting of the instruments. The data indicate that endodontic instruments have almost ideal behavior in torsion but less than ideal behavior in bending.