Properties of endodontic hand instruments used in rotary motion. Part 1. Cutting efficiency.

Cutting efficiency of 24 different types of endodontic hand instruments, which are primarily designed for a rotary (reaming) working action, was investigated under standardized conditions. With a computer-driven testing device, resin specimens with simulated cylindrical canals were instrumented using a defined working motion simulating the clinical use of the instruments. Maximum penetration depth was the criterion for cutting efficiency. Sample size was 12 instruments for each type and size (#25 and #35). Nitinol K-files showed the least cutting efficiency. Stainless steel reamers and especially K-files showed better cutting efficiency than Nitinol K-files. Flexible stainless steel instruments displayed the best results. With regard to cutting efficiency, flexible stainless steel instruments were clearly superior to stainless steel reamers and K-files, and especially to Nitinol K-files.