Endodontic hand instruments: cutting efficiency, instrumentation of curved canals, bending and torsional properties

In an assessment of the usefulness of different root canal instruments, two aspects are of particular interest for the endodontist: the cutting efficiency of the instruments and their ability to enlarge curved canals without undesirable changes of the canal shape such as the formation of zips and elbows. This review paper is based on own investigations on the cutting efficiency and instrumentation of curved canals. Additionally, two parameters which are described in ISO 3630-1, resistance to bending and resistance to fracture, are discussed. With regard to cutting efficiency in rotary motion, flexible stainless steel reamers and K-files clearly display the best results and are superior to conventional stainless steel as well as titanium-based reamers and K-files. Regarding cutting efficiency in linear motion, stainless steel Hedström files made by certain manufacturers are significantly superior to stainless steel and titanium-based Hedström files of other brands. Flexible stainless steel instruments with modified noncutting tips clearly produce the best canal shape in curved canals. With only rare exceptions, all the instruments tested fulfilled the requirements of the ISO standard concerning resistance to fracture and resistance to bending.