High precision, simulated cutting efficiency measurement of endodontic root canal instruments: influence of file configuration and lubrication.

A high precision method is presented for measurement of root canal instrument cutting efficiency in pure, linear movements. Operator-independent instrumentation is achieved by means of an automatic, mechanical test rig mounted as an accessory in an Instron tensile testing machine. It is now possible to do reliable cutting simulation that closely represents clinical motions. Cutting efficiency is assessed via "wear" volume measurement by means of three-dimensional surface mapping on bovine bone serving as a dentin substitute. A volume precision of 3 x 10(-3) mm3 is achieved which is equivalent to a weight resolution better than 10 micrograms. In particular, cutting efficiency data for K-type and H-type files is presented showing an enhanced performance (by roughly a factor of 3) in the latter case. Lubrication is also shown to increase the cutting efficiency (+200% for the K file and +30% for the H file). Water and 2.5% sodium hypochlorite solutions have equivalent effects.