MEASUREMENT OF THE CUTTING EFFICIENCY OF ENDODONTIC INSTRUMENTS - A NEW CONCEPT

The cutting efficiency of endodontic instruments was measured using an original experimental technique that incorporates new concepts to sim ulate clinical conditions. Five designs of #ISO 030 endodontic instrum ents, K-reamer (Maillefer), Flexofile (Maillefer), Helifile (Micro-meg a), K-flex (Kerr), and Unifile (De Trey), were chosen and their cuttin g efficiency assessed at their full working length of 16 mm on two Ple xiglas parallelepipeds tilted to follow the 2% conicity of the instrum ents. For each instrument, four series of 25 cuts were carried out and each cut made on a new flat, smooth Plexiglas surface with an even ha rdness of 33 VHN. Instruments were tested under a simulated clinical c ondition of a quarter clockwise turn ROTARY MOTION followed by a PULL ACTION at 16 mm/s rate, with a fixed load on the instrument of 325 g. Water irrigation at a rate of 85 ml/s was supplied before each procedu re. Cutting efficiency was evaluated in terms of mass of Plexiglas cut (using a Mettler analytic balance with accuracy of 3 x 10(-5) g) per unit of energy used by the instrument, i.e. mg/J. Unifile was found to have the best cutting efficiency of 0.80 +/- 0.01 (Mean +/- SD) and l owest cutting efficiency loss followed by Flexofile 0.70 +/- 0.03 then Helifile 0.36 +/- 0.01 then K-flex 0.51 +/- 0.07. K-reamer was found to have the lowest cutting efficiency of 0.16 +/- 0.05.