Changes in root canal morphology in simulated curved canals over-instrumented with a variety of stainless steel and nickel titanium files

The purpose of this project was to observe the amount of apical and mid-cur ve transportation produced by a range of nickel titanium (NiTi), titanium a lloy and stainless steel (SS) files. Tests were carried out in simulated cu rved root canals produced in epoxy resin blocks. Seven commercially availab le file types were tested using sizes 15 to 40. Instrumentation was carried out to 1 mm beyond the apex. Changes in canal dimensions were measured at 10x magnification under a shadowgraph. There were substantial differences in the amount and the pattern of apical and mid-curve transportation produced. The amount of transportation increas ed with each subsequent size of file. Under the same conditions, nickel tit anium files produced significantly less transportation than stainless steel files. The least apical transportation was obtained with the NiTi Mity Tur bo and the most by the SS K file and SS Hedstrom file. The least mid-curve transportation was produced by the NiTi Mity Turbo and the most by the SS H edstrom file.