The influence of the manufacturing process of rotary files on the shaping of L-shaped canals

Background. The nickel-titanium alloy used in the production of nickel-titanium files contains approx. 56% nickel and 44% titanium by weight. To improve the properties of nickel-titanium files, the manufacturers introduce some innovations in the production process. Their purpose is primarily to decrease the stiffness of the instruments while increasing the resistance to cyclic fatigue, which reduces the risk of file separation. One of the most popular processes is the heat treatment of the nickel-titanium alloy. Objectives. The aim of the research was to determine the influence of the manufacturing process of rotary files on the shaping of L-shaped canals. Material and method. Fifty L-shaped resin canals were instrumented (10/group) with ProTaper Universal (R), ProTaper Next (R), Hyflex CM (R), Hyflex EDM (R), orWaveOne Gold (R) files, with the same apical size of 25. Each L-shaped resin canal was photographed both before and after instrumentation. Differences between the change of the working length and apical transportation were analyzed statistically. Results. The smallest mean loss of the working length was observed after instrumentation with Hyflex CM files. Statistically significant differences in the working length were found between ProTaper Universal and Hyflex CM (p = 0.0032), ProTaper Universal and Hyflex EDM (p = 0.021), and ProTaper Universal and WaveOne Gold (p = 0.0112) files. The lowest apical transportation was noted in the case ofWaveOne Gold files. In terms of apical transportation, statistically significant differences were observed between ProTaper Universal and WaveOne Gold files (p = 0.0254). Shaping L- shaped canals with the ProTaper Universal file system resulted in the greatest changes in the working length (x = 0.35 mm) and apical transportation (x = 0.034 mm). Conclusions. The study, with its limitations, shows that in the files whose nickel-titanium alloy was subjected to a thermal treatment process, a smaller loss of the working length and lower values of apical transportation were observed.