Abstract:

Objective To compare the cutting abilities and shaping abilities of three kinds of single formed nickel-titanium instruments for the simulated curved root canals， and to provide the basis for their clinical applications. Methods A total of 40 single curved resin simulated root canals were selected and randomly divided into Reciproc Blue group， WaveOne Gold group， M3-L group， and ProTaper Gold group， and there were 10 single curved resin simulated root canals in each group. The simulated root canals in each group were prepared according to the user manuals， and the preparation time， difference in weights of simulated root canals before and after preparation， difference of bending angles of simulated root canals，apical deviations， removal amounts of internal and external resin， centering ratios of simulated root canals in various groups were recorded. Results The preparation time of the simulated root canals in WaveOne Gold group was shorter than those in the other three groups （P<0.05），and the preparation time of the simulated root canals in ProTaper Gold group was longer than those in the other groups（P<0.05）. There was no significant difference in wieight of the simulated root canals among four groups before and after preparation （P>0.05）.The differences of bending angles of the simulated root canals in M3-L group before and after preparation was smaller than those in the other three groups （P<0.05）.After preparation， the removal amount of internal resin of the apical zone （1－4 mm） was larger than extermal resin（P<0.05）， and the removal amount of external resin of the middle zone （5－8 mm） was larger than internal resin（P<0.05）； at the positions 1， 3 and 6 mm from the apical foramen， the differences between the centering ratios of the simulated root canal in ProTaper Gold group and 1 was the largest， which was larger than those in the other three groups （P<0.05），and the differences between the centering ratio of the simulated root canals and 1 at each observation point in the other groups were not statistically significant （P>0.05）. Conclusion Reciproc Blue， WaveOne Gold and M3-L single formed nickel-titanium instruments can keep the shape of root canals better， and have better preparation efficiencies and center positioning ability than the ProTaper Gold multi-file system. Domestic single nickel-titanium instrument M3-L can better maintain the original curvature of the root canals.

Key words: Nickel-titanium instrument, Single file, Cutting ability, Forming ability, Heat treatment