Objective To compare the shaping abilities of four different heat-treated nickel-titanium endodontic files in preparing severely curved resin simulated root canals specifically at the apical region.Methods Fifty resin simulated root canals were prepared using ProTaper Universal,ProTaper Next,WaveOne Gold,Twisted File,and HyFlex CM.The preparation time,changes in working length before and after preparation,and canal deviation within the 5 mm range of the apex were recorded.Results There were statistically significant differences in preparation time(P<0.05),with ProTaper Universal taking the longest and Twisted File the shortest.There were no significant differences in the changes of working length.Within a 5 mm range,HyFlex CM had the lowest canal deviation(P<0.05);within a 3mm range,there were no significant differences in canal deviation between HyFlex CM and WaveOne Gold.Conclusions All five nickel-titanium rotary files were capable of safely preparing severely curved canals.The four heat-treated nickel-titanium files showed significantly less deviation in the apical region of the canals compared to traditional nickel-titanium instruments.The HyFlex CM and WaveOne Gold files showed the least deviation,with HyFlex CM being the most suitable for preparing severely curved canals due to its multiple-file system.
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