Comparison Of The Cyclic Fatigue Resistance Of Three Different Engine-driven Nickel-titanium Instruments In Vitro Studies

Objective: Cyclic fatigue is one of the main factors of instrument separation of nickel-titanium files.The aim of this study is to compare the anti-cyclic fatigue performance of three kinds of nickel-titanium rotary instruments,M3-Pro,ROTATE and Mtwo,so as to provide reference for the selection of nickel-titanium rotary instruments in clinic.Methods: Two groups of imported nickel-titanium files Mtwo,ROTATE and one group of domestic nickel-titanium files M3-Pro(21 mm long,25 #/0.06 taper)were selected in this study,20 instruments from each system was performed in vitro static cyclic fatigue resistance test.Each group of nickel-titanium instruments were divided into two subgroups and presoaked in Na Cl O solution and distilled water at 36 ° C for 5 minutes,then,the anti-cyclic fatigue properties of nickel-titanium files were tested by using a zirconia root canal simulator under the condition of 36 °C immersion in the corresponding medium solution,the simulated root canal length was 19 mm,the bending angle was 60°,the bending radius was 5 mm,and the center of curvature was 5.5 mm from the top of the artificial root canal.The three nickel-titanium files were activated by using a 6:1 reduction handpiece powered by a torque-controlled motor,The device is set to a continuous rotation mode of350 rpm and 2n/cm torque.The number of cycles of cyclic fatigue and the length of broken fragments were analyzed by one-way analysis of variance(ANOVA)and Tukey’s multiple comparison tests at a significance level of p<0.05.Results: Compared with distilled water group,the mean value of sodium hypochlorite group was decreased,but significant difference was only observed in ROTATE and M3-PRO group(p<0.05).The number of cyclic fatigue value of M3-Pro was significantly higher than that of other groups in both distilled water and sodium hypochlorite water conditions(p<0.05),ROTATE next,and Mtwo has the lowest number of cyclic fatigue value.There was no statistically significant difference in mean fractured length among all groups(p>0.05).Conclusion: 1.The anti-cyclic fatigue ability of three nickel-titanium instruments is M3-Pro >ROTATE >Mtwo.2.The use of sodium hypochlorite solution can reduce the cyclic fatigue resistance of M3-Pro and ROTATE.