Differences in cyclic fatigue resistance between ProTaper next and ProTaper universal instruments at different levels

Introduction: New designs and alloys have been developed toincrease cyclic fatigue (CF) resistance of rotary files. the aim of this study was to compare CF resistance of ProTaper Universal (PTU) ; Dentsply Tulsa Dental, Tulsa, OK) and ProTaper Next (PTN, Dentsply Tulsa Dental) instruments at different points of curvature. Methods: A total of 420 files (240 PTU, S1, F1, f2 and F3 and 180 PTN, X1, X2 and X3) were divided in 14 groups of 30 instruments each. Instruments in groups s1-5, F1-5, X1-5, F2-5, x2-5, F3-5, and X3-5 were tested at 5 mm from the tip. groups F2-8, X2-8, F3-8 and X3-8 were tested at 8 mm (F2/X2 and F3/X3, respectively, had the same diameter at 8 mm). All files were rotated at 300 rpm until fracture. CF resistance was tested in stainless steel curved canals (60º, r=3 mm). Time to fracture was recorded. The mean half-life and beta and eta were calculated for each group and were compared with Weibull analysis. Results: PTN instruments will last significantly longer than PTU files with a probability higher than 98% at all tested levels except for S1, which was the significantly more resistant instrument to CF at 5 mm from the tip. Conclusions: PTU S1 was significantly the most resistant instrument at 5 mm from the tip. PTN files were significantly more resistant to CF than PTU instruments at all the other tested levels