LAUSR

Aim: This study aims to compare the cyclic fatigue resistance of new and used ProTaper Universal (PTU) and ProTaper Next (PTN) rotary nickel-titanium systems using artificial canals. Materials and Methods: Twenty sets of PTU and PTN were included in the present study. The groups were set as follows: Group A: 10 new sets of PTN instruments; Group B: 10 clinically used sets of PTN instruments; Group C: 10 new sets of PTU instruments; and Group D: 10 clinically used sets of PTU instruments. The cyclic fatigue tests were performed using a specially manufactured dynamic cyclic fatigue-testing device, which has an artificial stainless steel canal with 60° angle of curvature and a 2 mm radius of curvature. New and used files were rotated until fracture, and the cyclic fatigue device stopped automatically by the fracture and showed the fracture time on the screen. The number of cycles to fracture for each group was calculated and compared using paired and unpaired t-tests using SPSS 21.0 software. Statistical significance was set at 5%. Results: For both rotary systems, the new instruments showed statistically higher cyclic fatigue resistance than the used instruments (P < 0.05). The mean number of cycles to fracture of PTN instruments was significantly higher than equivalent file sizes of PTU instruments (P < 0.05). Conclusions: Within the limitation of the present study, reduction in the cyclic fatigue resistance for PTN and PTU instruments was observed after clinical use when compared to new groups.