Comparative evaluation of cyclic fatigue resistance of D-RaCe and ProTaper retreatment instruments in curved artificial canals

Aim To compare the cyclic fatigue resistance of D-RaCe and ProTaper rotary nickel-titanium (NiTi) retreatment files when used in curved artificial canals. Methodology A total of 120 new D-RaCe DR2 and ProTaper D3 retreatment files were tested in stainless steel artificial canals having 45 degrees and 60 degrees angles of curvature. Thirty instruments of each of the file systems were tested in both angles of curvature (n = 30). The retreatment instruments were rotated until fracture to calculate the number of cycles to failure. The length of each fractured fragment was recorded. Data were analysed by independent sample t-test. Fractured surfaces of the instruments were analysed by scanning electron microscopy. Results In the canal with 45 degrees angle of curvature, no significant difference was observed between the retreatment systems (P > 0.05); on the other hand, in the canal with 60 degrees angle of curvature, D-RaCe DR2 instruments had greater cyclic fatigue resistance than ProTaper D3 (P < 0.05). No difference was observed between the retreatment instruments regarding the lengths of fractured fragments (P > 0.05). The fracture surfaces of the instruments had morphologic characteristics of ductile fracture. Conclusions D-RaCe DR2 instrument exhibited greater cyclic fatigue resistance than ProTaper D3 only in root canals with 60 degrees angle of curvature.