A comprehensive in vitro comparison of mechanical properties of two rotary endodontic instruments

Aim: The aim of the present study was to compare two different nickel–titanium (NiTi) rotary files, F-One Blue and F2 Protaper Gold (PTG), evaluating their properties such as cyclic fatigue resistance, torsional resistance, and bending properties. Materials and methods: Sixty F-One Blue (25.06) and 60 PTGF2 have been randomly divided into 3 groups of 20 instruments each. Each group was tested in a different way, in order to analyze three different properties: cyclic fatigue resistance, torsional resistance, and flexibility. Cyclic fatigue resistance was evaluated by inserting the instruments for 16 mm in a stainless-steel artificial canal with a 90° angle and 5 mm of curvature with recommended speed and torque. Time to fracture was recorded using a chronometer (1/100 seconds). The number of cycles to fracture (NCF) was then calculated. Fragments were collected, and their lengths were measured. Torsional resistance was evaluated on the apical 3 mm of each of the files to calculate torque to fracture (TtF) using an endodontic motor (KaVo, Biberach, Germany), which automatically recorded the torque values every 1/10 s. All instruments were rotated at the same speed (300 rpm) and torque value (5.5 Ncm). Flexibility was evaluated using a calibrated load cell supported by a computer program. All the collected data were statistically analyzed (t-test) with a significance level set at 5%. Results: A significant difference in terms of cyclic fatigue resistance, torsional resistance, and flexibility between F-One Blue and F2 PTG was found (p < 0.05). The mean value of NCF was 604.16 (SD ± 23.32) for F-One Blue and 300.5 (SD 19.92) for F2 PTG. The mean value of TtF was 1.41 Ncm (SD ± 0.01) and 1.39 Ncm (SD ± 0.01) for F2 PTG. The mean value of bending test was 29 gcm (SD ± 1.15) for F-One Blue and 50 gcm (SD ± 2.30) for F2 PTG. Conclusion: F-One Blue better resists to flexural and torsional stresses and seemed to be more flexible. Since F-One Blue mechanical tested performances were better than the F2 PTG ones, these instruments should be considered a very promising instrument. Clinical significance: As evidenced by the results of this study, F-One Blue should be considered a very promising instrument that could improve endodontic clinical practice.