Abstract
Introduction. Sudden fracture of instruments without previous warning signs, which occurs due to cyclic and torsional fatigue, represents the biggest problem and one of the most difficult complications during endodontic therapy. The aim of this research was to check the influence of diameter of the instruments on the appearance of cyclic fatigue in simulated canals in full rotation. Material and Method. The study analyzed 24 ProTaper Universal instruments (12 instruments with a diameter of 25 and 12 instruments with a diameter of 30) and 24 ProTaper Next instruments (12 instruments with a diameter of 25 and 12 instruments with a diameter of 30). The instruments were tested in an artificial canal stuffed in a metal block at an angle of 45? and a corner radius of 5 mm. The operating time of each instrument until fracture was measured, and then the number of cycles to fracture (NCF) was calculated. The length of the fractured fragments (FL) was measured with a Vernier caliper. Results. The number of cycles to fracture was higher (p < 0.001) in instruments of the ProTaper Universal group of diameter 25 (367.83 ? 17.00) compared to instruments of diameter 30 (329.33 ? 12.86) of the same group. The number of cycles leading to the fracture in instruments of the ProTaper Next group of diameter 25 (1189.33 ? 18.97) was higher (p < 0.001) compared to instruments of the same group of diameter 30 (971.08 ? 15.26). Conclusion. Obtained results indicated that with an increase in the diameter of rotating endodontic instruments, there is a decrease in the resistance to cyclic fatigue.
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