Cyclic Fatigue Resistance of “Replica-Like" and Original Reciprocating Instruments in Single and Double Curvatures

Objective: To compare the cyclic fatigue resistance of conventional and heat-treated "replica-like" reciprocating instruments with their original counterparts under single and double curvatures and assess tip size discrepancies against manufacturer-reported values."
Methods: Eighteen instruments were used per group for the study. Two measurements at the instrument's tip were made with a digital calliper. Cyclic fatigue resistance was evaluated under single (60°, 5 mm radius) and double curvatures (60°, 5 mm radius each) in a 37°C water bath. Time to fracture (seconds) was recorded and analysed with appropriate statistical tests (p= 0.05).
Results: the tip sizes of all instruments were smaller than the value purported by the manufacturers (0.25mm) and outside the range of values obtained, with significant differences for all groups (p<0.001). Time to fracture were as follows: Reciproc R25: single curvature: 171.5±38.9, double curvature: 133.4±47.4; Reverso Silver: single curvature: 169.0±104.8, double curvature: 57.8±20.0; Reciproc Blue R25 single curvature: 355.4±86.4, double curvature: 140.5±67.7; Reverso Blue: single curvature: 359.5±102.8, double curvature: 142.9±69.0. Reverso Silver presented with a significantly lower time to fracture overall when compared with the Blue instruments (p=0.002) and with all instruments in double curvatures (p<0.05). In single curvatures, blue files had longer times to fracture (p<0.05). When comparing single versus double curvatures, only Reciproc R25 had no significant differences regarding time to fracture (p=0.54).
Conclusion: The tip sizes of the instrument tested were smaller than what is reported by the manufacturers. The cyclic fatigue resistance of the conventional “replica-like” instrument (Reverso Silver) was significantly lower than the blue "heat-treated" comparators. Double curvature hastened fracture. (EEJ-2024-11-174)