Cyclic Fatigue, Torsional Strength and Angular Deflection of Different Reciprocating Instruments: A Critical Analysis of Its Clinical Relevance.

Objective: To evaluate the cyclic fatigue fracture resistance, torsional fatigue, and angular deflection of Reciproc Blue (RB), WaveOne Gold (WOG), One Reci (OR), and Plex RC-One (RC-One) instruments for managing root curvatures in simulated canals.

Methods: A sample size calculation determined 10 samples per group (5 instruments for the cyclic fatigue test and 5 for the torsional fatigue test) for detecting significant differences. The study included 40 NiTi instruments (25 mm) from four reciprocating systems groups: RB R25, WOG 25, OR 25, and RC-One 25. Instruments were inspected for defects. Bending tests assessed memory control. Static cyclic fatigue tests used an artificial 60° curved canal with motorized activation. Torsional fatigue followed ISO 3630-1, measuring torque and angular deflection until failure. Fractured surfaces were analyzed using automated image analysis and measured with Rhinoceros 8.0 software. Statistical analysis included central tendency and dispersion measures, followed by ANOVA to identify statistically significant differences between groups.

Results: The bending test showed RC-One retained shape after pressure, while RB exhibited moderate resistance. WOG and OR did not demonstrate satisfactory bending resistance. Analysis of cyclic fatigue revealed RC-One had the highest resistance, followed by RB, OR, and WOG (p<0.001). RB required the highest torque for fracture, followed by RC-One, WOG, and OR (p<0.001). WOG had the lowest deflection angle at fracture, followed by OR, RB, and RC-One (p=0.0399). SEM and intelligent automated image processing analysis showed RC-One and RB had wear zones indicative of slow fracture, while WOG and OR displayed 100% rapid fracture dimples. RC-One had 41.86% slow fracture and 54.14% rapid fracture, while RB had 17.83% slow and 82.17% rapid fracture. Torsion tests revealed similar features in RC-One and RB, supporting their high and similar torsional resistance and deflection, unlike WOG's lower resistance and OR's lowest resistance with the highest deflection.

Conclusion: The best performance in the bending test was obtained by RC-One, followed by RB, while most failures were observed in WOG and OR. RC-One showed significantly higher cyclic fatigue resistance in severe curvatures than RB, WOG, and OR. RB and RC-One exhibited very similar torsional resistance values, significantly higher than OR and WOG. RC-One displayed superior angular deflection results compared to the other instruments. (EEJ-2024-08-135).