Taher AL OMARI, Anas AL JADAA, Yazan AL-ZAIN, Haytham ABDULAZZIZ, Amre R. ATMEH, Rashid EL ABED
European Endodontic Journal - 2026;11(8):391-398
Background: To compare the dynamic cyclic fatigue resistance, bending stiffness and phase transformation characteristics of blue heat-treated instruments, VDW Rotate (VR) and Azur Blue (AzB), at a simulated intracanal temperature of 34 +/- 1 dereceC. Methods: Fifty-eight new instruments (n = 29 per group) were allocated as follows: dynamic cyclic fatigue testing (n = 12), bending stiffness evaluation (n = 12), differential scanning calorimetry (DSC) (n = 1), X-ray diffraction (XRD) (n = 2) and energy-dispersive X-ray fluorescence (EDXRF) (n = 2). Dynamic cyclic fatigue testing was conducted in an artificial canal (18 mm length, 1.4 mm diameter, 45 derece curvature, 5 mm radius) at 34 +/- 1 dereceC. Time to fracture was recorded and converted to the number of cycles to failure, and fractured segment lengths were measured. Bending stiffness was evaluated with a 3 mm deflection range at 34 +/- 1 dereceC. Differential scanning calorimetry, energy-dispersive X-ray fluorescence, X-ray diffraction and scanning electron microscopy were used for metallurgical and fractographic analyses. Results: Differential scanning calorimetry revealed austenitic finish temperatures (AuF) of 35.8 dereceC for VDW Rotate and 39.4 dereceC for AzB. Azur Blue showed significantly higher cyclic fatigue resistance (2039 +/- 250 vs. 1609 +/- 222 cycles), lower bending stiffness (0.85 +/- 0.07 vs. 1.07 +/- 0.08 N) and longer fractured fragment length (4.87 +/- 0.44 vs. 3.27 +/- 0.75 mm) than VDW Rotate (P < .05). Conclusion: Azur Blue showed higher cyclic fatigue resistance, whereas VDW Rotate showed higher bending stiffness. These differences were more consistently associated with phase transformation behaviour than with external geometry alone.
