Beyond the Surface: Engineered Nanocoating Reshapes NiTi Instrument Behaviour—A Laboratory Study

AIM: To compare the geometric and metallurgical features and mechanical performance of two contemporary reciprocating nickel-titanium instruments manufactured with and without additional engineered nanocoating technology. METHODOLOGY: Excalibur (n = 57) and Excalibur Pro (n = 57) size 25/0.05 instruments were evaluated. Geometric and surface characteristics were assessed by scanning electron microscopy and 3D optical scanning with model superimposition. Elemental composition and phase transformation behaviour were characterized by energy-dispersive X-ray spectroscopy and differential scanning calorimetry, respectively. Mechanical performance was evaluated through cyclic fatigue resistance, maximum torque, angle of rotation at fracture, bending and buckling resistance, cutting efficiency and surface microhardness. Data were compared using independent-samples Student's t-test, Mann-Whitney U test, or a linear mixed-effects model, as appropriate, with significance set at 5%. RESULTS: The instruments showed high geometric correspondence, with only subtle differences in tip configuration and both exhibited a near-equiatomic NiTi composition. Differential scanning calorimetry revealed distinct phase transformation profiles, with Excalibur Pro showing lower transformation temperatures than Excalibur. No significant differences were observed in cyclic fatigue resistance or cutting efficiency (p > 0.05). Excalibur exhibited higher maximum torque (p < 0.001), buckling resistance (p = 0.029) and surface microhardness (p = 0.001). Conversely, Excalibur Pro showed a greater angle of rotation at fracture (p = 0.005) and required a higher load to achieve 45° deflection (p < 0.001), indicating lower flexibility. CONCLUSION: The reciprocating NiTi instruments with and without an engineered nanocoating exhibited distinct metallurgical and mechanical profiles despite their high geometric similarity and comparable elemental composition. The nanocoated instrument showed lower phase transformation temperatures and a distinct balance of torsional, bending, buckling and microhardness properties, while no statistically significant differences were detected in cyclic fatigue resistance or cutting efficiency between instruments. These findings demonstrate that the nanocoated instrument exhibits a distinct overall mechanical profile, which should be interpreted as reflecting the combined contribution of surface characteristics and thermomechanical features rather than the effect of the nanocoating alone.