Mechanical and Metallurgical In Vitro Evaluation of Electropolished Versus Non-Electropolished Rotary and Reciprocating Instruments.

Aim: To evaluate the effect of electropolishing on the mechanical properties of One RECI and One Curve mini nickel-titanium (NiTi) instruments by comparing electropolished and non-electropolished versions of each instrument type.

Methodology: Electropolished and non-electropolished One RECI (reciprocating) and One Curve mini (rotary) NiTi instruments, all manufactured with identical geometry and heat treatment, were evaluated. Instrument design was analysed by light microscopy and scanning electron microscopy, while metallurgical characterisation was performed using energy-dispersive X-ray spectroscopy (EDS) and differential scanning calorimetry (DSC). Mechanical performance was assessed through torsional resistance, bending and buckling load, surface microhardness, and cutting efficiency. Statistical comparisons were performed using the independent samples t-test or the Mann-Whitney U-test, with significance set at p < 0.05.

Results: Design and metallurgical analyses confirmed that electropolished and non-electropolished instruments within each group were equivalent in terms of geometry, cross-sectional design, tip configuration, elemental composition, and phase transformation temperatures. Electropolishing significantly enhanced flexibility in both instrument types, as indicated by reduced bending loads and lower buckling resistance (p < 0.05). However, torsional strength was significantly reduced in the electropolished One RECI instruments, reflected by lower maximum torque and angle of rotation prior to fracture (p < 0.05). No significant torsional differences were observed in the One Curve mini group (p > 0.05). Surface microhardness and cutting efficiency remained unaffected by electropolishing in both systems (p > 0.05).

Conclusions: Electropolishing improved the flexibility of both One RECI and One Curve mini NiTi instruments without compromising their surface microhardness or cutting efficiency. However, its impact on torsional resistance was system-dependent, resulting in reduced strength only in the reciprocating One RECI instruments.