Influence of an Innovative Anti-Corrosive Solution on Resistance of Endodontic NiTi Rotary Instruments: A Preliminary Study

Abstract

Objective:To evaluate the effects of deionised water, blood, phosphate-buffered saline (PBS) and a new anti-corrosive solution based on methoxy propyl amine (MOPA) on the cyclic fatigue resistance of endodontic NiTi rotary instruments under in vitro conditions. Methods: Forty ProTaper F1 files were provided and divided to four groups (n=10). Samples were first autoclaved and then stored in deionised water, blood, PBS or MOPA for 24 hours. Cyclic fatigue was tested with a custom-made stainless-steel block including artificial canals (curvature angle=30 degree, radius of curvature=5 mm). After immersion in test solutions, samples were rotated 300 rpm until fracture occurred. The number of cycles to failure (NCF) was calculated using recorded fracture time. Results: Data were analysed by the Kolmogorov-Smirnov, Levene, ANOVA and Scheffe statistical tests. Samples in blood group showed the lowest and samples in MOPA group showed the highest NCF values. Significant difference was observed between groups (p=0.001). NCF value of PBS group was significantly more than the NCF values of samples in blood and deionised water groups (p<0.05). Conclusion:The tested novel anti-corrosive solution significantly increased the fracture resistance of the endodontic NiTi rotary instruments by reducing the cyclic fatigue. In contrast, blood and deionised water caused more corrosion and resulted in earlier file fracture. Keywords: anti-corrosion, cyclic fatigue, NCF, NiTi rotary INTRODUCTIONThe advent of NiTi rotary instruments to the field of endodontic was a revolutionary change. These devices are made of pseudo-elastic alloy of nickel and titanium (Nitinol 55) and have an incredible influence on the mechanical preparations of root canals (1). The instrumentation of narrow and curved root canals can be challenging for many clinicians. Walia et al. showed that Nitinol files are at least two to three times more flexible than stainless steel (SS) files (2). The flexibility can enable the instrument to be used in curved and complex root canals with more facility and lower root canal shape alterations (3).Many investigators have shown that the unexpected separation of NiTi rotary instruments, apart from higher strength and flexibility, remains a clinical challenge. This undesirable event can occur without any significant deformation seen on the surface of instrument (4). Different causes, such as cyclic fatigue, static and dynamic torsional fatigues, have been attributed to the fracture of these devices (5). Cyclic fatigue is described by the alternating tension and compression cycles, which occur inside the structure of an instrument when it is moving through the maximum curvature of root canal (6). The cyclic fatigue is generally a concern in curved canals, and the many ABSTRACT HIGHLIGHTS• Deionized water and blood can negatively influence the structure of NiTi made devices. • Methoxy propyl amine (MOPA) novel solution is an anti-corrosive agent, which can increase the cyclic fatigue resistance and delay separation of NiTi made rotary...