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Introduction: The aim of this study was to evaluate the bending and cyclic fatigue resistance of Wave One Gold (WOG) and XI Blue (X1B) instruments when tested at body temperature (36°C ± 1°C) with and without subjected to an alloy cooling protocol. Materials and Methods: A total of sixty instruments (n=30) were tested. Forty instruments (n=20) were randomly selected and divided into two groups: body temperature (BT; n=20) and body temperature with cooling protocol (CP; n=20). Cyclic fatigue test was performed until fracture in a conventional stainless-steel device with water bath equipment to simulate body temperature. CP group instruments were subjected to 5 seconds of spray cooling every 30 seconds. Time to fracture was recorded in seconds. Resistance to bending at an angle of 45 degrees was evaluated using twenty instruments (n=10). Fractured surfaces were examined under scanning electron microscopy (SEM). Statistical analysis was performed at a 5% significance level. Results: There was no difference in the cyclic fatigue resistance between instruments in BT groups (P>0.05). Cooling protocol significantly increased the cyclic fatigue resistance of X1B instruments (P=0.0003) and WOG instruments (P=0.0003). Results: WOG instruments had a significantly lower cyclic fatigue resistance compared to X1B instruments in CP group (P=0.0001). There were no significant differences between the values of resistance increase presented by the instruments after cooling (P>0.05). Bending test presented no statistically significant differences between the tested instruments (P>0.05). Both instruments in both groups showed typical features of cyclic fatigue behavior under SEM. Conclusions: XI Blue #25.06 and WaveOne Gold #25.07 instruments presented similar cyclic fatigue resistance. The investigated clinical-replicable cooling protocol improved the cyclic fatigue resistance of the tested instruments, with XI Blue #25.06 presenting a greater cyclic fatigue resistance after cooling. Both instruments presented a similar bending capacity. [ABSTRACT FROM AUTHOR]

The Nickel-Titanium (NiTi) alloy was developed by the metallurgist William Buehler, and it has since been introduced into various fields of knowledge due to its properties of super elasticity and shape memory effect. The introduction of NiTi revolutionized endodontics as it enhanced safety in the biomechanical preparation of curved root canals, even in larger diameters. Its utilization offered advantages over stainless steel files. This study aimed to conduct a literature review of the advancements in the mechanical properties of the NiTi alloy used in the manufacturing of endodontic instruments. The bibliographical research was conducted from the electronic search of articles indexed in English in electronic databases (PubMed, Scopus, and Web of Science) without time restrictions. Articles were identified by crossing the following descriptors: NiTi, Nitinol, and Endodontics. The initial endodontic instruments made of NiTi were austenitic, and, therefore, less flexible. The incorporation of new manufacturing methods, such as electropolishing and heat treatments allowed the creation of instruments with higher amounts of martensitic phase, resulting in greater flexibility and enhanced fracture resistance and ensuring safety in treating curved canals. The introduction of NiTi in the manufacturing of endodontic instruments is associated with an improved safety and efficiency in biomechanical preparation compared to stainless steel files. Heat treatments enabled the production of more flexible and fracture-resistant instruments for curved canal preparation. [ABSTRACT FROM AUTHOR]