# Impact of Metallurgical and Geometric Features on the Cyclic Fatigue Strength of Reciprocating Endodontic Files

## TL;DR

This study compares the cyclic fatigue strength of four reciprocating NiTi endodontic files, finding that Reciproc Blue performs best due to its metallurgical and geometric features.

## Contribution

The study integrates geometric, metallurgical, and mechanical evaluations of reciprocating NiTi files in a comparative analysis.

## Key findings

- Reciproc Blue showed the longest active blade length, highest spiral density, and best surface finish.
- Reciproc Blue had the highest cyclic fatigue strength, while Easy-File Flex had the lowest.
- WaveOne Gold had the highest R-phase start and finish temperatures.

## Abstract

Background: Nickel–titanium (NiTi) endodontic instruments have undergone significant improvements in heat treatment processing and geometric design, aimed at enhancing flexibility, cutting efficiency, and fatigue strength. Reciprocating motion was introduced to increase cyclic fatigue resistance, which remains the predominant mode of failure in NiTi endodontic file systems. Although these instruments are widely used in both clinical practice and research, few comparative studies have integrated geometric, metallurgical and mechanical evaluations of the most commonly used reciprocating systems. Methods: In the present study, four single-file reciprocating NiTi systems (Reciproc Blue, WaveOne Gold, EdgeOne Fire, and Easy-File Flex) were evaluated for their geometric design, metallurgical composition, and cyclic fatigue strength. Stereomicroscopy and scanning electron microscopy were employed to assess active blade length, spiral configuration, and surface finish, while elemental composition and phase transformation temperatures were analyzed using energy-dispersive X-ray spectroscopy and differential scanning calorimetry. Ten instruments from each group were tested for cyclic fatigue using a standardized curved stainless-steel canal at room temperature, and the time to fracture was recorded. Fatigue data were statistically analyzed using Mood’s median test, with significance set at p < 0.05. Results: Reciproc Blue exhibited the longest active blade length, highest spiral density, and superior surface finish. R-phase start and finish temperatures were highest in WaveOne Gold and lowest in Easy-File Flex. Reciproc Blue demonstrated the higher cyclic fatigue strength, whereas Easy-File Flex showed the lowest. Conclusions: These findings suggest that the metallurgical and geometric characteristics of the Reciproc Blue file significantly enhance its strength to cyclic fatigue compared with the other instruments evaluated.