Shaping Ability of Mtwo, ZenFlex, E-FLEX ONE, and E-FLEX EDGE Nickel–Titanium Rotary Instruments in Curved Root Canals: A Micro-Computed Tomography Study

Nickel–titanium (NiTi) rotary instruments are widely used in endodontics because of their flexibility and shaping efficiency. Nevertheless, canal transportation and excessive dentin removal remain concerns, particularly in curved canals. To address these limitations, heat treatment processes have been introduced to improve the mechanical properties of NiTi alloys, especially flexibility and resistance to deformation. This study aimed to compare the centering ability, canal transportation, and dentin volume changes produced by four different heat-treated NiTi file systems. Forty-eight canals were randomly divided into four groups. Images of each canal were captured before and after root canal preparation using micro-CT. Data-Viewer was used to superimpose the pre- and post-instrumentation photos. The centering ratio, canal transportation, and volume change were then measured by CTAn application. E-FLEX EDGE demonstrated the highest centering ratio in the apical and middle thirds of the root canal, whereas E-FLEX ONE showed the highest centering ratio in the cervical third. Additionally, E-FLEX EDGE exhibited the least canal transportation in the apical and middle regions. In contrast, ZenFlex demonstrated the least canal transportation at the cervical region. Regarding dentin removal, E-FLEX EDGE showed the greatest dentin volume change, while Mtwo exhibited the lowest dentin volume change. ZenFlex and Mtwo were the most effective in preserving dentin, supporting the concept of minimally invasive endodontics. In severely curved canals, ZenFlex and E-FLEX EDGE demonstrated favorable shaping performance, with ZenFlex maintaining canal anatomy and E-FLEX EDGE exhibiting excellent centering ability.