Components of nickel titanium rotary files
- Tip size: Diameter of the file's tip, measured in 100ths of a millimeter.
- Taper: Gradual increase in diameter along the file's working surface.
- Flutes: Grooves on the working side of the file that provide cutting edges and space for debris collection.
- Helix angle: Angle between the cutting edge and the long axis of the file.
- Measuring stop: Rubber piece used to mark desired length on the file.

Separation of nickel titanium rotary files
- Torsional failure: Occurs when the tip of the file is locked but the shank exceeds the elastic limit of the alloy.
- Cyclic fatigue: File rotates continuously under flexion in curved root canals, causing spread of defects and cracks.
- Discarding decision: Dependent on operator's skills and judgment to prevent file separation.

Properties of nickel titanium rotary files
- Superelasticity: Stress remains constant despite the increase in strain until the whole NiTi mass has converted to the martensite form.
- Shape memory: Nickel titanium rotary files have the ability to return to their original shape after deformation.
- Flexibility: Nickel titanium rotary files are highly flexible compared to stainless steel files, making them superior for rotary root canal preparation.
- Use in dentistry: The use of nickel titanium rotary files is a common practice in dentistry.
- Introduction to the market: The first nickel titanium rotary file was introduced in 1991.

Other features of nickel titanium rotary files
- Radial land: Peripheral portion of the instrument that is flat and smooth, designed to center the file in the central space.
- Pitch: Distance between a point on the leading edge and the corresponding point on the adjacent edge.
- Variable pitch: Decreases the screwing effect.
- Measuring lines: Some designs incorporate measuring lines for accurate length measurement.
- Color-coded stoppers: Measuring stops can be color-coded corresponding to the size and number of a file.

References
- Eleazer, P. D., Glickman, G. N., McClanahan, S. B., Webb, T. D., & Justman, B. C. (2012). Glossary of Endodontic terms.
- Plotino, G., Grande, N. M., Cordaro, M., Testarelli, L., & Gambarini, G. (2009). A review of cyclic fatigue testing of nickel-titanium rotary instruments.
- Martin, B., Zelada, G., Varela, P., Bahillo, J. G., Magán, F., Ahn, S., & Rodriguez, C. (2003). Factors influencing the fracture of nickel‐titanium rotary instruments.
- McSpadden, J. T. Mastering endodontic instrumentation. Chattanooga, TN: Cloudland Institute (2007): 51-2.
- Parashos, Peter, Ian Gordon, and Harold H. Messer. Factors influencing defects of rotary nickel-titanium endodontic instruments after clinical use.