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.

Nickel titanium rotary file (Wikipedia)

A nickel titanium rotary file is an engine-driven tapered and pointed endodontic instrument made of nickel titanium alloy with cutting edges used to mechanically shape and prepare the root canals during endodontic therapy or to remove the root canal obturating material while performing retreatment. The first nickel titanium rotary file was introduced to the market in 1991. Superelasticity and shape memory are the properties that make nickel titanium rotary files very flexible. The high flexibility makes them superior to stainless steel files for the purpose of rotary root canal preparation. The use of nickel titanium rotary files in dentistry is a common practice.

Nickel–titanium (NiTi) show the phenomenon of superelasticity where the stress remains constant, despite the increase in strain up till a certain range. Their superelastic property is caused by the austenite transforming into the martensite form. The strain remains constant during this transformation until the whole NiTi mass has converted to the martensite form, which would indicate that the superelasticity phase has ended.^{[citation needed]}