Rotary File Fatigue – How to Prevent Separation?

File breakage in maxillary molars is not a rare sight, but definitely no less than a nightmare.

But the latest research says that file separation is not only predictable but also preventable¹.

Great news, so what do we know now that makes it easier to avoid breakage? Let’s find out.

Why Files Break: The Two Mechanisms

Failure of NiTi rotary files can occur due to torsional overload or cyclical bending fatigue².

Torsional overload occurs when the file tip binds in the canal while the shaft continues to rotate, and the file literally separates³. 

Cyclic fatigue is a more progressive, localized, and permanent structural change in the file. It happens due to repetition patterns that cause micro-cracks and ultimately fracture. 

Therefore, every time a file bends going around a curve, microscopic cracks form. Eventually, it fractures without warning.

How Does File Type Affect Fracture Risk?

A 2024 systematic review and meta-analysis compared the cyclic fatigue resistance of rotary and reciprocating NiTi file systems using artificial canal models¹.

It was found that reciprocating files can withstand more cycles before fracture than rotary ones, especially in curved or double-curved canals. 

Motion type surely plays a role, but other factors like alloy composition, heat treatment, and cross-sectional design can also affect fracture resistance.

Another comparative evaluation of cyclic fatigue resistance of three different NiTi rotary file systems directly compared heat-treated systems, including CM wire, blue-wire, etc, in simulated curved canals. It confirmed the superior performance of heat-treated alloys over traditional super-elastic NiTi⁴.

5 Evidence-Based Strategies to Prevent File Separation

1. Create a Glide Path First (Non-Negotiable)

Use hand files before rotary files and create a straight line, also known as a glide path. The access into a canal via a hand file significantly reduces the incidence of file breakage.

Why it matters: Glide path files show less resistance and reduce torsional stress on larger rotary files. Preflaring the coronal portion before using rotary files in the apical third of the canal prevents binding⁵.

Clinical protocol:

• Run the canal with #10 K-file to working length
• Use dedicated glide path files like PathFiles, G-Files, or #15 hand file before rotary shaping
• Never force a glide path file; if it binds, recapitulate and irrigate

2. Use Slow, Controlled Pecking Motion

Using an up-and-down motion with the electric slow-speed handpiece that does not allow the file to bind within the canal can also reduce the incidence of file breakage⁶.

The technique:

• 2-3mm amplitude pecking motions
• Apply minimal apical pressure
• Remove file after every 2-3 pecks to clear debris
• Never let the file bind or stall

3. Respect the Single-Use Principle Especially in Curved Canals

Each use cycle fatigues the file. The tighter the curvature, the more fatigue accumulates in the file².

Evidence-based recommendations:

• Use file only once in severely curved canals
• Maximum 3 uses for moderate curves
• Maximum 5 uses for straight canals 

Clinical reality check: Don’t procrastinate changing files. Remember, a separated file can cost time, patient stress, and potential failure; which is way more than the cost of a new file.

4. Know Your File Metallurgy

Not all NiTi files are equal and it is crucial to understand the differences.

Conventional superelastic NiTi include Standard files like ProTaper, K3, etc. They have -

• Good flexibility
• Moderate cyclic fatigue resistance

Heat-treated NiTi like CM Wire, MaxWire, Gold Wire specifications-

• Heat treatment procedures enhance flexibility, fatigue resistance, and clinical performance
• Have superior cyclic fatigue resistance
• More expensive but safer in challenging cases

Clinical tip: Use heat-treated files for severely curved canals, calcified canals, and retreatments⁷.

5. Watch for Warning Signs

Files don't always break without warning. You can look out for these red flags⁶:

• File resistance increases suddenly
• File doesn't advance during normal technique
• Unusual vibration or sound during the use
• Flute edges show visible wear or unwinding

If you see any red flag, discard the file immediately. Never push through in these circumstances⁷. 

What If It Does Separate?

If a file breaks, successful removal mainly depends on the location of the file in the canal rather than the specific technique employed for removal⁸.

Location matters⁸:

• Coronal third: Often retrievable with ultrasonic tips or Masserann trephines
• Middle third: More challenging; may require bypass or incorporate-and-seal approach
• Apical third: Usually unretrievable; incorporate and seal if the canal is already cleaned and shaped

Document, inform, discuss options. Separated files aren't always treatment failures, but honesty and informed consent are mandatory.

Final Takeaway

File separation is rarely "bad luck" and is usually the result of predictable mechanical failure from torsional overload or cyclic fatigue.

Prevention through proper technique and understanding file mechanics is the way to go.

References

1. De Pedro-Muñoz A, Rico-Romano C, Sánchez-Llobet P, Montiel-Company JM, Mena-Álvarez J. Cyclic Fatigue Resistance of Rotary versus Reciprocating Endodontic Files: A Systematic Review and Meta-Analysis. J Clin Med. 2024;13(3):882
2. Abdellatif D, Iandolo A, Scorziello M, Sangiovanni G, Pisano M. Cyclic Fatigue of Different Ni-Ti Endodontic Rotary File Alloys: A Comprehensive Review. Bioengineering (Basel). 2024 May 16;11(5):499. doi: 10.3390/bioengineering11050499.
3. American Association of Endodontists. Trends in Rotary File Design [Internet]. Chicago (IL): AAE; 2025 Jan 27.
4. Hamid T, Malik A, Kumar A, Anjum S. Comparative evaluation of cyclic fatigue resistance of thermomechanically treated NiTi rotary instruments in simulated curved canals with two different radii of curvature: An in vitro study. J Clin Diagn Res. 2024;18(4):ZC23–ZC27. 
5. Lup VM, Malvicini G, Gaeta C, Grandini S, Ciavoi G. Glide Path in Endodontics: A Literature Review of Current Knowledge. Dent J (Basel). 2024 Aug 14;12(8):257.
6. Zubizarreta-Macho Á, Mena Álvarez J, Albaladejo Martínez A, Segura-Egea JJ, Caviedes Brucheli J, Agustín-Panadero R, López Píriz R, Alonso-Ezpeleta Ó. Influence of the pecking motion frequency on the cyclic fatigue resistance of endodontic rotary files. J Clin Med. 2019 Dec 24;9(1):45.
7. Chien PYH, Wan B, Walsh LJ, Peters OA. Experimental and 2-step finite element analysis of cyclic fatigue resistance of conventional and heat-treated rotary endodontic nickel-titanium instruments. Appl Sci. 2023;13(4):2080.
8. Fan Y, Gao Y, Wang X, Fan B, et al. Expert consensus on management of instrument separation in root canal therapy. Int J Oral Sci. 2025 Jun 9;17:46.