“A dentist who has not separated a tip of a file, reamer, or broach has not done enough root canals.” — Louis Grossman
There are essentially 2 reasons for rotary rotary instrument separation inside a canal:
1) Cyclic fatigue (file rotating inside a curved canal for extended period of time):
Factors contributing to cyclic fatigue are: overuse of rotary NiTi files, spending too much time inside the canal during instrumentation, canal curvature (degree and abruptness of the curvature), improper speed setting for the handpiece and the file tapers (larger tapers break faster).
2) Torsional fatigue (too much friction between the rotary file and the canal wall):
Factors contributing to torsional fatigue are: improper endodontic access, using too much apical pressure during instumentation, not following the proper sequence for a particular file system, not using lubricating agent/irrigants, using greater tapered files inside a tight/calcified canal and using handpieces with no torque control or auto reverse option.
Attempting to control the factors above will greatly minimize the risk of file separation. But even in a perfect situation, a patient’s canal anatomy can bring the man-made technology to its knees.
What to do if a file breaks inside a canal?
1. Stay calm. It is not the end of the world.
2. Try to remove it only if the separated portion is in the coronal segment of the tooth and not past the root curvature. This step also requires good magnification, illumination and proper tools (such as different ultrasonic tips).
3. Bypass it if the separated segment is apical to the curvature of the root using hand-instruments and finish the shaping of that canal with hand-files. Sometimes the separated file comes loose and can be easily flushed out.
4. Make it part of the filling if the file has completely blocked the canal. This may not affect the prognosis negatively [Crump and Natkin 1970, Spili et al. 2005] depending on the initial status of the pulp and whether or nor the separation happened towards the beginning or the end of cleaning and shaping stage.
5. Follow up the healing and the resolution of symptoms. Endodontic surgery may be needed if symptoms persist or the PA lesion does not heal.