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Endodontics

Authors: Dr. Annil Dhingra
 

We are in the world of rotary Nickel Titanium instruments. We found all the canals, the cleaning and shaping are going well, and all of a sudden you feel a snap, and your rotary file breaks ? Shocked there is a sinking feeling in stomach, your mood changes and you are in the middle of nowhere. . You verify with radiographand now you are in a tight spot – the radiograpghconfirms the darkest fear of the day --- file seperatedand now you are in dilemma should I or should I not tell the patient . Now what?

A separated file will immediately change the level of complexity and involvement of an endodontic case by altering the outcome of cleaning, shaping, and filling of the canal. What are some of the factors that cause files to break, how can separation be prevented, and what are the options post-file separation? All nickel titanium instruments undergo cyclic fatigueand torsional stress—are two main causes of breakage of NiTi endodontic files. Cyclic fatigue is when a material has repeated stress placed on it over a period of time and, ultimately, this repetition breaks the material. It is similar to taking a piece of wire and bending it back and forth until it separates. Torsional stress is when an object is twisted with an applied force; when a portion of material is locked into place and the rest continues to rotate, a breaking point is reached and breaking or snapping occurs.

How does cyclic fatigue and torsional stress apply to NiTi files? While the properties of NiTi files make it the best files for cleaning and shaping, the rotational movement in curved canals will bend these files once per revolution, ultimately leading to work hardening and brittle fracture, also known as cyclic fatigue.Further, if a portion of the file binds in the canal and the shank continues to rotate, fracture will occur.

The following are things to consider when performing root canal therapy, with the use of NiTi files:

  • Size—an increase in diameter or cross-sectional area of an instrument will decrease a material’s resistance to cyclic fatigue.
  • Taper—an increase in taper decreases resistance to fracture.
  • With regard to size and taper, a coronal root canal curvature is more dangerous than an apical one in terms of fracture, and a very acute canal curvature generates more fatigue than one with a larger radius.
  • Larger tapers and larger-sized instruments will require increased torque, therefore decreasing fracture time.
  • Cutting flute depth—deeper-cutting flutes will increase the file’s ability to bind, increase the need for applied force (torque), and subsequently make the metal more prone to fracture.
  • Lubrication/file cleaning—copious amounts of gel lubricants and NaOcl are recommended to lubricate the canal to prevent binding of the flutes to the dentin. In addition, the files should be cleaned after each use with an gauze for complete debris removal.
  • Instrument use frequency— files should be kept to single use, especially when used in curved canals.
As per recommendation of American Association of Endodontists :
  • Have good access preparation to create a straight-line access.
  • Don’t force the files. NiTi works best when applied in a passive manner.
  • Try to instrument difficult canals with a hand file first, thus creating a guide path for rotary instrumentation.
  • Don’t try to bypass ledges—a straight pathway created with a K-file is recommended prior to NiTi manipulation.
  • Avoid cutting with the entire length of the file to prevent fracture potential. Most NiTi files have noncutting tips and should be advanced only in a canal that has been opened (i.e., with a K-file).
  • The file should maintain a constant rotation while inserting and withdrawing from the canal to prevent sudden changes in direction (and fracture potential).
  • Maintain length control.
  • With regard to rotational speed and torque of electric motors—studies have shown that fractures occur less when working at low speeds and low torque settings.
  • Multiangle radiographs will allow for assessing canal curvatures and better prepare the operator for potential complications.

When a file does break, three possibilities exist for care: retrieval, bypassing of the file (with subsequent completion of the endo), or the broken piece can function as a true blockage within the canal system. While a separated file can present a barrier to mechanical manipulation of the canal, it is the inability to completely remove the pulp and associated tissues and subsequently obturate properly that precede infection, inflammation, and ultimately loss of the tooth. Therefore, the best scenario is removal, which can be influenced by file type, location of the break within the canal, anatomy of the tooth (diameter and curvature), and the size of the broken piece. . Even if a file can’t be removed, evidence of healing, in some cases, has been observed if proper cleaning and shaping has been done.

Due to the curvature not easily observed in a lingual fashion on 2-D radiographs, separated instruments are most commonly seen at the middle apical one-third of mesial canals of mandibular molars and at the same location of the mesio-buccal roots of the maxillary molars. This information is helpful when deciding if a file can be retrieved or not. 

There are various methods to remove a broken instrument. But all these methods present with complications and are best performed under the care of a endodontist who is well trained and has sufficient experience. A general guideline is that the removal of a broken file that is located beyond a canal curvature should not be routinely attempted due to limited success of file removal, increased risk of perforation, and reduction of root strength.

In the event that removal or bypassing the broken piece is not successful, leaving the fragment in situ is the least conservative approach to care. Success of therapy is increased if separation occurs toward the end of the treatment in the apical third of the tooth. The patient should be informed.

Complications do happen during endodontic procedures .However file breakages can be reduced when a case is treatment planned accordingly, familiarity with instruments and their limitations; follow proper steps and protocols for treatment.