A previous dentist had performed a pulpotomy on tooth No. 18 to get the patient out of pain, but the patient still had percussion and biting sensitivity. The canals were very calcified and curved. I performed endodontic treatment and checked my file, and it came up short—literally!
The severity of the canal created a file separation with a size 30/.04. The odds of rotary file separation are 7 times greater than for hand files. The probability of separating a file in an apical third is 6 times greater than in the coronal and middle thirds of the canals.
Cyclic fatigue and torsional stress are the 2 main causes of breakage for NiTi endodontic files. Sometimes it can be a manufacturer defect or operator error as well.
|Figure 2. The x-ray of the completed case reveals 4 canals, each with independent apicies and the separated file in the mesiolingual canal.||Figure 3. This image shows a different angle of the post-op. Should we be worried about the file that separated?|
|Figure 4. The one-year recall showed the file still in place with no periapical pathology or symptoms after core buildup.|
Cyclic fatigue is when a material has repeated stress placed on it during a period of time. Ultimately, this repetition breaks the material. It’s 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.
I told the patient about the file separation and documented it in the chart, which is the standard of care. I did not want to try to remove the file to make the x-ray look good. This would have removed more precious dentin and made the x-ray look worse.
This was a vital case with no lesion. I was already at the apex with a size 15 hand file and a previous size 25/.04, so I knew based on the studies that the outcome was going to be favorable.1 A lesion would have reduced the chance for success by only 5% to 7%.2,3
For the record, any file can separate. Don’t buy into those marketing schemes!
At the one-year recall, the area looked good, and the patient was asymptomatic.
- Crump MC, Natkin E. Relationship of broken root canal instruments to endodontic case prognosis: a clinical investigation. J Am Dent Assoc. 1970 Jun;80(6):1341-1347.
- Fox J, Moodnik RM, Greenfield E, Atkinson JS. Filing root canals with files radiographic evaluation of 304 cases. N Y State Dent J. 1972 Mar;38(3)154-157.
- Spili P, Parashos P, Messer HH. The impact of instrument fracture on outcome of endodontic treatment. J Endod. 2005 Dec;31(12):845-850.
Additional Short Case Studies