So, why do root canal files break?
1. Operator errors
- pushing rotary files, no glyde path, instrumenting dry, overusing files
2. File defect
- It is extremely unlikely that a file has a manufacturing defect, however it can have defects and/or fatigue from multiple use.
3. Root canal anatomy
- Canals are generally not round. They can be bunch of different shapes: tear drop, figure eight, oval… There are also fins and isthmuses where a file may get caught and inevidably break.
The important thing is if a procedural error happens, and most of these occur during intra-operative stage as we saw from the last post, a prudent clinician should evaluate why the error occured to minimize such things in the future.
Had a very humbling experience yesterday…
I broke a file in a seemingly straight-forward case!
Had a patient that came in for a root canal #30. This tooth is asymptomatic, perio probings are 5mm or less, no response to cold, WNL to percussion and palpation, periradicular area radiographically. Tooth #31 is planned to be extracted due to extensive endo-perio involvement and loss of furcal bone due to a fracture.
I believe that my yellow protaper got caught in a fin, but this doesn’t make me feel any better. The reason I think it was a fin is because during instrumentation, my instrument was “grabbed” as it was rotating (so it started screwing into the canal actively) and it snapped in the ML canal before my foot was off the pedal. Now, this canal had a glyde path, patency, instrument had a lubricant on it, and a previous instrument in a Protaper series (white protaper) was to the apex with out problems.
mid-op #30, broken file ML canal
Once the file broke, I continued with instrumentation of three other canals and an x-ray was taken with master cones. This film shows that the ML canal is fairly straight, root walls are rather thick and the access to the instrument in the apical 1/3 is possible. The file was then removed using the microscope and ultrasonic instruments in the following order: buc1, cpr#4, cpr#5 and finally cpr#6.
Instrumentation was then completed and canals were obturated using Resilon obturation material in a warm vertical fashion and a thin layer of glass ionomer resin was placed over each orifis as a barrier. This patient was then scheduled for a routine 6 months follow-up.
post-op1 #30, instrument removed
post-op#2, instrument removed
These types of cases remind us that the root canal system is a network of very complex and delicate structures and we must treat it with the utmost care and respect!