Charlie Nicholas explores the reasons why a file may fracture and what to do in the event of these instruments breaking.
A recent systematic review indicated that the overall incidence of endodontic file fracture was 2.27% (Gomes MS et al, 2021).
In real-world terms, this probably means there is a good chance general dentists performing endodontic treatment may indeed encounter this issue at some point in their careers.
The potential difficulty lies in the physics and chemistry of the files we use, which, of course, are made of metal.
We have all seen for ourselves that if we bend a paperclip back and forth, the material starts to displace. This is known as work hardening.
As this movement continues, the crystal line changes. The metal actually becomes a bit more like a ceramic and subject to stress fracture.
With endodontic files, there are two causes of fracture (or a combination of both):
- Torsional stress – essentially, this is the result of the file twisting while the tip is stuck in the root canal and is more common in narrow canals
- Cyclic fatigue – this may occur when the file rotates freely in a curved canal while it is being subjected to repeated cycles of tension and release.
Mitigating the risks
As with everything in life, prevention is better than cure. It is key that we clinicians do everything we can to mitigate the risk of file fracture.
The good news is that metal technology advancements have made inroads here in the form of heat-treated files.
The process that many endodontic file manufacturers use, including Endoperfection, involves heat treatment. The heat treatment changes the crystalline structure of the metal.
In a nutshell, the metal always ‘thinks’ it is warm, making the nickel titanium ‘happier’ to be bent.
There is plenty of evidence supporting the efficacy of this development, including Endoperfection’s own research.
We tested heated and non-heated versions of our Varyflex files at 250rpm around a 40-degree curvature.
The non-heated file fractured at 43 seconds, while the heat-treated version took 13 minutes and 26 seconds. The results speak for themselves.
As for minimising the risks during treatment, there are a few simple tips to bear in mind:
- Run each file at the correct speed and torque settings
- Do not work underneath cusps, rather go around the coronal curve
- Use smaller files where possible – don’t just reach for the largest that will fit. File manufacturers have a range of sizes; Endoperfection, for example, has just launched the Varyflex Neo range with small constant tapers that make them ideal for use in narrow or curved canals
- Consider using a reciprocating action, which is not infallible but may reduce the possibility of breakage
- If you feel like the flutes are grating in the canal, check the flutes to see if they are showing signs of unwinding. If they are, that is the point at which the file may fracture.
Separation anxiety
Despite best efforts, things can go wrong. The first thing to do is not to panic!
It is important to note at this point that breaking a file is not in itself negligent. It can be, but it still happens even if you do everything right.
So, as a small aside, in terms of record keeping, which is really an issue beyond the scope of this article, I would suggest that everything that is said in your conversation with the patient and the choices you make, alongside any action taken, must be recorded in their notes in full, accurately, and contemporaneously.
Be open with the patient about what is happening. In my experience, the term ‘separated file’ is better received that ‘broken’ or ‘fractured’.
Simply tell them what has occurred, that it is known to happen from time to time, it can be challenging, but you know how to help to get this sorted.
Now, you may feel up to the job or you may choose to refer. Either is fine, as long as you know your own limits and work within them judiciously.
There are a few pieces of equipment that can be helpful in these circumstances, such as Steiglitz tweezers, which can be useful if the broken file is simply sticking out of the canal.
You might also want to have to hand: wedging/micro tubes, cyanoacrylate (aka superglue) and methyl methacrylate, to snap-set the glue in the tube.
This will hopefully enable you to pull the whole thing out, including the fractured file.
On a more technological level, the IRS instrument removal ultrasonics system is designed to assist in the removal of intra-canal obstructions by dislodging them and, hopefully, making them relatively easy to retrieve.
When to refer
What I would say is that, for the most part, file removal is challenging and unless the broken file is in the top part of the canal and you have straight line access, chances are you need to refer.
Of course, file removal is not always possible.
A broken file left in the canal does not necessarily mean that treatment is doomed. However it does need careful monitoring.
For example, sometimes the broken part can be bypassed, and successful endodontic treatment completed.
It depends on the individual circumstances. I would suggest that if you, as a general dentist, think this is the best option, you do need to be transparent with your patient about what is happening and refer them to make sure this is the best outcome that can be achieved.
No matter what happens, always remember that effective communication will see you through any circumstance.
Be honest, be open and be clear, and you and your patients can get through anything together, including separated files.
I would also suggest that a confidence-building course dedicated to broken file removal will help to stand you in good stead in such circumstances
It is something that is being developed by Endoperfection right now, so keep your eyes peeled for dates and locations.
References
Gomes MS et al. (2021) Clinical fracture incidence of rotary and reciprocating NiTi files: A systematic review and meta-regression; Australian Endodontic Journal; 47(2): 372-385
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