Nickel Titanium instruments are the fastest and most efficient way to prepare the root canal system in a tooth. However, one of the biggest problems in using them is the issue of file separation. This event can compromise a tooth in such a way that a relatively straightforward procedure can end in the need for surgery or extraction.
The instrument itself doesn’t cause the problems. It’s the fact that it will block the canal and preclude further shaping and cleaning which is mandatory in endodontics. It is therefore essential to know when the file separated and how clean the canal was before this happened.
Why does it happen?
The actual reasons for instrument fracture are multi factorial and are mostly dependent on clinicians’ experience and the numbers of times the file has been used. Hopefully with the new Government recommendations to discard files after a single use rather than to sterilise them, the incidence of separation will reduce.
However, one study into file separations unsurprisingly found an increased incidence of NiTi rotary file separations (1.68 per cent) compared with stainless steel file systems (0.25 per cent) approximately seven times as many. In addition, the probability of separating a file in the apical third was 33 times more than in the coronal third. The highest percentage of instrument separation occurs in mandibular molars (55 per cent, usually in mesial roots) followed by maxillary molars (33 per cent, usually in buccal roots).
File separation may even occur in the hands of highly skilled professionals. As Louis Grossman, one of the founding fathers of endodontics once reported, ‘A dentist who has not separated a tip of a file, or a broach, has not done enough root canals’.
Once a file has separated, a decision needs to be taken as to whether to accept the situation, obturate as best as possible and monitor or to attempt to either bypass the instrument to attempt retrieval.
Steps to take
As frustrating as it may be when a file separates, not every separation must be removed and the astute clinician would determine steps to be taken according to the specific clinical conditions presented:
1. Was the tooth vital or necrotic (and probably infected) before treatment? If the tooth is not infected and copious amounts of irrigants had been used before the separation and the instrument itself cannot be bypassed, it is best to leave it there with the obturation and simply follow up.
2. In infected teeth, has the file separated at the beginning of the preparation or at the end, when the canals are ‘clean’? If there is preoperative periradicular radiolocency and the tooth is infected, every effort is made to first bypass the separation (especially if two canals share the same apex). Generally removing the instrument by troughing around it leaves to a loss of tooth tissue and a weakening of the root. If too much tooth is removed, there is a procedural risk of perforation, therefore bypassing using fine stainless steel instruments and enlarging by hand is preferable. Once bypassed, the obvious temptation is to go back in with a NiTi instrument, but it’s advised not to, as it is more than likely that it too will break.
Removing a file that is located beyond the curvature (when we can not see it after a straight line access) really increases procedural risks as inevitably a lot of tooth is removed and this reduces the root resistance to fracture
3. Taking the right approach could hugely increase prognosis and tooth survival. One should not try to remove a separation without such knowledge, skill and suitable equipment. Adequate visualisation is essential either using loupes and a light source or ideally a microscope.
Whenever the file separates, it is important that the patient is made aware of the problem and the prognosis. It is not negligent breaking a file. With their narrow pathways and multiple curvatures, canals are difficult spaces to get to. Instruments can fracture even in the best of hands.
Should treatment fail and the tooth remains symptomatic or without healing, an endodontic surgical approach or extraction may be necessary.
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