One of the most frequent adverse events reported is the separation (or fracture) of an endodontic instrument within a tooth. Dr Simon Parsons, dentolegal consultant at Dental Protection, looks at what we can do to reduce our risk of procedural error and how we might manage these cases should they arise.

Case study

A young, recently graduated dentist commenced RCT on a lower molar for a patient who had recently given birth. At the second appointment, a file separated, unknown to both the patient and the clinician.

The tooth remained symptomatic and, due to the part-time availability of the treating dentist, the patient sought urgent pain relief at another dental practice where the separated file was discovered during preoperative radiography. The unhappy patient was referred to an endodontist who was unable to retrieve the file. It was agreed, due to the ongoing symptoms, that it was best that the tooth be extracted by an oral surgeon.

The oral surgeon could not achieve adequate local anaesthesia to extract the tooth conventionally, so the patient was subsequently booked in for treatment under general anaesthesia. This incurred considerable inconvenience and expense to the new mother who needed to make alternate childcare arrangements.

Once the clinician became aware of this, they sought advice from Dental Protection and the case was resolved by reimbursing the patient the specialist and hospital costs. This was essential as the patient had not been warned about the possibility of file separation, which had not been identified at the time and consequently there was no valid consent in place for this case. Regretfully, the patient had already complained to the Dental Council, and the clinician endured considerable anguish during the protracted management of the complaint. While the actual occurrence of file separation may not necessarily have been avoidable in this instance, early identification of it may have expedited appropriate patient management and eliminated a complaint to the Dental Board, improving the outcome for all parties.

How likely is file separation and should we forewarn about it?

It can be difficult to know exactly how often files fracture within teeth and remain there because they cannot be removed. This may be due to reasons such as lack of awareness of the fracture itself, a failure to inform the patient or deal with the issue, or endodontic failure requiring tooth extraction. Clinicians may have fractured a file and then successfully retrieved it, in which case such an event would be unreported.

However, it is not uncommon for patients to be first advised of a file separation when seeing a new dentist and having radiographs taken. This naturally raises doubt in a patient’s mind about the ethics and clinical ability of the previous treating dentist and can lead to a complaint or claim.

So why don’t we tend to forewarn our patients of this risk? It may well be because we don’t see it as a likely outcome to our care, given that studies typically report the incidence of file separation as being between 0.5% and 5% of cases investigated.[i] A recent study of 571 Protaper Next rotary files discarded by endodontists according to conventional reuse protocols showed an incidence of fracture in almost 20% of X1 files and unwinding in a further 10%, despite these not being discarded due to known failure but simply in accordance with protocol.[ii] These authors noted that the fracture of rotary nickel-titanium instruments (NiTi) can occur from torsion (exceeding the elastic limit of the alloy due to binding of the file while torqued), cyclic fatigue, or a combination of both factors. Such research underlines the need for careful protocols in the reuse of rotary endodontic files and suggests that fractures may arise during instrumentation without the clinician being aware of it, especially when using fine rotary files.

Although file separation may indeed occur much less frequently than some other endodontic complications such as overfilling or underfilling, its detrimental impact can be significant especially in cases of periapical infection, resulting in a reduction in success of up to 14%.

Clinicians are obliged to communicate common adverse outcomes, as well as uncommon but potentially serious complications, as part of achieving consent for procedures. We recommend that all endodontic patients are forewarned of the risk of file separation as part of the routine disclosure of the risks associated with endodontic therapy before treatment commences. Naturally, this would also need to be documented in your clinical records.

How might we reduce the risk of file separation?

Some file separations may be unavoidable due to crystallographic issues in the alloy that can predispose to failure, or manufacturing defects. While we have all heard occasional reports of new NiTi rotary files fracturing soon after first being used in a canal, most file separations seem to arise from errors in instrumentation technique, or reuse of rotary files an excessive number of times.

Clinicians can reduce the risk of file separation by careful preoperative case assessment (with referral of cases with anatomical complexity or likely procedural difficulty to specialists), ensuring straight line access into canals wherever possible, removal of coronal constrictions through a crown down approach and fastidious irrigation.

Careful use and reuse of files is a must. Visual inspection of files under magnification is essential where they are being reused, even on the same patient, eg from one canal to the next. Visibly damaged files must be discarded and reuse protocols for rotary files strictly adhered to. Clinicians are wise to set rotary motors at correct speed and torque settings prior to starting each and every case.

Management of a file separation

Determining the best long-term approach to these events depends on the individual case, since the objective of the endodontic treatment with or without a fractured instrument remains the same, namely to disinfect the root canal system and prevent its recontamination.[iii]

Disclosure of the complication to the patient must occur if you are unable to correct the situation during the normal course of treatment and avoid irreversible harm or a compromised outcome. If file retrieval is not possible, prompt referral to a specialist for assessment and remedial treatment is wise. This is usually at the referring practitioner’s cost unless the patient has been specifically forewarned of a high risk of this complication and offered a specialist referral, but has elected to proceed with treatment regardless. Even then, emotive conflict can occur.

Any decision to monitor, bypass or remove a separated file fragment should be made in consultation with the patient. Factors to be considered may include any constraints in the root canal accommodating the fragment, the stage of root canal preparation, the potential complications of the treatment approach adopted, the strategic importance of the tooth involved and the presence (or absence) of periapical pathosis.[iv] The presence of a fractured instrument need not reduce the prognosis if the canal system is already well-disinfected and there is no evidence of apical disease, in which case file retention or bypass may be considered.[v]

Endodontics is never easy and complications can occur even in experienced hands. Always contact Dental Protection if you are unsure about how best to manage a patient following a treatment complication.