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Student Life - Association of British Oral and Maxillofacial Surgeons Essay Prize (Coronectomy: Safe

Left: Diagramatic representation of a coronectomy with lingual and inferior alveolar nerves visible.

Right: Radiographic view pre-coronectomy and immediately post-coronectomy, showing retained roots.


The Association of British Oral and Maxillofacial Surgeons (ABOAMS) runs an essay prize each year with a set title. This years title was 'Coronectomy: Safe surgery or defensive practice?' I was lucky enough to win both the Barts and then the UK wide prize.

Excerpts from Essay:

What is coronectomy and why is it an option?

Extraction of an impacted mandibular third molar (MTM) carries an inherent potential risk of causing inferior alveolar nerve injury (IANI). IANI may lead to a subsequent neurosensory deficit that may be temporary or permanent (>3 months). 1The reported incidence of IANI ranges from 0.41% permanent to 8% temporary. 2 3 4 5 The primary risk factor in IANI is the proximity of the roots to the Inferior alveolar nerve (IAN) canal. 2 When roots are in close approximation to the IAN canal the incidence of IANI can be as high as 4% permanent and 20% temporary. 6 In around 70% of IANIs patients experience an uncomfortable or painful neuropathy which may limit daily or social function. This often leads to significant psychological distress and sequelae. 7

Coronectomy is the removal of a tooth crown with intentional root retention. When used on lower posterior teeth it is a procedure designed to minimise IANI. The coronectomy was first described in 1984 by Ecuyer and Debian 8 in a paper entitled “Surgical Deductions” and then subsequently in 1989 by Knutsson et al. 9. However, it was not until June 1997 and a seminal presentation by O’Riordan 10 to the BAOMS at their summer conference entitled: “Uneasy lies the head that wears the crown” that the coronectomy was brought into the collective consciousness of the oral surgery community. There have been regrettably few well-designed studies since and coronectomy has experienced a mixed reception. 11

Amid concerns of post-operative infections, unpredictable root migration/apical periodontitis and poor wound healing, some have branded the coronectomy as merely “half an extraction”, a poor alternative to odontectomy and an example of defensive dentistry. 12 Conversely, some vehemently advocate it, attesting that – correctly done, in skilled hands, IANIs are reduced and coronectomy is an example of safe minimally-invasive dentistry. The author hopes to consider these perspectives and the various merits and shortcomings of the coronectomy.

So, does it work?

There is a lack of good quality evidence available so it's hard to say with absolute certainty. However, In three studies that compared coronectomy with a control group there was a clear and statistically significant reduction in the rate of Inferior Alveolar Nerve Injury (IANI) and multiple studies recorded 0% incidence of IANI. These figures are all largely supportive of the efficacy of coronectomy.

What are the risks?

  • Coronectomy failure rates were generally low. Failure was defined as a need for complete removal during or after the procedure. Renton et al. experienced a higher rate of failure (38.3%); this may have been related to their decoronation technique where coupland elevators were used to split the crown from the roots.

  • In the case of post-operative infections the rates were comparable in all studies to those found in conventional odontectomy and were within normal ranges.

  • Root migration is clearly a common occurrence, being found in every study but is unpredictable and does not always lead to re-operation. Some studies did not express root migration per patient but reported average distances, these were excluded.

  • Dry socket incidence in most cases were comparable between coronectomy and conventional extraction. In the case of Renton et al. The dry socket rate was higher (12%) but there was no significant difference between dry socket in either the coronectomy/control group.

  • Re-operation rates were generally low and appear inflated by low sample sizes in some studies. In all cases there was no incidence of IANI during reoperation.

What is defensive dentistry?

Defensive practice is a deviation from normal protocol to safeguard from litigation. It can be positive - excessive treatment, or negative – avoidance of risky procedures. Defensive dentistry lowers care quality and increases health risks, healthcare costs and the risk of breakdown in patient-dentist relations. 27

In our increasingly litigious society temptation to minimise the risk of malpractice claims can be an extremely strong motivator - perhaps significant enough to induce a risk-averse clinician to ‘undertreat’ in the hopes of preventing a potential lawsuit. A recent study concluded that the majority of physicians tend to routinely adopt a defensive professional culture. 27

There is precedent for such worries - one such example of an IANI following MTM extraction was recently settled with $1,000,000 in compensation. 28 Whilst extreme, this is not an isolated case as similar claims are being made every day.

This ‘Compensation Culture’ has previously been attributed in a House of Commons Report 29 to media portrayal of ‘no-win no-fee’ cases. This phenomena can be traced back to the introduction of Conditional Fee Agreements (CFAs) in the Courts and Legal Services Act 1990 and the amendments to CFAs in the Access to Justice Act 1999.


The issue of IANI is a medicolegal and a clinical one. An estimated 77,000 patients underwent MTM removal between 2009-2010. 30 Even with the lowest reported rates of nerve injury (0.41%) 5 there are still at least 287 patients per year experiencing IANIs. Consequently, any technique that may reduce IANIs is worthy of further consideration.

Just as coronectomy is controversial now, there are many examples in dental history – Hall’s technique, Atraumatic Restorative Technique and Resin Retained Bridges. Following refinement and research they are now broadly considered to be good examples of minimally invasive dentistry. 33 More randomised control trials are needed to further establish the long term success/failure rate of coronectomy. 32 A good evidence base is required upon which to create definitive selection criteria for patients who could potentially benefit from a minimally invasive option.

The technique of coronectomy itself is neither safe surgery nor defensive practice. However, the thought process behind case selection may be either. The interests of the patient should be foremost in the mind of any conscientious clinician and the decision should be based on evidence, not risk-aversion alone. Only then will we deliver safe surgery rather than defensive practice.

This is the essay in poster format and was presented at the ABOAMS conference in Berlin.

Thanks for reading guys,

Bye for now.

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