Open Access
J Oral Med Oral Surg
Volume 24, Number 2, June 2018
Page(s) 93 - 99
Section Article pédagogique / Educational article
Published online 29 June 2018

© The authors, 2018

Licence Creative CommonsThis is an Open Access article distributed under the terms of the Creative Commons Attribution License (, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


The extraction of third molar, especially mandibular, is a very standard procedure in oromaxillofacial surgery. In cases where the inferior alveolar nerve (IAN) is in close proximity to the roots of the mandibular third molar (3MM), there is a minimal risk of nerve injury. Previous studies have reported that third mandibular molar extraction causes approximately 0.5–1% of chronic IAN injuries [1,2]. IAN injury must nevertheless be minimized to avoid adverse consequences impeding the patient's quality of life. These consequences may be caused by sensorineural disorders such as hypoesthesia, dysesthesia, anesthesia, etc., as well as the neuropsychological and functional disorders that may also result (chronic pain, long-term changes in the body schema, a functional deficit that may impact social function: drooling, biting, the altering of certain facial expressions etc.) [3,4].

Pedagogical objectives

Preoperative assessment

A standard preoperative assessment is performed to identify the current and past medical history of the patient and to have a better grasp of the anesthesia modalities required for the intervention. Some X-rays are required for planning the intervention. First, a panoramic X-ray and initial examination of the mandible will make it easy to detect possible risks. Seven predictors of increased risk of IAN injury have been reported in previous studies [5,6]:

  • Disruption of the lamina dura* (Fig. 1a)

  • Dental root translucency* (Fig. 1b )

  • Root canal deviation* (Fig. 1c)

  • Translucency around the roots (Fig. 1d)

  • Root curvature (Fig. 1e)

  • Narrowing of the roots (Fig. 1f)

  • Narrowing of nerve root canal (Fig. 1g)

  • *: Statistically significant according to Rood et al. (1990) [5].

Following this, a three-dimensional cone-beam computed tomography (CBCT) should ideally be performed, which will pinpoint nerve proximity. If a bone plate is interposed between the nerve tissue and the tooth root to be extracted, possible risks to the nerves are decreased. A coronectomy can only be considered when direct contact is observed between IAN and the root.

This technique, also known as a partial odontectomy, was first outlined by Ecuyer et al. in 1984 [7]. It is widely used in Anglo-Saxon countries but is rarely used in France.

The patient will receive prescriptions, including analgesics, adapted to the clinical situation (palliative 1 or 2), a local antisepsis (chlorhexidine 0.2%) to be taken 24 h after the intervention, and antibiotic prophylaxis (in accordance with current recommendations for dental avulsions of mandibular wisdom teeth: 2 g of amoxicillin 1 h before surgery or 600 mg of clindamycin in case of a penicillin allergy [8]).

Precise and reliable information is provided to the patient and informed consent is obtained.

At the end of this preoperative assessment:

  • The indications for a coronectomy should be decided in a rational manner by the surgeon;

  • Informed consent should be obtained from the patient;

  • Drug prescriptions appropriate to this intervention should be prescribed.

thumbnail Fig. 1

(a)The different x-ray images that should alert the surgeon. Loss of lamina dura of canal, (b) radiolucent of mesial apex, (c) deviation of the canal, (d) periapical radiolucent area,  (e) curvature of roots, (f) narrowing, (g) narrowing of the canal.

Operative technique

After intraoral disinfection (with 10% povidone iodine or 0.2% chlorhexidine), an intrasulcular incision is made from the first to second molar. This is followed by a distovestibular relieving incision of a few millimeters at a 45° along the external oblique line (Fig. 2a).

Next, a full-thickness gingival flap is elevated (Fig. 2b). The flap is supported on a retractor so that a clear view of the operating site is ensured. Some authors advocate using a lingual protection plate, which will create a deep coronoradicular separation without the risk of lingual nerve injury [9].

Alveolectomy is the performed using either round or fissure bur attached to a contra-angle handpiece with constant saline irrigation until the enamel–cement junction is exposed (Fig. 2c).

Coronoradicular separation is performed using a fissure or Lindhemann bur attached to a contra-angle handpiece with saline solution irrigation. Then, the crown is separated from the radicular complex (Fig. 2d). The separation axis should be perpendicular to the long axis of the tooth. The risk here is the creation of an incomplete segment, resulting in a residual amelodentinal substance which would require a repeat surgery. (Fig. 3). The immobilization of the root complex is required; otherwise, infection risk is increased. [9].

Amelodentinal substance 2–4 mm deep to the alveolar rim is delicately removed with a round bur, which is reported to enhance new bone growth (Fig. 4) [9].

The dental pulp tissue does not require any special treatment [10]. Bone smoothening, rinsing, and suturing are performed. A postinterventional retroalveolar or panoramic dental X-ray should be performed to confirm that there is no residual amelodentinal lamina and to serve as a reference for any residual roots. Regular clinical and radiological follow-up is required every 6 months for a period of 1–2 years and annually thereafter. This will make it easier to intercept any complications, to assess the migration of the residual roots and, if necessary, to predict possible avulsions (Fig. 5).

The operative technique must allow:

  • a clear view of the optimal operating site;

  • a clear section of the crown without any mobility of the radicular complex.

thumbnail Fig. 2

(a) Incision, (b) Full-thickness flap elevation, (c) alveolectomy to the cemento-enamel junction, (d) crown separation and enamel reducing to 2–4 mm below the level of alveolar crest.

thumbnail Fig. 3

Failed separation causing the necessity of a new intervention.

thumbnail Fig. 4

Drawing of crown separation and enamel reducing.

thumbnail Fig. 5

(a) Immediate post-operatory radiographic control, (b) at 12 months. It can be noted the coronary migration of the roots.

Literature review

The aim of this literature review is to answer the following issues regarding the coronectomy:

  • decreasing the risks of nerve injury;

  • risk of infection;

  • the clinical outcomes of roots retained in the bone;

  • the need for the endodontic treatment of residual roots;

  • periodontal healing of the operative area.

Consequently, a keyword search was conducted using such scientific databases as “PubMed,” “Google Scholar,” and “ScienceDirect.” The French and English results for the keywords “coronectomy” and “partial odontectomy” were analyzed and 298 references were found.

Nineteen articles remained after eliminating case studies with <30 subjects, clinical cases, literature reviews, letters to the editor, and articles that were insufficiently detailed (Fig. 6):

  • 3 meta-analyses [11,12]

  • 4 randomized controlled trials [13,14]

  • 5 nonrandomized controlled trials [6,16]

  • 6 prospective cohort follow-up studies [9,1724]

  • 7 retrospective studies [2527]

  • 8 randomized controlled trial without statistical analysis [15].

Each article was assessed according to the study design, sample size, including how many 3MM, the presence of a control group, the radiological diagnosis which allowed for the inclusion of subjects, the average follow-duration up (in months), and the level of proof according to the French National Authority for Health (HAS) scale [28].

thumbnail Fig. 6

Flow chart of the bilbiographic review.

Decreasing nerve injury risk

The randomized controlled studies by Renton et al. (2005) and by Leung et al. (2009) found statistically significant outcomes, showing that coronectomy showed a lower incidence of nerve damage than conventional extraction. In radiologically at-risk patients, nerve damage was reported in 0–0.65% cases for coronectomies, whereas it was reported in 2.64–19% cases for standard avulsions [13,14]. In addition, two meta-analyses, one by Long et al. (2012) and the other by Cervera-Espert et al. (2015), both dealing with the same studies had similar results showing an 89% reduction in the nerve damage risk for coronectomies compared to a standard 3MM avulsion. In summary, many studies (nonrandomized controlled, prospective, and retrospective) found similar results favoring coronectomy (Table I).

The coronectomy minimizes the risk of IAN nerve damage compared to conventional surgical techniques.

Table I

Main characteristics of the selected studies.


Intraoperative complications

Apart from the complications inherent to any oral surgery (for example; bleeding, pain, fracture, etc.), two specific complications should be highlighted.

In the event of intraoperative mobilization of the radicular complex, it must be avulsed. Indeed, according to Patel et al. (2013), this increases the risk of postoperative infection [26,29]. This risk is higher in conical root cases and in female patients.

In the case of insufficient coronoradicular separation, amelodentinal residue may be observed at the end of the procedure. This will require reintervention to avoid the increased risk of infection.

Postoperative infections

For methodological reasons, controlled group studies were used to investigate short-term (<2 months) postoperative infections, such as dry and suppurative alveolitis. On the other hand, long-term infections (≥2 months) caused specifically by coronectomies were investigated by prospective studies, because they have long-term follow-up.

Suppurative alveolitis: Controlled studies conducted by Rendon et al. (2005) Leung et al. (2009), and Hatano et al. (2009) found no statistically significant difference between the two groups [6,13,14]. Other noncontrolled studies found suppurative alveolitis rates for coronectomies that were comparable to the rates found in the literature for standard avulsions (4% for Leung et al. (2016) and 2.64% for Aravindaksha et al. (2015) [15,17]).

Dry socket: Studies by Leung et al. (2009) and by Hatano et al. (2009) found a statistically significant difference in favor of the coronectomy, wherein conventional avulsions had a dry socket rate of 2.7–8.47% compared to the lower rate of 0–1.96% for coronectomies [6,13]. Other studies did not specifically address this parameter.

Long-term infections: The presence of residual roots in the socket forces the practitioner to consider the potential risk of a long-term infection. The study conducted by Leung et al. (2016) which monitored a cohort of 612 coronectomies for 60 months, discovered only two (0.33%) infections (at 12 and 24 months) [17]. All the other studies had shorter postoperative monitoring and found no long-term infections.

It seems that the postoperative infection rates are similar for both techniques.

The fate of the residual roots

Different studies highlight a phenomenon of root migration toward the crown. Leung et al. (2009) note a migration of 3.06 mm (±1.67 mm) after 24 months with a migratory peak within the first 3 months, followed by a stabilization up to 36 months (13) (Fig. 7). These results have been confirmed by Kohara et al.’s study (2015) (111 teeth monitored for a period of 36 months), which found that 68% roots had migrated, with a peak at 3 months and stabilization at 3.5 mm after 36 months [18]. This study found increased migration in women and younger subjects. The study done by Goto et al. (2012) focusing on conical roots also confirms this [21]. Hatano et al. (2009) and Kouwenberg et al. (2016) found similar migration rates of 84–85% [6,22].

In certain situations, the roots re-erupt in the oral cavity after migration. A reintervention will therefore be guided by symptomology: pain, infection, or the patient’s discomfort.

Leung et al. (2016) during the 60-month follow-up of 612 coronectomies, observed a re-eruption rate of 2.1% [30]. The coronectomies are conducted without nerve damage, thanks to the apparent distancing between the nerve structures and the roots as a result of migration. Cilasun et al. (2011) and Renton et al. (2005) indicated that no reintervention was needed after a follow-up of 17 and 25 months, respectively [14,16].

A mesiocrestal migration of residual roots (frequently observed) sometimes requires reintervention, but all safety protocols are observed with respect to IAN.

thumbnail Fig. 7

The roots migration, from Leung et al. (2009) [13].

Endodontic treatment is required

Sencimen et al. (2010) established two groups with each group having eight patients. In one group (experimental group), the coronectomy was supported by endodontic treatment with mineral trioxide aggregate of the roots. In the other group (the control group), the tooth with the coronectomy received no treatment [18]. A significant complication rate is found in the group receiving the endodontic treatment (seven avulsions needed for the eight residual root complexes).

Some studies have histologically analyzed the pulp tissue of the extracted teeth after their re-eruptions [18,31]. The dental pulp of these teeth was the key determinant in most cases (some cases of partial necrosis were discovered with the necrotic tissue located coronally to the vital apical pulp tissue).

Finally, the long-term prospective studies in which clinical and radiological follow-up was performed reported no signs of pulpal necrosis [17].

Endodontic treatment of residual roots is not necessary.

Periodontal healing

According to Vignudelli et al. (2016), from the 9th month after the coronectomy, the pocket depth distal to the second molar and the distance between the bone crest and the bottom of the bone defect reach normal physiological levels [32].

Kohara et al. (2015) confirmed this using 3D CBCT imaging, which revealed that in >90% cases, there were pockets <4 mm as well as new bone growth above the roots [18].

Leaving residual roots in place does not affect the periodontal prognosis of the adjacent tooth.


The use of the coronectomy as a technique for extracting mandibular wisdom teeth seems to significantly decrease the risk of nerve damage in cases of proximity between IAN and the dental roots without increasing the intraoperative or postoperative complications. It is a simple technique that does not require endodontic treatment of the residual roots. Long-term reinterventions and infections are infrequent.

Coronectomy is therefore a surgical technique of interest which should be more widely taught and practiced. The use of this technique could significantly decrease the postoperative neurological complications that are often the reason for medicolegal cases.

Conflicts of interests

The authors declare that they have no conflicts of interest in relation to this article.


 Yolaine David


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All Tables

Table I

Main characteristics of the selected studies.

All Figures

thumbnail Fig. 1

(a)The different x-ray images that should alert the surgeon. Loss of lamina dura of canal, (b) radiolucent of mesial apex, (c) deviation of the canal, (d) periapical radiolucent area,  (e) curvature of roots, (f) narrowing, (g) narrowing of the canal.

In the text
thumbnail Fig. 2

(a) Incision, (b) Full-thickness flap elevation, (c) alveolectomy to the cemento-enamel junction, (d) crown separation and enamel reducing to 2–4 mm below the level of alveolar crest.

In the text
thumbnail Fig. 3

Failed separation causing the necessity of a new intervention.

In the text
thumbnail Fig. 4

Drawing of crown separation and enamel reducing.

In the text
thumbnail Fig. 5

(a) Immediate post-operatory radiographic control, (b) at 12 months. It can be noted the coronary migration of the roots.

In the text
thumbnail Fig. 6

Flow chart of the bilbiographic review.

In the text
thumbnail Fig. 7

The roots migration, from Leung et al. (2009) [13].

In the text

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