Case report

Coronectomy is a widely-accepted technique in managing symptomatic impacted wisdom teeth.1 The fundamental principle is to prevent trauma to the inferior dental nerve (IDN).2 Many publications have demonstrated its positive outcomes. The authors would like to share and highlight the use and importance of this technique in oral and maxillofacial surgery. The technique of coronectomy should be considered in cases other than wisdom teeth.

A 10-year-old female was referred to the orthodontic department at Pinderfields Hospital regarding delayed eruption of permanent teeth and severe crowding. She presented in the mixed dentition with a Class I skeletal pattern and Class I incisal relationship. There was an anterior cross-bite along with severe crowding in both upper and lower arches and it was seen that there was insufficient space for all the permanent teeth to erupt.

Clinical and radiographic investigation was undertaken. An orthopantomogram (OPG) confirmed presence of all successors. It also revealed a severely infraoccluded lower right second deciduous molar (85) significantly below the occlusal plane, preventing eruption of the adjacent permanent premolars and canine (Fig. 1).

Figure 1
figure 1

Pre-operative OPG

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Interceptive orthodontics was part of the management plan in this case, using an upper removable appliance to correct the anterior cross bite. However, the 85 required a multidisciplinary approach involving orthodontist and oral and maxillofacial surgeons.

Problem list

  • Severe crowding of the upper and lower arches

  • Anterior-posterior skeletal discrepancy

  • Upper anterior cross-bite

  • Transverse skeletal discrepancy

  • Variation in mandibular body heights

  • Infraoccluded and impacted 85.

Aetiology

This case presents with malocclusion due to skeletal growth disturbances. No evidence is seen in which soft tissue or habits play a role.

A cone beam computed tomography (CBCT) scan was taken to further assist in surgical planning for managing the infraoccluded 85 (Figs 2 and 3).3

Figure 2
figure 2

CBCT-sagittal view

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Figure 3
figure 3

CBCT-coronal view

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The CBCT demonstrates the 85 roots are contacting the inferior cortex of the mandible. Additionally, it shows no clear cortical outline between the IDN and the roots, while displaying intimate contact with the middle third of both roots.

Initial considerations before the CBCT result were to surgically remove the 85. Following a multidisciplinary discussion with a consultant orthodontist and a maxillofacial surgeon, it was advised there is high risk of injuring the IDN and possible mandibular fracture. Thus a coronectomy of the 85 was considered (Fig. 4).

Figure 4
figure 4

Advantages and disadvantages of coronectomy versus complete removal of the '85'

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Orthodontic movement of the teeth in the years ahead may be compromised to a degree. However, careful analysis using the CBCT scan demonstrated the roots of the 85 are lying very low and in contact with the inferior cortex of the mandible. This was deemed orthodontically acceptable because as the patient's mandible continues to grow and the height of the body increases there would be no or relatively little impaction on the permanent teeth. Furthermore, in the future if orthodontic forces were to be applied to the permanent teeth, leading to contact against the roots of the deciduous tooth, it would be sufficient to further activate the resorption process.4,5,6Therefore, the permanent teeth would not be obstructed from erupting and movement during orthodontic treatment would not be hindered.7

IDN damage is an important factor in deciding how to proceed. Injury to the nerve may lead to temporary or permanent altered sensation to the lower lip, chin and tongue. In real terms, this may have a profound effect on daily functions such as speaking, eating, kissing and even playing a wind instrument. Weighing up the risks and benefits along with the patient's choice, we planned for a coronectomy of the 85 under general anaesthetic. We believe that minimally invasive surgery would give an increased margin of safety to avoid injury to the IDN and adjacent structures. Combining this thought process along with the patient's age and the fact that the roots were lying very low in the mandible, we felt the planned procedure was justified.

Like all coronectomy techniques the patient was warned of risks of requiring a complete removal or a second procedure in the future. Piezosurgery was used due to its ability to deliver precise cuts in confined areas. The coronectomy of the 85 was conducted as planned with no complications. Figure 5 shows an OPG taken three months post-operation.

Figure 5
figure 5

Orthopantomogram taken three months post-operation (please forgive the image which displays the upper retainer and earrings in situ)

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The patient was monitored at three monthly intervals and to date a one-year post-operative review demonstrates that the patient is asymptomatic with no reported episodes of infection. The lower right first and second premolars have now partially erupted. This case demonstrates that this surgical problem can be managed to reduce the chance of injury to the IDN and without damage to the adjacent teeth, or the integrity of the lower border of the mandible.8

It is important that all clinicians, GDPs, oral surgeons, orthodontists and maxillofacial surgeons are aware of alternative approaches in managing infraoccluded deciduous teeth. The coronectomy technique is a surgical option and should be given due consideration. A multidisciplinary approach and the use of CBCT aided in providing a solution to this problem.