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Revista Española de Cirugía Oral y Maxilofacial

versión On-line ISSN 2173-9161versión impresa ISSN 1130-0558

Rev Esp Cirug Oral y Maxilofac vol.31 no.4 Madrid jul./ago. 2009




Rational application of coronectomy when treating lower impacted third molar

Empleo racional de la coronectomía en la extracción de terceros molares incluidos



C. Recio Lora1, D. Torres Lagares2; M. de Maeztu Martínez3; M.M. Romero Ruiz4; J.L.Gutiérrez5

1 Profesora del Master en Cirugía Bucal. Facultad de Odontología. Universidad de Sevilla.
2 Profesor Ayudante de Cirugía Bucal. Universidad de Sevilla.
3 Doctor en Odontología. Práctica privada en Cirugía Bucal.
4 Profesor del Master de Cirugía Bucal. Universidad de Sevilla.
5 Profesor Titular Vinculado de Cirugía Bucal. Director del Master de Cirugía Bucal.
Universidad de Sevilla. Jefe de Servicio de Cirugía Oral y Maxilofacial. Hospital Universitario Virgen del Rocío de Sevilla.





Third molars are the teeth that most frequently fail to erupt and remain impacted or retained inside the bone. A large percentage of our patients have impacted wisdom teeth and many of these patients also have pathologies that require surgical treatment. Applied coronectomy technique of the impacted third molar was first described by Ecuyer and Debien in 1984. The described it as partial elimination of the tooth in question, deliberately leaving part of the root inside the bone. This was proposed to avoid injuring the inferior dental nerve in cases where there was a close relationship between the two anatomical structures. Although the objective of the procedure is very clear, it is still controversial. Therefore, the surgeon should evaluate the possibility of an infectious complication of pulpar origin. We present the successful clinical case that uses this technique, as well as an analysis of the distinct authors' opinions this technique and its advantages and disadvantages.

Key words: Impacted Third Molar; Tooth Extraction; Nervous lesion; Coronectomy.


Los terceros molares son los dientes que, con más frecuencia, sufren el fracaso de su erupción y quedan incluidos o retenidos dentro de los maxilares. Un gran porcentaje de nuestros pacientes presentan los cordales incluidos y, de ellos, una parte importante se acompaña de patología que hace aconsejable su tratamiento quirúrgico. La técnica de la coronectomía aplicada al tercer molar incluido fue descrita por primera vez por Ecuyer y Debien en 1984 como la eliminación parcial de dicho diente, dejando deliberadamente parte de su raíz en el interior de la mandíbula. Fue propuesta para evitar la lesión del nervio dentario inferior (NDI) en aquéllos casos en los que existía una íntima relación entre ambas estructuras anatómicas. Aunque el objetivo de la técnica es muy claro, no está libre de controversia, ya que el cirujano debe valorar la posibilidad de una complicación infecciosa de origen pulpar. Presentamos un caso clínico exitoso de esta técnica, junto al análisis de la postura ante la técnica de los distintos autores, así como sus ventajas e inconvenientes.

Palabras clave: Tercer molar incluido; Extracción dentaria; Lesión nerviosa; Coronectomía.



Third molars are the teeth that most frequently fail to erupt and remain impacted or retained inside the bone.1 Although unerrupted third molars can be asymptomatic all ones life, due to their anatomic location and singular embryological conditions, they frequently cause other pathologies.1 Because of the symptoms that they produce or the potential risk of infectious, tumoral, mechanical or nerval complications, the correct procedure is third molar surgical extraction.1 Even though there is consensus in the literature that, since we can not predict which teeth will successfully erupt and which will not, if there is enough space the non erupted and asymptomatic wisdom tooth should be left where it is. We can not forget that this extraction is one that involves risks.1

Among the complications involved in the extraction of an impacted third molar, the most severe is injury of the inferior dental nerve. It occurs in 3-5% of cases and remains permanent in 0.5-1% of cases. Therefore, during ostectomy, odontosection, dislocation or curettement procedures there is a high risk of injuring the inferior dental nerve.1

Applied coronectomy technique of an included third molar was first described b Ecuyer and Debien in 1984 as the partial elimination of the tooth deliberately leaving part of the root inside the bone. This was proposed to avoid injuring the inferior dental nerve in the cases where there was a close relationship between the two anatomical structures.3 Although the objective of the procedure is very clear it still controversial. Therefore, the surgeon should evaluate the possibility of an infectious complication of pulpar origin.4,5

We present a case where coronectomy was successfully used on an impacted third molar. Afterward, we will analyze the opinions of various authors regarding technique in order to clarify when coronectomy can be considered the technique of choice to treat symptomatic compacted wisdom teeth, after a correct radiological study and analysis of its advantages and disadvantages.


Clinical Case

We present the clinical case of a 25 year old patient who consults the doctor because of repeated episodes of pain and inflammation near the inferior left semi impacted third molar. (Fig. 1A) The patient's medical history shows no prior medical conditions of interest and the patient is not taking regular medication aside from the antibiotics and anti inflammatory medication for his current problem, the patient is a non-smoker and in good health.

After the clinical examination our first test is a orthopantomogram (Fig. 2A). It allows us to see that the wisdom tooth in question is found in close relation to the canal of the inferior dental nerve, finding radiological signs that are clear indicators that there will be high risk of nerve injury during extraction operations. So, we see curves in roots, darkness near the apex (mesial root) and thinning of the upper cortical of the canal that touches the distal root.

Although the orthopantomogram gives us a pretty clear image we decided to take a CT in order to correctly plan the case before deciding on a therapeutic treatment. The CT images verify that there is contact between the wisdom tooth and the Inferior Dental Nerve and that due to that contact there is a high risk of damaging it during extraction.

In this situation we inform the patient of the option to carry out a coronectomy or a partial extraction of the symptomatic third molar. With this technique we try to eliminate the clinical cause which is pericoronaritis. Since we successfully closed the wound and the roots remain compacted the unity of the Inferior Dental Nerve is preserved.

The patient was informed of the possible complications including: infection caused by pulpar which would require reintervention to complete the extraction. Reintervention would also be necessary if, in the long term, the roots were to migrate and, because of their exposure, continue to create pericoronaritis. If this were to occur the relationship between the roots and the Inferior dental nerve would not be as clear and as a result the extraction would not be as clear leading to a very compromised situation.

After getting the informed consent of the patient we decide to perform coronectomy using the following surgical technique (Figs. 1 A, B and C): Administration of prophylaxis antibiotic. Making a "saddle" incision and lifting the full thickness of the flap, similar to the one used for complete wisdom tooth extraction. A cut is made in the crown with a fissure drill starting at the vestibular board and continuing at a 45 degree angle. This section is ready to have force applied on the roots with elevators: to do this it is important to be very careful not to injure the lingual nerve when we approach the lingual board. Afterwards we continue to eliminate dental tissue with the same fissure drill or with a round drill gaining access from the upper part. This can be a little easier to do with the round drill than with the fissure drill. When this is done the area is at least 3 mm below the bone crests. With this we try to make the bone regenerate over the roots and including them inside the mandible. The exposed radicular surface should not be treated. Finally we eliminate the follicle remnants without mobilizing the roots, the remaining tooth and the wound sutured with stitches that will fall out after a week or two. We should perform radiological controls after 1 month and again after six months (Fig. 3) and a year later.

All of these steps were carried out in our case and the patients did not show any signs of complications 1 year after the intervention.



Incidence of inferior dental nerve damage during compacted third molar surgery is about 3-5%, with permanent nerve damage in 0.5-1% of cases.2,6 Although the percentages are not very high this injury and the limitations it involves for the patient are very important, therefore we should try to avoid it in every case.1

Panoramic radiography is the standard radio graphical test to analyze the anatomical relationship between compacted third molars and the inferior dental nerve. Many authors agree that there are a series of high risk radiological signs associated with a close relationship between the two anatomic structures.12,14:

1. Darkening of roots or lingual image in the area where they cross the dental canal.

2. Disruption or obliteration of the dental canal corticals.

3. Dental canal deviation in the root contact area.

4. Root angulations around the canal.

5. Root thinning that could cause a perforation or opening in the nerve.

6. Root bifurcation.

7. Thinning of the dental canal.

8. A distance of less than 1mm between the roots and the upper dental canal cortical.

9. Close contact between the dental canal and the roots.

10. Overlapping of the two structures.7,8

If we look at the panoramic radiograph of the clinical case presented we see that many of the radiological signs that we presented coincide with these signs. We could see a radio lucid image of the left inferior third molar apex, with curves in the roots in the area of the dental canal and stumping of same corticals. We also see that it looks like is direct contact between the wisdom tooth roots and the dental cavity just like an overlapping of the images. This is confirmed by the CT image (which we should refer when there are doubts about the risk involved or when making a therapeutic decision).9,10

In the majority cases with third molar symptoms, these are semi impacted causing a quadrant of pericoronaritis. Because of the communication that is established with the buccal half; therefore elimination of the crown and its follicle tissue annex could solve the problem.4 It is clear that the complete extraction of the wisdom tooth does not involve a high risk of damaging the inferior dental nerve; this is the chosen therapeutic opinion.1 But if the radiological evaluation shows high risk of paraesthesia after extraction we would consider possibly doing a coronectomy.

Although a coronectomy seems to be a good solution in these compromised cases, its use is still controversial. The surgeon should bring up the possibility that an infection starts because of retained roots or because of the pulp section4. In response to this topic there are long term studies that show that the risk of posterior infection is low.4,11-14

In 1997 Freedman,11 presents a case where he follows a previously published coronectomy case for 5 years and he completes a study with 32 more cases. It was only necessary to re enter because of inflammation in one case and the rest of the patients had satisfactory progress.

In 2004 Pogrel and cols.13 did a study of 41 patients with radiological data that suggested possible injury of the inferior dental nerve during impacted third molar extraction. They carried out 50 coronectomies and at least 6 months of follow-up. There were no inferior dental nerve injuries in any of the patients. There was one lingual nerve injury, probably because of the use of a retractor chosen by the authors. One patient had to be re operated on in both wisdom teeth because of failed scarring and the persistence of symptoms.

Another patient had to be re operated on because of root migration. After six months this phenomena was seen in 30% of the patients.

In 2005, Renton and cols.14 presented a study of 128 patients with radiological evidence related to impacted wisdom teeth and inferior dental nerve. 102 wisdom teeth in the sample were completely removed and 94 had coronectomies. 58 of which were carried out successfully and 36 ended up having the tooth removed completely because of mobilization of the roots during surgery. After 25 months of follow-up the following data was reported: in the patients who had complete extraction 19 had an Inferior dental nerve injury, none in the successful coronectomies and 3 in the cases of failed coronectomies. There was apex migration of the roots that had been left impacted in the mandible bone, and the risk of infection and alveolitis did not increase in coronectomy cases.

The results of these studies show that coronectomy is a technique that has a low incidence of complications, although apex migration of the roots could be considered as such in cases where reintervention is necessary.

In our clinical case after 12 months of follow-up we have not seen infectious complications nor compromised quality of patient life. Although, there is slight mobilization towards the crest roots.

To get results similar to the ones described we should emphasize correct selection of the case. According to Pogrel and cols.13, a coronectomy should not be performed in the following situations:

1. Infected teeth, especially if the roots are affected.

2. Teeth that have moved during extraction operations, since the roots could act as a foreign body and favor infection or migration.

3. Teeth that are horizontally impacted along the inferior dental canal because the selection of the crown could damage it (it is advised to use coronectomy in the case of vertical, mesial or distal angled wisdom teeth where the section could be carried out without complicating the results of the technique).

Regarding surgical technique although many authors defend the elimination of the tooth reaching as close as 2 mm from the inferior dental nerve, we think it is more tactful to eliminate only the necessary part of the tooth to allow for direct closing of the gum (2 mm below the bone crest)4,9

Protecting the lingual flap is another topic of controversy. Pogrel and cols.13, suggest carrying out a simple lingual flap retraction, despite the fact that in their work they have lingual paraesthesis that they attributed to flap retraction.

Other studies have demonstrated that this procedure compromises the integrity of the nerve.15 Our way of carrying out extractions of compacted third molars does not include retraction of the lingual flap, so in coronectomy clinical case that we present we did not use that technique.



In conclusion, coronectomy is a technique that should only be used when the surgeon decides that complete third molar extraction would put the inferior dental nerve at great risk. The patient should always be informed and give their consent. It is not an easy procedure and it requires more skill and perfection than a complete extraction. Even though, in well selected cases, adequate long term results make it an applicable technique with sufficient guaranties.



Daniel Torres Lagares
Facultad de Odontología. Universidad de Sevilla
C/ Avicena s/n. 41009 Sevilla. España

Recibido: 28.08.2007
Aceptado: 16.03.2009




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