Key points
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Coronectomy is considered a reasonable and safe treatment alternative for patients who demonstrate elevated risk for injury to the inferior alveolar nerve with the removal of third molars.
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The procedure has been documented in the oral and maxillofacial surgery literature as a treatment alternative to extraction of third molar in patients considered at elevated risk for permanent nerve injury.
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Coronectomy is particularly appropriate for patients who are older than 25 years and who report low tolerance for the possibility of posttreatment neurosensory deficit at the consultation.
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Appropriate patient selection for coronectomy is paramount.
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Periodic follow-up assessments are required, and patient compliance is essential.
Coronectomy was first described by Ecuyer and Debien in 1984 as an alternative procedure to traditional extraction of third molars. Several reports have been published since regarding the technique, indications, efficacy, and outcome of this procedure. Most recently, it has been investigated as an alternative to traditional surgical extraction of third molars, particularly for those with an increased risk of damage to the inferior alveolar nerve (IAN). Several studies have demonstrated that coronectomy does significantly decrease the risk of iatrogenic injury to the IAN, with some studies also suggesting a lower complication rate. This article discusses the indications for coronectomy, the author’s technique, and the complications and outcomes of this procedure.
Indications
The main indication for performing a coronectomy is to prevent iatrogenic injury to the IAN when removing a third molar. Therefore, the ability to determine whether the IAN is at high risk is paramount and should be well understood.
The frequency of IAN damage after extraction of a third molar ranges anywhere from 0.4% to 8.4%. Panoramic radiographs are traditionally used in the preoperative evaluation of patients who will undergo surgical extraction of mandibular teeth. Increasingly, computed tomography scanning is used to evaluate the relationship of the tooth to the IAN in 3 dimensions, but is not yet the standard of care, owing to cost and the increased exposure of the patient to radiation. Certain radiographic features that depict an increased risk of iatrogenic IAN damage when extracting third molars include darkening of the root, narrowing of the apices, deflection of the root, diversion of the IAN canal, narrowing of the IAN canal, and interruption of the white line of the IAN canal. Coronectomy may decrease the incidence of damage to the IAN in these cases of increased risk.
Pogrel and colleagues performed 50 coronectomies on 41 patients who were at significantly increased risk of IAN damage from panoramic radiographic assessment, and found no postoperative cases of inferior alveolar nerve involvement. Similar results were reported by Leung and Cheung, who performed 171 coronectomies and 178 surgical extractions (controls) of third molars on 231 patients. Nine patients in the control group presented with IAN sensory deficit versus 1 patient in the coronectomy group, demonstrating a statistically significant decrease in IAN damage using coronectomy for high-risk patients.
Indications
The main indication for performing a coronectomy is to prevent iatrogenic injury to the IAN when removing a third molar. Therefore, the ability to determine whether the IAN is at high risk is paramount and should be well understood.
The frequency of IAN damage after extraction of a third molar ranges anywhere from 0.4% to 8.4%. Panoramic radiographs are traditionally used in the preoperative evaluation of patients who will undergo surgical extraction of mandibular teeth. Increasingly, computed tomography scanning is used to evaluate the relationship of the tooth to the IAN in 3 dimensions, but is not yet the standard of care, owing to cost and the increased exposure of the patient to radiation. Certain radiographic features that depict an increased risk of iatrogenic IAN damage when extracting third molars include darkening of the root, narrowing of the apices, deflection of the root, diversion of the IAN canal, narrowing of the IAN canal, and interruption of the white line of the IAN canal. Coronectomy may decrease the incidence of damage to the IAN in these cases of increased risk.
Pogrel and colleagues performed 50 coronectomies on 41 patients who were at significantly increased risk of IAN damage from panoramic radiographic assessment, and found no postoperative cases of inferior alveolar nerve involvement. Similar results were reported by Leung and Cheung, who performed 171 coronectomies and 178 surgical extractions (controls) of third molars on 231 patients. Nine patients in the control group presented with IAN sensory deficit versus 1 patient in the coronectomy group, demonstrating a statistically significant decrease in IAN damage using coronectomy for high-risk patients.
Contraindications
The success of coronectomy depends on the survival of the retained root fragments with the successful formation of osteocementum and bone over the roots. Any tooth with active caries into the pulp, or demonstrating periapical abnormality should not be considered for coronectomy. Horizontally impacted teeth and teeth associated with tumors or large cysts should be excluded. The coronectomy procedure can otherwise be accomplished with vertically positioned, mesially tilted, and distally angulated teeth. Other local factors excluding coronectomy are patients scheduled for an osteotomy in the future. Patients excluded for systemic reasons from undergoing coronectomy include immunocompromised patients (chemotherapy, AIDS, radiation therapy, immunomodulating drug therapy, and so forth), poorly controlled diabetics, and those patients who are to undergo radiation therapy.
Technique
The technique used by the authors and described here is similar to that described in the literature, for example by Pogrel and colleagues.
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First the patients are evaluated radiographically for root proximity to the IAN. If the patient is at significant increased risk for damage to the IAN, the option of coronectomy is discussed as an alternative to third-molar extraction. Criteria for selection involves the degree of root development, the degree of associated abnormality, the age of the patient, and patient tolerance for the potential of sustaining permanent neurosensory disturbance ( Fig. 1 A–D ).
Fig. 1 Patients noted to be at elevated risk for injury to the inferior alveolar nerve. ( A ) A 41-year-old woman presenting with pericoronitis, teeth #17 and #32. ( B ) A 69-year-old woman presenting with pericoronitis and caries, tooth #17. ( C ) A 41-year-old man presenting with pericoronitis, tooth #17. ( D ) A 41-year-old woman presenting with pericoronitis and infection, tooth #32. - 2.
Once coronectomy has been decided upon for treatment, informed consent is obtained. Included in the consent process is a thorough discussion of the rationale for coronectomy. Risks including, but not limited to, infection, neurosensory disturbance, coronal migration of retained root fragments requiring surgical retrieval, and the potential need for additional surgical procedures are discussed. The possibility that extraction of the tooth may be necessary in the event of extensive decay, active infection, and mobility of retained roots is also included in the consent process.
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IAN blocks including long buccal infiltration are accomplished with 2% lidocaine with 1:100,000 epinephrine and 0.5% bupivacaine with 1:100,000 epinephrine. A full-thickness mucoperiosteal incision is elevated with posterior buccal release. If necessary, a conservative buccal trough is made using a #6 round carbide bur on a nitrogen-driven surgical hand piece, allowing access to the cementoenamel junction of the tooth. Care is exercised to maintain as much crestal bone height as possible by minimizing the width of the buccal trough. After exposure is obtained, a 701 fissure bur is used and a horizontal/transverse cut is made through the tooth at the level of the cementoenamel junction. Visualization is important to ensure adequate sectioning of the crown without perforation through the lingual bone plate. The crown is delicately fractured and separated from the residual roots of the tooth using a straight elevator. Effort is directed at minimizing any mobilization of the residual roots. On removal of the crown, any sharp fragments of retained tooth structure are smoothed down with a 2.3-mm diameter diamond round bur with simultaneous copious saline irrigation. The remaining enamel is typically reduced approximately 3 mm below the buccal crest of alveolar bone ( Fig. 2 A–J ).
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Root canal treatment is not indicated during coronectomy. Sencimen and colleagues found that patients having coronectomy with root canal treatment had a much higher infection rate than those patients who underwent coronectomy without root canal treatment. Seven of the 8 patients undergoing root canal treatment developed postoperative infections, whereas only 1 of 8 patients in the control group developed an infection. The investigators suggested that mobilization of the root during root canal therapy and/or prolonged procedure time may contribute to the higher infection rate in the study group.
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