Article: Coronectomy of Mandibular Third Molar Four Years of Follow Up of 130 Cases
Coronectomy and Inferior Alveolar Nerve Protection in Lower Third Molar Surgery
Injury to the inferior alveolar nerve (IAN) during the removal of mandibular third molars remains one of the most significant clinical concerns in oral and maxillofacial surgery. In recent years, this issue has also gained increased medicolegal attention due to the unpredictable nature of nerve recovery. While many patients experience spontaneous improvement following nerve injury, others suffer permanent sensory deficits, making prevention a priority whenever possible.
For impacted lower third molars in close proximity to the inferior alveolar canal, coronectomy, also known as partial odontectomy or deliberate root retention, has emerged as a reliable technique to reduce the risk of inferior alveolar nerve injury (IANI).
Rationale for Coronectomy
The goal of coronectomy is to remove the crown of the impacted third molar while intentionally leaving the roots undisturbed when they are intimately associated with the inferior alveolar nerve. By avoiding root manipulation, the risk of direct nerve trauma, compression, or traction injury is significantly reduced.
Because the consequences of inferior alveolar nerve damage can be permanent and unpredictable, adopting a nerve-sparing approach is often preferable in high-risk cases identified through clinical examination and radiographic imaging, particularly cone beam CT.
Surgical Technique of Coronectomy
The most effective technique for partial odontectomy involves sectioning the tooth at approximately a 45-degree angle in the bucco-lingual plane, allowing for controlled removal of the crown. After crown removal, the remaining root fragments are further reduced so they lie at least 3 mm below the crestal bone level.
This 3-mm reduction is supported by animal studies demonstrating that sufficient bone formation occurs over retained vital root fragments at this depth. Achieving this clearance reduces the risk of postoperative exposure and infection.
Primary closure of the surgical site is recommended to further minimize the risk of infection and dry socket. Importantly, there is no indication to treat or extirpate the pulp of the retained roots. In fact, root canal treatment of retained roots has been shown to be contraindicated. Animal studies have demonstrated that retained roots remain vital with only minimal degenerative changes.
Inferior Alveolar and Lingual Nerve Outcomes
Coronectomy has consistently demonstrated a favorable neurologic safety profile. In Pogrel’s landmark series, there was only one reported case of mild, transient lingual paresthesia, lasting approximately five days and attributed to lingual retraction rather than the coronectomy itself. No cases of permanent lingual nerve injury were reported.
Other studies have shown a slightly higher incidence of transient lingual paresthesia, particularly when lingual retractors are used, but no permanent lingual nerve injuries have been documented. These findings reinforce the importance of careful soft-tissue handling and judicious use of lingual retraction.
Complication Rates Associated With Coronectomy
Overall, coronectomy is associated with a low incidence of complications, particularly when compared with full extraction in high-risk cases. Reported complication rates include:
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Inferior alveolar nerve injury: 0–9.5%
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Lingual nerve injury: 0–2%
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Postoperative pain: 1.1–41.9%
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Swelling: ~4.6%
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Dry socket symptoms: 2–12%
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Infection: 1–9.5%
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Pulp disease: ~0.9%
These outcomes support coronectomy as a predictable and safe alternative when nerve injury risk is elevated.
Indications and Contraindications
Coronectomy is most appropriate in cases where radiographic evidence suggests intimate contact between the third molar roots and the inferior alveolar nerve. It is particularly useful when complete extraction would pose a significant neurologic risk.
However, the technique is contraindicated in the presence of:
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Active infection
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Tooth mobility
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Horizontally impacted third molars adjacent to the nerve
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Non-vital teeth or existing pathology involving the roots
Careful patient selection remains essential for successful outcomes.
Clinical and Medicolegal Considerations
Given the increasing awareness of inferior alveolar nerve injury and its potential legal implications, coronectomy provides surgeons with a defensible, evidence-based alternative to full extraction in high-risk cases. Proper documentation of risk assessment, imaging findings, and informed consent is essential when choosing this technique.
Conclusion
Coronectomy is a safe, effective, and nerve-sparing technique for the management of high-risk impacted mandibular third molars. When performed using proper technique and appropriate case selection, it significantly reduces the likelihood of inferior alveolar nerve injury while maintaining low complication rates. As such, coronectomy should be considered a valuable option in the contemporary management of lower third molars with close nerve proximity.
