Coronectomy
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Direct answer
When a lower third molar's roots grooved or wrapped around the inferior alveolar canal on CBCT, deliberately removing only the crown and leaving the roots — coronectomy, or intentional partial odontectomy — trades a small chance of later root surgery for a large drop in nerve injury. The crown is sectioned at the cementoenamel junction region so that 2-3 millimetres of root complex sit below the alveolar crest with a vital pulp, and the mucosa is closed primarily over it. Large published series report inferior alveolar nerve deficits near zero to one per cent after coronectomy, against the double-digit risk predicted for full removal in these high-risk anatomies. Case selection is everything: infected or carious roots, and roots that become mobile during surgery, must come out whole.
What you must remember
- Definition and goal: remove the crown, leave a vital root complex 2-3 millimetres below bone, covered by watertight primary closure; the nerve is protected because the roots never move.
- Ideal candidate: a young patient, deep impaction, CBCT showing canal grooving by the roots, interruption of the canal cortex, canal deviation, or J-shaped roots hugging the canal.
- Contraindications: caries extending into the root complex, apical or pericoronal infection, cystic change, immunosuppression, previous radiotherapy to the jaw, and teeth with short roots already at the crest.
- The intraoperative rule: if the roots mobilise during sectioning, abandon the coronectomy and remove them completely — retained mobile roots harbour bacteria and invite infection.
- Technique points: buccal envelope flap only, generous trough around the crown, section angled from the buccal side with copious irrigation, minimal manipulation of roots, bone smoothed and closed without tension.
- Root migration is expected: most retained roots drift coronally over months; the majority stay buried and asymptomatic, and a small percentage — commonly quoted in single digits — need a second, usually simpler removal.
- Follow-up: baseline radiograph, clinical review, and patient education that migration is normal, not failure.
- Alternate name for vivas: intentional partial odontectomy; do not confuse it with accidentally retained root fragments, which carry infection risk precisely because they are dead and uncovered.
The decision point, worked through
A 28-year-old has recurrent pericoronitis around a deeply placed mesioangular 38. The orthopantomogram shows the canal intersecting the roots; CBCT confirms the buccolingual canal lying grooved within the root complex on two consecutive slices. The consultation is honest arithmetic: full removal in this anatomy carries a nerve deficit risk in the region of ten to twenty per cent by classic high-risk estimates, while coronectomy in published series brings it to under about one per cent — against perhaps a one-in-twenty chance of needing the roots retrieved later. She chooses coronectomy.
In theatre, the sequence discipline matters more than the score. The flap is buccal, the lingual tissue untouched. A bur trough frees the crown circumferentially down to the cementoenamel junction; the section runs from buccal to lingual at roughly 45 degrees so the crown lifts out mesially without levering the roots. The roots are checked — immobile, pulp pink in the sectioned face — bone is smoothed so no spicule tent the flap, and the mucosa closes over saline-irrigated debris-free beds. At six months the roots have migrated two millimetres towards the crest and the mucosa is intact: success is silence.
High-yield viva angles
Indian examiners ask three things. First, consent: both coronectomy and complete removal must be offered and documented, because the operation planned can change on the table. Second, the failure routes: root migration (usually harmless), secondary infection around retained roots, and the rare need for reoperation — each with its management. Third, the philosophical objection some seniors still raise, that leaving roots violates surgical principle; the counter is evidence-based and worth quoting — nerve injury after full removal of high-risk teeth can be permanent, whereas second-stage root retrieval, when needed, is usually straightforward because the roots have migrated away from the canal. Where CBCT is unavailable in peripheral Indian practice, the correct answer is referral rather than blind coronectomy on a two-dimensional film.
Frequently asked questions
How much root is deliberately left below the crest?
Two to three millimetres, so that bone can close over the vital root complex and the mucosa heals primarily without a dead space.
When is coronectomy absolutely contraindicated?
Root caries, apical or pericoronal infection, cystic change, immunosuppression and previous jaw radiotherapy — retained infected roots guarantee failure.
What happens to the retained roots over time?
Most migrate coronally and stay asymptomatic; a small single-digit percentage require later removal, which is typically simpler than the original surgery would have been.
What should be done if the roots become mobile during sectioning?
Proceed to complete removal, since mobile retained roots are devitalised, bacteria-laden and destined to infect.
By roughly how much does coronectomy reduce nerve injury risk?
Published series report deficits near zero to one per cent, compared with the high double-digit-percentage risk predicted for full removal when the canal is grooved by the roots.