During root canal treatment of a mandibular molar, calcium hydroxide is extruded beyond the apex. What complication is most likely?

Correct answer: B. Paraesthesia or anaesthesia of the lower lip and chin

• A. Taste on the anterior two-thirds travels with the chorda tympani via the lingual nerve. The lingual nerve runs along the medial aspect of the mandible in soft tissue, not within the mandibular canal, so it is not injured by apical extrusion.
• B. CORRECT. Extrusion of calcium hydroxide through the apex of a mandibular molar carries the paste into the inferior alveolar canal. Calcium hydroxide has a pH near 12.5 and is directly neurotoxic — it causes chemical injury and a compressive, inflammatory reaction within the confined bony canal. The inferior alveolar nerve supplies the lower lip and chin via its mental branch, so the patient presents with lip and chin paraesthesia or frank anaesthesia. Management is prompt surgical decompression and removal of the material if a large volume has been extruded, since delayed removal predicts permanent deficit.
• C. Whole-tongue numbness would require bilateral lingual nerve injury and is not a consequence of periapical extrusion in a single tooth.
• D. The posterior third of the tongue is supplied by the glossopharyngeal nerve, which lies nowhere near the mandibular root apices and is not involved.

Note: Two overfill accidents to keep straight. Sodium hypochlorite extrusion causes IMMEDIATE severe pain, rapid ballooning swelling and bleeding into the canal. Calcium hydroxide extrusion causes a more delayed picture dominated by paraesthesia. Both are managed by stopping, decompressing, and — for large extrusions near the canal — early surgical removal.