During root canal treatment of a mandibular molar, calcium hydroxide is inadvertently extruded through the apical foramen into the mandibular canal. What is the MOST likely consequence?

Correct answer: B. Numbness and altered sensation of the lower lip

• A. ❌ Ankylosis follows trauma and replacement resorption, not an intracanal medicament.
• B. ✅ CORRECT — Calcium hydroxide has a pH near 12.5. When forced into the inferior alveolar canal it produces a chemical burn and liquefaction necrosis of the nerve, causing PARESTHESIA / ANESTHESIA of the lower lip and chin. Management is prompt surgical decompression and irrigation of the canal if a large volume was extruded, plus close neurosensory monitoring.
• C. ❌ Bleeding into the canal during instrumentation suggests contact with vital pulp tissue or a sodium hypochlorite accident, not calcium hydroxide extrusion.
• D. ❌ Lip MOVEMENT is motor (facial nerve, VII). The inferior alveolar nerve is purely SENSORY — so the deficit is numbness, not weakness.

Note: Distinguish sensory from motor: numb lip = IAN (V3, sensory). Droopy/immobile lip = facial nerve (VII, motor).