After biomechanical preparation, you irrigate and the patient suddenly responds with severe pain, facial edema, and bleeding from the canal. What happened?

Correct answer: B. NaOCl (sodium hypochlorite) accident

• A. Instrument separation causes cessation of progress in the canal — not acute facial edema and bleeding.
• B. A SODIUM HYPOCHLORITE ACCIDENT occurs when NaOCl (bleach irrigant) is extruded BEYOND the root apex into the periapical tissues, sinuses, or subcutaneous tissues. It causes: severe, immediate, burning pain, rapidly developing facial EDEMA (often dramatic cellulitis-like swelling within minutes), ecchymosis (bruising), and bleeding from the canal. It is one of the most dramatic endodontic emergencies. Management: stop irrigation immediately, position patient upright, ice packs, analgesics, monitor — most resolve without antibiotics.
• C. A vital pulp would cause pain during instrumentation but NOT the explosive facial edema and burning pain of NaOCl extrusion.
• D. Root perforation causes bleeding and possible pain but does NOT cause the rapid facial edema and burning pain characteristic of NaOCl accident.