During root canal treatment of tooth #17, after cleaning and shaping, the dentist irrigates and a patient experiences SUDDEN PAIN and bleeding emerges from the MB canal. What happened?

Correct answer: C. Hypochlorite accident (NaOCl extrusion beyond apex)

• A. Incorrect. Ledge formation causes an instrument to bind in the canal — it does not produce sudden pain and bleeding upon irrigation.
• B. Incorrect. Perforation might cause bleeding but typically occurs during access or instrumentation, not specifically during irrigation.
• C. Correct. HYPOCHLORITE ACCIDENT occurs when sodium hypochlorite (NaOCl) is extruded beyond the root apex into the periapical tissues. Classic presentation: SUDDEN, SEVERE PAIN during irrigation, followed by profuse bleeding from the canal (due to tissue necrosis and capillary disruption), and possible rapid facial swelling. This is a recognized endodontic emergency.
• D. Incorrect. Instrument separation would not cause immediate bleeding and severe pain upon irrigation.