A non-vital tooth that was endodontically treated has internal discoloration causing a grayish appearance. The patient wants conservative bleaching. Which agent is used for internal bleaching of this tooth?

Correct answer: C. Sodium perborate (mixed with water or saline)

• A. Sodium hypochlorite is the irrigant used during root canal treatment to dissolve organic tissue — not an internal bleaching agent.
• B. Hydrogen peroxide 3% (commercial concentration) lacks the sustained release effect of sodium perborate for intracoronal bleaching. Higher concentrations (30%) have been used but increase the risk of external cervical resorption.
• C. CORRECT. Sodium perborate is the agent of choice for intracoronal (walking) bleaching of non-vital endodontically treated teeth. It is safer than concentrated hydrogen peroxide (which can cause external cervical resorption). Sodium perborate is mixed with water or distilled water, placed in the pulp chamber, and sealed for several days.
• D. Carbamide peroxide 10% is used for EXTERNAL bleaching (nightguard vital bleaching or over-the-counter whitening) — it is not placed inside the pulp chamber for internal bleaching.