Which material is most commonly used for internal (non-vital) tooth bleaching?

Sodium perborate is the preferred material for internal (intracoronal) bleaching of non-vital discolored teeth using the 'walking bleach' technique. It is placed inside the pulp chamber (after removing gutta-percha to 2-3 mm below the CEJ) and sealed with a temporary restoration. Sodium perborate releases hydrogen peroxide slowly, bleaching the tooth from within. It is preferred over concentrated hydrogen peroxide alone because it is safer and poses less risk of external cervical resorption. Sodium perborate mixed with water or 30% hydrogen peroxide can be used. Carbamide peroxide is used for external vital bleaching. Sodium fluoride is not a bleaching agent.