Internal tooth bleaching is an option for patients who want to whiten their teeth after undergoing endodontic treatment. Teeth can become discolored and stained from the inside from blood and other fluids. Internal bleaching works from the inside out – a peroxide gel is placed in the cleaned, empty pulp chamber and the gel works directly inside the tooth on the dentin layer. Internal bleaching is performed after the root canal has already been cleaned, sealed and filled.