Especially in the anterior segments, discolored endodontically treated teeth can present a cosmetic problem. As an alternative to the fabrication of full crowns or the use of composite resin or ceramic veneers, the dentist can use tooth bleaching as an esthetic treatment. The techniques for external bleaching of vital teeth have been described in various literature reviews (Attin, 1998; Wiegand, 2006).
For internal bleaching of nonvital endodontically treated teeth, the “walking bleach” technique has been recommended, in which a bleaching agent is put into the pulp chamber for a certain period. This procedure, which includes an intentional devitalization of vital, severely stained teeth to render possible intracoronal bleaching treatment, should only be undertaken after proper consideration of the possible risks, and the patient must be fully informed.
A possible cause for discoloration of nonvital teeth is vital pulp extirpation, or traumatically induced internal bleeding of the pulp, which can lead to diffusion of blood products into the dentinal tubules. Breakdown of blood via chemolysis leads to release of iron. This iron, in combination with hydrogen sulfide released by bacteria, lead to the formation of iron sulfide, which causes a gray discoloration of the tooth.
In addition to blood metabolic breakdown products, the breakdown products of proteins from a necrotic pulp can also cause tooth discoloration. This may also be the case when, following inadequate access cavity preparation, pulp tissue remnants remain within the pulp chamber, usually in the region of the pulp horns.
Discoloration of the crown of an endodontically treated tooth can also be caused by the root canal filling material itself. Also some medicaments (e.g., Ledermix) can cause tooth discoloration. Such tooth discoloration, depending on the responsible substance, can in some cases be effectively treated by bleaching (van der Burgt, 1986). It is worthy of note, however, that this does not hold true for discolorations caused by metal ions (silver pins, amalgam) (Glockner and Ebeleseder, 1993).
In the clinical investigations published to date, initial good results, that is, immediately following bleaching, have been reported. The optimum result is color consistency of the bleached tooth with its neighboring tooth. However, over the course of time, the tooth sometimes becomes darker again (Friedman, 1997). The current theory about the etiology of this subsequent darkening is a poorly sealed restoration that permits diffusion of pigments and penetration by bacteria.
It is interesting that the “success” of bleaching is usually more positively appraised by the patient than by the dentist or by the investigator in a clinical trial. In the published long-term studies spanning a timeframe of 8–16 years, success rates of 45%–93% are reported, but also included in these studies are cases where the color comparisons with adjacent teeth are not perfect but clinically acceptable (Attin et al., 2003; Amato, 2006).
Today, preparations containing hydrogen peroxide are the most commonly used bleaching agent. Depending on the pH value, light effects, temperature, presence of Ko-catalysts or metallic reactions, free hydrogen peroxide can release various radicals (H., O., OH., HO.2), hydroxyl (OH–) or perhydroxyl ions (OOH–), which are responsible for the oxidative or reduction and therefore bleaching characteristics of hydrogen peroxide.