An overview of tooth-bleaching techniques: chemistry, safety and efficacy.

Tooth discolouration results from varied and complex causes that are usually classified as being either intrinsic or extrinsic in nature. Extrinsic discoloration arises when external chromogens are deposited on the tooth surface or within the pellicle layer. Intrinsic discoloration occurs when the chromogens are deposited within the bulk of the tooth (usually in the dentine) and are often of systemic or pulpal origin (1, 150). A third category of stain internalization has been described to include those circumstances where extrinsic stain enters the tooth through defects in the tooth structure (1). Tooth discoloration creates a wide range of cosmetic problems, and, as the dental profession and the public strive for a more esthetically pleasing appearance, considerable amounts of time and money are being invested in attempts to improve the appearance of discolored teeth. A study assessing the impact of teeth on personal esthetic satisfaction found that dental variables (including tooth color) were more important than orthodontic variables, suggesting that the appearance of the teeth was a greater contributing factor to an esthetic smile than their position within the arch (101). In another study, of 254 patients, it was found that the appearance of the dentition was more important to women than to men and that the esthetics of the dentition was more important to younger patients (147). The methods available to manage discolored teeth range from the removal of surface stain, bleaching or tooth-whitening techniques and surgical techniques to camouflage of the underlying discoloration, using veneers and crowns. The use of a variety of bleaching techniques has attracted most interest from the dental profession because these techniques are noninvasive and relatively simple to carry out. Contemporary bleaching systems are based primarily on hydrogen peroxide or one of its precursors, notably carbamide peroxide, and are often used in combination with an activating agent such as heat or light. Bleaching agents can be applied externally to the teeth (vital bleaching), or internally within the pulp chamber (nonvital bleaching) (41, 54). Both techniques aim to bleach the chromogens within the dentine, thereby changing the body color of the tooth.