3. How is hydrogen peroxide used to whiten teeth?
The SCCP opinion states:
US Food and Drug Administration (FDA) approved both hydrogen peroxide and carbamide peroxide as oral antiseptic agents in 1983 (FDA, 1983). The products of 10-15% carbamide peroxide and 1.5-3% hydrogen peroxide preparations are classified in Category I, which includes agents that are generally recognised as safe (GRAS) and effective. A Subcommittee of FDA (2003) concluded that hydrogen peroxide is safe at concentrations of up to 3 percent, but there are insufficient data available to permit final classification of its effectiveness at 1.5 to 3 percent concentrations for long-term over the counter (OTC) use as an antigingivitis/antiplaque agent.
The colour of the teeth is influenced by a combination of their intrinsic colour and the presence of any extrinsic stains that may form on the tooth surface. Intrinsic tooth colour is associated with the light scattering and adsorption properties of the enamel and dentine, with the properties of dentine playing a major role in determining the overall tooth colour. Extrinsic stains tend to form in areas of the teeth that are less accessible to tooth brushing and the abrasive action of a toothpaste and is often promoted by smoking, dietary intake of tannin-rich foods (e.g. red wine) and the use of certain cationic agents such as chlorhexidine, or metal salts such as tin and iron. In the USA, 34% of an adult population reported that they were dissatisfied with their current tooth colour (Odioso et at., 2000) and in a survey of 3215 subjects from the UK 50% perceived they had some kind of tooth discoloration (Alkhatib et al., 2004).
Tooth colour can be improved by a number of methods and approaches including whitening toothpastes, professional cleaning by scaling and polishing to remove stain and tartar, internal bleaching of non-vital teeth, external bleaching of vital teeth, microabrasion of enamel with abrasives and acid, placement of crowns and veneers. Three bleaching approaches exist for external bleaching of vital teeth: 1) dentist supervised night guard bleaching, 2) in-office or power bleaching and 3) mass market bleaching products. Night guard bleaching typically uses a relatively low level of whitening agent applied to the teeth via a custom fabricated mouth guard and is worn at night for at least 2 weeks. In-office bleaching generally uses relatively high levels of whitening agents, for example 25–35% hydrogen peroxide containing products, for shorter time periods. The whitening gel is applied to the teeth after protection of the soft tissues and the peroxide may be further activated by heat or light. The in office treatment can result in significant whitening after only one treatment visit but may require multiple treatment appointments for optimum whitening. Mass market products typically contain low levels of whitening agent (e.g. 3–6% hydrogen peroxide) that are self-applied to the teeth via gum shields, strips or paint-on product formats and typically require twice per day application for up to 2 weeks (Joiner, 2006). External bleaching of vital teeth is generally carried out with hydrogen peroxide or carbamide peroxide.
A tooth bleaching system based on sodium chlorite applied to the tooth surface and activated under acidic conditions has been described in the literature. Other potential vital tooth bleaching systems outlined in the literature includes peroxide plus metal catalysts, oxireductase enzymes, sodium percarbonate, sodium perborate and potassium peroxymonosulphate (Joiner, 2006). The use of the three latter chemicals will be briefly discussed in Appendix to the present Opinion. Sodium percarbonate and sodium perborate have been found in commercially available tooth bleaching products. Sodium perborate has been proposed classified as a substance toxic to reproduction in category 2 (Search Working Database
. If this classification is adopted it will not be possible to use sodium perborate in tooth whitening products.
The first articles on bleaching teeth using night guard whitening bleaching were published in 1989 (Christensen, 1989a, b; Haywood and Heymann, 1989). The mechanism by which teeth are whitened by oxidizing materials such as hydrogen peroxide and carbamide peroxide are not fully understood. Evidence points towards the initial diffusion of peroxide into and through the enamel to reach the enamel dentine junction and dentine regions. In vitro experiments have demonstrated the penetration of low levels of peroxide into the pulp chambers of extracted teeth after exposure times of 15–30 min. The levels of peroxide measured in these experiments is considerably much lower than that needed to produce pulpal enzyme inactivation (Joiner and Thakker, 2004).
It is assumed that the whitening effects are primarily due to degradation of high molecular weight, complex organic molecules that reflect a specific wavelength of light and is responsible for the colour of the stain. The resulting degradation products are of lower molecular weights and are less complex molecules that reflect less light and result in a reduction or elimination of the discoloration (Flaitz and Hicks, 1996). Both the dentin and the enamel change colour as a result of the easy passage of the peroxide and urea through the tooth. Extended treatment times have been developed for difficult situations. Heavy tobacco stains may require as much as three months of treatment. Tetracycline-stained teeth have responded in two to six months of nightly treatment, although not to the extent of normal teeth. Single dark teeth can also be bleached successfully.
Home-based chemically-induced whitening of teeth in adults has recently been reviewed by the Cochrane collaboration. The authors concluded: “There is evidence that whitening products work when compared with placebo/no treatment. There are differences in efficacy between the products, mainly due to the levels of active ingredients, hydrogen peroxide and carbamide peroxide. All trials were however short term and the majority of the studies were judged to be at high risk of bias and were either sponsored or conducted by the manufacturers. There is a need for pragmatic long-term and independent clinical studies that include participants representing diverse populations. There is also a need to evaluate long-term harms. Several studies reported (where measured) the common side effects of tooth sensitivity and gingival irritation, and people should be informed of this” (Hasson et al., 2006).
For the purpose of this Opinion the terms “tooth whitening products” and “tooth bleaching products” define the same kind of products.
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