Teeth Whitening - The Science

How Does Teeth Whitening Work?

Teeth whitening is the bleaching process that removes stains from enamel and dentine of the teeth (W Chan 2007)

Enamel and dentine are porous and semi-permeable like a sponge. The peroxide gel/solution flows and diffuses freely through them. (McEvoy 1989)

Typically enamel consists of 80-90% of inorganic minerals and 10-20% of organic matrix and fluid by volume.

It is believed the 10-20% of organic matrix of the enamel is responsible for the colour of the teeth. This is true in teeth with opaque enamel, but in translucent enamel the stains in the dentine needed to be removed so that the enamel will appear whiter.

Teeth whitening is all about how the peroxide gel diffuses through enamel and removing stains in enamel and dentine.

Diffusion is dependent on the concentration of the peroxide gel, contact time and temperature of the peroxide gel at the teeth surfaces (W Chan 2003-2007)

The rate of flow of the peroxide through the enamel and dentine is directly related to the concentration of the peroxide gel. (Zaragoza 1984: G.Christensen 1997 CRA; James C Brooms Compendium 1998)

Higher temperature helps to activate the peroxide gel at the teeth surfaces and also enhances its diffusion into enamel.

Hydrogen peroxide (H2O2) breaks down into water (H2O) and oxygen radicals (O).

The oxygen radicals (O) react only with the colour substances (chromo gens) which are organic polyphenois on or within the teeth.

Organic polyphenois are long conjugated unsaturated macrostructures consisting of C=C bonds.

These long chained molecules absorb light thus contributing to their colours.

The unsaturated C=C bonds are broken down into smaller molecules, thus absorbing less light and making the teeth appear whiter.

References: Bosch and Coops 1994; Goldstein and Garber 1995; Nathoo 1997; Croll 1997; SCCNFP of EU Commission 1999.

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