Why do teeth become darker and what is the mechanism of action of whitening gels?

The internal coloration in the dentin is the result of natural pigment and stain molecules in the form of large, long chains stuck in the microstructure of the teeth. These color molecules have a magnetic molecular link with atoms called chromophores, and chromophores are responsible for the absorption of light waves of various wavelengths. As these molecules grow, more chromophore content absorbs more light and they appear darker.

In addition to its natural color, all teeth are colored and darkened over time. Coloring of teeth begins in two ways;

1. External coloring materials and organic pigments are an additional source of staining from what we eat and drink and are absorbed in the microstructure of the teeth becoming an internal stain,

2. The color molecules in the tooth's own structure consistently get bigger and join together to form larger and therefore darker molecules.

All peroxide-containing whitening gels were developed to release hydrogen peroxide. Hydrogen peroxide is decomposed into water and other components: molecular oxygen, oxygen ions, hydrogen ions and free radicals. Oxygenation, ions and free radicals cause physical and chemical break down of molecules that cause coloring and is needed to physically remove these molecules from the structure of the tooth by diffusion.

Whitening is obtained as a result of smaller molecular fragmentation and removal of these from the tooth structure by diffusion.

However, in order for this whitening mechanism to function effectively, whitening gels must meet three requirements;

1. Should not loose its effectiveness and % concentration,

2. Should release more free radicals rather than releasing only water and oxygen,

3. In addition, should sustain this chemical reaction long enough to penetrate deeply into the tooth.

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