Constant ebb & flow of mineral at the tooth surface The whiteness of our teeth depends on the color of dentin, also known as 'ivory', which forms the main body of each tooth, under a surface we know of as dental enamel. Enamel is also critical to the beauty of our teeth, as sound, healthy enamel is semi-transparent, revealing the true color of the ivory beneath. If the enamel becomes minutely scratched, or covered in plaque or stains, or its mineral is dissolved and thinned by plaque acids, the tooth surface becomes not only cloudy and dull, but can fall into decay, requiring professional treatment.

The main component of dentin (70%) and enamel (97%) is “hydroxyapatite" - a natural calcium phosphate and our third largest body component, as it also comprises 60% of bone. Human saliva, rich in calcium and phosphate ions, can be described as a saturated solution of hydroxyapatite, which it supplies constantly to the teeth to replace mineral dissolved out by plaque acids during 'demineralization,' the first step towards tooth decay. Saliva supports and protects the teeth, by neutralizing plaque acids and restoring lost mineral. This natural healing process is known as 'remineralization.'

Ideally demineralization and remineralization should balance each other at the tooth surface, so that no net loss of mineral occurs. But conditions such as excess plaque, inadequate saliva flow, or frequent intake of acidic foods or carbohydrates which plaque bacteria turn into acids can upset the balance, driving the equation overwhelmingly in the direction of demineralization, and finally tooth decay.

It is now known, however, that early-stage demineralization (incipient caries or 'white spot' lesions) can be reversed if sufficient mineral is provided in time, avoiding progress into decay and the need for surgical intervention. A breakthrough in dental care : remineralizing toothpaste Remineralizing toothpaste, containing nanoparticle hydroxyapatite, was developed in the 1970's by Sangi Co., Ltd, to meet this need. First launched in 1980, the Apagard family of products have sold over 50 million tubes, and after extensive laboratory tests and field trials, their active ingredient was approved as an anticaries agent in Japan in 1993, and designated Medical Hydroxyapatite to distinguish it from other types of hydroxyapatite such as dental abrasives. Sangi's original hydroxyapatite, though largely nanometer in size, contained mostly three-figure nanoparticles (100 nanometers and above) and a proportion of micron-sized particles. In 2003 this was reduced to two-figure nanometer size (mainly 20-80 nanometers), which laboratory tests show is even more effective in remineralizing tooth enamel. (1 nanometer = one millionth of a millimeter)