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)

A Comparison with Fluoride
Fluoride in drinking water and oral care products has had unquestionable influence in reducing tooth decay worldwide. When it was first introduced into U.S. water systems, the reduction in new caries in schoolchildren was as high as 35-60%. But excessive intake can lead to dental or skeletal fluorosis, and as a result the amount permitted in oral care products and community water systems is controlled.

Nanoparticle hydroxyapatite, though not widely known, has been used in toothpaste in Japan for almost three decades. In field trials leading to its approval as an anticaries agent in 1993, the reduction in new caries among Japanese schoolchildren using the nanoparticle hydroxyapatite-containing toothpaste once daily over a period of three years was 36-56% compared with children using a non-hydroxyapatite containing toothpaste. Hydroxyapatite is a biocompatible substance, used widely in bone grafts and health foods, and can be swallowed without concern, including by children. It has no known toxic or negative environmental effect.

Fluoride, though not a remineralizing substance in itself, strengthens the teeth against decay by promoting uptake of calcium and phosphate ions from saliva and other sources into the enamel (remineralization). At the same time, it forms a new substance, fluorapatite, on the tooth surface, more resistant to plaque acids than the enamel's original hydroxyapatite. The most active element in the periodic table, fluoride is supplied in toothpaste in the form of compounds such as sodium fluoride (NaF) or sodium monofluorophosphate (MFP).

In contrast Nano mHAP, supplied in the form of nanocrystals, is a calcium phosphate almost identical chemically to the hydroxyapatite of our teeth. It has been shown in vitro to remineralize subsurface demineralized lesions and fill microscopic surface fissures, restoring both surface and subsurface enamel, and to bind and precipitate out of solution cariogenic bacteria such as mutans streptococci. Unlike fluoride, Nano mHAP adds nothing 'new' to the teeth, but by restoring and maintaining the enamel's mineral density and surface smoothness - making it glossier, more translucent and less susceptible to plaque attachment and to decay - Nano mHAP can be used with confidence to protect not only the health but also the beauty of our teeth.