Tooth enamel is the most mineralized tissue of human body. Its composition is 96 wt.% inorganic material (Hydroxyapatite) and 4 wt.% organic material and water. In dentin, the hydroxyapatite represents 70 wt.%. This inorganic material gives an appearance of bright white and eliminates the diffuse reflectivity of light by closing the small pores of the enamel surface. The process of de- and remineralization is governed by the degree of saturation of oral fluids (saliva and plaque) with respect to apatite minerals.

The nano-hydroxyapatite has a strong ability to bond with proteins, as well as with fragments of plaque and bacteria, when contained in toothpastes. This ability is due to the size of nanoparticles, which considerably increase the surface area to which proteins can bind.Besides. nano hydroxyapatite also acts as filler because it repairs small holes and depressions on enamel surface, a function enhanced by the small size of the particles that compose it.