Hydroxyapatite is the natural form of calcium that makes up most of your enamel and your bones. It is natural bone building substance of your body. Nano means very small and tiny. In order to bond effectively to your enamel, we use a patented process to "nano-ize" the hydroxyapatite. This makes for a very effective way to mineralize and strengthen your teeth. Our patented form has been clinically tested for highly effective sensitivity relief. As a bonus, hydroxyapatite is naturally pure white and so it provides a whitening boost as well.