This is a very, very important question to ask. There are a number of toothpastes that promote hydroxyapatite but as this is an expensive ingredient, especially in a nano form, the actual amount can be just a token amount. Based upon clinical studies, a minimum 10% concentration is recommended for full effectiveness. We have exceeded this in our toothpaste formulation with a full 11% hydroxyapatite (6% in the nano form). That is why we believe our toothpaste to be the best there is for sensitivity relief and for mineralizing your enamel.