See also the bioactive glass compounds BioMin (fluoro calcium phosphosilicate) and NovaMin (calcium sodium phosphosilicate), which come in toothpastes that also include fluoride to cover all the bases.
BioMin F is as effective as nanohydroxyapatite, and is less expensive than the Apagard nanohydroxyapatite toothpaste. (BioMin F is not yet available in the U.S. and needs to be imported.)