“…Hydroxyapatite is used as such in toothpastes [25][26][27] and bone regeneration [28,29], or as substituted in its lattice with various physiological elements to enhance its bioactivity, like Zn [30], Zn-carbonate [31], Sr [32,33], Zn and Sr [34], Cu and Zn [35], Zn and fluoride [36], fluorine [37], Ag and fluoride [38], Mg and Sr [39], Mg [40], Mg and Zn [41], Mg and Si [42], Ag [43], and Si [44]. These components play various roles; for some, the particular role they play in the substituted HAP is known; for others, it is only assumed.…”