Magnesium-substituted hydroxyapatites

1. A stable, phase-pure magnesium-substituted crystalline hydroxyapatite comprising from about 10 wt % to about 29 wt % magnesium, wherein at least 80 wt % of the magnesium content of said magnesium-substituted hydroxyapatite is substituted for calcium ions in the hydroxyapatite lattice structure, wherein said magnesium-substituted hydroxyapatite is made by a process comprising the step of mechanochemically comminuting and dissolving while hydrothermally reacting without external heating a source of calcium ions, a source of magnesium ions, a source of phosphate ions and a source of hydroxide ions, at least one of which is soluble in water, in a aqueous reaction medium until said magnesium substituted-hydroxyapatite is formed, wherein at least one of said source of calcium ions, source of magnesium ions, source of phosphate ions and source of hydroxide ions is water-insoluble or forms a water-insoluble apatite precursor.

2. The phase-pure magnesium-substituted crystalline hydroxyapatite of claim 1 , wherein essentially all of the magnesium content is substituted for calcium ions in the hydroxyapatite lattice structure.

3. The phase-pure magnesium-substituted crystalline hydroxyapatite of claim 1 , comprising crystal agglomerates having a particle size between about 5 nm and about 100 microns.

4. A biocompatible hard tissue implant comprising the magnesium-substituted hydroxyapatite of claim 1 .

5. The biocompatible hard tissue implant of claim 4 , comprising a metal or polymeric implant coated with said magnesium-substituted hydroxyapatite.

6. The biocompatible hard tissue implant of claim 4 , comprising a polymeric composite.

7. A granular fill for direct incorporation into human or animal tissues comprising the magnesium-substituted hydroxyapatite of claim 1 .

8. The granular fill of claim 7 , comprising a metal or polymeric composite for filling dental cavities.

9. A dentifrice composition comprising the magnesium-substituted hydroxyapatite of claim 1 .