Table 4.

Principal calcium phosphates used as biomaterials. HAp, hydroxyapatite.

Name and Chemical Formula	Crystal Structure	Density	Usage
Monocalcium phosphate monohydrate Ca(H2PO4)2·H2O	Triclinic	2.23	In solution: as liquid phase in certain cements
Anhydrous monocalcium phosphate Ca(H2PO4)2	Triclinic	2.57	In solution: as liquid phase in certain cements
Dicalcium phosphate dihydrate CaHPO4·2H2O	Monoclinic	2.30	Thin deposits, cements and composites
Dicalcium phosphate anhydrous CaHPO4	Triclinic	2.93	Thin deposits, cements and composites
Amorphous Tricalcium phosphate Ca3(PO4)2·nH2O	Three polymorphs based on temperature	–	Thin deposits, cements and composites
Octocalcium phosphate Ca8(PO4)4(HPO4)2·5H2O	Triclinic	2.67	Cements
Tricalcium phosphate β Ca3(PO4)2	Rhombohedral	3.07	Resorbable bioceramics, cements, composites
Tricalcium phosphate α Ca3(PO4)2	Monoclinic	2.86	Resorbable bioceramics, cements, composites
Tetracalcium phosphate Ca4(PO4)2O	Monoclinic	3.05	Cements
Hydroxyapatite phospho-calcium Ca10(PO4)6(OH)2	Hexagonal (the stoichiometric HAp is monoclinic at temperatures <212 °C, whereas in other cases, the small quantities of impurities lead to a change from monoclinic to hexagonal)	3.16	Cements, composites, ceramics and thin films