Improvement of mechanical properties of self setting calcium phosphate bone cements mixed with different metal oxides

Calcium phosphate cements (CPC), based on multicomponent powder mixtures of calcium orthophosphates with medium particle sizes in the region of 1 - 20 mum, set isothermally in an aqueous environment to form hydroxyapatite (HA). HA cement reactants include tetracalcium phosphate (TTCP), tricalcium phosphate (TCP), dicalcium phosphate anhydrate (DCPA), dicalcium phosphate dihydrate (DCPD), monocalcium phosphate (MCPA) or octacalcium phosphate (OCP). The aim of this study was to improve the mechanical performance of TTCP / DCPA cement by adding several metal oxides to tetracalcium phosphate during the fabrication process. Cements based on tetracalcium phosphate mixed with silica or titanium oxide showed significant increases in compressive strength, approximately 80 - 100 MPa, whilst no change in the mechanical behavior of CPC was observed if zirconia was added. Xray diffraction measurement confirmed the setting reaction of doped cements was similar to that of pure CPC. Low crystalline HA was found to be the main constituant of set cement; additional phases, such as calcium titanate or calcium zirconate, were not involved in the reaction. A mechanical reinforcement effect was thought to result from changes in the thermodynamic or kinetic solubilities of doped tetracalcium phosphates, this would lead to slower HA crystal formation and a more cross-linked cement structure.