Bio-Resorption Of Implanted Brushite And Monetite Cements 

Objective:  The success of bone regeneration procedures is limited by low resorption rates associated with the use of hydroxyapatite (HA) based grafts. A significant reduction in the rate of resorption occurs following hydrolysis of CaHPO₄·2H₂O (brushite) to HA in vivo. Both brushite and monetite cements are chemically similar, yet their in vivo behaviour differs as it has been shown that CaHPO₄ (monetite) does not re-precipitate into HA. Thermal hydrolysis of set brushite cement can result in the conversion to monetite; hence they can be utilized as precursors to the anhydrous monetite form. This study evaluates the resorption and changes in the physico-chemical properties of brushite and monetite cements after subcutaneous implantation.

Method:  Implants were prepared by utilizing different powder to liquid ratio and by varying processing conditions to achieve different combinations of brushite and monetite cements. Microstructural analysis was carried out using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The change in the physico-chemical properties along with progression of microstructure and bio-resorption of cements was evaluated by subcutaneous implantation in rats for up to 12 weeks.

Result: Implants were produced with high or low percentage porosity (55-75% and 30-50% respectively) and with high and low SSA (18-22 and 0.5-1 m²/g respectively). All cements showed a significant increase in their percentage porosity post implantation. We observed that brushite implants demonstrated a phase change to octacalcium phosphate (OCP) and HA. No phase conversion was observed in monetite implants. All monetite implants resorbed to a significantly greater extent when compared with brushite implants. 

Conclusion:  Monetite implants prepared by varying the processing conditions resorbed to a greater extent and did not convert to HA when compared with equivalent brushite implants. By modifying the processing conditions, the in vivo behaviour can be modified leading to graft preparation with a higher clinical efficacy.