Effects of Powder to Liquid Ratio on Novel DCPD Cement

Objective: To evaluate the effects of powder to liquid ratio on the phases, setting time, compressive strength and porosity of a novel DCPD cement made using monocalcium phosphate monohydrate (MCPM) and hydroxyapatite (HA).

Methods: Cylindrical specimens of DCPD cements were made by mixing MCPM and HA in molar ratios of 2:0.5 adding 100mM sodium citrate in a powder to liquid mass (P/L) ratio of 0.5, 0.75, 1, and 1.25, and then casting into Teflon molds (1/8in diameter, 1/4in height). For each P/L ratio, the setting time was evaluated by a Gilmore needle apparatus, initial phase composition was determined by x-ray diffraction analysis, the porosity was calculated from volume and weight, and the compressive strength was evaluated using a materials tests system at a loading rate 1 mm/min.

Results: Specimens from all powder to liquid ratios consisted of pure DCPD, indicating a complete dissolution of HA and the subsequent reaction between MCPM and HA. The setting time decreases from 54.33 (1.26) to 1.5 (0.0) minutes as the P/L ratio increases from 0.5 to 1.25. The porosity decrease from 69.71 (2.55)% to 55.24 (0.09)%. The compressive strengths increase from 0.53 (0.07) to 1.96 (0.32) MPa. The compressive strength follows a logarithmic decrease as the porosity of the cement increases. The results show that the P/L of 1.0 offers the best combination of setting time and compressive strength.

Conclusion: Novel DCPD cement successfully made by mixing MCPM and HA powder with distilled water. DCPD cements made with a 1.0 P/L ratio offers a desirable balance between strength and setting time. Future studies will investigate the synergistic effects of other setting time modifiers on the physical properties and biological properties of this novel DCPD cement.