Powder/Liquid Ratio Effects on Mechanical Properties of Modified β-TCP Cement

Objectives: Calcium-phosphate-cement (CPC) is widely utilized as bone-substitution materials. The objective of this study was to develop a new CPC with fine injectability, short setting-time, and high strength, resulting in expanding its applications. The powder/liquid (P/L) ratio of CPC was varied and its effect on properties of CPC was investigated.
Methods: β-tricalcium-phosphate powder was mechano-chemically modified by ball-milling. After milling for 24 h (modified; mβ-TCP), the powder was mixed with CaCl₂ solution, and then NaH₂PO₄ solution at a P/L ratio of 4:1:1 or 5:1:1. Mechanical properties of set cements were measured using compression-strength (CS) test and diametral-tensile- strength (DTS) test. To evaluate injectability, cement paste after mixing was filled in a syringe, and the plunger was depressed with increasing load until 300 N. The injectability was evaluated using paste injectable time after mixing. The porosity of set cement 7 days after mixing was measured using a gas pycnometer.
Results: Set-cement-5:1:1 demonstrated much shorter setting time than set-cement-4:1:1. 1 hour after mixing, the CS and DTS of set-cement-4:1:1 were 0.53 MPa and 0.08 MPa, respectively, and those of set-cement-5:1:1 were 13.6 MPa and 2.86 MPa, respectively. 14 days after mixing, the CS and DTS of set-cement-4:1:1 were 37.05 MPa and 6.94 MPa, respectively, and those of set-cement-5:1:1 were 42.48 MPa and 7.37 MPa, respectively. The initial-strength of set-cement-5:1:1 1 hour after mixing was higher than that of set-cement-4:1:1, however, the strength 14 days after mixing was not significantly different. Cement-paste-4:1:1 and cement-paste-5:1:1 were injectable up to 7 hours and 30 mins after mixing, respectively. Porosity of set-cement-4:1:1 and set-cement-5:1:1 were 42% and 38%, respectively.

Conclusions: The mβ-TCP in this study possibly demonstrates shorter setting time using higher P/L ratio. P/L ratio increase from 4:1:1 to 5:1:1 increased initial strength and decreased porosity without clinically serious reduction of injectability.