Figure 4. Relationships between (A) Ca and (B) PO₄ release and nano-DCPA volume fraction V_DCPA. The curves are best fits to the measured data by Eqs. 6–8, yielding Ca = 4.46 V_DCPA1.6, PO₄ = 66.9 V_DCPA^2.6, and SR = 105 V_DCPA^1.9. The correlation coefficient r = 0.99 for all three equations. Ca and PO₄ in these equations are ion concentrations and have the units of mmol/L. V_DCPA is unitless; e.g., V_DCPA = 0.25 means a volume fraction (volume of DCPA/volume of composite) of 25% (0.25 is equivalent to 25%).