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Figure 3. Remineralization potential. (A) Diagram demonstrating the potential of DCPA-whisker composites to form hydroxyapatite. The straight line in the middle represents the hydroxyapatite solubility isotherm line. The line at the upper right corner represents the solubility isotherm for DCPD (dicalcium phosphate dihydrate, CaHPO4·2H2O). The dots represent log([Ca2+][OH–]2) vs. log([H+]3[PO4] 3–) from the measured Ca and PO4 concentrations. (B) Degree of saturation SR < 1 means that the solution is undersaturated, and SR > 1 means supersaturated, with respect to hydroxyapatite. (C) Thermodynamic driving force for remineralization. The larger the negative value of the Gibbs free energy 
G0, the lower the energy state for hydroxyapatite precipitation, and the higher the remineralization potential. Values near the right axis are filler level mass fractions.
