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Effects of Calcium Phosphate Nanoparticles on Ca-PO₄ Composite

Paffenbarger Research Center, American Dental Association Foundation, National Institute of Standards and Technology, Building 224, Room A-153, Stop 8546, Gaithersburg, MD 20899-8546, USA.

View larger version (9K): [in this window] [in a new window]   Figure 1. Mechanical properties. (A) Flexural strength, (B) elastic modulus, and (C) hardness, vs. filler level for the nano-DCPA-whisker composites. Values for the stress-bearing, non-releasing hybrid control (TPH, Caulk/Dentsply) are also included. Each value is the mean of 6 measurements for strength (mean ± SD; n = 6), and 10 measurements for elastic modulus and hardness (mean ± SD; n = 10), with each error bar showing the standard deviation (SD). Line connects the datapoints for visual clarity.

View larger version (14K): [in this window] [in a new window]   Figure 2. Ca and PO4 release. (A) Ca ion release and (B) total ionic PO4 release, from the nano-DCPA-whisker composites vs. filler level and immersion time. The symbols on the x-axis represent the hybrid control (TPH, Caulk/Dentsply) and the unfilled resin that had no Ca or PO4 release. Each value is the mean ± SD; n = 3. Lines connect the datapoints for visual clarity.

View larger version (13K): [in this window] [in a new window]   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.

View larger version (8K): [in this window] [in a new window]   Figure 4. Relationships between (A) Ca and (B) PO4 release and nano-DCPA volume fraction VDCPA. The curves are best fits to the measured data by Eqs. 6–8, yielding Ca = 4.46 VDCPA1.6, PO4 = 66.9 VDCPA2.6, and SR = 105 VDCPA1.9. 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. VDCPA is unitless; e.g., VDCPA = 0.25 means a volume fraction (volume of DCPA/volume of composite) of 25% (0.25 is equivalent to 25%).