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Nano DCPA-Whisker Composites with High Strength and Ca and PO₄ Release

¹ Building 224, Room A-153, Stop 8546, Paffenbarger Research Center, American Dental Association Foundation and
² National Institute of Standards and Technology, Gaithersburg, MD 20899-8546, USA

View larger version (32K): [in a new window]   Figure 1. Synthesis of nano DCPA particles. (A) Schematic of the spray-drying apparatus. "HEPA" refers to High Efficiency Particulate Air Filter. The glass column was heated with electrical heating tapes and thermally insulated with a fiberglass tape, reaching an average temperature in the column of 80°C. (B) TEM of nano DCPA particles. Arrows indicate particles about 50 nm in diameter. (C) XRD pattern indicates that the powder was a poorly crystalline DCPA.

View larger version (11K): [in a new window]   Figure 2. Composite flexural strength. Heat-cured nano DCPA composite: •. Chemically cured nano DCPA composite with HEMA: . Chemically cured nano DCPA composite without HEMA: . Specimens (A) without immersion, (B) after 1 day’s immersion, and (C) after 56 days’ immersion. Each value is the mean of 5 measurements, with the error bar showing 1 standard deviation (SD) (mean ± SD; n = 5). Two-way ANOVA identified significant effects of resin composition and DCPA:whisker ratio (p < 0.05), with no significant interaction between the two factors (p = 0.86). The 56-day immersion decreased the strength of the chemically cured DCPA-whisker composites, but not the heat-cured DCPA-whisker composites and the controls (p > 0.1).

View larger version (19K): [in a new window]   Figure 3. PO4 and Ca release for the 3 groups of composites. Each value is mean ± SD; n = 4. The nano DCPA:whisker mass ratio was designated as D:W. For each group, two-way ANOVA showed significant effects of D:W and immersion time, with a significant interaction between the 2 parameters (P < 0.05). Increasing the D:W ratio significantly increased the PO4 and Ca concentrations (P < 0.05). At each D:W, increasing the immersion time significantly increased the PO4 and Ca ion concentrations. The hybrid control and inlay/onlay control had no detectable release.