Ethoxylated bisphenol dimethacrylate-based amorphous calcium phosphate composites

Abstract

Improving the anti-demineralizing/remineralizing and mechanical properties of amorphous calcium phosphate (ACP) composites has been the focus of our recent research. In this study, an ethoxylated bisphenol A dimethacrylate (EBPADMA) was blended with triethylene glycol dimethacrylate (TEGDMA), 2-hydroxyethyl methacrylate (HEMA) and methacryloxyethyl phthalate (MEP) to form experimental resins with different EBPADMA/TEGDMA molar ratios (0.50, 0.85 and 1.35) and a constant HEMA/MEP molar ratio (8.26). Composites were prepared by admixture of either unmilled or milled zirconia-ACP filler (40% by mass) and photo-activated resin (60% by mass). One aim was to test if improved ion release can be achieved by elevating the EBPADMA/TEGDMA ratio while lowering the level of surface active methacryloxyethyl phthalate in the resin without adversely affecting the biaxial flexure strength (BFS), degree of vinyl conversion (DC) and water sorption (WS) of composites. A second aim was to assess the effect of using milled vs. unmilled ACP on these properties. Ion release of all composites was significantly above the theoretical minimum necessary for remineralization. Calcium ion release was not impeded by binding with the carboxylic acid groups of MEP. Increased supersaturation was attained with increasing EBPADMA/TEGDMA ratio in the resin. Variations in resin composition had no effect on BFS or DC of composites. The BFS of the milled ACP composites was higher than the BFS of unmilled ACP composites (56% and 79%, respectively for dry and wet specimens). DC of composites was only moderately reduced (13.6% and 7.3%, for unmilled and milled ACP, respectively) compared to unfilled resins. WS decreased in the following order: unmilled ACP composites > milled ACP composites > copolymers. Fine-tuning of the resin and utilizing milled ACP filler improved the remineralizing potential of ACP composites without impeding their DC, BFS or WS.