Matrix resin effects on selected physicochemical properties of amorphous calcium phosphate composites

Amorphous calcium phosphate (ACP)-filled bioactive composites show promise in a number of dental applications. This study focused on polymer-filler bonding as a way to improve physicochemical properties of these composites. Photoactivated resins were formulated from ethoxylated bisphenol A dimethacrylate (EBPADMA), triethylene glycol dimethacrylate (TEGDMA), 2-hydroxyethyl methacrylate (HEMA) and methacryloxyethyl phthalate (MEP) with four different EBPADMA/TEGDMA mass ratios (1.0, 0.67, 0.5 and 0.25) and a constant HEMA/MEP mass ratio of 2.0. Composites were prepared with the zirconia-ACP (mass fraction 40%). Composites and copolymers were evaluated for their biaxial flexure strength (BFS), degree of vinyl conversion (DC) and water sorption (WS). Composites were also assessed for mineral ion release and polymerization shrinkage (PS). Independent of resin composition, the average BFS was 130 +/- 24 MPa for both the dry and aqueous-immersed copolymers, but was 70 11 MPa for the dry composites and 47 +/- 7 MPa for the wet composites. The average DC of all of the composites was 84 +/- 5% and showed little dependence on resin composition. The WS of both copolymers and composites was 3.2 +/- 0.6% with resin composition being a factor in only one formulation EBPADMA/TEGDMA 0.67. Overall ion release was significantly above the theoretical minimum necessary for remineralization. However, Ca ion levels were lower than that observed previously for similar composites based on resins without MEP. This is most likely due to their binding with the carboxylic acid groups of MEP. Since the DC of the copolymers and the PS of the composites both increased with decreasing EBPADMA/TEGDMA ratio in the resin, elevating the EBPADMA/TEGDMA ratio in the resin seems to be an obvious way to improve the PS of composites without adversely affecting the BFS, WS and/or ion release, while only marginally reducing the DC.