Characteristic Polymerization Shrinkage Behavior of UDMA/Acidic Monomer Resins

Objectives: This investigation seeks to evaluate the effect of UDMA/acidic monomer resin composition on the polymerization shrinkage. Methods: 5 kinds of diluent monomers for UDMA, methacrylic acid (MAA), acrylic acid (AA), methyl methacrylate (MMA), 2-hydroxyethy methacrylate (HEMA) and tri(ethylene glycol) dimethacrylate (TEGDMA), were used in this study. The volumetric polymerization shrinkage (PS) of UDMA-based resins were calculated from the densities of the uncured and fully photocured resins. Results: All the PS of UDMA based resins were greatly influenced by the kind and fraction of diluent monomer, and increased with increasing the fraction of diluent monomer. PS of UDMA/MAA and UDMA/AA resins with acidic monomer mole fractions lower than 0.67, which represents the stoichiometric ratio between UDMA imino groups and acidic monomer carboxyl groups, are almost equal to that of the UDMA/TEGDMA resin. PS per methacryloyl group (PS/C=C) was not affected by the fraction of TEGDMA in the resin. On the other hand, MAA and its derivatives as a diluent monomer for UDMA were different in nature from TEGDMA. While PS/C=C of UDMA/MMA and UDMA/HEMA resins was increased with increasing fraction of diluent monomers, that of UDMA/acidic monomer resins below 0.67 in mole fraction of acidic monomers was not increased with increasing fraction of acidic monomer. Special attention should be given to the finding that PS/C=C (1.63 x 10^-20%) of UDMA(0.33)/AA(0.67) resin decreased in comparison with that (1.72 x 10^-20%) of UDMA resin even with an increase the fraction of AA (p<0.05, Scheffe's test). Conclusions: PS of UDMA/acidic monomer resins below 0.67 in mole fraction of acidic monomers is almost equal to that of UDMA/TEGDMA resin. jiro_t@md.okayama-u.ac.jp