Characteristic Water Durability Behavior of UDMA/Methacrylic Acid Resin

Objectives: This investigation seeks to evaluate the water durability of urethane dimethacrylate (UDMA)/acidic monomer unfilled resins. Methods: Three acidic monomers, methacrylic acid (MAA), acrylic acid (AA) and methacryloylethyl phthalate (MEP), as well as tri(ethylene glycol) dimethacrylate (TEGDMA) were compared as diluent comonomers with UDMA. The influence of water immersion on the mechanical properties (MP) of UDMA-based resins was examined by three-point bending on fully cured resins. The water uptake (WU) of UDMA-based resins was determined gravimetrically on the specimens used for MP measurements. Results: The flexural strength (FS) of UDMA/acidic monomer resins with compositions providing stoichiometric balance of imino groups from UDMA and carboxyl groups from the acidic monomer were evaluated in comparison with UDMA homopolymer and a UDMA/TEGDMA resin as a typical dental matrix resin. All the FS and WU of UDMA based resins were greatly affected by the kind of diluent monomer and period of water immersion, with the FS values decreasing with increasing water immersion time. Though FS of the UDMA/TEGDMA resin was inferior to that of UDMA homopolymer, all the UDMA/acidic monomer resins had significantly superior FS compared with UDMA homopolymer prior to water immersion. However, FS of UDMA/acidic monomer resins, except UDMA/MAA resin, greatly decreased with increasing WU in comparison to UDMA and UDMA/TEGDMA resins. Special attention should be given to the finding that FS of UDMA/MAA resin (153 ± 6MPa) remained superior in comparison with that of UDMA homopolymer (141 ± 10MPa) after immersion in water for one year, even though the saturated WU (6.5 mass%) of former resin was twice that (3.1 mass%) of latter resin. (p<0.05, t-test). Conclusions: UDMA/MAA resins have significantly superior FS compared with UDMA homopolymer even after storage in water for a year. jiro_t@md.okayama-u.ac.jp