Dental application of binary urethane monomer mixtures:strengthened resin matrix

The strengthened resin matrices in six experimental binary visible light-cured (VLC) urethane monomer mixtures were examined in terms of mechanical strength. A 60 wt% bis-GMA/40 wt% binary monomer mixture was used as a control sample. A dry state (1 day in air at 37 degrees C) and a wet state by immersion in distilled water (7 and 30 days at 37 degrees C) were investigated. The compressive strength and diametral tensile strength of urethane monomer samples had values equivalent to, or greater than those of a control sample in the dry state, but had increased values in the wet state. The nano-indentation hardness values in experimental urethane monomer mixtures were greater than that in a control sample in the dry state, showing that immersion in water gave increased strength (maximum increase was about 2.5 times) in six binary urethane monomer mixtures. The compressive strength of the samples in the dry and wet states exhibited linearly increasing elastic modulus values for the resin matrix in the range about 50 to 2600 MPa. The toughened resin matrix had smaller amounts of residual monomer in the urethane monomer mixtures (0.41 to 5.03 wt%) compared with that of the binary 60bis-GMA/40TEGDMA mixture (0.71 to 6.26 wt%). This study has revealed that resin matrices are strengthened by the use of four-functional urethane monomers in experimental binary urethane monomer mixtures.