Dynamic mechanical properties of a visible light curable urethane dimethacrylate based dental resin

The purpose of this study was to evaluate dynamic mechanical properties of urethane dimethacrylate (UDMA) and triethylene glycol dimethacrylate (TEGDMA) based dental resin. Dynamic mechanical properties of a visible light (lambda = 400-500 nm) curable UDMA/TEGDMA (70:30 in wt%) resin were investigated for specimens uncured, light-cured for 40 s, and heated to 175 degreesC subsequent to the irradiation for 40 s. Differential scanning calorimetry (DSC) was also employed as a complementary technique. For the light-cured specimen, two abrupt drops in the log storage modulus (E') and two peaks in the tan delta vs. temperature curve corresponding to the glass transition were observed. The storage modulus was slightly increased with increasing temperature between the two modulus drops. The DSC experiment showed that the light-cured specimen contains residual living groups trapped by the fast reaction, which lead to further reaction during post-cure heat treatment. This further thermal reaction is considered to be responsible for the modulus increase. After heating to 175 degreesC above the DSC exothermic peak, most of the residual groups in the light-cured specimen were found to be reacted, showing a single decrease in modulus and a single peak in the tan delta curve, and no exotherm in the DSC curve. With the aid of DSC data, the further thermal cure reaction with increasing temperature may occur within the glass transition region. The occurrence of the thermal reaction gives rise to the inaccuracy in determining the glass transition temperature (T-g).