Time-Temperature-Intensity-Transformation Cure Diagram for Visible Light Curable Dimethacrylate Resins

The cure behavior of two dimethacrylate resin formulations activated by visible light (λ = 400-500 nm) was investigated by means of a rapid monitoring dynamic mechanical technique. Storage modulus (G � ) and tan δ vs. time data were obtained for different light intensities (20-600 mW cm −2 ) and cure temperatures (25-60 ◦ C). Gelation and vitrification time were estimated from initial rise of Gand maximum peak of tan δ vs. time curve, respectively, and used to construct time-temperature-intensity-transformation (TTIT) cure diagram. Physical states of material in the regions divided by the estimates of the transforming times were incorporated in the cure diagram. It was found that the dimethacrylate systems undergo phase transformation initially from liquid to rubber and finally to glass. Effects of intensity and temperature on the gelation and vitrification are discussed and compared for the two formulations. Visible light curable dimethacrylate resins are widely used as an important base material for dental restora- tive composites as a consequence of their advantages such as the short application time and the aesthetic performance in clinical applications. However, there remain many issues of the dimethacrylate based den- tal resins. Rapid reaction of the light curing systems leads to incomplete cure, 1-5 reducing the mechanical strength and increasing the swelling of the material. Unreacted monomers trapped in the incompletely cured material could be extractable, causing various troubles in the body. 6-9 Shrinkage during photo-polymerization is also one of principal drawbacks in practical applica- tions. 10, 11