Influence of light-activation protocol on methacrylate resin-composite evaluated by dynamic mechanical analysis and degree of conversion

The aim of this study was to evaluate the degree of conversion (DC) and to identify the viscoelastic properties: storage modulus (E’), loss modulus (E”), tangent delta (tan δ), and glass transition temperature (T _g ) of a microhybrid resin-composite light-activated by three different protocols. A Filtek Z250 (3 M ESPE) shade A3 was inserted in a Teflon mold (21 mm × 5 mm × 1 mm for viscoelastic properties; and 5 mm × 1 mm for DC) and light-activated according to the following light-activation protocols: (S) 1,000 mW/cm² × 19 s, (HP) 1,400 mW/cm² × 14 s, and (PE) 3,200 mW/cm² × 6 s, all set up to deliver 19 J/cm². Viscoelastic properties was assessed by dynamic mechanical analysis (DMA) (n = 3), performed in single cantilever clamped mode. DC (n = 5) was measured by FTIR on top (T) and bottom (B) surfaces, and the data was submitted to a split-plot one-way ANOVA. For DC, there was a significant effect for surface factor and light-activation protocols factor. Top surface showed higher DC than B in all experimental conditions. Light-activation protocols S and HP resulted in higher DC than PE and were similar between them. Viscoelastic properties (E’, E”, tan δ, T _g ) were not affected by light-activation protocols. It could be concluded that light-activation protocols influenced DC but not influenced the viscoelastic properties.