Viscoelastic properties of low-shrinking composite resins compared to packable composite resins.

The aim of this study was to evaluate the viscoelastic properties of novel low-shrinking composites and compare them to those of packable composites. Six materials were tested: Clearfil Majesty Posterior (CM), ELS Extra Low Shrinkage (EL), Filtek P60 (FP), Filtek Silorane (FS), Prodigy (PR) and Surefil (SU). Static and dynamic testing was performed and materials were tested dry and wet at different temperatures (21°C to 50°C). Shear and flexural modulus, loss tangent, dynamic viscosity, Poisson's ratio and creep recovery were calculated among others. Significant differences were found both between the two groups and between materials belonging to the same group. CM presented the highest shear and flexural modulus and EL the lowest. All materials were softened by an increase of temperature, while FS was the least affected by water and PR showed to be the most susceptible. Different approaches used to overcome polymerization shrinkage lead to materials with different properties.