Flexural creep deformation and recovery in dental composites

Objectives: Three different popular composite resin systems for dental restorative applications are microfilled, minifilled and midifilled types in which deformation under stress and recovery after stress removal may be strongly influenced by filler parameters and resin formulation. The purpose of this in vitro study was to evaluate these differences in selected composite resins. Materials: Three composites, Clearfil (midifill), Charisma (minifill) and Durafill (microfill), were evaluated. Elastic, viscoelastic and viscous deformation of the composites under a constant stress and the subsequent recovery on removal of stress were measured. Dynamical mechanical properties of these materials were also characterized. Results: The mean values (and SD) of elastic, viscoelastic and viscous components of overall deformation (mm), respectively, under a constant stress of 45(5) KPa were as follows: Clearfil, 0.17(0.03), 0.06(0.02), 0.03(0.05); Charisma, 0.34(0.1), 0.09(0.04), 0.14(0.03); Durafill, 0.68(0.06), 0.14(0.03), 0.23(0.03) The results show that there are significant differences (P<0.0001) between the different composite resins in the elastic, viscoelastic and viscous segments of deformation. The microfilled system deformed significantly more than the minifilled, and the minifilled system more than the midifilled. Storage modulus values evaluated by dynamic mechanical analysis were also significantly different (P<0.0001). The observed differences were readily explained by the differences in the type and volume fraction of the filler content in the composites. Conclusions: Differences in time dependent deformation and recovery as well as dynamic mechanical properties of dental composites were strongly influenced by filler parameter differences. The clinical performance of restorations may be strongly influenced by the observed differences.