Time-dependent deformation of composite restorative materials in compression.

The strain of six composite resins, including microfine and conventional types, has been measured in compression as a function of time. Compressive loads have been used in separate experiments to produce a wide range of applied stress in samples of clinically-appropriate size. The magnitude of visco-elastic response generally decreases with increasing % of filler in the composite. Additionally, the very substantial linear strain, up to 20%, observed in some microfine composites suggests the visco-elastic deformation of both organic filler, as well as resin matrix, at high stress levels. Caution is therefore indicated with regard to the clinical use of microfine restorative materials in high-stress-bearing situations.