The purpose of this study was to investigate the viscoelastic properties related to handling characteristics of composite resins.

A custom designed vertical oscillation rheometer (VOR) was used for rheological measurements of composites. The VOR consists of three parts: (1) a measuring unit, (2) a deformation induction unit and (3) a force detecting unit. Two medium viscous composites, Z100 and Z250 and two packable composites, P60 and SureFil were tested. The viscoelastic material function, including complex modulus E^* and phase angle δ, were measured. A dynamic oscillatory test was used to evaluate the storage modulus (E'), loss modulus (E") and loss tangent (tanδ) of the composites as a function of frequency (ω) from 0.1 to 20 H_z at 23℃.

The E' and E" increased with increasing frequency and showed differences in magnitude between brands. The E^*s of composites at ω = 2 H_z, normalized to that of Z100, were 2.16 (Z250), 4.80 (P60) and 25.21 (SureFil). The magnitudes and patterns of the change of tanδ of composites with increasing frequency were significantly different between brands. The relationships between the complex modulus E^*, the phase angle δ and the frequency ω were represented by frequency domain phasor form, E^* (ω) = E^*e^iδ = E^*∠δ.

The viscoelasticity of composites that influences handling characteristics is significant different between brands. The VOR is a relatively simple device for dynamic, mechanical analysis of high viscous dental composites. The locus of frequency domain phasor plots in a complex plane is a valuable method of representing the viscoelastic properties of composites.