Rheologic properties of flowable, conventional hybrid, and condensable composite resins

Objectives This research was undertaken to investigate the viscoelastic properties related to handling characteristics of five commercial flowable, two conventional hybrid and two condensable composite resins and to investigate the effect on the viscosity of filler volume fraction of composites. Methods A dynamic oscillatory shear test was used to evaluate the storage shear modulus (G'), loss shear modulus (G"), loss tangent (tan delta) and complex viscosity (eta(*)) of the composite resins as a function of frequency (omega)-dynamic frequency sweep test from 0.01 to 100 rad/s at 25 degrees C-using an Advanced Rheometric Expansion System. To investigate the effect on the viscosity of the composites of the filler volume fraction, the filler weight% and filler volume% were measured by the Archimedes' principle using a pyknometer. Results The complex viscosity eta(*) of flowable composites was lower than that of the hybrid composites and significant differences were observed between brands. The complex viscosity eta(*) of condensable composites was higher than that of hybrid composites. The order of complex viscosity eta(*) at omega=10 rad/s in order of decreasing viscosity was as follows, Synergy compact, P-60, Z-250, Z-100, Aeliteflo, Tetric flow, Compoglass flow, Flow it and Revolution. The complex viscosity of flowable composites, normalized with respect to Z-100, was 0.04-0.56 but Synergy compact was 2.158 times higher than that of Z-100. The patterns of the change of loss tangent (tan delta) of the composite resins with increasing frequency were significantly different between brands. Phase angles delta ranged from 30.9 to 78.1 degrees at omega=10 rad/s. All composite resins exhibit pseudoplastic behavior with increasing shear rate. The relationships between the complex shear modulus G(*), the phase angle delta, and the shear rate omega were represented by the frequency domain phasor form, G(*)(omega)=G(*)e(i delta)=G(*) 90 degree angle delta. Only a weak relationship was found between filler volume% and the viscosity of the composite resins. Significance This investigation shows that the viscoelasticity of composites in the same class is significantly different between brands. This rheologic property of composite resins influences the handling characteristics of the materials. The locus of frequency domain phasor plots in a complex plane is a valuable method of representing the viscoelastic properties of composite resins.