Rheological characterization of composites using a vertical oscillation rheometer

Objectives. The purpose of this study was to investigate the viscoelastic properties related to the handling characteristics of composites. Methods. A custom-designed vertical oscillation rheometer (VOR) was used for the 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. A dynamic oscillatory test was used to evaluate the storage modulus (E'), loss modulus (E ''), and loss tangent (tan delta) of the composites as a function of frequency (omega) from 0.1 to 20 Hz at 23 degrees C. Results. The E' and E '' increased with increasing frequency and showed differences in magnitude among brands. The complex moduli E-* of the composites at omega = 2 Hz, normalized to that of Z100, were 2.16 (Z250), 4.80 (P60), and 25.21 (SureFil). The magnitudes and frequency characteristic of loss tangent differed significantly among brands. The relationship among the complex modulus E' the phase angle delta, and the frequency omega was represented by the frequency domain phasor form E-*(omega)e(i8) = E-*(omega)angle delta. Significance. The viscoelasticities of composites, which influence handling characteristics, are significantly different among brands. The VOR is a relatively simple device for the dynamic rheological measurement of dental composites. The loci of the frequency domain phasor plots in a complex plane are a valuable method of representing the viscoelastic properties of composites. (C) 2006 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.