Rheological characterization of composites using a vertical oscillation rheometer.
OBJECTIVE
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 20Hz 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(idelta)=E*(omega) angledelta.


CONCLUSIONS
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.
Department of Conservative Dentistry and Dental Research Institute, College of Dentistry, Seoul National University, Jongro-Gu, Seoul, South Korea. inboglee@snu.ac.kr
In Bog
IB
Lee
Byeong Hoon
BH
Cho
Ho Hyun
HH
Son
Chung Moon
CM
Um
D003188:Composite Resins; D019245:Compressive Strength; D003799:Dental Stress Analysis; D004548:Elasticity; D008422:Materials Testing; D009991:Oscillometry / Q000295:instrumentation*; D012212:Rheology; D033081:Shear Strength; D014783:Viscosity
D003188:Composite Resins