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Department of Conservative Dentistry, College of Dentistry, Seoul National University, Korea.
Corresponding author: Chung-Moon Um. Department of Conservative Dentistry, College of Dentistry, Seoul National University, 28 Yoengun-dong, Chongro-gu, Seoul, Korea, 110-749. Tel: 82-2-2072-3953, 2651, Fax: 82-2-2072-3859, inboglee@snu.ac.kr
The purpose of this study was to investigate the viscoelastic properties related to handling characteristics of composite resins.
Methods
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 Hz at 23℃.
Results
The E' and E" increased with increasing frequency and showed differences in magnitude between brands. The E*s of composites at ω = 2 Hz, 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*eiδ = E*∠δ.
Conclusions
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.
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Figure 1-a
Diagram of the VOR (vertical oscillatory rheometer)
Figure 1-b
The geometry of measuring unit
Figure 2
The relationship between strain ε(t), stress σ(t) and phase angle δ in dynamic oscillatory test
Figure 3
The relationship between storage (real) modulus E', loss modulus (imaginary) modulus E", complex modulus E* and phase angle δ in a complex plane
Figure 4
Storage modulus E' increased with increasing the frequency and showed differences in magnitude between brands
Figure 5
Loss modulus E" increased with increasing the frequency and showed differences in magnitude between brands
Figure 6
Complex modulus E* increased with increasing the frequency and showed differences in magnitude between brands
Figure 7
Phase angle δ of composite. The patterns of the change of δ of samples with increasing frequency showed the different characteristics of the composites between brands
Figure 8
Loss tangent as a function of frequency
Figure 9
Relative complex modulus of composites normalized to that of Z1 at ω = 2 Hz
Figure 10
Phasor presentation of E* and δ, E*eiδ= E*∠δ, of composites at ω = 2 Hz in a polar coordinate system
Figure 11
Locus of frequency domain phasor plots, G*(ω)eiδ = ∣ G*(ω) ∣ ∠δ of composites in a complex plane
Table 1
Phasor presentation of the complex modulus E* and phase angle (δ) of composite resins at various frequencies, E* (dyn/cm2) ∠δ(°)
Table 2
Phasor presentation of the complex shear modulus G* and phase angle (δ) of composite resins at various frequencies, G* (dyn/cm2) ∠δ(°)
Rheological characterization of composites using a vertical oscillation rheometer
Figure 1-a
Diagram of the VOR (vertical oscillatory rheometer)
Figure 1-b
The geometry of measuring unit
Figure 2
The relationship between strain ε(t), stress σ(t) and phase angle δ in dynamic oscillatory test
Figure 3
The relationship between storage (real) modulus E', loss modulus (imaginary) modulus E", complex modulus E* and phase angle δ in a complex plane
Figure 4
Storage modulus E' increased with increasing the frequency and showed differences in magnitude between brands
Figure 5
Loss modulus E" increased with increasing the frequency and showed differences in magnitude between brands
Figure 6
Complex modulus E* increased with increasing the frequency and showed differences in magnitude between brands
Figure 7
Phase angle δ of composite. The patterns of the change of δ of samples with increasing frequency showed the different characteristics of the composites between brands
Figure 8
Loss tangent as a function of frequency
Figure 9
Relative complex modulus of composites normalized to that of Z1 at ω = 2 Hz
Figure 10
Phasor presentation of E* and δ, E*eiδ= E*∠δ, of composites at ω = 2 Hz in a polar coordinate system
Figure 11
Locus of frequency domain phasor plots, G*(ω)eiδ = ∣ G*(ω) ∣ ∠δ of composites in a complex plane
Figure 1-a
Figure 1-b
Figure 2
Figure 3
Figure 4
Figure 5
Figure 6
Figure 7
Figure 8
Figure 9
Figure 10
Figure 11
Rheological characterization of composites using a vertical oscillation rheometer
Phasor presentation of the complex modulus E* and phase angle (δ) of composite resins at various frequencies, E* (dyn/cm2) ∠δ(°)
Phasor presentation of the complex shear modulus G* and phase angle (δ) of composite resins at various frequencies, G* (dyn/cm2) ∠δ(°)
Table 1
Phasor presentation of the complex modulus E* and phase angle (δ) of composite resins at various frequencies, E* (dyn/cm2) ∠δ(°)
Table 2
Phasor presentation of the complex shear modulus G* and phase angle (δ) of composite resins at various frequencies, G* (dyn/cm2) ∠δ(°)