The change of the initial dynamic visco-elastic modulus of composite resins during light polymerization

Min-Ho Kim; In-Bog Lee

doi:10.5395/JKACD.2009.34.5.450

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Kim and Lee: The change of the initial dynamic visco-elastic modulus of composite resins during light polymerization

Original Article

Journal of Korean Academy of Conservative Dentistry

Journal of Korean Academy of Conservative Dentistry 2009; 34(5): 450-459.

Published online: 30 September 2009

DOI: https://doi.org/10.5395/JKACD.2009.34.5.450

The change of the initial dynamic visco-elastic modulus of composite resins during light polymerization

Min-Ho Kim, In-Bog Lee

Department of Conservative Dentistry, School of Dentistry, Seoul National University, Korea.

Corresponding Author: In-Bog Lee. Department of Conservative Dentistry School of Dentistry, Seoul National University 275-1, Yeongeon-dong, Jongno-gu, 110-768, Korea. Tel: 82-2-2072-3953, Fax: 82-2-2072-3859, inboglee@snu.ac.kr

Received 6 May 2009 Revised 18 June 2009 Accepted 9 July 2009

(open-access):

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

The aim of this study was to measure the initial dynamic modulus changes of light cured composites using a custom made rheometer. The custom made rheometer consisted of 3 parts: (1) a measurement unit of parallel plates made of glass rods, (2) an oscillating shear strain generator with a DC motor and a crank mechanism, (3) a stress measurement device using an electromagnetic torque sensor. This instrument could measure a maximum torque of 2Ncm, and the switch of the light-curing unit was synchronized with the rheometer.

Six commercial composite resins [Z-100 (Z1), Z-250 (Z2), Z-350 (Z3), DenFil (DF), Tetric Ceram (TC), and Clearfil AP-X (CF)] were investigated. A dynamic oscillating shear test was undertaken with the rheometer. A certain volume (14.2 mm³) of composite was loaded between the parallel plates, which were made of glass rods (3 mm in diameter). An oscillating shear strain with a frequency of 6 Hz and amplitude of 0.00579 rad was applied to the specimen and the resultant stress was measured. Data acquisition started simultaneously with light curing, and the changes in visco-elasticity of composites were recorded for 10 seconds. The measurements were repeated 5 times for each composite at 25±0.5℃. Complex shear modulus G^*, storage shear modulus G', loss shear modulus G" were calculated from the measured strain-stress curves. Time to reach the complex modulus G^* of 10 MPa was determined. The G^* and time to reach the G^* of 10 MPa of composites were analyzed with One-way ANOVA and Tukey's test (α= 0.05).

The results were as follows.

1. The custom made rheometer in this study reliably measured the initial visco-elastic modulus changes of composites during 10 seconds of light curing.

2. In all composites, the development of complex shear modulus G^* had a latent period for 1~2 seconds immediately after the start of light curing, and then increased rapidly during 10 seconds.

3. In all composites, the storage shear modulus G' increased steeper than the loss shear modulus G" during 10 seconds of light curing.

4. The complex shear modulus of Z1 was the highest, followed by CF, Z2, Z3, TC and DF the lowest.

5. Z1 was the fastest and DF was the slowest in the time to reach the complex shear modulus of 10 MPa.

Keywords: Light cured composites, Visco-elastic modulus, Rheometer, Dynamic oscillating shear test, Complex shear modulus

Figures and Tables

Figure 1

Configuration of the custom made rheometer.

Figure 2

Circuit diagram of the instrument.

Figure 3

The relationship among shear strain γ(t), stress τ(t), and phase angle δ in a dynamic oscillatory test.

Figure 4

The relationship among storage (real) modulus G', loss (imaginary) modulus G", and phase angle δ in a complex plane.

Figure 5

Parallel plate geometry.

Figure 6

Representative strain-stress curves of composites during light curing as a function of time.

a. Z-100. b. Z-250. c. Z-350. d. DenFil. e. Tetric Ceram. f. Clearfil.

Figure 7

Complex modulus (G^*) of composites as a function of time.

Figure 8

Storage modulus (G') as a function of time.

Figure 9

Loss modulus (G") as a function of time.

Figure 10

Time to reach the complex modulus of 10 MPa.

Table 1

Composite resins used in this study.

Table 2

Time to reach G^* of 10 MPa, G^* and Loss tangent of composites at 2 s and 10 s.

^*Same superscripts in the column means no statistical significant difference.

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