Published online Nov 30, 2003.
https://doi.org/10.5395/JKACD.2003.28.6.457
The effect of viscosity, specimen geometry and adhesion on the linear polymerization shrinkage measurement of light cured composites
Abstract
Objectives
The aim of study was to investigate the effect of flow, specimen geometry and adhesion on the measurement of linear polymerization shrinkage of light cured composite resins using linear shrinkage measuring device.
Methods
Four commercially available composites - an anterior posterior hybrid composite Z100, a posterior packable composite P60 and two flowable composites, Filtek flow and Tetric flow - were studied. The linear polymerization shrinkage of composites was determined using 'bonded disc method' and 'non-bonded' free shrinkage method at varying C-factor in the range of 1~8 by changing specimen geometry. These measured linear shrinkage values were compared with free volumetric shrinkage values.
The viscosity and flow of composites were determined and compared by measuring the dropping speed of metal rod under constant load.
Results
In non-bonded method, the linear shrinkage approximated one third of true volumetric shrinkage by isotropic contraction. However, in bonded disc method, as the bonded surface increased the linear shrinkage increased up to volumetric shrinkage value by anisotropic contraction. The linear shrinkage value increased with increasing C-factor and approximated true volumetric shrinkage and reached plateau at about C-factor 5~6. The more flow the composite was, reduced linear shrinkage was measured by compensation radial flow.
Fig. 1-a
The structure of instrument to measure linear shrinkage.
Fig. 1-b
The geometry of composite specimen sandwiched between two glass plates. Polymerization shrinkage creates axial (vertical) and radial (horizontal) contraction of the specimen.
Fig. 2
Linear polymerization shrinkage curves of composites as a function of time at C-factor ≈ 6.
Fig. 3
a) Linear shrinkage of Z1 as a function of C-factor. b) Linear shrinkage of P6 as a function of C-factor. c) Liner shrinkage of FF as a function of C-factor. d) Linear shrinkage of TF as a function of C-factor.
Linear polymerization shrinkage of composites measured using bonded disc method. The linear shrinkage value increased with increasing C-factor and approximated volumetric shrinkage and reached plateau at about C-factor 5~6.
Fig. 4
a) Linear shrinkage of Z1 as a function of specimen geometry. b) Linear shrinkage of P6 as a function of specimen geometry. c) Liner shrinkage of FF as a function of specimen geometry. d) Linear shrinkage of TF as a function of specimen geometry.
Linear polymerization shrinkage of composites measured using non-bonded disc method with Vaseline. The linear shrinkage is not affected by specimen diameter and is approximated the theoretical linear shrinkage value calculated from true volumetric shrinkage value.
Fig. 5
Peak time (peak shrinkage rate time) of Z1 as a function of C-factor.
Fig. 6
Relative viscosity of composites based on flow normalized to Z1.
Table 1
Materials used in this study
Table 2
Volumetric polymerization shrinkage and linear shrinkage of composite resins at varying C-factor
Table 3
Cure speed based on Peak Time (P.T.) of composites at varying C-factor
Table 4
Consistency (viscosity) based on the flow of composite resins
References
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