The effect of viscosity, specimen geometry and adhesion on the linear polymerization shrinkage measurement of light cured composites / 대한치과보존학회지

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.