Multiple correlations of material parameters of light-cured dental composites

Abstract 

Objectives

The aim of this study was to explore the correlations between the Knoop hardness, Young's modulus, viscosity, and polymerization shrinkage of an experimental dental composite, in order to determine the temporal variations of the material properties during the polymerization process.

Methods

The digital image correlation method was employed to measure the polymerization shrinkage along the curing depth of bar-shape specimens (cross-section 4mm×2mm and length 10mm) of an experimental composite RZE045. The shrinkage data were correlated with the Knoop microhardness measured on specimens prepared in consistent conditions. Another series of tests were performed on cuboid composite samples (cross-section 4mm×4mm and height 5mm) with different degrees of conversions to determine the correlations among microhardness, Young's modulus and viscosity. Further correlations between shrinkage, Young's modulus and viscosity were then derived, from which the temporal variations of the mechanical parameters during curing were estimated.

Results

Along the curing depth, the Knoop microhardness of the experimental composite RZE045 decreased more rapidly than its volumetric shrinkage. A power function was employed to describe their relation. On the other hand, Knoop microhardness was found to be proportional to Young's modulus and viscosity. These linear correlations also seemed to be applicable to other materials including unfilled resins, silica glass and other dental composites.

Significance

Correlations between material parameters of dental composites allowed the rapid temporal variations of Young's modulus and viscosity during curing to be estimated based on the measured polymerization shrinkage-strain history.

Keywords: Dental composite, Material parameters, Correlation, Degree of conversion