Marginal gap formation of light-activated restorative materials: effects of immediate setting shrinkage and bond...

The purpose of this study was to explore multiple correlations between shrinkage, bonding and marginal gap parameters, immediately after light-activation, for three classes of restorative materials. The correlations of interest were between: (a) their marginal gap formation in tooth cavities, (b) their free setting shrinkage-strain determined by two different measurement methods ((i) the marginal gap-width in a non-bonding Teflon cavity and (ii) a linear (diametral) measure of shrinkage-strain), and (c) their shear bond strengths to enamel and to dentin.

The maximum marginal gap width and the opposing width (if any) in the tooth cavity were measured immediately (3 min) after light-activation. Two factors for the setting shrinkage-strain and the shear bond strength to enamel and to dentin were measured concomitantly.

Out of the set of restorative materials investigated, those that produced a smaller marginal gap in the tooth cavity had a smaller marginal gap in the Teflon cavity. There was a highly significant correlation between the two parameters (r=0.914, p<0.001). However, no relationship was observed between the marginal gap in the tooth cavity and the immediate diametral shrinkage-strain (p>0.05). Thus the restorative materials that produced a smaller marginal gap in the tooth cavity did not generally have a smaller diametral setting shrinkage-strain. Furthermore, no relationship was observed between the marginal gap in the tooth cavity and the shear bond strength to enamel or to dentin (p>0.50).

For light-activated restorative materials during the early stage of setting (<5 min), the free shrinkage-strain, measured by marginal-gaps in Teflon cavities, had a greater correlation with immediate marginal-gaps in tooth cavities than either the immediate diametral shrinkage-strain or the bond strengths to the tooth structure.