Setting shrinkage strains of chemical-cured glass ionomer-based dental restorative materials
Shrinkage strains are exhibited by the current formulations of chemical-cured dental restorative systems. In resin-modified glass ionomer systems, these have been linked to filler contents, types and quantity of monomer. Post-gelation rigid contraction that follows onset of cure leading to marginal defects is a clinically significant factor, although flow is noted to compensate for shrinkage effects during pre-gelation phase. The bonded-disk technique was employed to study the shrinkage strains of chemical-cured and light-activated glass polyalkenoate-based cements at two clinical temperatures of 37EC and 60EC over a period of 2 hours. Magnitudes of shrinkage strains obtained were subjected to one-way ANOVA and Schefe's 0.5 significant level statistical analysis. The time-dependent shrinkage strain data characteristic of the materials indicated a linear initial rigid and rapid contraction, which is appropriately represented by the Kohlrausch-Williams-Watts stretched exponential decay curve. The kinetics of shrinkage was expressed by the overall time constant and the initial contraction strains at 30 s, following the onset of cure. Data obtained after 15 minutes up to 2 hours indicated high contraction strains at 60EC compared to that at the intra-oral temperature, 37EC. There is a relatively slow development of contraction strains in glass ionomer-based systems compared to resin-based ones. This is, however, a positive quality for the glassy materials in their use as marginal seals. Nevertheless, contraction strains in dental restorative systems with their destructive shrinkage stresses remain unresolved.
JOURNAL OF THE GHANA SCIENCE ASSOCIATION Volume 2 No. 3 (2000) pp. 103-112