Studies in the setting of polyelectrolyte cements

Abstract

Specimens of zinc polycarboxylate dental cement have been prepared from aqueous solutions of citric, lactic and ( +)-tartaric acid respectively, and the effect of these acids on the setting characteristics and compressive strength determined. All three acids are stronger than poly(acrylic acid) yet, at 20% concentration, gave variable results in terms of their effect on setting: (+)-tartaric acid shortened the working time by comparison with pure water, whereas both citric and lactic acids extended it, all three extended the setting time. In all three cases, the setting profile was less sharp than with pure water, as quantified by the ratio of setting to working times. Similar results were obtained for ( + )-tartaric acid at 10 and 15% concentrations, but at 5%, the working time was marginally longer than for pure water. Compressive strength at 24 h was determined for all three acids at 20% concentration, and found to be unaffected by the changes in setting chemistry, all being of the order of 90-95 MPa (i.e. the same as for pure water). The slight differences between the strengths for the different sets of cements were not statistically significant.