A rheological study of the role of additives on the setting of glass-ionomer cements.

The effects of various additives on the setting of the glass-ionomer cement system was studied by means of cone and plate viscometry. The action of (+)-tartaric acid, the most important additive, on the setting reaction depended on its concentration. Low concentrations accelerated the development of viscosity of the cement paste, while high concentrations retarded it. At intermediate concentrations, (+)-tartaric acid had an interesting, uniquely favorable effect on setting characteristics. First, it induced a lag period in the setting process during which the viscosity of the cement paste remained constant. This lag period was followed by a sharp, almost exponential, increase in viscosity. Thus, (+)-tartaric acid was found to have a dual effect on setting, first inhibiting gelation and then accelerating it. The practical effect is to prolong working time and sharpen setting. No other hydroxyacid, not even meso-tartaric acid, combined these advantageous effects. Meso-tartaric acid, for example, repressed the development of viscosity at all stages of the reaction. Other hydroxyacids either accelerated or retarded the development of viscosity throughout the course of the reaction.