Studies in the setting of polyelectrolyte materials

The setting behaviour and compressive strengths of zinc polycarboxylate and glass polyalkenoate dental cements activated with sodium chloride solutions of different concentrations and also with artificial saliva have been studied. The results show that the effect of sodium chloride in these cements is concentration dependent. Saturated brine so increased the speed of set of the zinc polycarboxylate that the cement became impossible to mix. Conversely, while having little effect on the speed of setting of the glass polyalkenoate, saturated brine caused the compressive strength to fall to 18 MPa (from 85 MPa with pure water). Neither of the low-concentration solutions (i.e. 0.154 m NaCl or artificial saliva) showed any significant effects on the strength of either cement but both were found to speed up the rate of the setting reaction slightly and to sharpen the set. This effect was too slight to be a source of serious practical concern when these materials are used in clinical dentistry.