STUDIES IN THE SETTING OF POLYELECTROLYTE MATERIALS .4. THE EFFECT OFSODIUM-CHLORIDE AND ARTIFICIAL SALIVA ON THE SETTING AND COMPRESSIVE STRENGTH OF GLASS-POLYALKENOATE AND ZINC POLYCARBOXYLATE DENTAL CEMENTS

The setting behaviour and compressive strengths of zinc polycarboxylat e and glass polyalkenoate dental cements activated with sodium chlorid e solutions of different concentrations and also with artificial saliv a have been studied. The results show that the effect of sodium chlori de in these cements is concentration dependent. Saturated brine so inc reased the speed of set of the zinc polycarboxylate that the cement be came impossible to mix. Conversely, while having little effect on the speed of setting of the glass polyalkenoate, saturated brine caused th e 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 art ificial saliva) showed any significant effects on the strength of eith er cement but both were found to speed up the rate of the setting reac tion slightly and to sharpen the set. This effect was too slight to be a source of serious practical concern when these materials are used i n clinical dentistry.