Studies on the setting of polyelectrolyte cements: part VI. The effect of halide salts on the mechanical properties and water balance of zinc polycarboxylate and glass-ionomer dental cements.

A study is reported in which a zinc polycarboxylate and a glass polyalkenoate dental cement, respectively, were prepared from aqueous solutions of NaCl, KCl, KBr and KI, all at 1 mol dm3 concentration, as well as from pure water. For the zinc polycarboxylate, setting as determined by oscillating rheometry was speeded up and water uptake was enhanced by the presence of the salts. Conversely, compressive strength at 24 h was unaffected. On the other hand, for the glass polyalkenoate, the setting reaction was slowed down, water uptake inhibited and compressive strength at 24 h reduced (from 94.3 MPa with pure water to 59.8 MPa with NaCl, 65.8 MPa for KCl, 67.0 MPa for KBr and 81.1 MPa for KI). Previous work with polyelectrolytes in aqueous solution suggests that the halides probably enhance the rate of the neutralization process. For the zinc polycarboxylate, this leads to a more rapid setting reaction. By contrast, for the glass polyalkenoate, it results in slower setting and weaker cements. This result is attributed to inhibition of the secondary setting reaction, involving the formation of the silicate/phosphate network, by enhanced neutralization, a process which is consequently concluded to occur earlier in the overall setting of these cements than had been assumed previously. Copyright 1998 Chapman & Hall