Alumino‐silicate polyacrylic acid and related cements

Abstract

Abstract The composition and setting reaction of cements formed from aluminosilicates and poly(acrylic acid), the ASPA cements, are described. Setting and hardening results from interactions between specially‐formulated, complex, fluorine‐containing calcium aluminosilicate glasses and aqueous solution of poly(acrylic acid) or similar poly(alkenyl carboxylic acids). Protons from the polyacid penetrate the surface of the glass decomposing the negatively charged aluminosilicate network to a siliceous hydrogel and releasing Al 3+ , Ca 2+ and F‐ ions. These ions migrate, probably as complexes, such as AlF 2+ , AlF 2+ and CaF + , into the polyelectrolyte phase where they cross‐link polyanionic chains, by ionic and possibly chelate binding, causing the cement to gel and set. Overall the reaction may be seen as one where flexible hydrogen bonds, in the liquid, are progressively replaced by more rigid ionic ones, leading to gelation. The set cement is a composite of glass particles sheathed by a silica gel bound by a metal poly anionic matrix. ASPA cements can attain a compressive strength of 200 N/mm 2 in 24 h and are adhesive under oral conditions to tooth materials. They find a number of applications in conservative and preventive dentistry. Certain naturally‐occurring aluminosilicate minerals react with poly(acrylic acid) to form cement but these are much weaker (not exceeding a compressive strength of 30 N/mm 2 ) and are weakened by water.