Strengthening effect of aluminum fluoride added to resin composites based on polyacid-containing polymer

Objectives. The study investigates the possible strengthening effect of aluminum ions liberated during long-time water storage of experimental resin composites containing a polymer with carboxylic acid groups. Methods. The organic part of the resin composites was formed by photopolymerization of methacrylate monomers. The monomer mixture was composed of UEDMA, HEMA or TEGDMA, and 0–40 mol% HEMAN (the adduct of HEMA and maleic anhydride). The filler part of the resin composites consisted of a conventional silanated glass filler and 1 or 5 wt% of AlF3·3H2O. The rupture strength and bending modulus were measured without water storage and after 1 month, 1 year, and 3 years of water storage at 37 °C of the resin composite. Results. The experimental composites that had been stored in water had lower rupture strength and modulus than the composites that were tested without water storage. Specimens containing 30 or 40 mol% HEMAN increased in strength, and specimens containing 20, 30, or 40 mol% HEMAN increased in modulus during the period of water storage. Depending on composition, values for strength and modulus obtained after 3 years of water storage was up to 50% higher than the values obtained after 1 month. Significance. The strengthening effect of aluminum fluoride may be interpreted as the result of increased crosslinking by aluminum ions and carboxylate groups. The results may serve as a basis for the improvement of the mechanical properties of polyacid-modified resin composites.