Microhardness of N-Vinylpyrrolidone Modified Glass-Ionomer Cements

The water soluble N-vinylpyrrolidone (NVP) monomer was used to prepare poly(N-vinylpyrrolidone-co-itaconic acid-co-acrylic acid) glass-ionomer copolymers, using a free-radical polymerization process. NVP modified terpolymer was mixed with glass powders from four commercial glass ionomer systems. Microhardness from the set cement was measured and compared to several commercial glass-ionomer systems. The Knoop hardness number (KHN) values were recorded on polished specimens conditioned for 48 hours and 7 days. One-way analysis of variance and Tukey-Kramer tests were used to determine the significant differences among the materials tested in each group. Among the four commercial cements, Ketac-Molar (KM) showed the highest value and α-Silver (AS) snowed the lowest value in KHN. Fuji II (F2) and α-Fil (AF) showed much the same values in KHN. At the same P/L ratio, NVP modified glass-ionomers showed higher KHN values than the AS, similar to the AF and F2, and lower than the KM. The effect of P/L ratios was evident and highest KHN values for each group were basically presented by the one with a higher P/L ratio. Higher P/W ratio did not improve the KHN for the AS and KM group, but improved the F2 group.