Glass-ionomer dental cements as novel solid-state buffers

This study examined the possible buffering effect of acid-base glass-ionomer cements. Commercial capsulated materials were used, namely: Riva Self Cure, Ketac Molar, Equia Forte and Chemfil Rock. Cements were prepared by vibratory mixing then cylinders (4 mm diameter, 6 mm height) prepared from them using metal moulds. They were cured in the moulds at 37 °C for one hour, then placed in 8 ml deionised water at 22 °C and stored for 24 h or 4 weeks. Then they were crushed to powders with a pestle and mortar. Ten samples per powder (0.05 g) were placed in individual 10 ml volumes of deionised water. For two sets of ten (24 h or 4 weeks old), 1.0 ml of 0.01 M HCl was added, equilibrated and the pH measured by calibrated electrode. For another two sets of ten (24 h or 4 weeks old), 1.0 ml of 0.01 M NaOH was added, equilibrated, and the pH measured. The pH of a control set of solutions (no cement powder) was also measured. Data were tested using 1-way ANOVA and Tukey HSD test. The original acid solution pH was 3.2, which rose to 4.4–5.5 depending on brand and age of cement. The original alkali solution pH was 11.3, which fell to 6.7–8.3 depending on the details of the cement. Differences from initial pH had Tukey HSD p values of 0.001 in all cases. It was concluded that acid-base glass-ionomers can act as solid-state buffers, a finding attributed to the carboxylic acid/carboxylate conjugate pairs within them.