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 degrees C for one hour, then placed in 8 ml deionised water at 22 degrees 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 solidstate buffers, a finding attributed to the carboxylic acid/carboxylate conjugate pairs within them. (C) 2021 The Authors. Published by Elsevier B.V.