Chemical durability of Dicor and lithia-based glass-ceramics

Objectives. The aim of this study was to analyze the effect of a nucleation agent (P2O5) and a colorant/nucleation agent (AgNO3) on the chemical durability of Li2Osingle bondAl2O3single bondCaOsingle bondSiO2 (LACS) glass-ceramics in 4% HAc solution, deionized-distilled water, and in pH buffer solutions of pH 1, pH 9, and pH 11. Methods. Glass powder [27.8 mol% Li2O, 2.5% Al2O3, 5.9% CaO, and 63.8% SiO2 (LACS)] was melted, poured into a cylindrical graphite mold (16 mm diameter), cooled, cut into 2.2 mm thick disks, polished through 1200 grit SiC, nucleated at 510°C for 3 h, and crystallized at 650°C for 6 h. Dynamic corrosion tests of LACS glass-ceramic, LACS glass-ceramic containing 1.0 mol% P2O5 (LACSP), LACS glass-ceramic containing 0.78 mmol% AgNO3 (LACSAg), and Dicor control specimens were performed in a shaker-bath unit at 80°C at a shaker speed of 30 cycles/min for periods of up to 15 d. Differences in mean weight loss and ionic concentration were analyzed for statistical significance (p = 0.05) using ANOVA and the Turkeyʹs Studentized Range Test. Results. The mean weight loss over 15 d in 4% HAc increased in the following order: LACS (0.21 ± 0.02 mg/cm2), LACSAg (0.25 ± 0.05 mg/cm2), and Dicor (0.27 ± 0.05 mg/cm2). The differences in mean values were not statistically significant (p > 0.05). The amounts of Li+ leached in 32 mL of pH1 and pH11 buffer solutions were 3.1 ± 0.3μg/cm2/mL and 243 ± 49.0 μg/cm2/mL, respectively, for the LACS group, and 3.0 ± 0.6 μg/cm2/mL and 166 ± 28.0 μg/cm2/mL for the LACSAg group. The differences in mean values are not statistically significant (p > 0.05). The high chemical durability in acidic environments of LACS glass-ceramics without P2O5 and their decreased durability at pH values of 9 and above were confirmed by SEM observations of the exposed surfaces. Significance. The weight loss for the three glass-ceramic systems was highest in pH 11 buffer solution, which represents an unlikely in vivo environment. From a toxicological viewpoint, the maximum amount of Li+ released from 28 fully dissolved crowns of LACS glass-ceramic at a temperature of 80°C (which is greater than any temperature experienced in the oral cavity) is approximately 1.2 mg; this amount appears to be below the daily limit of 2 mg allowable from food sources.