The Effect of Thermocycling on the Microhardness of Contemporary Glass Ionomer-Based Restorative Materials: An In Vitro Study

Glass ionomer-based restorative materials are widely used in pediatric dentistry because of their chemical adhesion to tooth structure, ion-releasing capacity, and clinical handling advantages; however, their mechanical durability under simulated oral aging conditions remains a critical factor influencing long-term clinical performance. This in vitro study aimed to evaluate and compare the surface microhardness of three contemporary glass ionomer-based restorative materials-Beautifil Bulk Restorative, EQUIA Forte HT, and Fuji II LC-before and after thermocycling. A total of 90 disc-shaped specimens (10 mm in diameter and 2 mm in thickness) were prepared, with 30 samples allocated to each material group. Microhardness measurements were performed using the Vickers hardness test at baseline and after 10,000 thermocycling cycles between 5 °C and 55 °C to simulate intraoral aging. Results were expressed as the mean ± standard deviation, and statistical analyses were conducted using non-parametric tests. Thermocycling resulted in a statistically significant reduction in microhardness values for all tested materials (<i>p</i> < 0.05). Beautifil Bulk Restorative exhibited the highest microhardness values both before and after thermocycling, followed by Fuji II LC and EQUIA Forte HT, with significant differences observed among all groups (<i>p</i> < 0.001). Within the limitations of this study, Beautifil Bulk Restorative may be considered a favorable option for restorations in young permanent teeth, whereas EQUIA Forte HT, exhibiting lower microhardness values, may be more suitable for primary teeth, where physiological wear is expected.