Effects of immediate and delayed light curing and polishing on the mechanical properties of resin-modified glass ionomer cements

Background: Resin-modified glass ionomer cements (RMGICs) are among the most widely used restorative materials in dentistry. Identifying the factors that influence their mechanical properties is essential for optimizing their clinical performance. However, the combined effects of immediate and delayed light curing and polishing on the mechanical properties and surface roughness of RMGICs have not been thoroughly investigated. Materials and Methods: This was an in vitro experimental study. Twenty-four disc-shaped specimens were prepared from two RMGICs: GC Fuji II LC and SDI RIVA Light Cure. Half of the specimens were light-cured immediately after placement, whereas the remaining specimens were light-cured after a 4-min delay. Each light-curing group was further divided into two subgroups according to the polishing protocol: immediate polishing and delayed polishing (after 24 h). Nano-indentation testing was performed to determine hardness, elastic modulus, and creep. Surface roughness was evaluated using atomic force microscopy (AFM). Data were analyzed using the independent-samples t -test, one-way analysis of variance (ANOVA), Tukey’s post hoc test, and three-way ANOVA. The level of statistical significance was set at P < 0.05. Results: Immediate light curing resulted in significantly higher hardness and elastic modulus than delayed light curing, whereas no significant difference was observed in cree P values. Immediate polishing produced a significantly higher elastic modulus than delayed polishing, while hardness and creep were not significantly affected by polishing time. GC Fuji II LC exhibited significantly higher hardness (0.96 ± 0.41 GPa) and lower creep (9.52% ±3.05%) than SDI RIVA Light Cure (0.74 ± 0.27 GPa and 13.73% ±3.33%, respectively). Surface roughness was not significantly influenced by the material type, light-curing protocol, or polishing protocol. Conclusion: Immediate light curing significantly improved the mechanical properties of the tested RMGICs, whereas immediate polishing did not adversely affect their performance. Therefore, performing both procedures immediately may reduce clinical chairside time without compromising the materials’ mechanical properties.