Aim: This study aimed to evaluate and compare the microleakage of a calcium silicate–based material (Biodentine) with glass ionomer cement (GIC) and composite resin in standardized coronal dentin cavities in-vitro. Materials and methods: Sixty extracted human third molars were used. Standardized dentin cavities (4×2×2 mm) were prepared and randomly assigned to three groups (n=20 of each): Biodentine, GIC (Fuji IX), and composite resin (Clearfil SE Bond + Filtek Z250). Following restoration, all specimens were stored in distilled water for 24 hours and subjected to 3000 thermal cycles. Microleakage was assessed after 0.5% basic fuchsin dye penetration and scoring under a stereomicroscope. Data were analyzed using Kruskal–Wallis and Bonferroni post hoc tests (p