Objective <p>Understanding the sealing ability of restorative materials to prevent microleakage and its consequent complications—such as secondary caries, postoperative sensitivity, and restoration failure—is imperative in clinical dentistry. This study aims to compare the microleakage performance of four restorative materials—bioactive composite resin (Activa Pronto), alkasite restorative (Cention N), compomer (Dyract Flow), and glass ionomer cement (Type 2 GIC)—in Class V cavities of extracted premolar teeth.</p> Materials and methods <p>Forty non-carious, intact premolar teeth were selected and prepared with standardized Class V cavities. The teeth were randomly assigned to one of four groups (<i>n</i> = 10) and restored with the respective materials. The restorations underwent thermocycling, followed by microleakage testing using rhodamine dye. Confocal laser scanning microscopy (CLSM), a technique that provides superior depth resolution and three-dimensional visualization of microleakage, was used to assess dye penetration at the tooth-restoration interface. Microleakage was then scored using a standardized grading system.</p> Results <p>Significant differences in microleakage were observed among the groups (<i>χ</i>² = 45.69; <i>p</i> &lt; 0.001). Group 1 (bioactive composite resin) demonstrated the lowest microleakage, with predominantly Grade 0 and Grade 1 scores, while Group 4 (GIC) exhibited the highest microleakage, characterized mainly by Grade 3 scores. Bioactive composite resin exhibited significantly lower microleakage than alkasite, compomer, and GIC (<i>p</i> &lt; 0.05). No significant difference was observed between alkasite and compomer.</p> Conclusions <p>Bioactive composite resin (Activa Pronto) provided the most effective seal against microleakage, followed by alkasite and compomer, with glass ionomer cement showing the least effective sealing properties.</p>