Introduction and objective <p>The clinical longevity of composite restorations relies on strong, long-lasting adhesion to dental tissues, minimizing microleakage and its associated complications such as bacterial infiltration, secondary caries, and pulp inflammation. This in-vitro study aimed to compare the shear bond strength of a nano-hybrid composite to dentin using two different adhesive systems: universal adhesive (UA) and two-step etch-and-rinse adhesive (ERA).</p> Materials and methods <p>Forty extracted, caries-free upper premolar teeth were randomly divided into four groups with different adhesive treatments. group 1: ERA without thermocycling, group 2: ERA with thermocycling, group 3: UA without thermocycling and group 4: UA with thermocycling. The occlusal surface of teeth was prepared to achieve flat dentin surface. Then adhesive was applied and composite was adhered to the area. The shear bond strength (Mpa) at fracture point was measured using Zwick/Roell ZO20 instrument while failure modes were analyzed under a stereomicroscope at 40x magnification.</p> Results <p>A significant difference in shear bond strength was observed between the adhesive systems (<i>P</i> &lt; 0.05). No significant differences were found between thermocycle and non-thermocycle groups within each adhesive type. However, the UA demonstrated significantly higher bond strength compared to the ERA (<i>P</i> &lt; 0.05). Failure analysis revealed that all the ERA failures were adhesive, while UA showed fewer adhesive failures, particularly without thermocycling.</p> Conclusions <p>According to the findings of the present study, the Universal adhesive provides higher shear bond strength to the deep dentin of the tooth than Etch and Rinse adhesive. Thermocycling didn’t significantly affect any of the adhesives.</p>