This prospective split-mouth clinical study aims to compare the clinical performance of a bioactive bulk-fill composite with a conventional microhybrid composite in Class II posterior restorations. In each participant, two comparable Class II cavities will be treated using different restorative approaches. In the experimental condition, a bioactive bulk-fill composite (Activa BioACTIVE Bulk Flow) will be placed at the gingival base and covered with a microhybrid composite (Filtek Z250). In the control condition, restorations will be completed entirely with the microhybrid composite (Filtek Z250).

Clinical performance will be evaluated according to FDI World Dental Federation criteria at baseline, 6 months, and 12 months. Primary outcomes include marginal adaptation, retention, and overall clinical success of the restorations. Secondary outcomes include surface properties and marginal staining.

The split-mouth design allows direct intra-individual comparison, thereby minimizing inter-individual variability and increasing the reliability of the findings. The results of this study are expected to provide evidence on the effectiveness of bioactive bulk-fill composites in improving the clinical performance of posterior restorations.

Inclusion Criteria:

• Adults aged between 18 and 50 years
• Patients requiring at least two comparable Class II restorations in posterior teeth
• Good general and oral health
• Ability to provide informed consent

Exclusion Criteria:

• Patients with systemic diseases affecting oral health
• Pregnant or lactating women
• Poor oral hygiene or high caries risk
• Teeth with pulp involvement or periapical pathology
• History of allergy to dental materials used in the study