This study (a double-blinded, prospective, randomized clinical trial) aimed to evaluate 2-year clinical performance of dual- and light-cure bulk-fill resin composites in Class ӀӀ restorations.

The null hypothesis tested in this study was that, there would be no difference in the 2-year clinical performance of all tested bulk-fill resin composites in Class II restorations.

Forty patients were enrolled in the study. Each patient received three bulk-fill resin composites Class ӀӀ restorations. One dual-cure and two light-cure bulk-fill resin composites were used for Class ӀӀ restorations following manufacturer's instructions. A universal adhesive was used with all restorations. All restorations were clinically evaluated after 1 week (baseline), 6 months, 12 months, 18 months and finally after 24 months using the FDI World Dental Federation criteria.

Inclusion Criteria:

• each participant should have at least three permanent molars and premolars that need to be treated with Class II restorations due to primary carious lesions.
• all participants required to have a full and normal occlusion and to maintain adequate oral hygiene.

Exclusion Criteria:

General exclusion criteria:

• heavy bruxism.
• poor oral hygiene.
• chronic or severe periodontitis.
• a history of allergies to any of the materials utilized in this study.
• pregnant or nursing females.

Specific exclusion criteria:

• fractured or visibly cracked teeth.
• rampant caries.
• faulty restoration opposite or adjacent to the tooth to be restored.
• atypical extrinsic staining.

Except the investigator, the participants and the two clinical examiners were blinded to the type of bulk-fill resin composite applied in each tooth (a double-blinded clinical trial).