This study was designed to evaluate and compare the two-year clinical performance of three universal adhesives in posterior composite restorations, based on International dental federation (FDI) criteria.

The description of the experimental design will follow the Consolidated Standards of Reporting Trials (CONSORT) statement. The present study will be a double blinded (patients and examiner) randomized clinical trial anticipating the split-mouth design. 30 adult patients seeking dental treatment in Operative Department clinic at Faculty of Dentistry, Mansoura University will be enrolled in the current study with a total of 90 teeth with Class I or II posterior composite restorations.

No advertisement will be made for participant recruitment, forming a sample of convenience. Each patient will sign a consent form before participating in the current study. The study will be conducted from November 2022 to November 2024 as a part of Doctoral dissertation. Mansoura University institution's ethics committee approved the form and protocol before conducting the study. The sample size was calculated based on a previous study with a similar study design. Parameters including a significance level of 5% (p < 0.05) and a power of 80% were used to calculate an appropriate sample size of 28 cases. Allowing for a 20% drop-out rate, the total sample size was set at 30 cases.

Inclusion Criteria:

• Patients will have at least 3 posterior teeth with carious lesions of ICDAS score 4, or 5.
• The teeth will have to be vital, without spontaneous pain and/or mobility.
• Patients must have a good oral hygiene.
• Patients with normal and full occlusion.

Exclusion Criteria:

• High caries risk patients with extremely poor oral hygiene.
• Patients with abutments.
• Patients with heavy bruxism habits and clenching.

Data will be available within 6 Months for 2 years