This study is conducted to assess the clinical effectiveness of 10% Dimethyl Sulfoxide in OT Primer prior to two step etch and rinse dental adhesive on the durability of composite restoration.

Randomized Controlled Clinical Trial After the power analysis calculation, 74 cervical lesions will be included in this study. Half of them will be pretreated with 10% DMSO/H2O (Dimethyl Sulfoxide/Water, OT Primer, OT Dent). Control groups will be bonded with SB (Single Bond2, 3M ESPE). Cavities will be restored with nanohybrid composite restoration (Z350 XT, 3M ESPE) under rubber dam isolation. Follow-ups will be performed by double-blinded evaluators at baseline and after 6m, 12m, 24m, and 36m using the FDI criteria. Photographic documentation will be performed for all restorations.

Sample size calculation The sample size was calculated based on a previous study by Vural et al in 2020, in which success rate of resin composite cervical restorations was 73% after 36 months. By implementing a two tailed Z test for difference between two independent proportions with an alpha level of 5% and a power of 80%. The minimum sample size needed was 30 per group in order to detect a difference of 25%. Sample size was increased by 25% to compensate for possible dropouts to reach 37 teeth per group. Sample size was performed using G*Power version 3.1.9.2 for windows.

Statistical Analyses Data was analyzed using Medcalc software, version 22 for windows (MedCalc Software Ltd, Ostend, Belgium). Categorical data was described as frequency and percentage, intergroup comparisons between interventions was performed using Chi-Square test with statistical significance level set at (P ≤ 0.05), intragroup comparison within each intervention was performed using the Cochran's Q test with statistical significance level set at (P ≤ 0.0083) after Bonferroni correction. Relative risk was used to assess the clinical significance. Survival rate was analyzed using Kaplan-meier and Log-rank test. The confidence limit was set at 95% with 80% power and all tests were two tailed.

Inclusion Criteria:

• Patients with Carious Cervical Lesions (CCL).
• Co-operative patients approved to participate in the study.
• Pulp is asymptomatic vital teeth.
• Presence of favorable occlusion and teeth are in normal contact with the adjacent teeth.

Exclusion Criteria:

• Patients with Non-Carious Cervical Lesions (NCCL).
• Xerostomia
• Bruxism and visible wear facets in the posterior dentition.
• Known inability to return for recall appointments.
• Fractured or visibly cracked candidate tooth.
• Current desensitizing therapy, including desensitizing dentifrices or other over-the-counter (OTC) products.
• Long-term use of anti-inflammatory, analgesic, or psychotropic drugs.
• Pregnancy or breast-feeding (potential conflicts with recall dates.
• Allergies to ingredients of resin-based restorative materials.
• Orthodontic appliance treatment within the previous three months.
• Abutment teeth for fixed or removable prostheses.
• Teeth or supporting structures with any symptomatic pathology.
• Existing periodontal disease or periodontal surgery within the previous three months.

In our clinical trial, double blinding will be performed, the participants and assessors will be blinded to the type of material used to reduce performance and ascertainment bias and also reduce biased estimates of treatment effects. The operator cannot be blinded in this trial because of the difference in the application procedures of each restorative material. Therefore, the operator (O.I.) will take care to treat the two allocation groups as equally as possible by standardizing the care of participants, frequency of follow-ups and management of complications.