Hamadan University of Medical Sciences Avicenna Journal of Dental Research 2423-7582 15 3 2023 09 30 Comparison of Repair Bond Strength of Bulk-fill and Conventional Composites With Different Bonding Systems 97 102 10.34172/ajdr.1611 EN Hafez Vahedpour https://orcid.org/0000-0002-2027-5138 Hamid Tavakkoli https://orcid.org/0000-0002-4591-9817 Zohreh Mousavi https://orcid.org/0000-0002-4866-2738 Journal Article 10.34172/ajdr.1611 2022 04 25 2022 11 26 Background: One of the advantages of resin composites as a restorative material is their repairability. The purpose of the current study was to compare the repair bond strength of conventional and bulk-fill composites with different bonding systems. Methods: In this in vitro study, sixty cylindrical specimens of materials were prepared according to the six groups under study (two types of conventional Gradia Direct and N-Ceram Bulk-Fill Tetric composites and three bonding systems: Single Bond Universal and Clearfil SE Bond and Single Bond 2). The samples were divided into 6 groups of 10 Single Bond/Gradia Direct composite (G1), Single Bond/Tetric N-Ceram bulk-fill composite (G2), Clearfil SE bond/Gradia Direct (G3), Clearfil SE Bond/Tetric N-Ceram bulk-fill composite (G4), single bond universal/Gradia Direct composite (G5), and Single Bond Universal/Tetric N-Ceram bulk-fill composite (G6). Repair bond strength in each group was measured using the Universal Testing Machine (Hounsfield). All data were analyzed by SPSS 21 using ANOVA, Student’s t-test, and chi-square statistical tests (P<0.05). Results: The highest and lowest bond strength (15.81±2.44 and 14.02±1.57, respectively) belonged to the Clearfil SE Bond-Tetric N-Ceram and Single Bond (Etch & Rinse)-Gradia Direct groups, respectively. The ANOVA test results demonstrated no significant difference in the bonding strengths of the study groups (P=0.537). Conclusions: Bulk-fill composite Tetric N-Ceram, apart from the bonding system, had higher repair bond strength compared to the conventional Gradia Direct composite. It seems that self-etch bonding systems (Clearfil SE Bond and Single Bond Universal) have had more bond strength than etch and rinse bonding (Single Bond 2 bonds).