Tehran University of Medical Sciences Frontiers in Dentistry 2676-296X 16 3 2019 05 29 173 180 EN Masoud Fallahinejad Ghajari Dental Research Center, Research Institute of Dental Sciences, Department of Pediatric Dentistry, School of Dentistry, Shahid Beheshti University of Medical Sciences, Tehran, Iran Amir Ghasemi Restorative Department, School of Dentistry, Shahid Beheshti University of Medical Sciences, Tehran, Iran Mohammadreza Badiee Dentofacial Deformities Research Center, Research Institute of Dental Sciences, School of Dentistry, Shahid Beheshti University of Medical Sciences, Tehran, Iran Zahra Abdolazimi Department of Pediatric Dentistry, School of Dentistry, Semnan University of Medical Sciences, Semnan, Iran Alireza Akbarzadeh Baghban Proteomics Research Center, Department of Basic Sciences, School of Rehabilitation, Shahid Beheshti University of Medical Sciences, Tehran, Iran 2018 07 16 2018 10 26 Objectives: This study aimed to assess the microshear bond strength (MSBS) of Scotchbond Universal adhesive, used in self-etch and etch-and-rinse modes, to primary and permanent dentin at 24 hours and six months. Materials and Methods: A total of 88 composite micro-cylinders were divided into eight groups (n=11) as follows: (A) Etch-and-rinse, 24 hours, primary dentin; (B) Self-etch, 24 hours, primary dentin; (C) Etch-and-rinse, six months, primary dentin; (D) Self-etch, six months, primary dentin; (E) Etch-and-rinse, 24 hours, permanent dentin; (F) Self-etch, 24 hours, permanent dentin; (G) Etch-and-rinse, six months, permanent dentin; (H) Self-etch, six months, permanent dentin. The MSBS was measured by a testing machine at a crosshead speed of 0.5 mm/minute. Data were analyzed using three-way analysis of variance (ANOVA). Results: The mean MSBS was 12.3±2.3 MPa in A, 18.8±4.1 MPa in B, 11.9±3.7 MPa in C, 16±2.9 MPa in D, 19.1±2.7 MPa in E, 22.8±4.1 MPa in F, 16.2±2.6 MPa in G, and 17.2±4.4 MPa in H. In the self-etch mode, the MSBS was significantly higher than that in the etch-and-rinse mode (P<0.001). The MSBS in permanent teeth was significantly higher than primary teeth (P<0.001). At six months, the MSBS significantly decreased in all groups (P<0.001). Conclusion: The micro-shear bond strength of Scotchbond Universal adhesive decreases over time and depends on the type of tooth and the mode of application of the adhesive. https://fid.tums.ac.ir/index.php/fid/article/view/2722 https://fid.tums.ac.ir/index.php/fid/article/download/2722/1755