Tehran University of Medical Sciences Frontiers in Dentistry 2676-296X 16 5 2020 01 13 342 350 EN Hosseinali Mahgoli Dental Research Center, Dentistry Research Institute, Tehran University of Medical Sciences, Tehran, Iran Mahnaz Arshad Dental Research Center, Dentistry Research Institute, Tehran University of Medical Sciences, Tehran, Iran kamran Rasouli Department of Prosthodontics, School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran Ali Akbar Sobati Department of Prosthodontics, School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran Ahmad Reza Shamshiri Research Center for Caries Prevention, Dental Research Institute, Tehran University of Medical Sciences, Tehran, Iran 2018 11 07 2019 06 10 Objectives: This study aimed to assess the effect of application of two types of zirconia primers on repair bond strength of composite to zirconia ceramic. Materials and Methods: In this in vitro, experimental study, 60 zirconia blocks were divided into five groups and subjected to the application of Z-Prime Plus (ZPP), Monobond Plus (MBP), Porcelain Bonding Resin (PBR), ZPP followed by PBR (ZPP+PBR) and MBP followed by PBR (MBP+PBR). They were then bonded to Z100 composite. The samples were then immersed in water at 37°C for 24 hours, thermocycled for 1000 cycles between 5-55°C and subjected to shear bond strength (SBS) test. The mode of failure was determined under a stereomicroscope and a scanning electron microscope (SEM). Results: The mean bond strength was the highest in ZPP+PBR group followed by MBP+PBR, ZPP, PBR and MBP group (22.29±8.86, 15.75±2.81, 12.02±3.24, 3.60±2.92 and 2.92±1.78 MPa, respectively). The effects of type of zirconia primer and use/no use of PBR on SBS were significant (P<0.05). The frequency of adhesive failure in MBP and PBR groups was significantly higher than that in MBP+PBR and ZPP+PBR groups (P<0.05). The cohesive failure was significantly more frequent in ZPP+PBR group than in ZPP, MBP and PBR groups (P<0.05). Conclusion: Simultaneous application of zirconia primer and PBR is the most efficient technique for repair of all-ceramic zirconia restorations with composite resin. https://fid.tums.ac.ir/index.php/fid/article/view/2920 https://fid.tums.ac.ir/index.php/fid/article/download/2920/1781