Tehran University of Medical Sciences Frontiers in Dentistry 2676-296X 16 5 2020 01 13 369 378 Behrad Tanbakuchi Dental Research Center, Dentistry Research Institute, Tehran University of Medical Sciences, Tehran, Iran Tabassom Hooshmand Department of Dental Biomaterials, School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran Mohammad Javad Kharazifard Dental Research Center, Dentistry Research Institute, Tehran University of Medical Sciences, Tehran, Iran Kiana Shekofteh Department of Dental Biomaterials, School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran Arian Hesam Arefi Dental Research Center, Zahedan University of Medical Sciences, Zahedan, Iran 2019 05 27 2019 10 13 Objectives: This study aimed to assess the shear bond strength (SBS) of molar tubes to the enamel surface of molar teeth using a resin-modified glass ionomer (RMGI) cement modified with amorphous calcium phosphate (ACP). Materials and Methods: In this in-vitro study, 60 extracted human third molars were randomly divided into four groups for bonding of molar tubes to the enamel surface. Fuji Ortho LC and Fuji Ortho LC modified with ACP (1.55 wt%) were used in groups 1 and 2, respectively. In group 3, the enamel surface was sandblasted, and bonding was then performed using Fuji Ortho LC glass ionomer modified with ACP. In group 4, molar tubes were conventionally bonded using Transbond XT composite. The SBS was measured using a universal testing machine. Results: The mean SBS of groups 1 to 4 was 10.22, 6.88, 9.4, and 13.68 MPa, respectively. Only the SBS of group 1 was not significantly different from that of groups 3 and 4 (P>0.05). Comparison of adhesive remnant index (ARI) scores of the groups revealed significant differences only between groups 1 and 4 (P<0.001) and between groups 1 and 2 (P=0.002). Conclusion: The results revealed that the addition of ACP to Fuji Ortho LC significantly decreased the SBS of molar tubes bonded to enamel compared to the conventional resin bonding system. Sandblasting of the enamel surface significantly increased the bond strength. Fuji Ortho LC modified with ACP is recommended for bonding of molar tubes to posterior teeth considering its cariostatic property. https://fid.tums.ac.ir/index.php/fid/article/view/3159 https://fid.tums.ac.ir/index.php/fid/article/download/3159/1776