en Dental implant Dental implant Original article Original article <strong>Background and Aim: </strong>The mismatch of the implant-abutment connection can produce instant stress and microleakage which result in mechanical and biological complications. This study aimed to investigate the influence of GapSeal^&reg; as a sealing material on the extent of microgap and microleakage at the external hexagon implant platform following cyclic loading.<br> <strong>Materials and Methods: </strong>Sixteen implants with an external-hexagon connection (BioHorizons External dental implant) were employed in this in-vitro experimental study. All implant-abutment sets were assigned to two groups and were molded in acrylic resins. GapSeal^&reg; was injected into the implants in the experimental (test) group. Then, implant assemblies were tightened with the torque of 30 N/cm, and 1200,000 loading cycles with the force of 100 N and the frequency of 1 Hz were applied. Every sample was immersed in a methylene blue dye to evaluate microleakage. Microgap was measured in six regions randomly using a scanning electron microscope (SEM). The data were entered into SPSS 22 and were analyzed using t-test.<br> <strong>Results:</strong> The mean&plusmn;SD microgap was 0.87&plusmn;0.35 &micro;m and 3.43&plusmn;1.61 &micro;m in the test and control groups, respectively. Methylene blue dye was observed in all of the specimens of the control group, while no liquid was seen in the test group. A significant statistical difference was found between the groups regarding the microgap and microleakage (P<0.0001).<br> <strong>Conclusion: </strong>Application of GapSeal^&reg; reduced the dimension of the microgap and decreased microleakage at the implant-abutment interface. Dental Leakage, Dental Implant-Abutment Design, Dental Marginal Adaptation 42 48 http://jrdms.dentaliau.ac.ir/browse.php?a_code=A-10-658-1&slc_lang=en&sid=1 A Zarbakhsh arashz1350@gmail.com 10031947532846009837 10031947532846009837 No Assisstant Prof, Prosthodontics Dept, Faculty of Dentistry, A Mazaheri Tehrani azitamt@yahoo.com 10031947532846009838 10031947532846009838 No Assisstant Prof, Prosthodontics Dept, Faculty of Dentistry, F Shamshirgar farinshamshirgar@gmail.com 10031947532846009839 10031947532846009839 No Assisstant Prof, Prosthodontics Dept, Faculty of Dentistry, H Khosroshahi hadikhosroshahi84@gmail.com 10031947532846009840 10031947532846009840 Yes Post Grduated Students, Prosthodontics Dept, Faculty of Dentistry,