Tehran University of Medical Sciences Frontiers in Dentistry 2676-296X 14 6 2017 12 16 321 328 EN Sakineh Nikzadjamnani Associate Professor, Dental Research Center, Dentistry Research Institute, Tehran University of Medical Sciences, Tehran, Iran; Department of Prosthodontics, School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran Abbas Azari Associate Professor, Dental Research Center, Dentistry Research Institute, Tehran University of Medical Sciences, Tehran, Iran; Department of Prosthodontics, School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran Somayeh Niakan Assistant Professor, Department of Prosthodontics, School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran Seyedeh Fatemeh Namdar Assistant Professor, Dental Materials Research Center, Mashhad University of Medical Sciences, Mashhad, Iran 2016 08 07 2017 09 18 Objectives: Chipping is one of the concerns related to zirconia crowns. The reasons of chipping have not been completely understood. This in-vitro study aimed to assess the effect of coping design on the fracture resistance of all-ceramic single crowns with zirconia frameworks.  Materials and Methods: Two types of zirconia copings were designed (n=12): (1) a standard coping (SC) with a 0.5mm uniform thickness and (2) a modified coping (MC) consisted of a lingual margin of 1mm thickness and 2mm height connected to a proximal strut of 4mm height and a 0.3mm-wide facial collar. After veneer porcelain firing, the crowns were cemented to metal dies. Afterwards, a static vertical load was applied until failure. The modes of failure were determined. Data were calculated and statistically analyzed by independent samples T-test. P<0.05 was considered statistically significant. Results: The mean and standard deviation (SD) of the final fracture resistance equaled to 3519.42±1154.96 N and 3570.01±1224.33 N in SC and MC groups, respectively; the difference was not statistically significant (P=0.9). Also, the mean and SD of the initial fracture resistance equaled to 3345.34±1190.93 N and 3471.52±1228.93 N in SC and MC groups, respectively (P=0.8). Most of the specimens in both groups showed the mixed failure mode.  Conclusions: Based on the results, the modified core design may not significantly improve the fracture resistance. https://fid.tums.ac.ir/index.php/fid/article/view/1475 https://fid.tums.ac.ir/index.php/fid/article/download/1475/978