The design of and materials for prosthodontic abutments and posts have significant influences on the fracture resistance of restored teeth. This in vitro study compared the fracture strength and marginal quality of full-ceramic crowns as a function of the inserted root posts via simulation of a five-year period of use. Test specimens were prepared from 60 extracted maxillary incisors using titanium L9 (A), glass-fiber L9 (B), and glass-fiber L6 (C) root posts. The circular marginal gap behavior, linear loading capacity, and material fatigue after artificial aging were investigated. The marginal gap behavior and material fatigue were analyzed using electron microscopy. The linear loading capacity of the specimens was investigated using the Zwick Z005 universal testing machine. None of the tested root post materials showed statistically significant differences in marginal width values (p= 0.921), except in the case of marginal gap location. For Group A, there was a statistically significant difference from the labial to the distal (p= 0.012), mesial (p= 0.000), and palatinal (p= 0.005). Similarly, Group B showed a statistically significant difference from the labial to the distal (p= 0.003), mesial (p= 0.000), and palatinal (p= 0.003). Group C showed a statistically significant difference from the labial to the distal (p= 0.001) and mesial (p= 0.009). Linear load capacity reached mean values of 455.8–537.7 N, and micro-cracks occurred after artificial aging, predominantly in Groups B and C. Through the chosen experimental design, it was shown that the root post material and root post length had no influence on the fracture strength of the test teeth before or after artificial aging. However, the marginal gap location depends on the root post material and its length, which is wider mesially and distally and also tends to be greater palatinally than labially.