Purpose: To compare the failure loads of teeth restored with endocrowns, post-core retained crowns without a ferrule, and post-core retained crowns with a ferrule provided after crown lengthening. Materials and methods: 27 mandibular molar teeth were collected, sectioned 1.5 mm above the cementoenamel junction (CEJ), and endodontically treated. Teeth were randomly assigned into three groups according to the type of final restoration (n = 9): endocrown (EC) group, post-core retained crowns without ferrule (CNF) group, and post-core retained crowns with ferrule provided following crown lengthening (CF) group. Lithium disilicate crowns and endocrowns were designed and fabricated using the Cerec system. Teeth were mounted in acrylic resin and subjected to thermocycling and oblique compressive loading until failure. Results: Mean fracture loads of the CF, CNF, and EC groups were 491.13 (± 6.93) N, 458.57 (± 5.26) N, and 584.48 (± 5.8) N, respectively. One-way ANOVA showed statistically significant differences between the groups (P 0.05). Fracture of the root was the dominant mode of failure in all groups. Conclusion: Molar teeth restored with endocrowns have superior fracture strength compared with those restored with post-core retained crowns. Keywords: endocrown, failure mode, fracture resistance, mandibular molar