Purpose: The purpose of this study was to evaluate the fracture strength and mode of failure of five different single-tooth abutment-implant combinations before and after cyclic loading in the artificial mouth. Materials and Methods: Eighty standardized maxillary central incisor crowns were fabricated for five test groups with 16 specimens each (group 1: Steri- Oss/Novostil; group 2: Steri-Oss/Anatomic abutment; group 3: Steri-Oss/straight HL; group 4: IMZ Twin +/Esthetic abutment; group 5: Osseotite/gold UCLA). Specimens were adhesively luted using Panavia 21, and half were artificially aged via chewing simulation and thermocycling. All nonaged and the surviving aged specimens were tested for fracture strength resistance using compressive load on the palatal surfaces of the crowns. Results: After exposure to the artificial oral environment, survival was as follows: six in group 1; eight in groups 2, 3, and 5; and seven in group 4. Median fracture strengths before and after loading in the artificial mouth were 537 N, 817 N, 893 N, 473 N, and 743 N for groups 1 to 5, respectively. There were no statistically significant differences in fracture strength before and after exposure to the artificial mouth. There were significant differences between the implant systems in both stages of the experiment. In all five groups, abutment-screw bending and abutment fractures (except group 1) were present after static loading, and all implant necks in group 4 showed distortions. Conclusion: The artificial mouth is a useful tool to check the implant-abutment-screw interface stability. The physical properties of screws and screw joints of groups 1 and 4 have to be improved. Groups 2, 3, and 5 have the potential to withstand physiologic biting forces. Int J Prosthodont 2003;16:167–171.