Purpose: This study compared the cuspal fracture resistances of posterior teeth restored with five different adhesive restorations. Materials and Methods: Eighty-four sound human molars were included in this study. Sample molars were divided into seven groups. The first five groups received mesio-occlusodistal cavity preparations and were restored with (1) amalgam combined with urethane dimethacrylate cement, (2) posterior composite, (3) direct composite inlay, (4) cast-metal inlay, and (5) complete ceramic inlay. The sixth and seventh groups were introduced in the study as controls. Samples of group 6 were prepared but were tested without restoration (prepared-only group). Samples of group 7 were intact teeth and were tested as unprepared. All samples were loaded axially until failure. Results: While the unprepared teeth had a significantly higher resistance than all other groups, the prepared-only teeth were the weakest. No significant differences were found in resistance to cuspal fracture among the restoration groups. Conclusion: The difference between the mean cuspal fracture resistance of the unprepared and prepared-only groups was statistically significant. Restoration groups were stronger than the prepared-only group. However, differences between the restoration groups were insignificant.