Objectives: To evaluate the effect of the surface preparation of a gold cylinder on the failure probability of highly filled all-composite restorations used as implant-supported prostheses, and to determine the effect of the location of load application. Method and Materials: Gold cylinders (Nobel Biocare) were prepared with 1 of 4 different surface preparations (n = 20 per surface treatment), and then an indirect resin composite (Targis, Ivoclar Vivadent) was applied. The 4 surface treatment conditions were (1) untreated (prep 1); (2) airborne-particle abraded with 50-µm alumina (prep 2); (3) airborne-particle abraded with 50-µm alumina followed by application of a metal conditioner (Alloy Primer, J. Morita) (prep 3); and (4) airborne-particle abraded with 50-µm alumina followed by application of the bonding primer for the indirect resin system (Targis Link) (prep 4). A compressive load was applied vertically at 1 mm and 2 mm from the access cavity on the occlusal surface until the restorations failed. Results: The prep 4 specimens had the highest fracture resistance. The fracture resistance at the 1-mm location was significantly higher than that at the 2-mm location. The failure load of the all-composite restorations with any of the surface preparations was lower than that of the resin-veneered restorations used as controls. Conclusion: The prep 4 conditions decreased the probability of fracture of the highly filled all-indirect resin composite restorations. Eccentric loading of the all-composite restorations should be minimized in light of the higher probability of failure associated with such a loading condition. Keywords: access cavity, all-composite restoration, failure, gold cylinder, implant-supported prosthesis, surface preparation