Background/purpose The purpose of this study was to determine fracture loads of human maxillary first premolars restored with condensable composite resin (Surefil, Dentsply) or leucite-reinforced ceramic inlays (ProCAD, Ivoclar Vivadent) in mesial occlusal distal cavity preparations of differing pulpal depths and isthmus widths. Materials and methods Ninety freshly extracted intact maxillary first premolars were divided into nine groups of 10. One group was an unprepared control. Eight groups of teeth were prepared to create different widths and depths of mesial occlusal distal cavities. Subsequently, teeth were restored with either condensable composite resin or ceramic inlay. Specimens were then subjected to axial loading with a 4.82-mm diameter steel ball in a universal testing machine at a crosshead speed of 0.5 mm/minute. Loads were applied against tooth structure, and the steel ball did not contact restorative material. Data were analyzed with multiple analysis of variance and Tukey post hoc testing. Results Mean fracture load of teeth restored with Surefil and a 3-mm cavity width was greater than in groups with a 2-mm cavity width (P = 0.0315). Teeth restored with ProCAD were observed to have significantly higher mean cusp fracture load compared to teeth restored with composite resin (P = 0.0003). Conclusion A bonded ceramic restoration restores the fracture load of a tooth comparable to an intact tooth independent of the examined design parameters, whereas the fracture loads of composite-resin-restored teeth were dependent on cavity widths. Cavity pulpal floor depth is not a significant factor of cusp fracture resistance in a tooth restored with either a ceramic inlay or composite resin. © 2012, Association for Dental Sciences of the Republic of China. Published by Elsevier Taiwan LLC. All rights reserved.