Nine maxillary premolars were restored with composite resin inlays involving large intracoronal cavity preparations. Buccal and lingual bonded strain gauges measured the cuspal flexure under a carefully controlled application of occlusal force. The intact tooth was compared with the corresonding preparation and final restoration. The preparation itself greatly reduced the coronal rigidity, but this was completely recovered in the restored tooth, within the functional force of 111 N. A stiffness ratio showed a 97% recovery. From the point of view of cuspal strength, this may mean that larger intracoronal restorations are feasible with this type of restoration. However, other factors, such as chairside time and complexity, and material properties, such as occlusal wear, have to be taken into consideration.