Objective: To evaluate two dental composite resin formulations when bonded to premolars as regards to the cuspal deflection, fracture resistance, micro-shear bond strength, polymerization shrinkage, degree of conversion and water sorption. Methods: Thirty premolars were used to measure the inward intercuspal deflection of MOD cavities filled with the 2 composites, after thermocycling, by a Universal measuring microscope after 15 minutes, 1 week and 1 month storage. On the same premolars, fracture resistance was measured by compression till fracture. Another 30 premolars were used to measure the micro-shear bond strength using a Universal testing machine following the same time intervals and after thermocycling. Results: T-Econom showed mean cuspal deflection (0.036 mm, 0.032 mm and 0.026 mm), fracture resistance (472.1 N, 461.2 N and 445.5 N) and bond strength (14.9 MPa, 12.3 MPa and 9.7 MPa) while P90 showed mean cuspal deflection (0.025 mm, 0.020 mm and 0.017 mm), fracture resistance (524.9 N, 512.2 N and 504.5 N) and bond strength 22.4 MPa, 20.2 MPa and 18.4 MPa in all the tested time periods. Conclusions: With large MOD cavities in premolars restored with Silorane-based composite or methacrylate-based composite; the Silorane-based composite offered lower cuspal deflection, higher fracture resistance and bond strength.