This work was aimed at the study by dynamic mechanical analysis (DMA) of dental composites consisted of a Bis-GMA/TEGDMA (50/50 wt/wt matrix and silica nanoparticles (Aerosil OX50) as filler, silanized with various silanes. The silanes used were 3-[(1,3(2)-dimethacryloyloxypropyl)-2 (3)-oxycarbonylamidol propyltriethoxy-silane (UDMS), 3-methacryloxypropyl-trimethoxysilane (MPS), octyltrimethoxysilane (OTMS), blends of UDMS/OTMS (50/50 wt/wt), or MPS/OTMS (50/50 wt/wt). The total amount of silane was kept constant at 10%, by weight fraction relative to the filler weight. The silanized nanoparticles were mixed with the dimethacrylate matrix (60%) filler by weight fraction). The composites were light cured and tested by DMA for the determination of storage modulus (E'), loss modulus (E ''), tangent delta (tan delta), and glass transition temperature (T-g). Measurements were performed in samples immediately after curing and samples stored in water at 37 degrees C for 1, 7, 30, or 120 days. OTMS-composite in which OTMS does not form covalent bond with the dimethacrylate matrix showed lower elastic modulus both in dry and wet conditions. The ability of bifunctional UDMS for crosslinking was found not to increase the elastic behavior of the composite, as it was expected, compared with that of MPS-composite, because of the high amount of the silane used. After immersion in water the elastic modulus of OTMS-composite remained constant, while that of the other composites increased after I day and then remained constant Lip to 120 days. (c) 2008 Wiley Periodicals, Inc.