A photo-polymerizable resin based on bisphenol-A-glycidyldimethacrylate monomer was loaded at both 10 and 50% by weight with particles of alumina of size scales in the 10 micrometers and submicrometer order, termed micro-alumina and nano-alumina, respectively. After curing, the viscoelastic properties of these materials were characterized by multifrequency dynamic mechanical analysis at 0.1, 1 and 10 Hz, carried out in bending mode under strain control across the range of temperatures of 2 to 62°C, normally occurring in the mouth. The storage moduli close to body temperature (37°C) and mastication frequency (1 Hz) was evaluated as the main result of the analysis, along with its change on frequency. The stiffest composite was the 50%wt loaded nano-alumina, which reached a modulus of ~6.8 GPa, comparable to those of commercial restorative composites, even in the absence of bonding agent coating of the fillers. The storage moduli at the same frequency but room temperature (25°C) were compared with the elastic modulus resulting from atomic force microscopy nanoindentation. These measurements confirmed the same ranking of materials as the dynamic flexural analysis, while providing elastic modulus values ~50% higher on average. From the dynamic analysis no thermal transition was observed in the considered temperature range, and a stiffening effect appeared at higher frequencies for all the composites.