The thermal and structural properties of nano-filled and micro-filled restorative composites (Filtek Supreme XT and Filtek Z250) are studied in comparison with the ones of teeth. Our results show slightly decreased values of the thermal constants of Filtek Supreme XT with respect of Filtek Z250. Both analyzed composite materials have the values of the thermal conductivity and diffusivity very close to the one of enamel, with the better fitting in the case of Filtek Supreme XT. Comparing the effusivities, a good compatibility with all dental tissues resulted. The thermal expansion coefficient is about two times higher for Filtek Supreme XT than Filtek Z250 which fits better with the one of teeth. The chemical composition is similar for both composites except for zirconium which indicate a lower percent of zirconia particle for Filtek Supreme XT.