The mechanical and physical properties of polymer matrix composites can be strongly affected by the introduction of nano-sized particles. However, the main difficulty in this term is their appropriate distribution. The aim of this study is to determine the microstructure homogeneity of nano-particles containing composites intended for dental applications. Its influence on selected mechanical and physical properties was also investigated.In the present study, the composites based on the bis - GMA and TEGDMA resins reinforced with a ceramic glass micro - filler and a nano - silica were fabricated. Volume fraction of ceramic phase was 45 - 60 %, including nano-silica. The volume fractions of the nano - filler were: 5, 10, 15, 20 %. The microstructures of composite materials were observed using high resolution scanning electron microscope. The homogeneity of nano-particles distribution was analyzed using the tessellation methods. It was found that for larger volume fractions, the nano-particles form agglomerates. Mechanical and physical properties, such as water sorption and solubility were determined and correlated with the tendency of nano-particles to agglomeration.