Aim. To study cytotoxicity of glass-ionomer cement 3MTMESPETMVitremer, nanocomposite for direct restorations 3MTMESPETMFiltekTMUltimate and nanocomposite particles 3MTMESPETMFiltekTMUltimate in the experiment with laboratory male Wistar rats. Methods. The experimental animals in precervical region of the first left superior molar had a cavity formed with the use of dental drill, which was filled with glass-ionomer cement 3MTMESPETMVitremer, nanocomposite for direct restorations 3MTMESPETMFiltekTMUltimate or nanocomposite particles 3MTMESPETMFiltekTMUltimate. On day 14 the animals were removed from the experiment, and sample of gingiva adjucent to the formed tooth cavity and sample of gingiva from the opposite side of dental arch were taken. Paraffin sections of the samples were prepared and were straightaway placed on a glass slide. For histologic study deparaffinized sections were stained with hematoxylin and eosin and immunohistochemical test with the use of primary antibodies to macrophage marker CD68, marker of cell proliferative activity Ki-67, mesenchymal marker vimentin, endothelial cell membrane antigen CD34 and cytokeratin CKP-PAN. Results. The results proving cytotoxic effect of nanocomposite particles 3MTMESPETMFiltekTMUltimate on the tissues surrounding teeth, were received. On the operated and contralateral sides morphologic changes of mucosa were found including the signs of inflammation, hyperkeratosis, and cell proliferative activity. Changes of gingival mucosa are mostly pronounced in animals whose tooth cavity was filled with nanocomposite particles. Conclusion. Taking into account the negative effect of nanocomposite particles discharging at erosion on gingival mucosa, we consider it reasonable to limit the use of the studied materials on occlusal surfaces exposed to heavy mechanical load leading to intensive erosion.