Introduction: In dentistry, a wide range of dental materials are used for the restoration of lost hard dental tissues. The question of whether and to what extent dental materials can be dangerous for patients, dental staff and the environment is of crucial importance. Therefore, all dental materials today must meet a series of special regulations and directives, which aims to guarantee efficiency and high quality and to ensure that only biocompatible materials can enter the market. Since dental materials in the oral cavity are subject to mechanical, chemical, thermal and other influences, constant monitoring and ex vivo and in vivo clinical research of all dental materials is necessary, even though they have passed all tests and received permission for official use. Objectives: The purpose of this research was to determine how biocompatible and safe modern composite materials and dental amalgams are for clinical use because, as materials used to make dental fillings, they come into direct and permanent contact with oral tissues. The aim was to evaluate the cytotoxic and genotoxic potential of composite material and dental amalgam, depending on the number of surfaces of composite and amalgam fillings and their age in the oral cavity, by analyzing cells of the buccal mucosa using the micronucleus test. Participants and methods: The research was conducted on healthy patients aged 10 to 20 years, using composite materials Filtek Z 550 and amalgam ANA 2000. In in vivo conditions, using a cytological brush (cytobrush), a smear of exfoliated buccal mucosa cells was taken, after which the cells, according to a certain protocol, were prepared for an expanded micronucleus test (cytomeassay). Results: Hypotheses testing was performed using a non-parametric approach, i.e. KruskalWallis one-way ANOVA. The results of the Kruskal-Wallis omnibus test show statistically significant differences between the groups of subjects without fillings, with amalgam fillings and with composite fillings for the following parameters of the micronucleus test: number of micronuclei (p=0.006), number of buds (p<0.001), number of binuclear cells (p< 0.001), the number of nucleoplasmic bridges (p<0.001) and the number of karyolysis (p=0.003). For the other parameters of the micronucleus test (morphological changes of the broken egg type, pyknosis, karyorexia, condensed chromatin), no statistically significant differences between the groups were observed. The number of micronuclei was statistically significantly higher in the group of subjects with amalgam fillings and composite fillings compared to the group without fillings. The results for nuclear buds, for the number of binuclear cells and the number of nucleoplasmic bridges show that the group with amalgam fillings had a statistically significantly higher number of these changes compared to the other groups. The number of caryolysis in the group without fillings was statistically significantly higher than in the group with amalgam fillings and the group with composite fillings. The results of the regression analysis of the relationship between the parameters of the micronucleus test and the number of amalgam and composite surfaces showed low values of R2, which indicates the fact that a relatively small part of the total variance can be explained by the number of amalgam/composite surfaces. Based on the results, it can be concluded that a certain degree of genotoxicity was observed by examining the buccal cells in all subjects. The buccal cells of subjects with amalgam fillings showed the highest level of genotoxicity, followed by those with composite fillings and the least buccal cells of patients without fillings. However, due to the possibility of repairing damaged DNA, the above results can be interpreted as relative indicators of genotoxicity. The parameters indicating cell cytotoxicity were not elevated either in subjects with composite or amalgam fillings. Multivariate regression analysis was performed to determine the associations between potential genotoxic factors related to patients' lifestyle and micronucleus test parameters. The aim of such an analysis was to examine which of the subjects' dietary and other habits could influence the results of the micronucleus test, in addition to the influence of amalgam and composite fillings. The results showed that the number of buds was statistically significantly higher for the four examined predictors (diagnostic radiation, consumption of cooked, dried meat and baked food). Diagnostic radiation was reflected on three (number of micronuclei, number of buds and number of pyknosis nucleoplasmic bridges), and coffee consumption on two (number of nucleoplasmic bridges and number of pyknose) indicators of cytotoxicity and genotoxicity. Conclusions: Amalgam fillings showed a genotoxic effect on buccal mucosa cells, composite fillings showed a limited genotoxic effect, while the number of surfaces of amalgam and composite fillings in the oral cavity did not significantly affect their genotoxic effect on buccal cells. Cytotoxic effects have not been proven for either amalgam or composite fillings. Due to the limited number of respondents who voluntarily participated in this research, the obtained effects of the material are indicative values and should be confirmed on a larger study group over a longer period of time. Composite and amalgam fillings remain in close contact with the tissues of the oral cavity (gingiva, pulp, oral mucosa) for a long time, during which degradation of the material and release of active substances may occur, so future research into their possible cytotoxicity and genotoxicity in vivo is necessary.