Nowadays, there seems to be a growing awareness of malocclusions and the need to wear orthodontic appliances. Most frequently used appliance is edgewise - a fixed appliance that consists of metal elements (brackets and wires) and composite elements used for the adhesion of brackets on the tooth surface. All of these elements contain potentially harmful substances that could induce oxidative stress and therefore damage the cell, reduce its metabolic activity and even lead to apoptosis and necrosis. Toxicity was tested on two strains of Saccharomyces cerevisiae yeast - W303 and wild type (WT), on two types of media (yeast peptone dextrose growth medium and artificial saliva), two types of composite materials were used (GC Ortho Connect and ConTec Go!), steel brackets and NiTi wires. The results showed that in solutions infused with these materials, there seemed to be inhibition in cell growth and changes in their morphology and function. In times of increased oxidative stress, cell size changed and they tend to group in multiple cell clusters. AO/PI and Yeast Viability Kit showed reduced viability in solutions infused with orthodontic materials, compared to the test solutions, as well as reduced metabolic activity tested using XTT assay. In summary, free radicals released from orthodontic materials have a negative effect on vitality, proliferation and viability in both yeast strains. Therefore, there is a need for a caution in using these materials in therapy, considering less harmful alternatives (ceramic brackets, bisGMA-free composites) and adding antioxidants to orthodontic therapy with fixed appliances