Introduction: Of the factors affecting the marginal permeability of restorations in the teeth, the state of stress-strain processes in the enamel with different design of the edge of the carious cavity has been poorly studied. The aim of this research was to study the influence of stress-strain processes in tooth enamel on the marginal permeability of class I restorations with a different design of the edge of the carious cavity.Materials and methods: We have examined 45 pulled out intact third molars, which were divided into three groups of 15 each, depending on class 1 carious cavities formed in them. In I group we formed a carious cavity without a bevel of enamel, in II - with external bevel of enamel, in III - with internal bevel of enamel. Carious cavities were restored with a microhybrid composite light curing material. The teeth were undergone thermocycling and a single vertical mechanical load, were covered with nail polish, placed in a 1% aqueous solution of methylene blue, separated in the medio-distal direction, and the depth of dye penetration was studied. The stress-strain state of the enamel was modelled by the finite elements method.Results: Nonparametric statistical analysis showed that there is a close relationship between the values of stress and strain in enamel and the marginal permeability of restorations. The higher are these values, the deeper is the penetration of the dye. When the edge of the carious cavity is formed with external bevel of enamel, the lowest penetration of the dye is observed, with the internal bevel - the maximal. The results obtained can be useful for clinicians in the preparation of class I carious cavities.Conclusions: The higher the values of stress and strain in enamel, the deeper the marginal permeability of restorations. When the external bevel of the enamel is formed, the dye penetrates least, and when the internal bevel is formed - the maximal.