The aim of the study was to determine the cytotoxic concentrations and incubation times of the commonly used dental adhesive system OptiBond Solo Plus in its non-polymerized form, and to test how it relates to oxidative stress by determining the reduced and oxidized glutathione (GSH and GSSG) levels as well as to study its influence on cell number and the expression of selected sulfur enzymes, with particular emphasis on cystathionine γ-lyase (CTH) and 3-mercaptopyruvate sulfurtransferase (MPST). All investigations were conducted on an in vitro model of human fibroblast cell line Hs27. Changes in cellular plasma membrane integrity were measured by the LDH test. The expression levels were determined by RT-PCR and Western blot protocols. Changes in cell number were visualized using crystal violet staining. The RP-HPLC method was used to determine the GSH and GSSG levels. Reduced cell number was shown for all tested concentrations and times. Changes in the expression on the mRNA and protein level were demonstrated for CTH and MPST enzymes upon exposure to the tested range of OptiBond concentrations. Levels of low-molecular sulfur compounds of reduced and oxidized glutathione were also established. Cytotoxic effect of OptiBond Solo Plus may be connected with the changes of MPST and CTH sulfur enzymes in the human fibroblast Hs27 cell line. The elevated levels of these enzymes could possibly show the antioxidant response to this dental adhesive system. OptiBond Solo Plus in vitro results should be taken into consideration for further in vivo tests.