Toxicity of methacrylate monomers in dental biomaterials - in vitro comparison of the cellular effects of HEMA and TEGDMA

Resin-based biomaterials are commonly used materials during dental treatments. 2-hydroxyethyl methacrylate (HEMA) and triethylene glycol dimethacrylate (TEGDMA) are the major exposures during and after treatment from these materials, as unpolymerized methacrylates leaks from the cured resin. Both HEMA and TEGDMA are shown to cause cytotoxicity in vitro. It has been suggested that both methacrylates induce toxicity through the same mechanisms. Other studies, however, indicate that there are different cellular responses when human monocytes are exposed to each substance. In these studies, HEMA is suggested to mainly affect cells through electrophilic stress, while TEGDMA is suggested to affect cells through oxidative stress. Immortalized human leukemia monocytic cell line THP-1 was exposed to HEMA (0.5-15 mM) and TEGDMA (0.25-5 mM) individually and in combinations. Cell viability was measured with MTT assay. Combination concentrations were chosen from the results of the individual exposure on the MTT assay. Glutathione (GSH) and reactive oxygen species (ROS) levels were measured using flow cytometry. Western blotting was used to quantify selected proteins. Individual and combined exposures of HEMA and TEGDMA resulted in a dose-dependent decrease in cell viability. Similarly, the GSH level also decreased in a dose-dependent manner, although significant at much lower concentrations than the viability loss. Only slight, mostly not significant, increases in ROS levels were measured. Level measurement of the selected proteins, Sequestosome 1 (p62), Heme oxygenase 1 (HO-1), and Pirin, showed an increase in cells exposed to HEMA and TEGDMA, both individually and in combinations. Based on the similar responses on the different cellular events, the study concluded that there were no data supporting the hypothesis that HEMA and TEGDMA induced toxicity by different mechanisms. The combination experiments indicated that the substance had an additive effect on each other. Further studies are needed to strengthen this new hypothesis, however.