HPLC analytical study of methacrylic monomers released from dental composite materials

Composite resins - largely utilized in dentistry and orthopaedics - are complex mixed materials formed by an organic polymerizable matrix coupled, through a silanic agent, with inorganic reinforcing filler. Resinous matrix is frequently composed by bis-phenol A glycerolate dimethacrylate with the addition of other less viscous methacrylic monomers like triethylenglycol-dimethacrylate, 2-hydroxyethyl methacrylate, urethane-dimethacrylate and, occasionally, 1,4-butanediol dimethacrylate, whose main function is to improve the handling and make easier the filler incorporation. After performing dental restorations with composite resins, small amounts of monomers are released into the oral cavity and - through dentinal diffusion - in pulpal tissues. This phenomenon may be due not only to the release of unpolymerized monomers - because the reaction is never complete - but also to compounds leached through erosion and chemical degradation caused by hydrolytic processes catalyzed by unspecific and human saliva-derived esterases. Subsequently, the reported monomers may produce, or at least contribute to, adverse biological effects, i.e. damages to the oral soft tissues - already observed in vivo - and a remarkable cytotoxic potential as shown by in vitro studies using primary and immortalized cultures. To rationalize the reasons of such cytotoxicity, the in vitro biocompatibility studies of materials containing methacrylates are today performed by multidisciplinary teams including toxicology, biology and chemistry experts. The mechanisms of the toxic effects caused by methacrylates are however not yet completely understood, probably because such compounds can act at different levels interfering with the cell cycle and DNA synthesis, increasing the production of reactive oxygen species, and inducing a depletion of intracellular glutathione. Through the in vitro cytotoxicity tests, researchers are attempting to determine all the cytotoxicity mechanisms. For these reasons is very important to evaluate the amount of monomers eluted from composite materials and HPLC analytical techniques are mostly suitable to this purpose. The present work summarizes the recent results about the detection of the methacrylic compounds - in complex systems like cells (primary gingival fibroblasts and 3T3-Swiss albino-mouse fibroblasts cell line) and culture media - obtained by HPLC, evidencing its key role in qualitative and quantitative analysis of the substances involved in cytotoxic processes.