In vitro cytotoxicity of solid epoxy-based dental resins and their components.

Objective: The objective of this study was to evaluate the effect of adding a spiroorthocarbonate (SOC) or a polyol on the cytotoxicity of epoxy-based dental resins.

Methods: Resins contained one of the epoxies: diglycidyl ether Bisphenol A (GY-6004); 3,4-epoxycyclohexanemethyl-3,4-epoxycyclohexane carboxylate (UVR-6105); vinyl cyclohexane dioxide (ERL-4206) or the three-epoxy mixture (Epoxy-M). The SOC was t/t-2,3,8,9-di(tetramethylene)-1,5,7,11-tetraoxaspiro[5.5]undecane (SOC). The polyols were polytetrahydrofuran (p-THF-250) and polycaprolactone triol (TONE-301). The photoinitiator (4-octylphenyl)phenyliodonium hexafluoroantimonate and camphorquinone were used for light curing the resins. Four types of resins (epoxy, SOC/epoxy, polyol/epoxy and SOC/polyol/epoxy) were evaluated for cytotoxicity as solids in the agar diffusion assay and as aqueous extracts in the MTT assay using L929 cells.

Results: In agar diffusion analysis, ERL-4206 and UVR-6105 resins were severely cytotoxic (+3), but the addition of SOC changed them to non-cytotoxic (-). Addition of 1-3% SOC changed Epoxy-M from mild (+) to non-cytotoxic. Adding SOC changed GY-6004 from moderate (+2) to mild (-) cytotoxicity. Generally, addition of SOC did not change cytotoxicity when added to polyol/epoxy combinations. Either polyol produced resins with reduced cytotoxicity when added to UVR-6105, but the opposite occurred when added to Epoxy-M resins. In MTT analysis, percent cell survival from 100 microliters resin extracts were statistically compared (ANOVA, p < 0.05). Epoxy-M and GY-6004 resin extracts were significantly less cytotoxic than UVR-6105 and ERL-4206 resin extracts were. Overall, the SOC component reduced the cytotoxicity of all SOC/epoxy combinations, except SOC/ERL-4206, which was significantly more cytotoxic than ERL-4206 resin extract. This may be the result of cell fixative effects observed for SOC/ERL-4206 in agar diffusion analysis. Addition of SOC produced significantly less cytotoxic SOC/polyol/Epoxy-M resins when compared to its non-SOC counterpart. The contrary result was obtained with SOC/polyol/UVR-6105 resin combinations. Consistent with agar diffusion results, adding polyol significantly decreased cytotoxicity of UVR-6105 resins. The cytotoxicity of these resins may be related to the 50% cytotoxicity (TC50) of their components as leachates. The TC50 values of the individual components were compared to BISGMA. Polyols, epoxy monomers, SOC monomer and camphorquinone were significantly (p < 0.05) less cytotoxic than BISGMA.

Significance: Addition of SOCs and polyols in the formulation of epoxy-based resins may contribute to development of biocompatible dental composites.