Cytotoxicity of HEMA-Containing and HEMA-Free Dental Bonding Substances

Methods: (i) Composite specimens were prepared in polyethylene blocks containing 5mm diameter cylindrical holes (cylinder-height 2mm), covered with a polyethylene-foil and light-cured from one end (40s). Combined “bonding/composite”-specimens were produced by applying bonding at first onto the polyethylene-foil and light-curing. Subsequently, polyethylene-moulds were placed on top of the bonding materials and composites prepared as described above. Specimens were incubated with L-929 fibroblasts for 72h. Cell numbers were determined by flow-cytometry. (ii) Eluates were prepared according to ISO 10993-12. Bondings were applied on a polyester foil and light-cured. These specimens were eluated 24h at 37°C in cell-culture medium (DMEM) under continous shaking (extraction ratio 6cm²/ml). The eluates were incubated undiluted or in dilutions 1:1, 1:2, 1:4, 1:8, 1:16, 1:32, 1:64 for 24h with L-929 fibroblasts. Thereafter the cytotoxicity was determined. In brief, MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] in a concentration of 1mg/ml medium was added to each well and culture plates were incubated at 37°C for 4 hours. Living cells converted the dye to formazan product with mitochodria. The solubilization reagent was then added to the cell-cultures, and left for 2h in a humidified atmosphere. Finally the absorbance was measured at 540nm.

Results: (i) Bonding substances had no significant influence on the cytotoxicity of composites, when applied as “bonding/composite”-specimens. (ii) The highest concentration of all tested bonding eluates and bonding/primer combinations was cytotoxic. The cytotoxicity diminished with increasing dilutions for all materials tested. Overall, there was no difference in the degree of cytotoxicity between HEMA-containing and HEMA-free bonding substances (p<0.01).

Conclusion: The presence or absence of HEMA in the composition of the tested bonding substances did not correlate with their cytotoxic potential.