Genotoxic potential of respirable fraction of composite dust on human bronchial epithelial cells

Objectives: To determine the genotoxic potential of the respirable fraction of composite dust on human bronchial epithelial cells.
Methods: Composite sticks (17.4x5.4x1.6mm) of three commercial dental composites (Filtek Supreme XTE, 3M ESPE; Grandio, Voco, Transbond XT, 3M ESPE) were ground in an enclosed plexiglass chamber (270x270x420mm), with a rough bur (grain size 100µm, speed 200,000rpm). Airborne respirable dust (<5 µm) was collected using a personal cyclone holding a cassette with a teflon filter (pore size 5µm) connected to a personal pump. Immediately after particle collection, the filter was removed from the cassette, weighted and transferred to a glass vial containing 2ml of cell culturing medium (DMEM/F + 0.2% FBS). Next, suspensions between 3µg/ml – 400µg/ml were applied to the cells. After 24h, cell viability (WST-1 assay) and membrane integrity (LDH assay) were evaluated. Furthermore, the genotoxic effect of a subtoxic concentration (50µg/ml) of composite dust was evaluated by the comet assay after a 3h exposure period. All experiments were performed in triplicate and repeated for 4 independent times (n=4). The results were statistically analyzed by one-way ANOVA. To evaluate cellular uptake of particles, cells were analyzed by transmission electronic microscope (TEM).
Results: For all three composite materials, a decrease in metabolic activity of 10 - 35% was observed only when the cells were exposed to the highest tested particle concentrations (100µg/ml – 400µg/ml). There was no toxicity linked to membrane disruption. All tested composites provoked a mild genotoxic effect after short-term exposure compared to the control. Ultra-morphological analysis of the exposed cells showed that respirable particles of all tested composites were taken up by the cells.
Conclusions: Respirable fraction of composite dust showed cytotoxic effects in the highest concentrations. Furthermore, genotoxicity was observed in the sub-toxic levels of composite dust. Future research should focus more on underlining mechanisms of these effects.