Toxic Mechanism of Five Dental Bonding Agents to CHO-K1 Cells

Objectives: To compare the cytotoxicity of five dentin bonding agents (DBAs), including three nano-DBAs (DBA-B: VOCO Futurabond NR, DBA-C: 3M Singlebond 2, and DBA-D: Dentsply Prime & Bond NT) and two non-nano-DBAs (DBA-A: VOCO Solobond M and DBA-E: Dentsply Xeno III) using Chinese hamster ovary (CHO-K1) cells.

Methods: CHO-K1 cells were exposed to different concentrations of DBAs (0.00025%-0.05%, v/v) or solvent control for some periods. Cytotoxicity of DBAs was evaluated by colony formation assay. For cell cycle analysis and reactive oxygen species (ROS) production, CHO-K1 cells were treated with DBAs and then stained with propidium iodide (40 ug/ml) or Dichlorofluorescein¨Cdiacetate (DCFH-DA), respectively, and finally subjected for flow cytometric analysis. The percentage of cells in G0/G1-, S-, G2/M- and sub-G0/G1 phases were determined The DCF fluorescence was used to evaluate cellular ROS levels.

Results: DBAs showed differential cytotoxicity to CHO-K1 cells. The potency of cytotoxicity was DBA-D>DBA-C¨RDBA-E>DBA-A>DBA-B. All five DBAs induced sub-G0/G1 cell population at higher concentrations. After exposure of CHO-K1 cells to DBA-B and DBA-E for 24 h, marked G2/M cell cycle arrest was noted, whereas DBA-A, DBA-C and DBA-D induced G0/G1 cell cycle arrest. DBAs also induced ROS production as indicated by an increase in DCF fluorescence after exposure to DBAs (DBA-A, DBA-B, DBA-C and DBA-E at a concentration of 0.005% (v/v) or higher, and DBA-D at a concentration of 0.025% or higher)

Conclusions: These five DBAs showed differential cytotoxicity to CHO-K1 cells. Cytotoxicity can be due to induction of apoptosis and arresting of cell cycles by components in DBAs and associated with ROS production. Absence or presence of nano-fillers is not the major cytotoxic factor for these DBAs. These results are useful for clinical operative restorative procedures (This study is supported by a grant from National Science Council, Taiwan)