Cytotoxic Effects of Whitening Strips on Epithelial Cells

Whitening strips (WS) represent a low-cost alternative of bleaching products used without dentist supervision. The main active component of WS is hydrogen peroxide (HP), known for its high cytotoxicity. However, there is no data about the possibility of low concentrations of HP released from WS to cause toxic effects to gingival epithelial cells. Objectives: To evaluate the cytotoxicity of WS containing 10% of HP directly on keratinocytes (HaCat) cultures. Methods: The cells were seeded in wells and incubated for 48 hours. Standardized round samples of WS were obtained and immersed in culture medium (DMEM) for 1 hour to obtain the extracts (DMEM + components released from the WS). The extracts were incubated in contact to the cells for 1 hour during 1 day (G1) or 5 days (G2). In the positive control (G3), 1 mg of a bleaching gel containing 35% HP dissolved in 1 mL of DMEM was applied for 1 hour on the cells. In the negative control (G4), fresh DMEM was used. The cell metabolism was evaluated by MTT assay (Kruskal Wallis and Mann-Whitney;α= 0,05%). The cell morphology was assessed by SEM. Results: Considering G4 as 100% cell metabolism, it was observed that in G1, G2 and G3 the cell metabolism decreased by 68%, 100%, and 100%, respectively. G1 was statistically different when compared to G4 (p<0.05). Significant difference was also observed when G1 was compared to G2 and G3 (p<0.05) in which only a few cells with notable morphological alterations remained attached to the glass substrate. On the other hand, in G4 a number of keratinocytes with normal morphological characteristics was observed on the substrate. Conclusions: Based on the methodology used in the in vitro study, it may be concluded that the direct toxicity of WS components to the HaCat cells is time-dependent.