Cytotoxic Effects of Zoom® Whitening Product in Human Fibroblasts

Abstract

Tooth whitening procedures are increasing; however, side effects can occur, such as damage to pulp cells, by the whitening products. This study aims to assess the cellular effects promoted by a whitening product, namely, the oxidative stress fostered by the active agent hydrogen peroxide, with and without photoactivation. Additionally, if cellular recovery occurred, we intended to determine the time point where cells recover from the tooth whitening induced damage. Human fibroblasts were exposed to hydrogen peroxide, Zoom^®, Zoom^® + irradiation, and irradiation alone. The following analysis was performed: metabolic activity evaluation by the MTT assay; cell viability, mitochondrial membrane potential, peroxides production, superoxide radical production, and reduced glutathione expression by flow cytometry. We determined the IC₅₀ value for all groups, and a dose-dependent cytotoxic effect was verified. At the times analyzed, hydrogen peroxide groups showed no metabolic activity recovery while a cell recovery was observed after 24 h (Zoom^®) and 48 h (Zoom^® + irradiation). Cell death was seen in hydrogen peroxide and Zoom^® + irradiation groups, mainly by apoptosis, and the irradiation had a cytotoxic effect per se. This in vitro study supports that whitening products with moderate hydrogen peroxide (HP) concentration have a temporary effect on cells, allowing a cellular recovery.

Keywords: cytotoxicity; fibroblasts; hydrogen peroxide; oxidative stress; tooth whitening.

Figure 1

Dose–response curves at 0 h, 24 h, 48 h, and 72 h, for hydrogen peroxide (HP) (A), Zoom^® (B), and Zoom^® + irradiation (C), expressed as the dose-related inhibition of cell proliferation, determined by the MTT assay. The results express the average of 6 independent experiments ± standard error.

Figure 2

Cell viability determined by flow cytometry using the annexin-V/propidium iodide (AV/PI) incorporation assay. v: vehicle; –: no compound administration. Results are presented as the percentage of live cells (V), early apoptosis (A), late apoptosis/necrosis (A/N), and necrosis (N). Statistical differences from the respective control are indicated by *, where * represents p < 0.05. The results express the average of 5 independent experiments ± standard error.

Figure 3

Oxidative stress analysis. (A) Mitochondrial membrane potential evaluation determined using the fluorescent probe JC-1. (B) Production of intracellular peroxides using DCFH2-DA. (C) Production of superoxide radical using DHE. (D) Expression of GSH using orange mercury. –: no compound administration. Statistical differences from the respective control are indicated by *, where * represents p < 0.05 and ** p < 0.01. The results express the average of 5 independent experiments ± standard error.