# Cytotoxicityicity of Bleaching Products: A Systematic Review
## 4 Materials and Methods  
Due to the high demand for dental bleaching, many products have emerged for this purpose. Introgenic problems can appear with the use of some of them, among which is the affectation of pulp tissue. Cytotoxicity is an adverse effect that is increasingly studied, since it can cause irreversible damage at the dental level [2]. The MTT assay is used in studies to verify cell viability [36]. Most bleaching products incorporate peroxides, which can be hydrogen or carbamide. [PERSON] et al. [31] studied the effect of various concentrations of HP (35%, 17.5%, 10%, and 8%) on dental pulp cells. It was determined that cytotoxicity is concentration dependent, assuming a significant increase in the application of HP at 35% compared to the rest. The same concentration was used in another study [33] applied to fibroblasts, where activation by phototherapy with a low intensity laser emitting in the visible red and near infrared was also used. Apart from the decrease in cell viability shown in the application of 35% HP, a compensatory effect was observed in the group that incorporated the low intensity laser. This is attributed to the fact that this type of therapy promotes the regeneration of injured tissues and under stress conditions can increase cell metabolism. On the other hand, light activation involves a degree of heating of the gel, an increase in molecular movement and greater kinetic energy. It leads to an acceleration in diffusion since the chances of reactions are increased [37]. However, the type of light used does not influence the cytotoxicity of the dental pulp [38]. \begin{table}
\begin{tabular}{c c c c c} \hline
**Author** & **Material** & **Cell** & **Assay** & **Cytotoxicity** \\ \hline \multirow{2}{*}{Rode} & \multirow{2}{*}{EWI, EWW, EWC, C, OB} & \multirow{2}{*}{Fibroblasts} & \multirow{2}{*}{MTT assay} & EWW \textgreater{} OB \textgreater{} C \textgreater{} EWC \textgreater{} EWI \\  & & & & EWW \textgreater{} OB, C, EWC \textgreater{} EWI *** \\ \cline{3-5}  & & & & MNT & EWW \textgreater{} OB, C, EWC y EWI ** \\ \hline \multirow{3}{*}{[PERSON]} & \multirow{2}{*}{WGH-10\%: C10} & \multirow{2}{*}{Fibroblasts} & \multirow{2}{*}{dye-uptake assay} & C22 \textgreater{} C10 \textgreater{} C16 at 2, 4, and 8 h \\  & & & NW: C22 & & \\ \hline \multirow{2}{*}{Soares} & \multirow{2}{*}{35\%, 17.5\%, 10\%, and 8\% HP} & \multirow{2}{*}{HDCP} & \multirow{2}{*}{MTT assay} & 35\% HP \textgreater{} 17.5, 10, and 8\% HP at 0 h and 72 h \\ \hline \multirow{2}{*}{Thacker} & 10\% CaO\({}_{2}\) and N-TiO\({}_{2}\) activated with visible light & Fibroblasts & LDH assay & HP at high concentration \textgreater{} CaO\({}_{2}\) and N-TiO\({}_{2}\)* \\ \hline \end{tabular}  
* *: \(p\) \(<\) 0.05 **: \(p\) \(<\) 0.01 ***: \(p\) \(<\) 0.001.  
\end{table} 
Table 4: _Cont._Therefore, whether to activate the materials in the procedure with light remains a subject of debate today; this procedure offers a range of potential benefits and the ability to promote recovery after the inevitable cell damage. [PERSON] et al. [28] established in their study that there is an inhibition of metabolic activity with peroxide-induced oxidative stress whenever photoactivation is present. However, irradiation with LED light has been shown to favor the restoration of activity as well as cell regeneration. Carbamide peroxide (PC) is another commonly used peroxide, typically applied at home in concentrations of 10-16%. Evidence suggests that it can also be cytotoxic. One study determined how the use of this agent at 22% compared to more typical percentages such as 16% or 10%, leads to a greater inhibition of cellular activity [32]. Sodium perborate (SP), despite its historical use, is currently in disuse [39]. It has been shown to be more harmful to teeth, resulting in erosions. Its cellular toxicity was found to be greater than that of HP [21]. However, the brand selected can have significant relevance despite using similar concentrations.