During caries progression, an interaction between the dental pulp, the bacteria and their by-products and the demineralized matrix components can lead to new dentin matrix deposition. The production of tertiary dentin requires a low level of inflammation that enhances the reparative response. There is evidence to suggest that low-grade oxidative stress could have similar results (Lee et al. 2006). It is also known that control of the infection is a prerequisite for vital pulp therapies to be successful. The aim of this project is therefore to explore the potential to use hydrogen peroxide in deep cavities to both eliminate infections and encourage regeneration. The potential biocidal effect of H2O2 to treat dentin infections was assessed by determining the Minimal Inhibitory Concentration (MIC) of H2O2 against E. faecalis, S. anginosus and S. mutans. The viability of dental pulp fibroblasts to these bactericidal concentrations was then studied using an MTT assay. Additionally, a suspension test was carried out to study the inactivation kinetics of the microorganisms when subjected to a clinically relevant exposure time of H2O2. Changes in the bacterial cell wall structure were also evaluated using Scanning Electron Microscopy (SEM) imaging. A validated ex vivo tooth slice model (Sloan et al. 1998) was also used to study the potential use of H2O2 in enhancing a regenerative response. Tooth slices were exposed to H2O2 and the dental pulp response was established by viable histological cell counts and immunohistochemistry for inflammatory (TNFα and IL-1β) and regenerative markers (DSPP and PCNA). Results: MIC of H2O2 was 1,250ppm for E. faecalis, S. anginosus and S. mutans. Dental pulp fibroblast viability was reduced significantly when exposed to bactericidal concentrations of H2O2 for 60 seconds or 5 minutes. The bacterial count was not reduced after 5 minutes of exposure to 1,000ppm H2O2 and no structural changes were observed using SEM. Tooth slices exposed to 1,000ppm or 300ppm H2O2 for 60 seconds or 5 minutes showed no significant reduction in cell counts. Immunohistochemistry showed the presence of inflammation in the vasculature and odontoblast layer, and the expression of dentin extracellular matrix protein DSPP in the odontoblast layer. In conclusion, bactericidal concentrations of H2O2 are cytotoxic to dental pulp cells cultured in monolayer. Moreover, at clinically relevant time exposures to H2O2 for decontaminating cavity preparations, the bacterial count was not reduced. However, results from this study suggest there may be a potential use for H2O2 to induce dental pulp regenerative response.