It has been demonstrated that the fast degradation rate of hydrogen peroxide (H2O2) into other free radicals increases the bleaching effectiveness of the product and minimize the diffusion of H2O2 through the dental structure. However, the negative biological effects of bleaching agents are directly proportional to the H2O2 concentration capable of diffusing across dentin. Therefore, the aim of the present study is to develop two polymeric formulations to act as a protective and catalyst barrier for H2O2, inhibiting the transdentinal diffusion of residual H2O2 to reach pulp cells. For this, the following two formulations will be tested: (1) Polymeric Primer (PR) - a layer that will be prepared by using hydroxypropyl methylcellulose (HPMC) polymer containing horseadish peroxidase (HRP) enzyme as a catalyst agent and (2) Polymeric Protective Strip (PS) - will be prepared by using polycaprolactone (PCL) polymer to act as a physical barrier to the diffusion of H2O2. For the in vitro analyzes, enamel and dentin discs obtained from bovine incisors will be standardized to a thickness of 2.3 mm and 5.6 mm in diameter and submitted to an intrinsic staining protocol. The groups will be divided as follow: G1- No-bleached samples (negative control); G2- gel with 35% H2O2 (positive control); G3-PS; G4-PR; G5-PS + 35% H2O2; G6- PR + 35% H2O2; G7- PS + PR + 35% H2O2. The color changes will be measured before and 24 hours after the bleaching session by means of UV-Vis spectrophotometer according to the CIE L*a*b* system. To assess the trans-enamel and trans-dentinal cytotoxicity of 35% H2O2 associated or not to the polymeric formulations, the enamel-dentin discs will be adapted to artificial pulp chambers (APCs) placed in wells of 24-well plates containing 1mL of culture medium (DMEM). After performing the bleaching procedures, an aliquot of the extracts (DMEM + H2O2 diffused through enamel and dentin) will be applied for 1 h on cultured odontoblast-like MDPC-23 cells. Then, cell viability (MTT assay) and oxidative stress (H2DCFDA probe) will be evaluated. The H2O2 capable of diffusing through the enamel-dentin discs will be quantified (leuco-crystal violet/peroxidase assay). Data will be subjected to specific statistical analysis.
News published in Agência FAPESP Newsletter about the scholarship: