Innovative therapeutic strategies for bleaching teeth with white spot lesions or enamel erosion: in vitro and in situ study

• Grant number: 24/17284-6
• Support Opportunities: Scholarships in Brazil - Doctorate
• Start date: March 01, 2025
• End date: February 29, 2028
• Field of knowledge: Health Sciences - Dentistry - Dental Materials
• Principal Investigator: Carlos Alberto de Souza Costa
• Grantee: Victória Peruchi
• Host Institution: Faculdade de Odontologia (FOAr). Universidade Estadual Paulista (UNESP). Campus de Araraquara. Araraquara , SP, Brazil

Abstract

The main objective of this project is to evaluate the influence of combined catalytic/remineralizing bleaching strategies on bleaching efficacy, trans-enamel/dentin cytotoxicity, and superficial structure of sound enamel, as well as enamel exhibiting white spot or erosion lesions subjected to both in-office and at-home bleaching therapies. This study will be carried out in four sequential phases. In the First Phase, a screening of different concentrations of titanium tetrafluoride (TiF4) will be conducted, to be incorporated into the formulation of a polymeric strip to be used to coat enamel before applying an in-office bleaching gel with 35% hydrogen peroxide (35% H2O2), and to be added to an at-home bleaching gel with 22% carbamide peroxide (22% PCarb). Thus, it will be determined the temperature generated by the incorporation of TiF4, as well as the pH of the products. Take into consideration the pH stability and reaction temperature parameters with time, the most promising concentrations of TiF4 will be selected for the Second Phase of the study. In this phase, a UV-reflection spectrophotometer (CIE Lab* System; ¿E00, ¿WID) will be used to evaluate the bleaching efficacy of the therapies. Additionally, the physical/chemical and mechanical properties of the dental enamel exposed to the therapies will be analyzed (Surface Microhardness - Knoop; Scanning Electron Microscopy - SEM; and Energy Dispersive Spectrometry - EDS). To evaluate trans-enamel/dentin cytotoxicity, enamel/dentin discs adapted into artificial pulp chambers will receive the in-office and at-home bleaching treatments selected, and the extracts (culture medium + components of the bleaching gels diffused through the discs) will be collected and immediately applied to odontoblast-like MDPC-23 cells. The cells will be assessed for viability (alamarBlue), morphology (SEM), and oxidative stress (carboxy-H2DCFDA probe). The amount of H2O2 diffused through the enamel/dentin discs (Leuco-crystal violet/Peroxidase), and the generation of hydroxyl radicals (OH*) will also be determined. In the Third Phase of this project, white spot lesions and early-stage erosion lesions will be artificially produced in enamel of enamel/dentin discs. The most promising in-office and at-home bleaching protocols established in the previous phase will be applied to the changed enamel surfaces. Bleaching efficacy and trans-enamel/dentin cytotoxicity caused by these bleaching protocols will then be analyzed, comparing the results with those obtained using discs with sound enamel. In the Fourth Phase, palatal devices containing enamel/dentin discs will be prepared with acrylic resin. The best bleaching protocols determined in the previous phases of this project will be applied to sound enamel as well as to enamel with white spot lesions or early-stage erosion lesions. The devices will be worn by 32 carefully selected volunteers. This will allow for an in situ evaluation of the effects of the bleaching therapies on the cross-sectional microhardness (Knoop), morphology, and chemical components of the enamel (SEM/EDS). An atomic force microscope (AFM) will be used to analyze the surface topography of the enamel, and the carbonate (CO2-3) and phosphate (PO4-2) bands in this mineralized tissue will be assessed by Fourier-transform infrared spectroscopy (FTIR). The numerical data obtained through the application of laboratory protocols will be subjected to specific statistical analysis.