Mechanism of action of histidine on fluoride reactivity with carious enamel

• Grant number: 17/02133-9
• Support type: Scholarships in Brazil - Master
• Effective date (Start): June 01, 2017
• Effective date (End): July 31, 2018
• Field of knowledge: Health Sciences - Dentistry
• Cooperation agreement: Coordination of Improvement of Higher Education Personnel (CAPES)
• Principal researcher: Cinthia Pereira Machado Tabchoury
• Grantee: Luziana Adelle Santos Pires Ferreira Marques
• Home Institution: Faculdade de Odontologia de Piracicaba (FOP). Universidade Estadual de Campinas (UNICAMP). Piracicaba , SP, Brazil

Abstract

Histidine, an amino acid that can act as a buffer, increases the reactivity of fluoride (F) with the dental substrate, in view of the higher formation of weakly bound ("CaF2") and strongly bound (FA) fluoride, as observed in previous studies. Since the effect of buffering does not appear to be responsible for the higher reactivity, suggesting an effect of the histidine molecule itself, the aim of the present study will be to evaluate the mechanism of action of histidine on the increase of fluoride reactivity with caries lesions in enamel. Three experimental, in vitro, blind studies with bovine dental enamel blocks will be performed. The dental blocks will be immersed in demineralizing solution for induction of artificial caries lesion and then will be selected and randomized. In the first experiment, the dental blocks will be treated at room temperature under agitation for 10 min with fluoridated solutions containing or not histidine and the following volume proportions of the treatment solution per exposed dental enamel area (n = 12 / group ): 2 mL / mm2; 1 mL / mm2 and 0.5 mL / mm2. In the second experiment, the dental blocks will be treated with solutions containing a fixed concentration of fluoride and variable concentrations of histidine (n = 12 / group): 0.1 M F and 0.1 M histidine; 0.1 M F and 0.05 M histidine and 0.1 M F and 0.025 M histidine. In the third experiment, the effect of histidine will be compared with arginine and acetic acid, from the following treatment groups (n = 12 / group): purified water (negative control); solution containing 0.1 M F (active control); solution containing 0.1 M F and 0.1 M histidine (pKa = 1.8 (-COOH), 9.17 (-NH3), 6.0 (R group)); solution containing 0.1 M F and 0.1 M arginine (pKa = 2.17 (-COOH), 9.04 (-NH 3), 12.48 (R group)); solution containing 0.1 M F and 0.1 M acetic acid (pKa = 4.8). All solutions of the 3 experiments, except purified water, will have the pH adjusted to 5.0. The caries lesion enamel blocks will react individually with the respective solutions. After the treatments, "CaF2" and FA formed in the enamel will be determined. For the analysis of the data, the level of significance will be set at 5%. (AU)