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Effect of histidine on the increase of fluoride reactivity with dental enamel

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Luziana Adelle Santos Pires Ferreira Marques
Total Authors: 1
Document type: Master's Dissertation
Institution: Universidade Estadual de Campinas (UNICAMP). Faculdade de Odontologia de Piracicaba
Defense date:
Examining board members:
Carolina Patricia Aires; Cecilia Pedroso Turssi
Advisor: Cinthia Pereira Machado Tabchoury

As observed in previous studies, histidine increases the reactivity of fluoride (F) with the dental substrate, in view to higher formation of loosely ("CaF2") and firmly bound fluoride (FA). In order to better understand the mechanism of action of histidine on the increase of F reactivity, it was the objective of the present research to evaluate whether this effect would be influenced by the volume of treatment solution and by the concentration of histidine. Two experimental, in vitro, independent, analyst-blind experiments, using bovine dental enamel blocks with caries lesion were conducted. The dental blocks (4x4x2 mm), pre-selected by surface microhardness, were immersed in demineralizing solution for induction of artificial caries lesion and then selected by surface hardness loss, randomized and distributed in the respective experiments and treatment groups. In experiment I, the dental blocks were treated with fluoridated solutions (0.1 M F) containing or not histidine (0.1M) and the following proportions of volume of treatment solution per exposed dental enamel area were assessed (n=12): 0.5 mL/mm2; 1 mL/mm2 and 2 mL/mm2. In experiment II, the dental blocks were treated with solutions (2 mL/mm2) containing a fixed fluoride concentration and variable histidine (n=12): purified water (negative control); solution containing 0.1 M F (active control); 0.1 M F and 0.025 M histidine; 0.1 M F and 0.05 M histidine and 0.1 M F and 0.1 M histidine. All solutions of the two experiments, except purified water, had the pH adjusted to 5.0. The enamel blocks reacted individually with the respective treatment solutions for 10 min under agitation (100 rpm) at room temperature. Then, the pH of the solutions was determined again and the concentrations (µg F/cm2) of "CaF2" and FA in the dental blocks were analyzed, using a specific ion electrode. The results were submitted to analysis of variance and Tukey test. The level of significance was set at 5%. In experiment I, the fluoridated solutions containing histidine presented lower pH variation after reaction with the dental blocks and higher concentration of "CaF2" and FA in the carious enamel when compared to fluoridated solutions without histidine (p <0.001), regardless of the proportion of solution per exposed enamel area (p>0.05). In experiment II, the fluoridated solutions with histidine also presented lower pH variation after reaction with dental blocks and higher concentration of "CaF2" and FA in the carious enamel when compared to fluoridated solutions without addition of histidine molecule (p<0.001). Among the different concentrations of histidine tested, the dental blocks of group 0.1 M F + 0.1 M histidine presented the highest concentrations of "CaF2" and FA, significantly differing from the other groups (p<0.05), with no difference observed between the 2 fluoridated solutions with lower histidine concentrations (p>0.05). Regression analysis was also performed between the concentration of histidine in fluoride solutions and the concentrations of "CaF2" and FA formed in enamel with caries lesion, and a dose-response effect was observed for the response variables (R2=0.5956; P<0.01; R2=0.7511, P<0.01, respectively). Considering the results obtained, it was concluded that the volume of the treatment solution did not influence the increase of fluoride reactivity by histidine. However, the highest concentration of histidine in the treatment solution led to greater reactivity of fluoride with enamel with caries lesion (AU)