Efeito da radioterapia e do flúor na composição química e nas propriedades mecânicas do esmalte submetido a ciclagem de pH in vitro

Abstract

The aim of this of this study was to evaluate the effect of radiotherapy, associated or not with fluoride topical application, on chemical composition, mechanical properties of enamel demineralization in vitro. Thirty third molars were randomly divided into three groups (n = 10): Non-irradiated (NI); Irradiated in relative humidity (UI); and fluorinated neutral gel (IF). Each group was subdivided into two subgroups (n = 5) according to the presence of pH cycling: with and without cycling. The teeth of the IU and IF groups were submitted to an irradiation protocol of 2Gy daily, five days a week, during seven weeks, totalizing 70 Gy. Chemical changes of enamel were quantified using Fourier Transform Infrared Spectroscopy (FTIR). The parameters evaluated were: matrix / mineral ratio (M / M) and relative carbon content (CRC). It was also evaluated the microhardness (VHN) and the modulus of elasticity (E) of the enamel at three depths (superficial, medium and deep). M: M and CRC were analyzed using two-way ANOVA and VHN and E data were analyzed using three-way ANOVA followed by the Tukey HSD test (α <0.05). The FTIR analysis (M / M and RCC) showed significant differences for irradiation, pH cycling and interaction between the factors (p <0.001). Without the pH cycling, the IF group presented the lowest organic matrix / mineral ratio and relative carbonate content. With the pH cycling, the organic / mineral matrix ratio increased and the relative carbonate content decreased, with the exception of the IF. VHN was influenced only by pH cycling (p <0.001), with higher values of VHN with pH cycling. ANOVA detected significant differences in E for irradiation (p <0.001), pH cycling (p <0.001) and for interaction between irradiation and pH cycling (p <0.001). An increase in E was found for the UI group without pH cycling. With pH cycling, the IU and IF groups were similar and presented higher values than NI. Fluoride associated with radiotherapy reduces exposure of the organic matrix and helps maintain the external morphology of irradiated enamel. However, it was not as effective in preserving the mechanical properties of enamel. Radiotherapy altered the elastic modulus of the enamel and its chemical composition.