## 4 Discussion
While there are data in the literature demonstrating the protective effect of fluorine due to the exchange of fluorine with calcium ions, responsible for the transformation of hydroxyapatite into fluoroapatite, which is less soluble in an acidic environment, there are no studies that can demonstrate the protective effect of lasers on the enamel surface, but only hypotheses, especially for lasers used with biostimulation powers (20). It is hypothesized that laser irradiation affects enamel water content and hydroxyapatite components such as carbonate, phosphate, and calcium ions. In fact, both water and carbonate ion contents decreased significantly, especially with laser irradiation, which would increase the crystallinity of hydroxyapatite and provide a relative improvement in the mechanical properties of enamel (6). This may justify the presence of this amorphous substance, which is found on the surface of the enamel when irradiated forming a kind of surface layer and has an additional protective value in an acid environment. Our study is in agreement with the research conducted by [PERSON] et al., in 2011 [PERSON] et al., in 2011 [PERSON] et al., in 2011 [PERSON] et al., in 2011 [PERSON] et al., in 2011, which showed that the absorption of fluoride ion in enamel is greater when irradiation with a diode laser is applied before the application of the amine fluoride gel on the enamel surface than when irradiation with a diode laser is applied before the application of the amine fluoride gel on the enamel surface or than when only the fluoride gel is used. This suggests that the diode laser increases the absorption of fluorine when it radiates the enamel through a fluorine gel layer. In studies conducted by [PERSON] et al., in 2019 [PERSON] et al., in 2019 [PERSON] et al., in 2019 [PERSON] et al., in 2019, the microhardness induced by diode laser and fluoride ions on the outer layer of enamel was evaluated and tested. The results of the study showed that the application of fluorine paint and diode laser irradiation significantly increased both the microhardness of enamel and fluoride uptake compared with the control group, and this significantly reduced the demineralization of enamel after immersing the samples in an acidic liquid. In addition, the authors hypothesized that increased resistance of enamel to demineralization after diode laser irradiation could be attributed to the surface melting and recrystallization of the hydroxyapatite crystals of the enamel, to the decrease in the permeability and solubility of enamel, and to the greater increase in precipitation of calcium fluoride. [PERSON] and [PERSON] in 1990 [24] suggested that the greater absorption of fluorine in enamel treated with a laser may be related to the thermal effects of the laser itself, which may cause changes in the surface layer of enamel (such as roughness) responsible for promoting the retention and absorption of fluoride in enamel. This could explain the results of our research in which the enamel, of the samples under study, pretreated with fluorine gel and then irradiated with a diode laser, limited the demineralizing effects on the enamel prisms after exposure to an acid environment more than the samples pretreated with laser and fluorine used individually. Certainly, the limitations of our study are the in vitro protocol and that the data obtained from our research require studies with a larger number of samples, but we believe that we can advance the possibility of recommending a standardized protocol that can be used for the prevention of enamel demineralization to be used in patients who have a structural alteration of the enamel, who are taking drugs for therapeutic purposes that cause a constant decrease in salivary pH, or who have limited oral hygiene options.