## 4 Discussion  
The surfaces of enamel that were untreated, after exposition to the acid solution (Group A), have a greater number of visible prisms than the surfaces of enamel that were treated with the diode laser before being exposed to the acid solution (Group O). On the contrary, the untreated enamel surfaces exposed to the acid solution (Group A) exhibit a number of prisms statistically equivalent to those observed on enamel surfaces treated with fluorine and then exposed to the acid solution (Group B). However, a marked difference is observed between the prisms of enamel of Group A and those observed in Group B. The enamel surfaces of the Group A samples exhibit prisms that are defined as \"well defined\", and show a central concavity. In contrast, the prisms observed in Group B are defined as \"shallow\", and these are characterized by a protuberance with respect to the surrounding surface and, apparently, resembling buttons. Such aspects of the enamel surface have previously  
Figure 5: This figure shows the images obtained by SEM, under 700\(\times\) magnification, of an area test from samples of Groups A (**a**), B (**b**), O (**c**), and X (**d**). SEM images represent an enamel surface of 168 \(\upmu\)m width and 120 \(\upmu\)m height resulting in an area of 19,600 \(\upmu\)m\({}^{2}\). A scale length of 20 \(\upmu\)m is reported in each image. been identified and described by [PERSON] et al., 2018 [PERSON] et al. (2018). The main difference between \"well-defined\" and \"shallow\" prisms lies in the amount and quality of material of which they are made. Well-defined prisms would appear as a surface from which material has been subtracted, exposing the central part of the prism. On the other hand, \"shallow\" prisms appear as a prism filled with a material added later. This hypothesis would be in line with the nature of the formation of fluorapatite crystals that could fill the concavities of the prisms and make them appear as reliefs with respect to the surrounding surface. On the other hand, the results obtained from Group X reveal a greater preservation of the structure of the enamel prisms in an acid environment when these are pretreated by a combined procedure using a fluorine gel associated with a diode laser irradiation, compared with the use of laser and topical fluorine individually. This is probably due to presence of amorphous material appearing to cover the enamel surface, preventing the demineralization of underlaying enamel prisms. This is in agreement with other studies that have used the application of laser and fluorine to protect the surface of enamel when exposed to an acid environment. It became clear that laser treatment significantly increases the deposition of fluoride on the surface of enamel when it is locally associated in gel. This uptake is even greater when fluoride is simply applied topically, and irradiation of laser passes through it before reaching the enamel surface (14; 15; 16). Our results show that irradiation of enamel with diode laser can protect enamel when exposed to the acidic environment with greater efficacy than topical application of fluoride gel alone, but in any case, statistically lower than when combined with topical application of fluoride. Similar results have been reported in the literature with lasers of different wavelengths (CO\({}_{2}\), argon, and Nd-Yag lasers) when applied to the surface of enamel as part of programs that use fluoride in topical form (17; 18; 19). Unfortunately, a comparison with these different wavelengths is not possible because the diode laser has a low absorption coefficient for enamel. In our study, the diode laser was used at low power (LLLT).