## 4 Discussion  
In the present study, a scanning electron microscope (SEM) and profilometer were used to test the effectiveness of two different types of toothpaste and a fluoride varnish in preventing erosion caused by an acidic environment present in the oral cavity. The SEM image results were in accordance with the findings of our study, showing differences between the surfaces even at higher magnification levels (Figure 2)  
The SEM results were not sufficient to demonstrate the actual change in the enamel surfaces caused by the acid attack; a profilometer was also used for this reason. Data obtained from the roughness analysis showed that the effect of acidification was detectable by the increase in roughness. The values were G1 0.46948 \(\upmu\)m \(<\) G2 2.17816\(\upmu\)m. In accordance with our findings, [PERSON] et al., 2017, after the acidification of twenty portions of human dental enamel with of orange juice at pH 3.2, found a statistical increase in the roughness of the samples subjected to acidification, showing that soft drinks are capable of increasing enamel surface roughness [21]. Similar results were also reported by [PERSON] et al., 2011, where the specimens were treated with a regular cola drink at pH 2.3: their surfaces were found to have a noticeable roughness caused by acid compounds presents in the soft drink [22]. To oppose this effect, it is recommended to brush with a fluoridated toothpaste containing between 1000 ppm and 1500 ppm of fluoride. After a sugar-rich or an acid-rich meal, the pH level decreases during the first 40 min, and the risk of the enamel surface degeneration under acid attack is higher; this happens especially if teeth are brushed soon after food or drinks consumption. This phenomenon is described in the Stephen's Curve diagram, which highlights the trend of acid changes during the first 40 min after eating. For this reason, it is recommended to wait at least 20 min before brushing, and generally 2 to 3 min brushing are enough to allow the spread of fluoride and remineralizing compounds all around the surfaces of the teeth. The combination of the mechanical plaque removal and the remineralizing action of the toothpaste allows the hard tooth tissue to return to its initial surface state: shiny and smooth. In such a manner, the tooth surface is protected from demineralization, erosion and the appearance of carious lesions [23; 24]. In our study, the SEM images and profilometer results demonstrate how the three different products (non-fluoride toothpaste, fluoride toothpaste and fluoride varnish) applied to G3, G4 and G5 had remineralization effects as they transformed the enamel surface to a statistically similar condition to G1 (Table 3). In support of the obtained results, the study of [PERSON] et al., 2020, evaluates the effect of four different products (a fluoride varnish, two different fluoride toothpaste and a non-fluoride toothpaste) on erosion lesions caused by a carbonated drink [25]. Through laser imaging of the speckle, the authors demonstrated that all the products proved able to protect the enamel from erosion. These conclusions are in agreement with the lack of statistical difference obtained by comparing the samples G1, G3, G4 and G5 in our study. These results show the importance of the use of a toothpaste or a varnish to restore the original tooth surface roughness, which, in the long term, can help in preventing more serious lesions, such as caries, teeth erosion and sensitivity. Analyzing the SEM results, it is easily notable that the G2 surface showed a rougher surface, especially at 3000 magnification, and the enamel surface appeared more uneven, with visible furrows. In contrast with that, images of G3 and G4 at the same magnification showed the typical aprismatic appearance of an intact surface that is remineralizing.