## 4 Discussion  
In the present study, a scanning electron microscope (SEM) and profilometer were used to test the level of protection that toothpastes can offer in the presence of erosion due to gastroesophageal reflux disease (GERD). SEM images show significant differences between intact enamel surfaces and those subjected to acid attacks (Figure 4A,B). SEM results are not sufficient to demonstrate the actual change to the enamel surfaces caused by the acid attack; a profilometer was also used for this reason. Data obtained from the roughness analysis show that acid attack causes a dissolution of hydroxyapatite crystals. This is because intrinsic erosion is caused by gastric juices reaching the oral cavity [2]. Tooth A recorded an average roughness of 0.0628 um, a value which increases exponentially in tooth B, subjected to the first acid attack. Roughness reached by tooth B has an average value of 0.3374 um. It is now known that eating disorders, such as bulimia and gastroesophageal reflux, cause an increase in tooth roughness and appearance of erosive lesions [14]. Frequent episodes of vomiting or regurgitation cause erosion at the level of the enamel, which is due to pH levels in the stomach reaching 1 or lower. Evidence associating GERD and dental erosion comes from two main areas: patients presenting with reflux symptoms who are then found to have dental erosion and patients presenting with erosion  
Figure 3: Box-plot regarding ‘Toothpaste B’. Tooth B, E and F represents tooth condition as in Table 1.  
who are then diagnosed with GERD. One of the first studies about association between dental erosion and GERD was carried out by [PERSON] et al. [5]. They diagnosed GERD using endoscopy to assess esophagitis in 20 patients. Dental erosion was diagnosed in four of these patients, concluding that patients diagnosed with GERD had an increased risk of developing dental erosion. [PERSON] [15] conducted a similar study with a larger sample size (117 patients reporting symptoms of GERD). Dental erosion was reported to involve 24% of tooth surfaces. Authors concluded that severe reflux disease of long-lasting duration was more likely to cause dental erosion than milder forms. Concerning the effect of toothpastes in the enamel remineralization process, it can be observed through SEM images that enamel surfaces of teeth C and E show the typical aprismatic appearance of an intact surface undergoing remineralization. (Figure 4C,E). The merely iconographic investigation of the SEM was also confirmed by the statistical analysis of the profilometer. Numerical data confirm that roughness in elements C and E has strongly decreased, with an average value of 0.1696 \(\upmu\)m for the first element and 0.260 \(\upmu\)m for the second. In this first part of the analysis of the results, it can be stated that these values confirm that the toothpaste used played an important role in repairing the damage that the 15% HCl caused to sample surfaces. Literature agrees that toothpastes play a fundamental role in erosion prevention. [PERSON] and [PERSON] [16] suggested that topical application of fluoridated but acidic products causes an initial dissolution of minerals contained in the enamel, thus increasing the local pH, but at the same time they are able to carry the creation of fluoro-hydroxyapatite, more resistant to bacterial attack. In addition, the buffering capacity of saliva and organic film led to a further protective effect. It seems that highly concentrated applications of mildly acidic fluoride are able to decrease the development of erosions in enamel and increase resistance to mechanical abrasion. In his study, [PERSON] [17] agrees with the effectiveness of toothpastes in preventing erosive lesions and considers them to be an essential tool.