## 4 Discussion  
The findings of this study offer significant insights into the microstructural effects of Mentadent Professional Resilience on dental enamel, as observed through SEM analysis. The results indicate that the product affects enamel morphology. This could be attributed to the product's formulation, which may facilitate the deposition of minerals onto the enamel surface, thus filling micro-pits and fissures [50]. The treated samples exhibited a pronounced remineralization effect. The increased surface irregularities and reduced visibility of microfractures and pits suggest more substantial mineral deposition. This could indicate an effective remineralization process, potentially protecting against enamel erosion and caries development. In particular, a key role could be played by the presence of hydroxyapatite in the product [34]. The remineralizing efficacy of nano-hydroxapatite (nHA), but more generally of hydroxyapatite (HA) in its nano form (nHA), is highlighted by this study. This is mainly attributable to the fact that the structure of HA is very similar to the mineral structure of enamel, which allows it to penetrate micro defects. Filling them in and creating a stronger surface provides restorative and protective benefits. This analysis agrees with the findings of [PERSON] et al., who showed that the HA matrix of enamel can be effectively fortified using HA-based treatments, thus improving microhardness and reducing susceptibility to future demineralization [2]. Fluoride is widely used in remineralization treatments, especially for remineralizing carious enamel lesions [51]. This is explained by fluoride's ability to generate fluorapatite, which is more resistant to acid attack due to its exchange with the hydroxyl group in hydroxyapatite. It is, therefore, logical that the more fluoride there is, the more numerous and larger the resulting crystals will be [16; 24; 39; 52; 53; 54; 55; 56; 57; 58]. This chemical mechanism is one of the pillars of dental caries prevention, especially in the early stages of demineralization. Traditional fluoride treatments work by binding fluoride ions with enamel hydroxyapatite to form a fluorapatite surface layer that resists acid dissolution. In this scenario, tooth polishing is key and should be carefully selected based on patients' needs. Tooth polishing allows you to remove plaque, biofilm, stains, and acquired pellicle, but excessive use of this procedure could lead to the wear of the superficial tooth structure, the loss of the fluoride-rich layer, and more accumulation of residues on the dental surface [59; 60]. Excessive polishing can compromise the protective function of the enamel, making it more susceptible to future erosion. Some studies, including those by [PERSON] et al., show that fluoride's remineralizing effect is primarily superficial, with limited ability to penetrate deeper subsurface lesions [61]. By contrast, nHA's biomimetic properties allow it to integrate more thoroughly into the enamel, addressing subsurface demineralization. This is especially beneficial for repairing initial carious lesions that fluoride alone cannot access. Our results align with these observations, as HA treatments significantly increased enamel microhardness, suggesting surface-level and potential subsurface repair. This comprehensive action of HA reduces the need for fluoride, particularly in populations at risk for fluorosis, as suggested by [PERSON] and [PERSON] [12]. [PERSON] et al. [37]. analyze how nano-hydroxyapatite crystals are fundamental to remineralizers on initial enamel lesions, which are superior to traditional fluorides used to date for this purpose. According to the existing literature, hydroxyapatite prevents caries by forming a protective barrier on enamel and reducing bacterial plaque adhesion. It also acts as a desensitizer by occluding exposed dental tubules and as a bleaching agent, proving a key component in preventive and dental care products. The study of [PERSON] et al. [62].