## 1 Introduction  
The goal of modern dentistry is prevention rather than treatment of dental caries. Topical fluoride in conjunction with oral hygiene is the most important means of prevention. Fluoride acts through three main mechanisms: it improves the resistance of the enamel,facilitates remineralization of initial enamel lesions, and interferes with microorganisms by inhibiting bacterial metabolism and the enzymatic process [1]. The most common forms of topical administration of fluoride are toothpaste, gel, varnishes, and mouthrinses. The protective effect of fluoride is due to the formation of a superficial CaF layer that prevents the enamel from being exposed to acids and dissolution [2; 3; 4]. However, some studies have shown that the efficacy of fluoride therapy in combating dental erosion is limited because it correlates with the constant presence of fluoride in the oral cavity. This means that, in order to achieve a protective effect, products with a higher fluoride concentration and a longer retention time must be used. For this reason, the use of fluoride to prevent erosive processes would require high patient compliance [5]. Recently, lasers have been proposed as an innovative procedure against the formation of dental caries or to support conventional therapy. In fact, many researchers propose lasers to improve conventional preventive therapies. Several lasers have been investigated, both alone and in conjunction with fluoride, to induce the formation of more resistant enamel to acid-induced dissolution. In the literature of recent years, there are numerous studies confirming the beneficial effects of diode laser on enamel, either alone or in combination with fluoride, increasing its resistance to acids or favoring the fluoride uptake, making it more resistant to caries [6; 7; 8; 9]. The application of laser on dental hard tissues leads to changes in the chemical and mechanical properties in the enamel, increasing the acid resistance of the lasered enamel and decreasing its permeability. The heat developed by the laser light not only prevents the formation of caries on the enamel surface, but also promotes the loss of water and carbon, the decomposition of the organic matrix, and the formation of refractory hydroxyapatite phases such as calcium phosphate or calcium pyrophosphate [10]. Moreover, in combination with topical fluoridation, it promotes the incorporation of fluoride into the hydroxyapatite structure, facilitating the formation of fluorohydroxyapatite and calcium fluoride (CaF\({}_{2}\)) both on the surface of enamel and within its crystalline structure, which serves as a fluoride reservoir against caries and facilitates the process of demineralization [11]. The effects of different types of lasers on the ultrastructure of enamel are controversial, and it is difficult to determine which is the best outcome. The variety of these changes is related to the different laser parameters used (modality of laser irradiation emission, wavelength, energy output, and exposure time) and the optical properties of the lasered tissues (hydration state, presence of chromophores, and their absorption coefficient). [PERSON] et al. (2011) evaluated the treatment with fluoride in combination with a diode laser and studied the laser-induced changes in the composition (contents in F) of enamel after laser irradiation and topical fluoride application [12]. The chemical analyses performed with the fluoride ion-selective electrode showed increased fluoride uptake for the group of teeth treated with diode laser and fluoride gel application compared with the teeth of the untreated group and the group of teeth treated with amine fluoride gel only. The conclusions of the study were that the combination of topical fluoridation and diode laser seems to be a promising preventive measure for dental caries and could be useful for effective and immediate fluoridation of teeth.