## 1 Introduction  
Dental erosion is defined as a chemical (acid-related) loss of dental hard tissue with a process independent from bacteria [1, 2]. Concerning the origin of the erosion-causing acid, a distinction between exogenous and endogenous erosion could be made [3]: extrinsic factors include the dietary regimen and the use of some medications, while intrinsic factors are mostly correlated to diseases such as gastroesophageal reflux (GERD), often affecting diabetic and obese individuals, bulimia nervosa (BN) and alcoholism [2]. The initial stage of dental erosion, that is a reversible process, is characterized by the softening of the enamel due to acidic demineralization of hydroxyapatite (HA) [4]. For this reason, the partially demineralized HA crystals may re-establish the original conformation if exposed to a favorable oral environment, at this stage [2]. The intrinsic remineralization due to the chemical composition of saliva is well documented, in fact at physiological pH, saliva is supersaturated with phosphoprotein-stabilized Ca\({}^{2+}\) and PO\({}_{4}\)\({}^{3-}\) ions, which are bioavailable for hard tissue development and maintenance, establishing an homeostatic equilibrium. However, salivary remineralization is a slow process, affecting only the surface of mild eroded tooth and improving neither the aesthetics nor the structural properties, in case of subsurface lesions [5]. Indeed, in case of patients affected by chronic GERD and BN, the self salivary remineralization process results inadequate: as the acidic impact persists, additional dissolution of the enamel matrix occurs, resulting in the layer-by-layer inorganic material loss, decrease of the enamel thickness and, occasionally, in dentin exposure [4]. This chronic situation, often leading to a painful experience for patients, requires professional dental assistance and, at the same time, the use of specific remineralizing and wear-protecting agents [6]. Fluorinated toothpastes are the most commonly used remineralizing agents that convert hydroxyapatite (HA) into the stronger fluoro-hydroxyapatite, which is more resistant to the acid wear [7]. Despite the use of remineralizing agents able to limit the inconveniences of drastic dental erosion, it is considered necessary the development of new combined strategies with the aim to avert hard tissue loss. To exert an antierosive effect, conventional fluorides (such as sodium fluoride (NaF)) appear to require an intensive and unrealistic fluoridation regimen [4]. On the other hand, the increase in prevalence of dental erosion among population, despite the use of fluoride-containing toothpastes, points out the need for more effective compounds [5]. Stannous fluoride (SnF\({}_{2}\)), titanium tetrafluoride, amine fluoride, HA nanoparticles, SnF\({}_{2}\) with amorphous calcium phosphate, zinc-carbonate-HA nanoparticles, potassium nitrate, chitosan, and various proteins, are only some examples of the developed components of toothpastes which efficacy in preventing enamel and dentin erosion have been investigated in the last years [8; 9; 10; 11]. Under these considerations, the combination between the remineralizing capacity and the promotion of surface resistance become an advisable goal for contemporary commercial products, towards an efficient treatment of patients afflicted by chronic dental erosions. At the state of the art, several studies showed the performances of different suitable agents with anti-errosive properties or remineralizing activity [12], but to the authors' knowledge, there is a lack of information regarding the combined use of these products. The present study aims to investigate the remineralization capability and the tooth-surface protecting attitude achievable combining two commonly used home-devices in case of teeth characterized by severe enamel erosion conditions.