Erosive Tooth Wear (ETW) is cumulative tooth substance loss, wherein the Dental Erosion (DE) stands as the primary etiological factor. Dental Erosion occurs as a consequence of chemical loss of mineralized tooth substance by the exposure to acids not originating from microorganisms [1], [2], [3]. ETW appears when the loss of superficial tissue is visible from the results of simultaneous and subsequent exposure to acids (DE) and mechanical forces such as brushing [4,5].

Natural wear occurs in dentition over time, however, the rate of physiological wear is extremely slow to maintain healthy tooth morphology and function throughout the lifetime. ETW can be defined as pathological when it exceeds the physiological level relative to the individual's age, marked by severity (e.g., dentin exposure) and by the interference with self-perception of well-being due to pain, functional and/or aesthetics compromises [1,4,6].

To control the progression of ETW, the most tested strategy is the application of fluorides, especially the most common one - Sodium Fluoride (NaF) [7,8,10]. The mechanism of action behind NaF is related to the formation of a mechanical barrier rich in Calcium Fluoride (CaF2), which adheres to the enamel surface, protecting the tooth structure against acids effects [8,9]. However, the CaF2 barrier has low resistance to acids [9,11]. Amine Fluoride (AmF), found in Elmex® products, operates via a similar mechanism [9,12]. To improve the effectiveness of Fluoride in preventing ETW, fluoride products containing polyvalent metals like Tin (Sn2+) and Titanium (Ti4+) have been investigated [9,10,13,14].

The mechanism of action of tin-containing fluoride products involves the formation of precipitates on the tooth surface (e.g., Ca(SnF3)2, SnOHPO4, Sn3F3PO4) that are more resistance to acids than CaF2 particles [9,15,16] thus reducing both enamel and dentin erosion independently of demineralized organic content preservation in case of dentin [17,18].

Investigations about the potential of TiF4 to prevent ETW have been performed since 1997 [19]. Studies indicate that formulations containing TiF4 (varnishes, mouthrinses and toothpastes) are as effective as NaF and Tin formulations against in vitro tooth demineralization (cavities and tooth erosion) and, occasionally, even superior under in vitro models [11,13,14,[20], [21], [22], [23], [24], [25], [26], [27], [28], [29]] and in situ studies [13,[30], [31], [32]].

Ti4+ reacts with apatite phosphate, forming a layer rich in titanium oxide and hydrated titanium phosphate, which is more acid-resistant than CaF2 [14,24]. The low pH of TiF4 also increases the amount of CaF2 formation and F penetration in enamel, compared to NaF, confirming its better interaction with the tooth structure [14,24]. While this mechanism data came from varnish studies, a similar effect is presumed with toothpaste, but at lesser extent due to its lower concentration compared to varnish.

Chitosan (Ch) is a biopolymer derived from the polysaccharide chitin, features a polycationic carbohydrate structure positively charged at low pH, with an affinity for surfaces with negative zeta potential like enamel [33,34]. This enamel characteristic facilitates the creation of negatively charged surface to the formation of Chitosan layers, enabling the polymer easy adsorption onto the surface producing stable protective barrier against acids [10,34]. Additionally, it has lubricating effects [26,27] that could reduce friction between toothpaste abrasives, toothbrush and tooth structure.

Our research group has tested 0.5 % chitosan at 75 % deacetylation, whose protective effect is well known [10,17,18], incorporated in both TiF4 solution and toothpaste against ETW [14,26,27]. Besides the degree of deacetylation, the viscosity of chitosan is another important factor that interferes on its action. In a range of 500 and 2000 mPas chitosan incorporated into a TiF4/NaF solution, enamel and dentin behave significantly different [26,27]. On the other hand, in case of toothpaste, a 2000 mPas chitosan had a incompatible viscosity to be incorporated into the formulation. Therefore, 0.5 % chitosan (75 % deacetylation, 500 mPas) associated or not to TiF4 toothpaste has been tested against ETW in vitro [14]. Despite no benefit has been seen by the incorporation of chitosan into TiF4 toothpaste against ETW, this polysaccharide increased the toothpastes'pH to a value suitable to be applied clinically.

Considering the benefits of TiF4 and chitosan and taking into the account that a commercial toothpaste to prevent ETW contains both a metal fluoride and chitosan, this work aims to compare the protective effects of TiF4 plus chitosan toothpaste and commercial toothpaste (Elmex, GABA®) on enamel and dentin erosion and erosion plus abrasion in situ.

The null hypotheses are: 1) There is no significant difference between both toothpastes in reducing ETW, irrespective of the challenge type (erosion vs. erosion plus abrasion); 2) There is no significant difference between the challenge type (erosion vs. erosion plus abrasion) on ETW, regardless of the toothpaste.