Dental caries is a prevalent public health problem that affects the quality of life of people worldwide [1]. Recognized as a multifactorial disease, dental caries demands the intricate coordination of multiple factors for clinical symptoms to manifest [2]. Prevention of caries includes good oral hygiene practices, oral health education, dietary counseling, avoiding a cariogenic diet, and also use of fluoride [3]. It is known that the topical application of fluoride products is commonly used in preventive programs, as well as its recommendation for individuals at high risk of developing dental caries [4]. The appropriate use of fluoride represents a significant breakthrough and is recognized as one of the most successful public health interventions by the World Health Organization [5].

Fluoride toothpaste (FT) containing a minimum of 1000 ppm F is highlighted as one of the topical administrations that reduce the incidence of dental caries [6]. In addition to disorganization of dental biofilm when associated with brushing FT is considered a rational method of delivering fluoride, increasing its concentration in the oral cavity during brushing [7,8]. Mouthwashes (MW), on the other hand, provide a simple method of self-application of F and act as an additional preventative measure against dental caries [4,9]. Their advantages include ease of use, access to difficult areas, minimal risk of gingival irritation, and low cost [4,9,10].

The use of products such as FT and MW promotes the retention of F ions in the oral cavity after their application, providing a degree of protection against the caries process [6,10,11]. Additionally, the common habit of rinsing the mouth with tap water post-brushing has been linked to decreased oral F retention [12,13]. Furthermore, several clinical trials on caries have demonstrated that oral hygiene habits significantly influence the efficacy of F. In addition to brushing frequency with FT, post-brushing rinsing behavior can be an influence in reducing enamel demineralization [12,[14], [15], [16]]. When investigating the impact of post-brushing mouth rinsing behavior on saliva F levels, it was found that the highest fluoride levels occurred when subjects chose to use mouthwash instead of expectorating toothpaste after brushing. Conversely, rinsing with water, expectorating, and swallowing the foam resulted in decreased retention of fluoride ions. Subsequent studies have highlighted the adverse effects of rinsing with water after brushing on intraoral fluoride levels, supporting the findings of the aforementioned clinical trials [12,13,15,16].

On the other hand, studies have evaluated the efficacy of products containing fluoride and incorporated inorganic phosphates, such as sodium trimetaphosphate (TMP) [17], [18], [19]. A prior study has explored the efficacy of TMP in mouthwashes, finding that the addition of this compound can increase the protective effect against enamel demineralization compared to fluoride-only products [19]. In their study, Favretto et al. [19] showed that the same mouthwash was superior in inhibiting enamel demineralization compared to mouthwashes containing 225 ppm F, with higher fluoride content observed in the enamel after its use. However, these studies did not assess a clinical scenario where a patient uses conventional toothpaste in combination with mouthwash and whether this combined approach effectively reduces dental demineralization [19].

Given the above about the anticaries action of TMP and consideration for patients at high risk of developing dental caries, it is important to investigate the effect of combining mouthwashes with fluoridated toothpaste in reducing dental demineralization. Therefore, this study aimed to evaluate in vitro the effects of combining FT and MW, whether supplemented with sodium trimetaphosphate (TMP) or not, on dental enamel demineralization. The null hypothesis posited that combining fluoridated toothpaste with mouthwashes, whether supplemented with TMP or not, would yield a similar protective effect against enamel demineralization compared to using fluoridated toothpaste alone.