Changes in oral microbiome in preschool children after using toothpaste with different fluoride concentrations.

Dental caries is one of the most prevalent chronic bacteria-induced diseases worldwide [1]. Previous studies have shown that dental caries is not caused by a single bacterium, such as Streptococcus mutans, but rather is a polymicrobial process [2]. Dental plaque is a microbial biofilm community composed of hundreds of distinct microorganisms that are omnipresent in the oral cavity and colonize tooth surfaces [3]. The human oral cavity is a highly diverse microbial habitat, with a relatively stable microbiota that can be influenced by environmental factors, diet, and overall health [4].

Fluoride is an effective substance in preventing dental caries through a number of mechanisms [5]. During enamel remineralization, fluoride ions can replace hydroxyl ions in hydroxyapatite, forming fluorapatite, which improves the acid resistance and hardness of enamel [6]. Fluoride also exerts a significant impact on acid-producing microorganisms within biofilm. When hydrofluoric acid (HF) enters bacterial cell, it dissociates into H and F ions due to the higher intracellular pH, leading to accumulation of fluoride ions and acidification of the cytoplasm. This results in a decrease in both the proton gradient and the activity of glycolytic enzymes such as enolase [7]. Studies have also shown that fluoride inhibits microbial growth by blocking enolase, the enzyme which catalyzes the conversion of 2-phosphoglycerate to phosphoenolpyruvate, thereby reducing bacterial metabolism and acid production. Thus, fluoride compounds possess antimicrobial properties through their negative impact on microbial energy production and growth [8].

Fluoride toothpaste is the most widely used method of fluoride delivery worldwide and has significantly contributed to the reduction in the incidence of dental caries observed in developed countries over the past few decades [9]. Previous studies have also shown that fluoride toothpaste can influence dental plaque biofilm [10]. After using fluoride toothpaste, there is an inhibition in the growth of Streptococcus mutans and Porphyromonas gingivalis, as well as an increase in the number of Streptococcus sanguis [11]. Using 16S rDNA gene amplification and sequencing, fluoride interference has been shown to have a selective effect on the composition of the oral microbiota in mice. Moreover, a recent in vitro study found that fluoride concentration in dental plaque affects the key toxicity factors of S. mutans, such as acid production, glucan synthesis and nutrient transport, though the implications in vivo remain unclear [12]. In addition to inhibiting bacterial metabolism, fluoride also promotes enamel remineralization [13], and its regulation of the microbiota may synergizes with this process. It is generally accepted that fluoride’s ability to reduce dental caries is mainly attributed to small but sustained elevations of fluoride concentration in dental plaque and saliva [[14], [15], [16]].

Use of higher concentration fluoride toothpaste can increase the level of fluoride ions in dental plaque. However, the effects of different concentrations of fluoride on the entire oral microbiome and the changes in this environment are not fully understood. The present study aimed to examine the short-term effects of different concentrations of fluoride in toothpaste on the composition of oral microbial communities. Specifically, 16S rDNA gene sequencing was performed on oral microbial samples collected from study participants before and after using different concentrations of fluoride toothpaste for one month. The objective was to describe the effects of fluoride toothpaste on the diversity and species abundance of oral microorganisms in preschool children.