Topical fluoride varnish application shifts dysbiotic dental plaque microbiome towards eubiosis in children with dental caries.

Objective: This study used high-throughput amplicon sequencing to examine the impact of long-term continuous fluoride treatment on the dental plaque microbiota of children aged 8 to 9 with mixed dentition.

Design: The study population consisted of twenty 8-9-year-old children with dental caries. Topical application of fluoride-varnish was weekly administered for one month to all subjects. Clinical indicators and anthropological data, such as the caries index (DMFT and dmft), were documented for every participant at baseline. A baseline assessment and a month after the fluoride varnish treatment were conducted for the salivary pH level and the Patient-Hygiene-Performance (PHP) index. Following application of the fluoride varnish, plaque samples were obtained both one month later and before (baseline) and were then used for 16S rRNA gene-based Next Generation Sequencing.

Results: The results showed significant differences in the community composition structure (p < 0.01). Notable caries-associated pathogens in the dental plaque microbiome were depleted whilst health associated phylum Proteobacteria was increased in the abundance following fluoride-varnish application. In children with mixed dentition, this study found that after one month of fluoride-varnish treatment, there was a significant decrease in the prevalence of the dominant pathogenic genera, , and , along with an increase in certain genera related to healthy oral condition, mostly from the phylum Proteobacteria, such as , , and .

Conclusions: Fluoride-varnish application may shift the community level microecology from dysbiosis to eubiosis. Moreover, application of fluoride-varnish with weekly intervals for one month reduced the caries-causing bacteria while enriching the rise of unique, ubiquitous genera primarily belonging to the Proteobacteria, which may plaque a defensive role against progression of caries. Furthermore, a rising pH level towards neutrality (pH 7) indicated a healthier oral environment following the application of fluoride varnish.