Background: Pre- and probiotics may help restore a dysbiotic oral ecosystem. The first years of life provide a window of opportunity to modulate the composition of the oral microbiota and prevent disease.

Objectives: The aim of the present study was to investigate the effect of a tablet containing inactivated Ligilactobacillus salivarius CECT 5317 and the cranberry extract on the development of caries in active preschool children.

Material and methods: The study employed a randomized, placebo-controlled, double-blind design. Preschool children (N = 73) with at least one active carious lesion were enrolled and randomly assigned to the test group or the placebo group. The intervention period was 3 months. Caries was assessed according to the International Caries Detection and Assessment System (ICDAS) II criteria at baseline and after 9 months, and oral hygiene was evaluated with the simplified oral hygiene index (OHI-S). The salivary counts of Streptococcus mutans and Lactobacillus spp. were determined at baseline, and then after 3 and 9 months through the conventional cultivation on TYCSB and MRS agar, respectively.

Results: Sixty children completed the trial (a dropout rate of 19%). The baseline caries prevalence was high in both groups (similar to 71%) and there were no major differences between the groups with regard to background variables. The 9-month incidence of initial carious lesions (ICDAS 1+2) was significantly lower in the test group as compared to the placebo group (p < 0.05). The plaque levels, and the salivary counts of S. mutans and Lactobacillus spp. remained unchanged in both groups throughout the study.

Conclusions: A daily intake of a tablet containing a paraprobiotic and the cranberry extract reduced the 9-month incidence of initial non-cavitated carious lesions in caries-active preschool children. The present study is one of the first to show the impact of synbiotics on the development of caries in children.