Salivary microbiota profile in adult and children population according to active dentin caries: a metagenomic preliminary analysis.

Objectives: The aim of this study was to investigate the relationship between active dentin caries (ADC), salivary biochemical parameters, and salivary microbiota composition in Spanish children and adults.

Methods: Saliva samples were collected from 80 subjects (40 adults and 40 children) divided between ADC and non-ADC. Salivary biochemical determination was performed by analysing total protein content (TPC) and total antioxidant activity (TAC) in saliva supernatants. DNA was obtained from the pellet of saliva samples using the Bacterial DNA kit and analysed with the Illumina NextSeq platform from all participants. Alpha diversity (Chao, Observed Features, Shannon and Simpson indices) and beta diversity (PCoA plot and PERMANOVA procedure) were analysed. In addition, Linear Discriminant Analysis Effect Size (LEfSe) was used to identify differential taxa between groups. All statistical analysis were performed with a 95% confidence level (p < 0.05).

Results: No significant associations were found between ADC and salivary biochemical markers in either the adult or pediatric age group, suggesting that these parameters alone may not sufficiently reflect cariogenic activity. Microbiota analysis at the phylum level did not show significant correlations with ADC; however, distinct associations appeared at the genus and species levels. In adults, several genera (Corynebacterium, Porphyromonas, Tannerella, Catonella, Filifactor, Parvimonas, and Dialister) were positively associated with ADC, reflecting a shift towards a dysbiotic microbiome composition that overlaps with periodontal and endodontic pathologies. Conversely, Haemophilus was negatively correlated with ADC, potentially indicating a protective role. At the species level, a positive correlation with ADC was found with Porphyromonas gingivalis, Porphyromonas endodontalis, Peptostreptococcus stomatis, Leptotrichia buccalis, Prevotella oris, or Corynebacterium matruchotii in the adult population. In children, microbial associations with caries were more limited, with Scardovia, a well-known acidogenic genus, positively correlated with ADC, and P. stomatis showing a negative association. Interestingly, P. stomatis exhibited opposite correlations in adults and children, possibly reflecting age-specific ecological roles. No significant differences in alpha or beta diversity were found either in adults or children participants.

Conclusions: Overall, these findings highlight a stronger and more diverse association between salivary microbiota and caries in adults compared to children. These results underscore the importance of age-specific microbial signatures in the aetiology of dental caries. The obtained differences suggest that caries development in adults may involve broader dysbiosis involving proteolytic and anaerobic organisms in addition to acidogenic species.