Summary
Background The etiology of dental caries remains poorly understood. With the advent of next generation sequencing, a number of studies have focused on the microbial ecology of the disease. However, taxonomic associations with caries have not been consistent. Researchers have also pursued function-centric studies of the caries microbial communities aiming to identify consistently conserved functional pathways. A major question is whether changes in microbiome are a cause or a consequence of the disease. Thus, there is a critical need to define conserved functional biomarkers at the onset of dental caries.
Methods Since it is unethical to induce carious lesions clinically, we developed an innovative longitudinal ex-vivo model integrated with the advanced non-invasive multiphoton second harmonic generation bioimaging to spot the very early signs of dental caries, combined with 16S rRNA short amplicon sequencing and liquid chromatography-mass spectrometry-based targeted metabolomics.
Findings For the first time, we induced longitudinally-monitored caries lesions validated with the scanning electron microscope. Consequently, we spotted the caries onset and, associated to it, distinguished five differentiating metabolites - Lactate, Pyruvate, Dihydroxyacetone phosphate, Glyceraldehyde 3-phosphate (upregulated) and Fumarate (downregulated). Those metabolites co-occurred with certain bacterial taxa; Streptococcus, Veillonella, Actinomyces, Porphyromonas, Fusobacterium, and Granulicatella, regardless of the abundance of other taxa.
Interpretation These findings are crucial for understanding the etiology and dynamics of dental caries, and devising targeted interventions to prevent disease progression.
Funding The study was funded by the National Institute for Dental and Craniofacial Research of the National Institutes of Health and the University of Minnesota.
Evidence before this study Studies have shown that dental caries, tooth decay, occurs as a result of disruptive imbalance in the oral ecosystem. Excessive dietary intake of fermentable carbohydrates is a critical contributor to disease progression by promoting bacterial production of acids, which shifts the microbial community to an imbalanced and a less diverse one. Studies have also shown that microbial associations with caries have not been consistent while their functions are relatively conserved across individuals. Still, the specific microbial functions associated with the dental caries onset is still unknown due to its infeasible clinical diagnosis.
Added value of this study This study applied a novel longitudinal ex-vivo model, integrated with advanced non-invasive bioimaging, for experimental dental caries induction. This model enabled the detection of the exact onset of the disease, which is undetected clinically. Then, the microbial communities accompanying the caries onset were analyzed for their microbial composition and metabolic functions in comparison to normal conditions. Our study identified five metabolites differentiating the caries onset. Further, we investigated the co-occurrence of these metabolic biomarkers with certain oral bacteria.
Implications of all the available evidence Our study provides carefully validated evidence for biomarkers of the dental caries onset. These data are critical for early diagnostics and development of timely intervention strategies to interfere with the disease progression that otherwise requires invasive and costly health care expenses. Moreover, our data open new avenues for developing therapeutics to neutralize the identified metabolic biomarkers or target the accountable bacteria for caries prevention.
Competing Interest Statement
The authors have declared no competing interest.
