Microbiota of Severe Early Childhood Caries (S-ECC): Their Preponderance,Site-specificity,and Clinical Control with Silver Diamine Fluoride

概要

Severe early childhood caries (S-ECC) is a globally prevalent, virulent variant of early
childhood caries (ECC), resulting in rapid, rampant destruction of deciduous tooth structure. It
primarily manifests as enamel/dentine lesions on the occlusal and/or proximal surfaces of incisors
and deciduous molars of preschool children. To date the microbiota of S-ECC has had little
attention compared to that of ECC. Hence, the focus of this investigation was to study in detail the
bacterial and fungal flora of S-ECC with particular reference to their preponderance, sitespecificity, and finally, the clinical management of the condition with topical silver diamine
fluoride (SDF).
First, the metagenomic data, derived using NGS studies, of 19 freshly collected clinical
samples, showed that the deep-dentine occlusal eco-niches support a more homogenous
community of bacteria in terms of their diversity, composition, and proportions, compared to the
proximal deep-dentine niches. The ubiquity of microbes with collagenolytic potential in these
niches tended to ratify the ecological hypothesis of dentine caries.
Second, the Candida biome and its cariogenic traits from dentin samples were analyzed. It
revealed for the first time, the profusion of yeast flora, particularly Candida species, in both the
occlusal and proximal S-ECC lesions. The multiplex-PCR investigation showed, at both niches,
mono, dual, and mixed Candida albicans species, and non-albicans Candida species (NACS) with
a predominance of the latter. However, proximal cavities had significantly more mixed-species
yeasts than the occlusal niches (p < 0.05). Furthermore, evaluation of the virulence traits of the
yeast isolates indicated that all Candida species were highly acidogenic, and aciduric, and prolific
biofilm formers, with a relatively high potential for protease production. A significant positive
correlation between phospholipase, and protease production of the tested clinical isolates
suggested that the caries-associated candidal flora have an arsenal of enzymes promoting dentinal
collagenolysis (p<0.05). These attributes clearly indicated their potency for tooth demineralization,
as well as their collagenolytic ability, adding further credence to the ecological hypothesis of
dentine caries.
Considering the profuse mycobiome and bacteriome of these deep dentinal niches, it was
tempting to evaluate a contemporary, chemo-mechanical interventional measure used in deepcaries management - the topical delivery of silver diamine fluoride (SDF). The in vitro data
derived, for the first time, using a battery of caries-associated yeast flora, demonstrated the robust
anti-candidal potency of this agent, in addition to its well-known antibacterial activity.
To conclude, the bacteriome and the mycobiome of S-ECC is diverse and complex. These
together with distinct differences in the occlusal and proximal S-ECC biomes, reported here for
the first time, imply that the high-density multispecies candidal mycobiome, in particular, plays a
pivotal role in this relatively common childhood disease. ...

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