The Role of Bacteria in the Caries Process

Abstract

Dental biofilms produce acids from carbohydrates that result in caries. According to the extended caries ecological hypothesis, the caries process consists of 3 reversible stages. The microflora on clinically sound enamel surfaces contains mainly non-mutans streptococci and Actinomyces, in which acidification is mild and infrequent. This is compatible with equilibrium of the demineralization/remineralization balance or shifts the mineral balance toward net mineral gain (dynamic stability stage). When sugar is supplied frequently, acidification becomes moderate and frequent. This may enhance the acidogenicity and acidurance of the non-mutans bacteria adaptively. In addition, more aciduric strains, such as 'low-pH' non-mutans streptococci, may increase selectively. These microbial acid-induced adaptation and selection processes may, over time, shift the demineralization/remineralization balance toward net mineral loss, leading to initiation/progression of dental caries (acidogenic stage). Under severe and prolonged acidic conditions, more aciduric bacteria become dominant through acid-induced selection by temporary acid-impairment and acid-inhibition of growth (aciduric stage). At this stage, mutans streptococci and lactobacilli as well as aciduric strains of non-mutans streptococci, Actinomyces, bifidobacteria, and yeasts may become dominant. Many acidogenic and aciduric bacteria are involved in caries. Environmental acidification is the main determinant of the phenotypic and genotypic changes that occur in the microflora during caries.

Functional profiles of coronal and dentin caries in children

“…Detection of genes to these species fit with the expanded ecological plaque hypotheses that proposes blooming of Actinomyces and non-mutans streptococci in early stages of dental caries [17]. Under this hypothesis, these species set up the environment for more acid-tolerant and acidogenic species that would include S. mutans, S. wiggsiae [33], Actinomyces sp.…”

“…Samples representing health and caries at the tooth surface and deep in dentin were examined to represent different disease stages. In caries, one might expect increased gene expression related to acid production [17], whereas in health-associated microbiomes gene expression would reflect that of a stable community able to counter acidic attack [6]. Long-term we sought which metatranscriptome activities characterized different clinical states and so that future studies could use the information in risk assessment and as targets for improved anti-caries therapies.…”

Cross-feeding and interkingdom communication in dual-species biofilms of Streptococcus mutans and Candida albicans

“…The excreted organic acids result in a strong localized pH drop that can cause lesions of the dental enamel and thus initiate caries development. S. mutans is a common inhabitant of the oral cavity and has long been recognized as one of the causes of dental caries, a highly prevalent biofilm-dependent polymicrobial oral infectious disease (Kutsch and Young, 2011;Takahashi and Nyvad, 2011;Burne et al, 2012). Biofilm formation in S. mutans is readily induced by dietary sugars that are transformed to extracellular polysaccharides by dedicated enzymes, which are therefore important targets of anti-caries strategies (Bowen and Koo, 2011).…”

Cariogenic microflora and pH in superficial and deep layers of occlusal carious lesions - A metagenomic analysis

“…Similar study have shown that microflora of clinically sound enamel surfaces contains mainly non-mutans Streptococci and Actinomyces, in which acidification is mild and infrequent. [25] Propionibacterium is an acidogenic bacteria with a prevalence of 7.3% of total population from phylum Actinobacteria. Total pooled count in the superficial layer was 12660, and deep layer was found to be 3949.…”