Microbial Aetiology of Dental Caries and Indicators of Caries Risk

The oral biofilm, under the “right conditions” will demineralise the underlying enamel or root dentine. The microbial composition of the biofilm capable of demineralising the dentition has been subjected to considerable investigation over many decades. Conventional cultural techniques, often directed at the enumeration of specific taxa, have been employed as have more recently molecular methods in which the composition of the microflora is derived from the sequence analysis of amplified and cloned16S rRNA. From such data the aetiology of the disease has been inferred; the two approaches give different answers. The microbial assessment of the “right conditions” is concerned primarily with the determination of the salivary levels of caries-associated organisms, usually mutans streptococci [Streptococcus mutans and Streptococcus sobrinus], lactobacilli and yeasts. Essentially the more of these taxa the greater is the risk of caries; but with some caveats. The lower the salivary levels of these taxa the lower the caries risk and the lower will be the caries activity. A difficulty exists that for many years the organisms, and especially the mutans streptococci, used to diagnose the presence of the “right conditions” have been regarded as the aetiological agents of dental caries. The molecular studies of the composition of the oral biofilm associated with sound surfaces, white spot lesions and frank cavities have demonstrated that the microflora is extremely diverse, with a single species never predominant, and that no individual taxon is necessary for the demineralisation of enamel or root dentine. These data suggest that provided the physiology of the biofilm, irrespective of its microbial composition, enables the fermentation of dietary carbohydrates to acid dental caries will follow in the absence of appropriate oral hygiene. The microbial assessment of the “right conditions” for dental caries should have wide application especially in infants during the first years of life prior to the clinical diagnosis of dental caries.