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.

Current scoring systems for dental caries do not consider the dynamic nature of the disease. The aims of the present study were to describe a new set of clinical caries diagnostic criteria which differentiate between active and inactive caries lesions at both the cavitated and non–cavitated levels and to evaluate the reliability of this criteria system in a population with high caries experience. Ten diagnostic codes were defined: 0 = sound; 1 = active (intact); 2 = active (surface discontinuity); 3 = active (cavity); 4 = inactive (intact); 5 = inactive (surface discontinuity); 6 = inactive (cavity); 7 = filling; 8 = filling with active caries; 9 = filling with inactive caries. Distinction between active and inactive caries lesions was made on the basis of a combination of visual and tactile criteria. The inter– and intra–examiner reliability was assessed through repeated examinations of 50 children by 2 recorders over a period of 3 years. The percentage agreement of caries diagnoses varied between 94.2 and 96.2%. The kappa values ranged between 0.74 and 0.85 for intra–examiner examinations and between 0.78 and 0.80 for inter–examiner examinations; 81.6% of all misclassifications involved non–cavitated caries lesions. Disagreement between sound surfaces and non–cavitated active or non–cavitated inactive lesions (31.3 and 31.2%, respectively) was more common than disagreement between non–cavitated active and non–cavitated inactive lesions (10.6%). The probability of reconfirming a sound, non–cavitated active or non–cavitated inactive caries lesion – given that the surface was diagnosed as either sound, non–cavitated active or non–cavitated inactive at the first examination – was 98.0, 68.7 and 72.5%, respectively. The results show that the use of a new set of clinical caries diagnostic criteria based on activity assessment can be performed with a high reliability, even when non–cavitated diagnoses are included in the criteria system.

In this essay we propose an extension of the caries ecological hypothesis to explain the relation between dynamic changes in the phenotypic/genotypic properties of plaque bacteria and the demineralization/remineralization balance of the caries process. Dental plaque represents a microbial ecosystem in which non-mutans bacteria (mainly non-mutans streptococci and Actinomyces) are the key microorganisms responsible for maintaining dynamic stability on the tooth surface (dynamic stability stage). Microbial acid adaptation and subsequent acid selection of ‘low-pH’ non-mutans bacteria play a critical role for destabilizing the homeostasis of the plaque by facilitating a shift of the demineralization/remineralization balance from ‘net mineral gain’ to ‘net mineral loss’ (acidogenic stage). Once the acidic environment has been established, mutans streptococci and other aciduric bacteria may increase and promote lesion development by sustaining an environment characterized by ‘net mineral loss’ (aciduric stage). Hence, high proportions of mutans streptococci and/or other aciduric bacteria may be considered biomarkers of sites of particularly rapid caries progression. This cascade of events may change the surface texture of caries lesions from smooth to rough (enamel) or hard to soft (dentin). These clinical surface features can be reversed at any stage of lesion development provided that the acidogenic/aciduric properties of the biofilm are resolved. From an ecological point of view it is therefore not only important to describe which bacteria are involved in caries, but also to know what the bacteria are doing.

Nyvad B, Kilian M: Microbiology of tbe early colonization of human enamel and root surfaces in vivo. Scand J Dent Res 1987; 95; 369-80.Abstract -This study describes the predominant early microflora on human teeth on the basis of microbiologic identification of 1742 fresh isolates. The isolates were obtained from four dental students who carried test pieces of enamel and root surface in the oral cavity for 4, 8, 12, and 24 h. During the experimental periods oral hygiene was discontinued. Under equal conditions root surfaces were more heavily colonized than were enamel surfaces. However, the composition of the microbiota was the same. Within the first 24 h the microflora was dominated by streptococci and Gram-positive pleomorphic rods. S. sanguis contributed only 6-18% of the early colonizers whereas S. mitis and S. oralis varied between 24^2% and 1-27% (mean values), respectively. The relative proportion of S. oralis increased significantly within the obsen/ation period while the proportion of S. salivarius and arginine-positive S. mitis showed a declining tendency. Acdnomyces species adsorbed to the tooth surfaces within the first 4 h but did not increase their relative proportions until after 8-12 h, possibly due to a long doubling time. In one individual, encapsulated bacteria resembling Stomatococcus mueilaginosus were observed among the early colonizers. The time-dependent shifts in the bacterial populations within 24 h corroborate parallel ultrastructural findings.Several studies have characterized the hu-minor contribution from actinomycetes. It is man microflora during early stages of colon-surprising that the present state of knowization of teeth (1-6). These studies have ledge on early microbial colonization has clearly demonstrated that the early coloniz-been pieced together from several indepeners primarily belong to the streptococci, in dent ultrastructural and microbiologic studparticular the S. sanguis/S. mitis/S. oralis ies. Only one study has applied a compara-(syn. S. midor, S. sanguis II) group, mth a tive approach to the description of the early

The capability of a soft drink or a juice to erode dental enamel depends not only on the pH of the drink, but also on its buffering effect. As the latter is the ability of the drink to resist a change of pH it may add to the effects of the actual pH. The aim of the present study was to compare the pH and the buffering effect of various soft drinks with their erosive effects and the solubility of apatite. In 18 soft drinks, mineral waters and juices available on the Danish market, pH and the concentrations of calcium, phosphate and fluoride were determined. The buffering effect was determined by titration with NaOH. Human teeth (n = 54) covered with nail varnish except for 3×4–mm windows were exposed to 1.5 liters of the drink for either 7 days or 24 h under constant agitation. The depth of the erosions was assessed in longitudinal sections. The depth was found to vary greatly from 3 mm eroded by the most acidic drinks and fresh orange juice to only slightly affected surfaces by most of the mineral waters. The dissolution of enamel increased logarithmically inversely with the pH of the drink and parallel with the solubility of enamel apatite. Orange juice, pH 4.0, supplemented with 40 mmol/l calcium and 30 mmol/l phosphate did not erode the enamel as the calcium and phosphate saturated the drink with respect to apatite. Generally, the lower the pH the more NaOH was necessary to bring the pH to neutrality. In particular the buffering effect of the juice was high. For all drinks, no effect of their low fluoride concentrations was observed.