In spite of having a high socioeconomic standing, in Iceland caries prevalence has remained stubbornly high. This study reports findings from a mixed fishing and farming community in East Iceland that has traditionally been associated with the highest prevalence of caries. A total of 188 children aged 3–16 yr (96.4% of residents of that age group) were examined. At 6 yr the mean dmfs score was 4.1, DMFS 0 and 48% were caries‐free. The mean DMFS score at 12 yr was 4.7 and 22.6% remained caries‐free but at 16 yr the DMFS score was 11.6 and no children were caries‐free. Caries was unevenly distributed within each age group and was more prevalent among residents of the fishing town than the surrounding farming district. In a pilot study conducted in 1989 mean counts of Streptococcus mutans for children aged 4–7 yr were 2.6 × 105 cfu/ml and declined to 4.6 × 104 cfu/ml in 1990 after a program of chlorhexidine brushing had been added to the routine caries preventive measures adopted in this community. It may therefore be possible to screen Icelandic children for caries risk and apply preventive measures to those demonstrated to be most in need.

Two hundred and seventeen approximal spaces, initially caries free, in 58 patients were studied clinically and radiographically, at intervals of 6 months, for 3 years. Samples of approximal dental plaque were removed for culture of Streptococcus mutans, Streptococcus sobrinus, and lactobacilli. During the study approximal caries developed in 16 subjects (27.6%) at 30 sites (13.8%), involving 42 teeth. 56 of 58 (96.7%) subjects harboured S. mutans at some time during the study, 62.1% lactobacilli, and 29.3% had S. sobrinus. The counts of S. mutans were significantly higher in those subjects that also carried S. sobrinus than in the remaining subjects. A persisting high count of S. mutans > 105 colony-forming units per millilitre (CFU/ml) or a count that rose by ≥ 1 × log10 CFU/ml during the study was seen in 25 of 30 sites that subsequently became carious (p < 0.001). Similarly, counts of lactobacilli that were consistently > 103 CFU/ml or rising by ≥l×logo CFU/ml were seen in 17 of 30 sites that became carious (p < 0.001). Although there were strong statistical associations between approximal caries and high or rising counts of these cariogenic bacteria, the bacterial counts were not good predictors of future approximal caries at that particular site.

BackgroundDental caries has been strongly associated with mutans streptococci, particularly Streptococcus mutans and S. sobrinus. Many studies have linked these organisms to the carious process and counts of mutans streptococci have been used to monitor caries risk. The high levels of caries generally found in Iceland have enabled several studies to be performed on the variation within strains of S. mutans.MethodsThis paper reports some studies showing phenotypic differences between strains of S. mutans that were related to whether the strain was isolated from an individual with active caries or from a caries-free subject.ResultsStrains from individuals with active caries generally adhered better to apatite, were more vigorous in decalcifying apatite and had bacteriocin-like activity that was likely to help the strain compete successfully with other strains, for example in the dental plaque biofilm.ConclusionsPhenotypic differences exist between strains of S. mutans depending on the caries activity of the individual from whom the strain was isolated.

Mutans streptococci have been correlated with human dental caries. Much is known about the role of Streptococcus mutans in the caries process, but the role of S. sobrinus is less clear. This bacterium has been reported to be very acidogenic and aciduric in vitro and cariogenic in rats and should, therefore, have at least some cariogenic potential in humans. This study was aimed at determining the possible relationship between S. sobrinus, S. mutans and dental caries in a longitudinal study by using a non-selective culturing method and species-specific monoclonal antibodies. At the beginning of this study, 158 children aged 4 yr were examined clinically and salivary mutans streptococci were counted on MSB agar. At 5 and 6 yr of age, the children were examined and mutans streptococci were detected by using speciesspecific monoclonal antibodies and MSB agar. The carriage rate of S. sobrinus increased between 5 and 6 yr from 25 to 48 per cent. The presence of this microorganism was significantly associated with canes incidence (P=O.O3). Relationships between the presence of S. sobrinus and salivary pH, buffer capacity or flow rate were not found. The presence of S. sobrinus or S. mutans was not significantly correlated with dmft when using the species-specific monoclonal antibodies. However, this correlation was highly significant (P < 0.001) when the mutans streptococci were detected by using the selective medium MSB. This suggests that differences in cariogenic potential occur within the species S. mutans or S. sobrinus. The present longitudinal study indicates that S. sobrinus is correlated with caries incidence, but its role in the initiation of caries could not be ascertained.

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