J.J. de Soet

Strain–Related Acid Production by Oral Streptococci

Acid production, in particular at low pH, is thought to be an important ecological determinant in dental caries. The aim of the present study was to determine the acid producing capability at different pH levels of 47 streptococcal strains, representing 9 species, isolated from human dental plaque. The bacteria were grown until mid log–phase under anaerobic conditions and acid production was measured in a pH–stat system at pH 7.0, 6.0, 5.5 and 5.0. At all pH values, the mean velocity of acid production (Vap) by Streptococcus mutans and S. sobrinus was significantly higher (p<0.01; ANOVA) than that of the other oral streptococci, including S. mitis, S. oralis, S. gordonii, S. sanguis, S. intermedius, S. anginosus, S. constellatus, and S. vestibularis. However, the Vap of some strains of S. mitis biovar 1 and S. oralis, particularly at pH values of 7.0 and 6.0, exceeded that of some strains of S. mutans. The Vap decreased with pH for all strains, but some strains of S. mitis biovar 1 and strains of the mutans streptococci maintained a relatively high rate of acid production. The results suggest that some strains of S. mitis biovar 1 and S. oralis may play an important role in caries development by modifying the environment in dental plaque to become favourable for the succession of aciduric species. The study furthermore emphasises the need for detailed species and biovar identification of oral streptococci and for recognition of the significant physiological differences that occur within single species.

Bacterial Counts in Carious Dentine under Restorations: 2–Year in vivo Effects

Little is known about the long–term effects of fluoride–releasing materials on carious dentine in vivo. The aim was to investigate the 2–year influence of a resin–modified glass ionomer cement (RM–GIC) and amalgam on the bacteriological counts of carious dentine that remained under class I restorations. To enable a split–mouth design, 33 molar pairs in 33 patients (mean age 15.1 years, SD 1.4) were selected, based on clinically and radiographically diagnosed occlusal dentine caries. The enamel of the carious molars was removed, and the carious dentine was sampled under aseptic conditions just beneath the dentinoenamel junction. The molars were alternately restored with RM–GIC or amalgam without further removal of carious dentine. The samples were processed for microbiological determination of total viable counts (TVC), mutans streptococci (MS), and lactobacilli (LB). The molar pairs of 25 patients were reevaluated after 2 years using the same clinical techniques and were permanently restored after complete caries removal. Both materials showed a substantial decrease in numbers of TVC and LB of the carious dentine after the 2–year period. Compared to amalgam, the decrease in the numbers of LB was significantly more pronounced for RM–GIC. No microorganisms were detected in only 11 molars (6 RM–GIC and 5 amalgam) after the 2–year period. Based on this study, we suggest that complete removal of carious dentine is still the best conservative treatment, irrespective of the restorative material used.

Acid production by oral strains of Candida albicans and lactobacilli.

Both Candida albicans and lactobacilli are common colonizers of carious lesions in children and adolescents. The purpose of this study is to compare the velocity of acid production between C. albicans and several Lactobacillus species at different pH levels and concentrations of glucose. Washed, pure resting-cell suspensions were obtained by culturing a total of 28 oral isolates comprising the species C. albicans, Lactobacillus rhamnosus, Lactobacillus paracasei paracasei, Lactobacillus paracasei tolerans and Lactobacillus delbrueckii lactis. Acid production from glucose was determined at a constant pH of 7.0, 5.5, 5.0 and 4.0 by repeated titrations with NaOH in an automated pH-stat system. Acid formation rates of yeast and lactobacilli proved to be similar at both neutral and low pH, while in a moderately acidic environment C. albicans produced less acid than the lactobacilli. Ion chromatographic analysis of the cell-free medium after titration revealed pyruvate to be the predominant organic acid anion secreted by C. albicans. The proportion of organic acids to overall acid production by the yeast was below 10% at neutral conditions, in contrast to 42–66% at pH 4.0. Compared to lactobacilli, yeast required a concentration of glucose that was about 50 times higher to allow acid production at half the maximum speed. Considering the clinical data in the literature about the frequency and proportions of microorganisms present in early childhood caries lesions, the contribution of oral lactobacilli as well as C. albicans to overall microbial acid formation appears to be important.

Acidogenesis by Oral Streptococci at Different pH Values

Streptococcus mutans is known to be one of the most cariogenic oral microorganisms. Recently, organisms classified as S. mutans have been shown to be genotypically heterogeneous and to form at least six separate species. In this study, differences in acid production between the mutans streptococci and Streptococcus sanguis were investigated at pH values from 5.0 to 7.0. While all of the species investigated were able to produce acids, Streptococcus sobrinus was found to be significantly more acidogenic than the others. S. sobrinus was capable of sustained acid production at pH levels below 6.0, while acid production by other species ceased or was strongly inhibited. These results indicate that S. sobrinus deserves more attention as a potentially cariogenic microorganism.

Prediction of dental caries in pre-school children.

Data obtained in a longitudinal study of caries incidence and caries-related factors were analysed with a view to producing a model for the prediction of caries. In direct correlations, caries incidence was significantly associated with bacterial, dietary and salivary variables; but when the data were examined by stepwise regression the strongest variables were the baseline caries score and misuse of sugar. Counts of Streptococcus mutans entered into the analysis but only as a relatively minor component. Similar significant relationships were seen with the determination of odds ratios. A caries activity test was formulated combining the following caries-associated variables: high counts of S. mutans, or lactobacilli, or the misuse of sugar, or frequent consumption of paediatric medicines. Regular use of fluoride tablets could compensate for paediatric medicine use or misuse of sugar. Such a caries activity test if it had been applied to the children at baseline would have had a positive predictive value of 0.76, a negative predictive value of 0.82, a sensitivity of 0.8 and a specificity of 0.78. Combining tests made the prediction of caries more accurate and in the population for which it was intended gave a reliable means of detecting those children most in need of enhanced caries prevention.

The Effect of Glass-Ionomer Cement on Carious Dentine: An in vivo Study

The effect of a glass-ionomer cement sealant on carious dentine was investigated clinically and bacteriologically. The study group consisted of 24 molar teeth, with small clinical visible occlusal dentine lesions, in 13 children (aged 7-18 years). Twenty of these molars were filled and sealed with a glass-ionomer cement (Fuji Ionomer Type III) and 4 with a resin sealant (Delton). From each molar, two dentine samples were collected aseptically with a time interval of 7 months. The first sample was taken after opening the lesion just beneath the dentino-enamel junction before application of the filling material (sample A), and the second beneath the removed filling material (sample B) 7 months later. Before collecting sample B the sealant was clinically evaluated and impressions were prepared in order to (re)evaluate the sealants later by scanning electron microscopy (SEM). After taking the second sample, the remaining fissures were opened to a standard depth, the caries which was still present was removed, and a composite resin restoration was applied. In all teeth, more glass-ionomer cement material was found by SEM compared to the clinical evaluation. In both the glass-ionomer- and the resin sealant-treated group, the median value of the total number of microorganisms (CFU) on blood agar was 100 times smaller in the B sample. Microorganisms were found in 90% of the B samples in the group treated with glass-ionomer cement; hard dentine was also found in 45% of the B samples from this group.(ABSTRACT TRUNCATED AT 250 WORDS)

In vivo cariostatic effect of resin modified glass ionomer cement and amalgam on dentine

Fluoride-releasing materials have been reported to be bactericidal in vitro. This may be of benefit to modern dentistry, which is directed to the preservation of tooth tissue during restorative treatment. Little is known about in vivo effects. The aim is to investigate the influence of a resin-modified glass ionomer cement (RM-GIC) on carious dentine that remains under restorations, compared to amalgam. Using a split month design, 40 molar pairs in 40 patients (mean age 14.9 years) were selected, based on clinically and radiographically diagnosed occlusal dentine caries. Under aseptic conditions, the enamel was removed and the carious dentine was sampled just beneath the dentino-enamel junction using a round bur. Without further removal of carious dentine, the molars of a pair were alternately restored with RM-GIC or amalgam. The colour and the consistency of the carious dentine were assessed. The samples were processed for microbiological determination of total viable counts (TVC), mutans streptococci (MS), and lactobacilli (LB). After 6 months the molars were reopened, similarly sampled and evaluated, and then permanently restored after complete caries removal. For both materials a substantial decrease in the numbers of TVC, MS and LB was found after the 6-month period. Also a positive effect was observed on the colour and the consistency of the remaining carious dentine, which was comparable for the two materials. RM-GIC showed a significantly larger decrease in counts of MS and LB than amalgam, but not for TVC. Since in only few cavities the number of bacteria decreased under the level of detection, it is still considered essential to remove all carious dentine during restorative treatment.

Red autofluorescence of dental plaque bacteria

Red autofluorescence of plaque and its relation to fluorescence of a single species in the biofilm was studied. Fluorescence images of non-disclosed and disclosed plaque of 28 first-year students were captured. The plaque samples were assessed by culture methods and studied for red autofluorescence. Species capable of producing red autofluorescence were cultivated from subjects with and without red plaque autofluorescence. Red autofluorescence was observed from Actinomyces odontolyticus, Prevotella intermedia and from Porphyromonas gingivalis and Peptostreptococcus micros grown together. The microbial findings indicated that the intrinsic characteristics of the mature biofilm itself are more responsible for the red autofluorescence than the characteristics of the single species.

Bacterial composition and red fluorescence of plaque in relation to primary and secondary caries next to composite : an in situ study

BACKGROUND/HYPOTHESIS Secondary caries has been suggested as the main reason for restoration replacement. We hypothesized that more caries-associated bacteria are found on composite resin restoration material, compared to sound tooth tissue. METHODS Both restored and unrestored dentin and enamel samples were placed in a full denture of eight subjects for 20 weeks. The microbiological composition of approximal plaque and the association between caries-associated bacteria and red autofluorescence of dental plaque was studied. Every 4 weeks the specimens were microradiographed using transversal wavelength independent microradiography (T-WIM). After 1 and 20 weeks red fluorescence pictures and plaque samples were taken. Samples were cultured for total anaerobic counts, mutans streptococci, lactobacilli, candida and Actinomyces odontolyticus. RESULTS Lesion depth in the dentin and enamel was positively associated with lactobacilli, and lesion depth in dentin was positively associated with A. odontolyticus, whereas no association was found between mutans streptococci and lesion depth. The red-fluorescent bacteria A. odontolyticus and lactobacilli did not correlate with red-fluorescent plaque, indicating that red fluorescence is probably not caused by a single species of these bacteria. After 20 weeks, a higher proportion of combined mutans streptococci and lactobacilli was found on restored tissue compared to non-restored tissue (P = 0.04). CONCLUSION The higher proportion of caries-associated bacteria on restored tissue indicates that the ecology on the surface of primary lesions differs from that on lesions next to composite, and that secondary caries next to composite may differ from the primary caries process.

The Effect of 6-Monthly Application of 40% Chlorhexidine Varnish on the Microflora and Dental Caries Incidence in a Population of Children in Surinam

This study is aimed at determining whether a commercially available varnish, containing 40% chlorhexidine, is able to reduce the numbers of mutans streptococci and lactobacilli in saliva, in a moderately caries-active population in Surinam. 238 children, ages 13–14 years, were selected from different schools in Paramaribo, Surinam. From these children, total dental status was recorded and saliva samples were taken. At baseline and every 6 months, a 40% chlorhexidine varnish (EC40®) was applied. The control group received a neutral gel that did not contain chlorhexidine. The numbers of salivary mutans streptococci and lactobacilli were calculated by standard methods, and the caries status was recorded every 12 months. The study lasted 30 months. The results indicate that chlorhexidine varnish did not decrease the numbers of cariogenic bacteria, nor did it decrease caries progression. Moreover, in this population with a low dental health care, children with lactobacilli present in the saliva above our detection level, the chlorhexidine varnish even tended to increase caries progression, possibly due to selection of aciduric and acidogenic oral bacterial species. We therefore conclude that 40% chlorhexidine varnish is not likely to decrease caries in children in a high-treatment-need population without treatment of the sources of infection.