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PREDOMINANT CULTIVABLE MICROFLORA OF PLAQUE ON REMOVABLE DENTURES IN PATIENTS WITH HEALTHY ORAL MUCOSA

Plaque from the fitting surface of upper full dentures in eight patients with healthy palatal mucosa was studied. To characterize the predominant cultivable flora, 916 isolates (100-128 from each sample) were subcultured from anaerobic roll-tubes. Streptococci constituted 0-81 per cent (median, 41 per cent) of the isolates with varying proportions of Streptococcus milleri, Streptoccus mutans, Streptococcus salivarius, Streptococcus mitior and Streptococcus sanguis. Staphylococcus aureus made up 0-13 per cent (median, 6 per cent). Gram-positive rods constituted 1-74 per cent (median, 33 per cent). Among these, Actinomyces israelii, Actinomyces naeslundii, Actinomyces viscosus and Actinomyces odontolyticus were the most common species, whereas lactobacilli were isolated only from two samples, constituting 21 and 48 per cent. Among Gram-negative bacteria, only Veillonella parvula was common, constituting 3-20 per cent (median, 10 per cent). Gram-negative rods were isolated only from three samples in small proportions making up 0-6 per cent (median, 0 per cent) of the flora. Forty-seven isolates (5 per cent) were lost. Cultures for yeasts on Sabouraud agar were positive for five samples and the yeast counts corresponded to 0-0.45 per cent (median, 0.002 per cent) of the total viable counts. The microflora of denture plaque is highly variable and is to a large extent similar to that of some forms of dental plaque.

Population structure of Actinobacillus actinomycetemcomitans: a framework for studies of disease-associated properties.

The Actinobacillus actinomycetemcomitans population consists of a large number of clones among which the ubiquitous leukotoxin gene operon appears very homogeneous. Population genetic analyses performed by multilocus enzyme electrophoresis together with DNA fingerprinting and analyses of genomic DNA restriction fragment length polymorphisms (RFLP) on 97 strains isolated over a period of 45 years revealed that each of the serotypes a, b, c, d and e comprise genetically isolated subpopulations and that successful horizontal transfer of genomic DNA between strains of different serotypes appears to be extremely rare in vivo. In contrast, recombination between strains of the same serotype in general appears to take place in nature. The results provide evidence that non-serotypeable strains are serotype antigen-deficient variants originating from strains of the known serotypes. Serotype b and c strains may contain transmittable DNA sequences not found in strains of the other serotypes.

Effect of fissure sealing on the microflora in occlusal fissures of human teeth

Abstract To study the survival of bacteria in sealed fissures, occlusal fissures from unerupted third molars were implanted into occlusal fillings in 11 students. The fissures were worn for 7 days to accumulate plaque. Control fissures were then removed for microbiological study. Experimental fissures were etched with 50 per cent phosphoric acid, sealed with NuvaSeal®, and removed either immediately or 2 weeks after sealing. All sealed fissures contained viable bacteria, although the viable counts were lower than in unsealed fissures worn in the same tooth. Among the bacteria studied using selective media, some species survived sealing better than others. Thus sealing eliminated Haemophilus and greatly reduced Strep, sanguis and Strep, salivarius, whereas numbers of Strep, mutans and lactobacilli were not changed by the sealing. The caries-preventive effect of fissure sealants may be due to a combination of 1) decrease in the number of viable bacteria, and 2) lack of sufficient fermentable carbohydrates for the remaining bacteria to accumulate acid in cariogenic concentrations.

An in vivo Method for the Study of the Microbiology of Occlusal Fissures

A method has been developed for the implantation of artificial fissures into human teethThe fissures, produced from Mylar film, were inserted into gold receptacles and placed in large amalgam restorations of 10 dental students. The production of.the fissures and the receptacles is described in detail. The fissures, which provided observation periods from 1 to 21 days, were used for cultural studies, paraffin sectioning, cryostat sectioning or electron microscopy. The preliminary analysis of the contents showed that colonies of intact microorganisms were present throughout the fissures although many dead bacteria were also seen. The majority of the microorganisms were gram-positive cocci. It is suggested that the artificial fissures constitute an experimental model system which permits studies of plaque formation under conditions similar to those of natural occlusal fissures.

Microbiological Studies of Plaque in Artificial Fissures Implanted in Human Teeth

Microbial colonization was studied in artificial Mylar ‘fissures’ implanted for 1, 3 and 7 days in a molar tooth in each of six subjects who maintained an excellent oral hygiene. The microflora of the ‘fissure’ content was studied by performing total microscopic counts as well as viable counts on various media. The samples contained mainly streptococci. The number of lactobacilli was low but tended to increase with time. The absence of spirochetes and the low numbers of spirilla, fusiforms and filaments support the hypothesis that fissures represent an ecological system differing from that on the smooth surfaces of the teeth.

The interaction of diet and microflora in experimental caries in the rat

Abstract Weanling rats were pretreated with tetracycline and erythromycin and subjected to a caries test period on either Diet 580 (associated with caries on all tooth surfaces) or Diet 585 (associated with caries in the sulci only). One group on each diet was maintained as controls, two groups were reinfected by exposure, one to donor animals which had been on Diet 580 and one to donors on Diet 585. Exposed animals on Diet 580 developed both sulcal and smooth-surface lesions, irrespective of the diet consumed by the donor animals from which they were infected. This indicates that a microflora capable of inducing smooth surface caries was supported by both diets and transmissible from both groups of donors. The control animals on Diet 580 developed lesions in the molar sulci only, indicating that a segment of their microflora which was essential for the induction of caries on the smooth surfaces had been selectively eliminated by the antibiotic treatment. All animals receiving Diet 585, whether they were uninfected controls or exposed to donors, developed carious lesions almost exclusively in the sulci. The results indicate (1) that a specific type of microflora is required for the development of smooth-surface caries and (2) that even in the presence of such a flora and a diet which can support it, smooth-surface lesions may not occur. It is suggested that in the case of Diet 585 this was due to the inability of microbial plaques to accumulate on the smooth surfaces of the molars.

A microbiological study of old plaque in occlusal fissures of human teeth.

As a part of our investigations on fissure plaque, the present study presents data on the microflora of ten natural occlusal fissures implanted for 200–270 days in lower molars of dental students. No