Paul H. Keyes

The infectious and transmissible nature of experimental dental caries: Findings and implications

Abstract In both hamsters and Osborne-Mendel rats dental caries appears to be an infectious and transmissible disease which involves a penicillin-sensitive flora. The findings reported suggest that if this flora is present or is inoculated into young animals, rampant caries can be induced by a high-carbohydrate low-fat diet within 35 days. When low to negligible caries has been found in animals similarly fed, the flora presumably has not been present in sufficient quantity to be pathogenic. Caries activity was markedly reduced in hamsters and rats after the penicillin-sensitive flora had been depressed prior to feeding the test diet. Hamsters whose flora had been depressed, in some cases, produced several generations of progeny with negligible activity. Marked differences in activity apparently result from alterations or variables in the flora which animals acquire, transmit, and develop during the course of an experiment. Thus, a number of interpretations, which have been made to explain differences in caries activity observed in past studies, must be reconsidered in terms of variations possibly induced in the microbic flora.

Periodontal lesions in the Syrian hamster—III

Abstract Three strains of hamsters are produced by the NIH Animal Production Center, the golden, the cream, and the albino. An active type of periodontal disease develops in golden and cream animals when they are fed a high carbohydrate diet, but it does not develop in the albino hamster tested under similar conditions. However, the disease can be readily induced in “noninfected” albino animals by an inoculation of scrapings of subgingival plaque from affected animals, and once acquired, either by direct inoculation or other contamination, it can be transmitted from generation to generation. Filamentous bacteria have been recovered from cultures of the plaque material in high numbers. In histological sections filamentous organisms are found deep in the gingival pockets, often surrounded by inflammatory cells. Under certain dietary conditions, the same organisms apparently invade the root surfaces and produce changes which might be classified as root surface caries. If the diet be changed, e.g. to one composed of commercial laboratory chows, the soft subgingival plaque will mineralize and form typical subgingival calculus. Periodontal lesions can be produced separately or together with enamel caries because different bacterial components are apparently associated with the two diseases.

Aerobic, gram-positive, filamentous bacteria as etiologic agents of experimental periodontal disease in hamsters

Abstract The bacteriology of a spontaneous periodontal disease of hamsters was investigated. This disease is characterized by a heavy, adherent, subgingival plaque and accompanies the feeding of a high carbohydrate diet. Pure cultures of aerobic branching filaments isolated from the plaque induced the disease when inoculated orally into uninfected albino hamsters. Other plaque organisms including streptococci and various unidentified gram-negative rods did not induce the disease. A filamentous strain “labelled” by making it resistant to terramycin was used to induce the disease and to trace implantation, persistence and transfer of the organism. The “labelled” strain was recovered in high numbers from all hamsters infected with this strain and its transfer from infected mothers to offspring was observed. Simultaneous inoculations with the aerobic filament and a specific streptococcus induced both periodontal disease and caries in the same animal.

The subgingival microbial flora associated with human dental implants

I n recent years the microbial colonization on different surfaces in the oral cavity has been studied by oral microbiologists. Resident bacterial populations have been examined from the buccal mucosa,’ the tongue,2 enamel,3 cemental root surfaces,4 epoxy resin crowns,s overhanging amalgam restorations,6 and surfaces of dentures? However, none of the studies has involved surfaces of dental implants, despite their wide use over the past 15 years for the replacement of teethin edentulous spores. Even with clear anatomic and morphologic differences, clinical and histopathologic descriptions of gingival inflammation, pocket formation, and alveolar bone loss around protruding dental implants that are remarkably similar to periodontal lesions associated with natural teeth have been reported.8s’2 With natural teeth the relationship between periodontal disease and the presence of periodontopathic microorganisms in subgingival plaque has become widely accepted. 13,14 In contrast little is known about the nature of the subgingival bacterial populations that colonize around dental implants and their relationship to peri-implant tissue conditions. Direct microscopic examinations of dental plaque enables a rapid and inexpensive study of subgingival bacterial types without encountering the many difficulties inherent in carrying out conventional bacteriologic culturing, and they have been used previously to characterize the microorganisms around natural teeth.‘5,‘6 In this investigation the subgingival microbiologic flora associated with 17 gingival tissue-protruding dental implants was studied with direct phasecontrast microscopy.

In vitro methods for the study of plaque formation and carious lesions

Abstract Streptococci known to be caries-conducive in experimental animals formed heavy bacterial plaques on extracted teeth, artificial teeth, stainless-steel wires and other objects. This was accomplished by cyclic exposures to a growth medium for 3 hr, 5% sucrose solution for 1 hr, and synthetic saliva for 3 hr in that order, for a total of 2 weeks. Streptococci known to be caries-inactive in animal tests did not form plaque under these conditions. Sucrose was required for plaque production and could not be replaced by glucose, fructose, galactose, lactose, sorbitol, or a mixture of glucose and fructose. The mucin in the synthetic saliva was found to be essential for plaque production in this test system. Filament-forming actinomycetes isolated from animal periodontal disease also formed a heavy plaque. Plaques were grown on a glass probe electrode using the above mentioned methods in order to obtain an estimate of acidity levels which develop under such deposits. In 5% sucrose the pH dropped to a range where enamel would be decalcified (4.5–5.0). The low pH values persisted under the plaque for 3 hr after the electrode had been subsequently transferred to synthetic saliva. Extracted human teeth were placed in an apparatus in which the various media described above could be automatically metered to an incubation chamber in preselected sequences for varying the time periods. Extensive plaque formation and incipient carious lesions developed within a 3-week period.

Dental caries in the Syrian hamster—IX

Abstract Streptomycin-resistant streptococci were developed from parent cariogenic strains isolated from a carious lesion in a hamster. These so-called “labelled” streptoccci are also cariogenic and are readily recovered and identified on selective culture media containing streptomycin, but they induce caries considerably more slowly than the parent strains or natural infection. To enhance caries activity and still have the advantages of labelled cariogenic organisms, attempts were made to implant a streptomycin resistant mutant strain (HSR-6) into the mouths of hamsters which harboured other cariogenic organisms. Recoveries, however, were only sporadically successful. This result has been attributed, at least in part, to competition between closely related strains for establishment within the oral microbial ecology. Yet, in a few cases the streptomycin-resistant mutant strain successfully established itself in association with other cariogenic forms, and several females which maintained the labelled streptococci passed them to succeeding generations. In addition this report shows again that caries can be induced in albino hamsters by the inoculation of pure cultures of certain streptococci, or by a flora passed from dam to offspring, or by direct transmission from cage mates. Many caries assays require not only a study of the activity of the disease but also a method for assessing associated microbiological conditions. These studies point the way toward more refined microbic evaluations in conventionally maintained laboratory animals.

Orthodontic therapy in patients with juvenile periodontitis: Clinical and microbiologic effects

The correction of malocclusions in juvenile periodontitis (JP) patients completing periodontal therapy is a problem of increasing clinical concern to orthodontists, since many teeth with severe alveolar bone loss in these patients can now be successfully treated without extraction. In this report, fixed edgewise orthodontic therapy was carried out after the completion of periodontal therapy on four JP patients. The orthodontic therapy included extensive intrusion of teeth severely affected by JP. Phase-contrast microscopic analysis of subgingival plaque from orthodontically treated teeth was used to monitor longitudinally the effects of fixed orthodontic bands on the subgingival flora and also to monitor the efficacy of topical and systemic antimicrobial therapy aimed at suppression of suspected periodontopathic bacteria. Orthodontic movement was completed on most periodontally compromised teeth without significant evidence of additional deterioration in periodontal status. However, within the first 6 months of orthodontic band placement, all patients had significant increases in the number of spirochetes and motile rods in their subgingival flora. Three of the patients also developed high levels of crevicular polymorphonuclear leukocytes around orthodontically treated teeth, indicating significant subgingival inflammation. Intensive antimicrobial measures, including topical inorganic salt applications and systemic tetracycline, were helpful in limiting clinical inflammation and subgingival colonization by periodontopathogens during orthodontic therapy. The results demonstrate that successful orthodontic repositioning can be carried out in treated JP patients. In addition, bacteriologic monitoring and chemotherapeutic suppression of periodontal pathogens may be valuable in the prevention of further destructive periodontal disease activity in periodontitis patients undergoing orthodontic therapy.

Plaque Formation and Implantation of Odontomyces viscosus in Hamsters Fed Different Carbohydrates

A sucrose diet supported implantation of Odontomyces viscosus and a caries-inducing streptococcus in albino hamsters. Caries and periodontal disease occurred simultaneously when both types of bacteria were implanted. Odontomyces, but not the streptococcus, became implanted in albino hamsters on a starch diet. Glucose and fructose diets also supported implantation of odontomyces and development of periodontal disease in golden hamsters. Caries development was minimal.

Determination of saliva and dental plaque pH in hamsters with glass micro-electrodes

Abstract Measurements of the pH of saliva, conjunctival fluid and dental plaques in situ were made in hamsters receiving a caries-conducive diet, by the use of glass microelectrodes specific for hydrogen ions. The pH of conjunctival fluid ranged between 6.3 and 7.3. The pH values for saliva ranged between 6.3 and 9.0 depending on the exposure to air, and presumably the amount of CO 2 lost to the air. All dental plaques fermented sucrose but only in hamsters in which dental caries was developing as a result of infection with cariogenic streptococci did the plaques ferment sucrose rapidly and attain strongly acid values. Thus caries in hamsters, like caries in man, seems to be associated with acidogenic activity of microbial plaques.

Hydrogen ion activity in dental plaques of hamsters during metabolism of sucrose, glucose and fructose

Abstract Hamsters receiving a high sucrose diet were infected orally with strains of Streptococcus mutans , known to induce dental microbial plaque formation and caries in these animals, or a strain of Odontomyces viscosus , which causes the accumulation of plaque deposits in the gingival sulcus but does not induce coronal caries lesions. Glass micro-electrodes were used to follow the pH changes following the application of concentrated or dilute solutions of sucrose, glucose, or fructose to the plaques in situ . The hydrogen ion activity of Strep. Mutans -induced plaque deposits increased rapidly upon the application of carbohydrate solutions, readily attaining pH values of 5.0 or lower. Plaques formed as a result of O.viscosus infection produced acid at a slower rate and to a lesser extent (minimum pH 5.4, average 6.4). Plaque deposits resulting from the indigenous oral microflora were scanty and produced very little acid (minimum pH 5.8, average 7.0). The amount of carbohydrate applied and the size of the plaque also influenced the rate and extent of hydrogen-ion activity change. Fructose was fermented at a slightly slower rate than glucose or sucrose by the plaques of animals infected with Strep. mutans . However, the relative ability of these carbohydrates to serve as substrates for acid production did not correlate with their reported relative efficacy as cariogenic dietary substrates, indicating that additional factors are involved in the development of caries in the hamster.