R.H. Larson

Caries development in rats of different ages with controlled flora

Abstract Sprague-Dawley rats were subjected to a 56-day caries test regimen on cariogenic Diet 580 started when they were 18, 21, 25, 30, 35 or 40 days of age. Comparisons of caries activity were made in three experimental groups: A—Controls; B—Animals “infected” by being housed with an older caries-active animal the first week on the test regimen; C—Animals pretreated for 5 days with erythromycin and then “infected” as in Group B. All animals were maintained on a noncariogenic laboratory chow prior to the beginning of the caries-test period. Animals sacrificed at 40 days of age without having been on the test regimen were caries-free. The “noninfected” animals of Group A showed so much variation that no valid correlation of caries activity with age could be demonstrated. Both groups of “infected” animals (B and C). whether or not pretreated with an antibiotic, showed comparable high levels of activity, which was consistently less for the older animals. The buccal and lingual surfaces, which tend to become more self cleansing in the older animals, showed a greater decrease in caries activity than the proximal and sulcal surfaces, whose anatomical features favor food and microbial plaque accumulation. While the results are in general consistent with the opinion that resistance to the carious process increases with age it appeared that the age of the tooth is not the sole determinant.

Caries Inhibition in the Rat by Water-Borne and Enamel-Bound Fluoride

Osborne-Mendel rats 22–25 days of age were subjected to a 7-day precaries test period during which they were fed a high starch diet and drank distilled water containing no added fluoride or with 10, 5

Frequency of eating as a factor in experimental dental caries

Abstract Caries activity on each of three caries-test diets was directly related to length of time that food was available to the animal and not due to the amount of food consumed. Increased caries activity was also demonstrated following the injection of ethylene diamine tetraacetic acid (EDTA). These results suggest that increased oral retention, whether resulting from changes in the feeding regimen or changes in the biologic status of the animal, may be the common causative factor associated with increased caries activity.

A strain-specific eating pattern as a factor limiting the transmissibility of caries activity in rats.

Abstract In Experiment I the caries activity of the Osborne-Mendel (O-M) and the NIH Black rat (BR) were compared under identical environmental conditions and it was shown that the low activity of the BRs was not due to the lack of implantation of a specific cariogenic oral microflora or to the inadequacy of the caries test diets used. The results of recording food intake of these free-fed rats showed that the O-Ms consumed more food and took more frequent meals than the BRs. In Experiment II the same high-frequency eating pattern (36 meals per day) was imposed on the BRs and O-Ms with the aid of an automatic programmed-feeding machine. The significant increase of caries activity in the BRs on this regime is in keeping with the hypothesis that the inborn habit of short and infrequent eating in the BRs, resulting in infrequent presence of substrate for cariogenic micro-organisms, may be one of the major factors responsible for the low level of caries activity of free-fed BRs.

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.

Reduction of dental caries in rats by intermittent feeding with sucrose substitutes

Abstract Osborne-Mendel rats which were fed diet 2000 and infected with plaque-forming caries-active organisms were given intermittent feedings of diets in which various carbohydrates or fasting periods replaced feedings of the sucrose diet. The sucrose-substitute diets were fed by different regimens in each of three experiments as follows: (1) intermittently, half the time throughout the entire experimental period; (2) continuously the first week of the experiment only, during the period of inoculation with the caries-active organisms; and (3) intermittently so as to provide approximately half the dietary intake, beginning after the week of inoculation with the caries-active organisms when the sucrose diet was fed continuously. All groups of animals fed a sucrose-substitute diet under one of these regimens developed significantly less caries on the smooth surfaces than those on the sucrose diet continuously, but showed a relatively minor decrease in the sulci.

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.

Experiments on local and systemic action of fluoride in caries inhibition in the rat

Abstract Fluoride administered to rats by gastric intubation was associated with an increase in fluoride uptake by the enamel and caries inhibition, but to a lesser extent than in animals consuming the same amount of fluoride in the drinking water. These differences were more pronounced in the first and second molars which erupted within 2 or 3 days of the start of the experiment than on the third molars which had at least two weeks of pre-eruptive exposure to systemic fluoride.

Genetic and environmental influences on dental caries in the osborne-mendel and the nih black rat

Abstract In these studies the Osborne-Mendel (O-M) rat has shown a significantly higher level of caries activity than the NIH Black rat (BR) whether caged with their own kind, or caged with O-M animals during the caries test period. The patterns of caries activity were also different in that activity in the BR was predominantly in the sulci, while activity in the O-M was divided between the sulci and the smooth surfaces. The hybrid animals exposed to an O-M mother or an O-M cage mate during the test period, developed somewhat more activity on the smooth surfaces than those not exposed. However, the level of caries activity of all hybrid animals was nearer that of the BR than the O-M. The causative factors for these differences have not been determined.

Development of Caries in the Hunt-Hoppert Caries-Susceptible and Caries-Resistant Rats Under Different Experimental Conditions

Rats of both Hunt-Hoppert lines, originally designated as caries-susceptible (Ca-S) and caries-resistant (Ca-R) lines, were highly susceptible to caries when subjected to a combination of diet and microflora that provided a challenge to the resistance of all surfaces of the teeth. Strain differences were indicated by the predominance of sulcal lesions in the Ca-S line and smooth-surface lesions in the Ca-R line.