Since the fact that microorganisms are found in the carious lesion was pointed by Milleru very early, numerous investigators participating with the problem of the experimental dental caries used to examine the bacteria which they applied for the experiment in a produced lesion. Invasiveness of limitted number of laboratory strains into an unerupted hamster tooth were tested in a test tube containing neutral broth by Hurst et al2) and they found that oral actinomycetes, Lactobacilli, S tr, tococci and Coηmebacteria were able to
do this. They also found that the invasion became much easyer under the acidic circumstance and such approved organisms for invasiveness micht be nourished by the dental substance alone. Before this experiment, Gins3) had isolated two filamentous organisms, Leρtothrix fragmentata and actinomycetes ,
from carious lesion as the real causer of the lesion, depending on the hypo thesis tnat only bacteria which be able to be nourished by dental substance will be capable to commence carious infection. Unfortunately, however, his results were obtained from a very few material.
Present experiment was set up to make a better picture of oral bac teria invasive into dental tissues.
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