IN VITRO PRODUCTION OF PLAQUES AND CARIES

¹ Department of Bacteriology, School of Medicine and Department of Operative Dentistry, School of Dentistry, University of Illinois, Chicago, Ill.

1. An apparatus is described which is designed to permit the constant microscopic observation of plaque formation and pre-plaque phenomena as well as cavitation. The device is not subject to the usual limitations of in vitro methods because of the apparent nature of the carious lesion. However, it is not conceived to be an infallible automaton as certain features of artificiality cannot be denied.

2. A caries-like lesion can be produced in enamel by the method described if the saliva is adjusted to an average pH range of 6.0 and if a hydrolyzable carbohydrate substrate be added to ensure the local proliferation of bacteria of salivary origin.

3. The lesion is, at least in part, a product of the acidogenic action of the bacteria as evidenced by the fact that only the enamel immediately beneath the plaque is affected.

4. Saliva adjusted to pH 6.0 was not found to be of decalcifying potency for enamel, but is slightly so for dentin.

5. The zoöglea of bacteria constituting the experimental plaque is far more adherent to the enamel in saliva held within the lower pH ranges than the higher.

6. The growth of the plaque was observed to occur, as is expected, in a centripetal fashion when viewed in the apparatus designed for the observation of the carious lesion.

7. The polymicrobic character of the plaque, other than being demonstrated by direct smear and plating techniques, was directly observable by the method herein described.

8. The initially produced lesion is discrete and well localized beneath the most proliferated portion of the bacterial plaque. However, the lesion is much more caries-like in its incipiency than later when the acid attack instigated by the bacteria on the surface is more diffuse.

9. The leptothrix, yeasts, oidium, and perhaps other filamentous forms probably contribute nothing to the causation of the lesion for lesions were produced in their absence. Their late appearance on a lesion makes one inclined to believe that they are merely environmental opportunists.

10. Other than lactobacilli, numerous streptococci were consistently found in smears from the periphery of the enamel. However, the caries-like lesions produced are probably the result of the acidogenic participation of the total local flora.