. [For himself and co-workers,
H. E. FRIESELL and M. 0. TRESCHER.]
Local environmental conditions are the main factors in the active causation of caries of fully erupted enamel. Deficient diet and defective nutrition, by being responsible for the construction of teeth that are more susceptible to the action of fermentation acids, are the most important factors during the period of tooth development. Improper diet and defective nutrition, by being responsible for salivary environment low in content of calcium phosphate, are of some, though minor, importance as predisposing factors in enamel caries. Artificial lesions that simulate natural enamel-caries have been prepared with organic acids. The halt that is sometimes observed in carious processes of enamel is due to presence of acid-insoluble protective organic coatings. Mouths in filthy hygienic condition are often free from caries. Carious lesions may increase, and make more rapid progress, during pregnancy.
Simple lactate- and citrate-buffer solutions, ranging in H-ion concentration from pH 4.0 to 8.0, dissolve enamel in relatively long immersion-periods. Enamel specimens from different teeth vary in susceptibility to the action of acids. Human saliva is generally saturated with tricalcium phosphate. Lactate- and citrate-buffer solutions, previously saturated with tricalcium phosphate, dissolve enamel only at H-ion concentrations greater than approximately pH 5.0. The only microorganism commonly found in food debris (in direct contact with progressive caries of enamel)—that can tolerate and produce additional acid in an environment below pH 5.0—is a lactobacillus having the following characteristics : Gram-positive rod, which usually produces (a) smooth colony ; (b) acid, but no gas, from dextrose, levulose, galactose, maltose, lactose, sucrose, mannitol, sorbitol, salicin, and dextrin ; (c) neither acid nor gas from arabinose, xylose, raffinose, and inulin. Its final pH in glucose-tomato broth generally ranges from 3.6 to 4.0. It can grow at a temperature of 15° C. It is agglutinated in high dilution by the Y type of L. acidophilus-antiserum, which does not agglutinate L. acidophilus of the X type.
Reference: J. Den. Res., 12, 759, 1932.