A number of factors acting singly or in combinations, at different ages and under various circumstances, may contribute to the incidence and continuance of caries. Among these factors are (a) localized acidity, and (b) rate of secretion of saliva.(a) Within dental plaques, the range of pH was 4.6-6.8; in simultaneously obtained specimens of saliva, it was 6.2-7.2. In every instance the plaque interior was more acid than the corresponding saliva. (b) Dental students (107) received clinical and x-ray examinations of their teeth at intervals of eight to twelve months. In the group having less than average secretion of saliva, the number of new smooth-surface carious cavities that developed in the periods between the first and third examinations was higher than average. In a selected group, all having high rates of secretion of saliva, there was little incidence or increase of caries during the same period.
References: J. Den. Res., 14, 218, 1934; 17, 299, 1938.
TUNNICLIFF, RUTH, and HAMMOND, CAROLYN : Foundation for Dental Research of the Chicago College of Dental Surgery, Loyola University, Chicago, Ill. (May 4, 1938).
Enamel is decalcified and dentin invaded with the same ease by either acidogenic streptococci or lactobacilli. In natural caries, cocci are the predominating, and often the only, organisms in the tubules. This fact indicates that cocci are the invading organisms in caries, irrespective of predisposing factors.
Microscopic rough (R) colonies generally associated with smooth (S) colonies of S. viridans have been isolated from brain-broth cultures of carious dentin and of pulps of carious teeth. Bacilli, coiled forms, crescents, straight or undulating filaments in R greening colonies, are changed, by transferring in 1 percent dextrose- broth, into cocci in pairs or short chains that form S colonies. S cultures isolated from carious dentin, and from mouths having no carious teeth, may be changed into microscopic or minute R colonies consisting of the morphologic forms that occur in colonies isolated as R. R colonies obtained from pulps and carious dentin of carious teeth appear to be dissociants of S colonies of S. viridans normally present in the mouth. R cultures produce less acid (pH 5.2-6.0) than S (pH 4.4-4.8) in 1 percent dextrose-broth (pH 7.0). Both R and S organisms grow in 1 percent dextrose-broth (pH 4.4-5.0). The organisms found in S and R colonies of S. viridans appear to correspond to the cocci, bacilli and ” tortuous threads ” described by Miller in tubules of carious teeth.
References: J. Am. Den. Assoc., 1938; Arch. Path., 1938.