Caries is associated with environmental factors related to oral food-retention and lactobacillus fermentation, and also with physiological factors related to calcium-phosphorus metabolism. Statistical analysis of incidence of caries by age and sex, in nearly 13,000 persons (not dental patients) representing an extensive cross-section of the population, indicates that initiation of new lesions continues past childhood and adolescence—at least until middle life—at a slowly and progressively decreasing rate. This reduction in rate of development of new lesions can be ascribed only in part to decrease in residual number of unaffected, decayable teeth at any particular age. Incidence of caries was significantly higher among women than among men throughout the entire age-range ; the difference was very slight below 34 years, but very marked above it.
Some non-structural variations in calcification have been demonstrated quantitatively by measurements of linear x-ray absorption coefficients. X-ray radiography also shows that human enamel contains structures associated with variations in radiopacity and therefore in calcification. Some of these structures are possible factors in the mechanism of caries, especially in relation to calcium metabolism. One of them is the Band of Schreger, hitherto universally accepted as an optical manifestation of the angle of section of individual enamel rods. Another is the outer surface-layer of enamel; but this may be a photographic artifact related to the Mackie Line.
References: Den. Cosmos, 1933, 1935, 1936; J. Den. Res., 1934, 1939.