Chemically, carious whole-teeth differ from sound ones apparently because the carious process removed relatively more enamel than dentin, and more inorganic than organic dentinal tissue. Carious whole-teeth show higher contents of moisture but little or no difference in inorganic percentages, nor in calcium, phosphorus or magnesium percentages of inorganic residue. There seems to be no relation between tooth hardness and caries incidence. Physically, three fundamental properties have been reported on a few teeth each. Quantitative x-ray absorption measurements show a hypercalcified dyke between the active caries-zone and the transparent and opaque reaction-zones. Hardness measurements also show a dyke of increased hardness (up to 100 percent harder) between the putty-like carious area and the reaction zones. In some cases this dyke has consisted of transparent dentin. Normal, transparent and opaque zones have identical x-ray diffraction patterns, and therefore identical molecular constitutions of the principal inorganic component (hydroxylapatite). Fluoride, added to a caries-producing diet given to rats from the time of weaning, reduced incidence of both fractures and caries in the molars. Since at least the first and second molars were fully calcified and had erupted before any fluoride was given, the molars chiefly involved did not have mottled enamel.
References: numerous since 1933; chiefly in J. Ant. Den. Assoc., 1933; J. Biol. Chem., 1933; Am. J. Roentg. Rad. Therap., 1934; J. Den. Res., 1934, 1937; Ind. Eng. Chem. (Anal. Ed.), 1938.