Caries in dentin causes pronounced chemical removal of both inorganic substance (classical decalcification of Miller) and organic material. Whole dry lesions from small, medium, and large cavities averaged respectively 5, 10, and 20 percent less inorganic material than normal dentin (weight basis), with wide variations for large cavities. Whole moist lesions, when large, also were variable in composition, but in general inorganic matter was lost twice as rapidly as organic (volume basis), the ensuing spaces being filled with water. The inorganic material in the carious zone as a whole shows no change in the calcium/phosphorus ratio, indicating that dentinal caries removes fundamental chemical units intact.underneath. The chemical variations indicated above may be understood when these parts of a carious lesion are considered separately. On the volume basis, hard pigmented dentin, next to normal, suffered a decrement in both organic and inorganic materials amounting to only a sixth of the original; soft pigmented dentin results when a fourth of the mineral salts is removed, and does not lose organic material until four-fifths of the inorganic has disappeared. Then organic matter diminishes rapidly, resulting in a uniform terminal product which has lost 85 and 40 percent of the original inorganic and organic materials, respectively. Transparent reaction-zones do not differ from normal dentin in composition.
References: Physical and microchemical studies of dental hard tissues, Ph.D. Thesis, University of Rochester, 1938; J. Am. Den. Assoc. (in press).