Abstract
The following is a preliminary report of a new method of determining linear X-ray absorption coefficients in plano-parallel ground sections of teeth. This coefficient is a precise measure of radiopacity, which, in radiographs of such sections, is usually interpreted as measuring degree of calcification. Variations in calcification of teeth may arise in several ways: (1) With increasing age there may occur a progressive diffuse deposition of calcium salts within the already calcified matrix. (2) Secondary deposition of calcium salts may occur locally in response to some abnormal condition. (3) Certain pathological conditions may cause local rarifactions. (4) Structures in the organic matrix may cause relative variations in calcification merely by spatial displacement of inorganic material.
Such variations in distribution of inorganic material correspond to differences in compactness or density of calcification; i. e., in weight of calcium salt per unit volume. However, the qualitative nature of radiopacity as ordinarily observed in a photographic film limits its value as a criterion of density of calcification for experimental purposes. To offset this limitation, Warren et al. 1 have measured the radiopacity by means of a Capstaff-Purdy densitometer for determining density of silver grains in photographic films. The precision of their method is stated to be of the order of 5% for sections 1 mm. thick and areas 0.5 mm. in diameter. Actually, it is even poorer than this since they used a mean thickness value throughout the section but did not include its precision measure in that of the entire determination.
Our experience with grenz-ray radiography of ground sections of teeth suggested that differences of considerably less than 5% may be significant in studies of normal calcification. In order to measure such differences, a method has been developed for the measurement of radiopacity which is good to 0.5% or better.
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