X-Ray Absorption Coefficients of Coronal and Root Dentin. ∗

Abstract

By means of the precision micro-method recently reported 1 , linear X-ray absorption coefficients were measured in various parts of the dentin of 4 non-carious human teeth (3 third molars, 1 premolar) from different individuals of ages from 17 to 68 years. The ground sections were approximately 300 micra thick and the disc-shaped areas of observation were 1 mm. in diameter. A photo-micrographic record of each section made it possible to correlate values of the coefficient with the structural characteristics of each disc. The number of independent measurements per tooth varied from 10 to 20, depending on the size of specimen; each measurement was done in duplicate.

The coefficients for each specimen showed considerable variation (as great as 20%) among themselves. Their mean values were 95.4 ± 0.9 units,† 96.3 ± 0.7, 94.1 ± 1.2 and 95.2 ± 0.6 respectively; even the greatest difference between these means is so small that its significance is statistically uncertain. It is worthy of note that the mean values for the 2 halves of any one section, taken with respect to its longitudinal axis, are unquestionably identical; the differences between such means were 0.2, 0.8, 0.8, and 0.1 units, or less than 1% of the means themselves. The maximum values for the several specimens (101.5, 100.7, 99.6, and 99.6) were so close together that any difference between them is likewise of questionable significance. Thus, for the several specimens studied, both the mean and the maximum values differ by no more than 276, an amount so small as to make the values practically identical. On the other hand, their minimum values varied significantly (89.3, 86.8, 79.3, and 81.7), due in part to structural variations. As yet it is impossible to establish any quantitative correlation with type of structure, possibly because the number of sections is too few to permit of generalization in this regard.