Three-dimensional mapping of mineral densities in carious dentin: theory and method.

X-ray tomographic microscopy (XTM), a three-dimensional X-ray imaging technique, has been used to quantitatively map mineral concentrations in carious dentin. Data analysis from the XTM study indicates that variations in the mineral concentration surrounding the caries can be imaged in three dimensions with a spatial resolution that is sufficient to detect calcified and enlarged tubule spaces in the lesion. A three-dimensional image of the subsurface lesion indicates that lesion penetration is along the direction of the tubules. The mineral concentration in the uninfected dentin was measured by the XTM to be 1.29 +/- 0.14 g/cm3 based upon the tabulated X-ray attenuation coefficients for apatite. This value is in excellent agreement with averaged estimates for the mineral concentration in dentin (1.4 g/cm3). Furthermore, the mineral concentration determined using XTM varies from 2.25 g/cm3 in the remineralized dentin to as low as 0.55 +/- 0.17 g/cm3 in the demineralized tissue. The high concentration of mineral in the remineralized region suggests that organic matter is lost and mineral is deposited at some time during the caries process.