Premolar, longitudinal section (40X)
This is a microradiogram showing two premolars. A microradiogram is actually an x-ray. You have to remember that an x-ray is a negative picture. It means that the lighter the area on the x-ray, the more minerals are contained in the tissue depicted.
The premolar to the left shows the extent of the enamel. A white spot, or subsurface carious lesion is seen below its right surface. It is called a subsurface- or white spot lesion because it looks macroscopically as a white spot in the enamel and the demineralization has taken place under the surface layer. Because of the lower mineral content, the x-rays penetrate this area more easily, and it turns out darker than the rest of the enamel.
The premolar to the right has a large cavity that stretches through the enamel and into the dentine. The dentine is fully mineralized except for the a lighter and darker zone around the pulp.