2.1 Tooth Samples and MicroCT
Teeth were collected from patients in the San Francisco Bay area with approval from the UCSF Committee on Human Research. The teeth were sterilized using gamma radiation and stored in 0.1% thymol solution to maintain tissue hydration and prevent bacterial growth.
The teeth were imaged using Microcomputed X-ray tomography (microCT) with a 10 µm resolution.  A Scanco microCT 50 from Scanco USA (Wayne, PA) was used to acquire the images.  MicroCT images of 120 teeth were examined and ten teeth with occlusal lesions chosen with distinct surface zones of mineral content approaching that off sound enamel were selected and designated as arrested while ten teeth were chosen for which the surface zones were not highly mineralized and those were designated as active lesions. Often lesions are present on the tooth that are only partially arrested and have both active and arrested areas [9].