Transverse Microradiography (TMR) or contact-microradiography is one of the most widely accepted methods used to assess demineralization and remineralization in dental hard tissues in in-situ and in-vitro studies. It is a highly sensitive method to measure the morphology of and the change in mineral content of enamel and dentin samples (Arends and Ten Bosch, 1992). In TMR the tooth sample to be investigated is cut into thin slices (about 80 ^m and 200 ^m for dentine samples). A microradiography image is made on high resolution film by X-ray exposure of the sections together with a calibration stepwedge. The microradiogram is digitized by a video camera or photomultiplier. The mineral can be automatically calculated from the gray levels of the images of section and stepwedge using a custom-made software. In examining the reliability of TMR, Exterkate et al. found that repeated microradiographs of the same thin enamel sections resulted in a negligible spread in mineral loss among them (Exterkate et al., 1993). Such reliability and the more recent application of computer imaging make microradiography a standard method used in caries research for the assessment of lesion profiles.

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