Mid-infrared reflectance microspectroscopy of human molars: Chemical comparison of the dentin–enamel junction with the adjacent tissues

Mid-infrared reflectance microspectroscopy was applied to the study of calcified tissues in human molars. Particular attention was focused on the dentin–enamel junction (DEJ). Major chemical components (apatite, organic matrix and water) and minor chemical components ( CO 3 2 - and HPO 4 2 - ions in apatite) were investigated. It was found that the average contents of organic matrix and CO 3 2 - ions increased in the order: enamel < DEJ < dentin. The smallest quantities of water and phosphates were observed in the DEJ, which finding can be explained by the loosest tissue packing in this location. The HPO 4 2 - ions were not detected in the DEJ, while in dentin their content was higher than in enamel. Differences between the reflection and transmission modes in the studies of calcified tissues were discussed.