Proteoglycans in cementum- and enamel-related predentin of young mouse incisors as visualized by cuprolinic blue

In rodent incisors, dentin associated with cementum (root-analogue dentin) appears to differ considerably from that associated with enamel (crown-analogue dentin), both with respect to the composition of certain matrix components and the mineral. Since it is not known whether these dentin portions also differ with respect to their proteoglycans, the morphological appearance and spatial distribution of these components was studied in predentin by employing cuprolinic blue, a dye selective for proteoglycans. Lower incisors of five-day-old mice were stained with the dye and processed for electron microscopic examination. Cuprolinic blue-positive precipitates were found in both cementum- and enamel-related predentin. In cementum-related predentin these structures were thick and short. In the enamel-related portion, however, they were long, slender and frequently stellate-shaped. The number of precipitates was similar between the two predentin portions and also no differences were found between the basal and the apical (adjacent to the mineralization front) aspects of the predentin layers. It is suggested that the differences in proteoglycan architecture among the predentin layers is somehow related to differences in the three-dimensional collagenous meshwork or to different patterns of mineralization.