Development of interglobular dentine in rat molars and its relation to maturation of enamel.

The development of interglobular dentine in the first upper and lower molars of Wistar rats aged 3, 7, 14, 21, 42 days was examined histochemically using a lectin, succinyl wheat germ agglutinin (sWGA), which is specific for N-acetyl-D-glucosamine. sWGA stained the interglobular dentine, predentin and Golgi area of odontoblasts. Interglobular dentine was not formed in the first molars of 3-day rats, but appeared in those of 7-day rats near the enamel-free area. In 14-day rats, interglobular dentine was present in most areas of the coronal dentine except the cervical area. At the interface between dentine and predentin, numerous sWGA-negative calcospherites were seen, suggesting that the interglobular dentine is formed actively there. In 21-day rats, the interlobular dentine was more numerous than in 14-day rats. Interglobular dentine was present in the cervical root dentine as well as in the coronal dentine, including the cervical area. The distribution of interglobular dentine in 42-day rats was similar to that in 21-day rats, but fluorescence of sWGA binding was less intense in the former. Because the development of interglobular dentine appeared to be time and position specific its relation to the stages of ameloblasts was analysed. Thin enamel matrix was formed at cusps in molars of 3-day rats and thickness of enamel matrix increased in 7-day rats. In these teeth, the ameloblasts were at the differentiating or secretory stage. The Golgi area and Tomes' processes of the secretory ameloblasts, the cells of intermediate layer and the enamel matrix were weakly positive with sWGA. The epithelial cells at the enamel-free area were also stained with sWGA. In 14-day rats, most of the ameloblasts in the first maxillary molars were at the maturative stage except in the cervical area, where the ameloblasts were at the transitional stage. sWGA stained the distal border and the Golgi area of the maturative ameloblasts as well as the cells of the papillary layer. The distal border of the maturative ameloblasts appeared either thick or thin, suggesting a ruffle-end and smooth-end of the cells. Ameloblasts were absent in the first molars of 21-day rats and the cervical part of the enamel was covered with the stratified epithelium like that of 42-day rats. The present study has demonstrated that interglobular dentine contains sWGA-binding glycoconjugates and the formation of the interglobular dentine is largely associated with the enamel maturation. These results suggest that matrix-to-cell interaction is important for the development of interglobular dentine.