Dual incorporation of (S-35)sulfate into dentin proteoglycans acting as mineralization promoters in rat molars and predentin proteoglycans

Autoradiographic investigations were carried out 0.5, 1, 2, 4, 24, 48, 72, and 120 hours after the injection of a single dose of [S-35]-sulfate on undemineralized molars of 7-15-day-old rats. In predentin, labeling was detected at 0.5 hours. Silver grain density reached a plateau value between 1 and 24 hours, then decreased and disappeared 120 hours after injection. In dentin, the mineralization front started to be labeled as early as 0.5 hours after injection. Labeling increased at the dentin edge between 1 and 2 hours, reached a maxima at 4 hours, then started to decrease, the labeled band seen 24 hours after injection being further incorporated into dentin. This band stood at constant distance from the dentin-enamel junction with stable grain density, even at 120 hours. This investigation proves the existence of two distinct groups of [S-35]-labeled proteoglycans, one exclusively related to predentin and disappearing with time, and the second one located in dentin behaves as a stable component. The fact that an early labeling appeared at the mineralization front which was further incorporated into dentin, confirms that dentin proteoglycans constitute an individual group of molecules that are not derived from predentin proteoglycans, and act as mineralization promoters.