Rat incisor dentin formed under low plasma calcium concentration: Relation of phosphophoryns to the affected dentin

Abstract:

When parathyroidectomized (PTX) rats were maintained on a diet containing 0.3% calcium and lacking vitamin D, the forming incisor dentin consisted of two distinct layers that differed in their degree of mineralization. The two layers could be distinguished by hematoxylin staining and by contact microradiography. The layer near the dental pulp was the hypomineralized dentin, different from a predentin, containing a small amount of mineral detected by electron probe and chemical analyses. The mineralization of the outer dentin was almost normal. Biochemical characterization demonstrated that the two dentin layers differed in their phosphophoryn content. The outer dentin contained two phosphophoryns, which is the pattern found in normal dentin. In contrast, the hypomineralized dentin contained only the lower molecular weight and lower phosphorylated phosphophoryn, which may be involved in crystal nucleation. From the distribution of lead, which marked dentin formed at the time of injection, it could be inferred that the mineralized dentin begins as a hypomineralized layer that undergoes secondary mineralization. The secondary mineralization occurs by the active calcium transport of the odontoblasts via odontoblastic processes.