We investigated the expression of Ca++ pump epitopes during enamel and dentin mineralization in the rat incisor. Secretory and maturation ameloblasts were studied as well as odontoblasts, using a monoclonal antibody (5F10) against human erythrocyte plasma membrane Ca++, Mg(++)-ATPase. A progressive increase in staining intensity in ameloblasts and the odontoblasts was observed beginning with the onset of mineralization. The mainly membrane-related labeling of ameloblasts showed variable intensity depending on the stage of enamel formation, whereas that of the odontoblasts showed even intensity during continued dentinogenesis. Staining of papillary cells was evident only during enamel maturation. Western blot analysis of freeze-dried ameloblasts was also used to determine the molecular weight of the Ca++ pump epitopes as well as the distribution and relative concentration of epitopes at each stage. An immunoreactive band of MW 140 KD and lower molecular weight bands that are more intense in late than in early maturation were demonstrated. Our studies suggest that the expression of plasma membrane Ca++ pump parallels the progression of mineralization in rat incisor enamel and dentin.

A modified Wachstein-Meisel medium containing lead or cerium as capturing ions was used to localize Ca2+-Mg2+ adenosine triphosphatase (ATPase; EC 3.6.1.3) in rat incisor ameloblasts during enamel formation. Sections representing different developmental stages were processed for electron microscopic cytochemistry. Distribution and intensity of the observed reaction product, which was almost exclusively associated with cell membranes, varied according to the stage of enamel formation. During the secretory stage, intense reaction product was evident along the entire plasma membrane of ameloblasts and papillary cells. The early transitional ameloblasts showed reaction product on their proximal and lateral cell membranes, but not distally. In late transitional (pre-absorptive) ameloblasts, distal cell membranes exhibited intense reaction product. During enamel maturation, smooth-ended ameloblasts showed reaction product proximally and laterally, but not distally. Ruffle-ended maturative ameloblasts exhibited intense reaction product along their lateral and distal membranes. The intensity of the latter was decreased but not eliminated by levamisole. In the transition from smooth-ended to ruffle-ended cells, the reaction product became evident distally, concomitant with the appearance of cell membrane invaginations. These data are consistent with a possible role for Ca2+-Mg2+ ATPase in controlling calcium availability at the enamel mineralization front.

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The neonatal line in developing human primary teeth was examined by means of phase contrast microscopy, microradiography and transmission electron microscopy. When thin sections were observed by light microscopy, the lateral dimensions of the line were not as extensive as had been previously reported. The line had a "staircase" configuration and appeared to be identical to published light micrographs of the stria of Retzius. On radiograms, the lateral extent of the hypomineralization was also decreased. The ultrastructural basis for the neonatal line appeared to be a localized change in configuration of enamel prisms along with a possible reduction in crystal concentration. The possibility that some rods actually end at the line could not be excluded, however.