Secretory ameloblasts and calcium distribution during normal and experimentally altered mineralization

The distribution of calcium in relation to secretory ameloblasts of the rat incisor was studied. An experimental model system in which enamel mineralization was temporarily inhibited by injecting sodium fluoride and cobalt chloride was used. Potassium pyroantimonate (PPA) cytochemistry, electron energy loss spectroscopy (EELS), and energy dispersive X-ray spectrometry (EDS) were used to clarify the role of the ameloblast in controlling calcium distribution during normal and experimentally altered enamel mineralization. Secretory ameloblasts chemically-preserved in glutaraldehyde either with or without PPA were analyzed for calcium; those preserved with PPA showed higher concentrations of calcium than did those preserved with glutaraldehyde only. Freeze-dried control and experimental tissues showed an increasing gradient of calcium from stratum intermedium cells to the distal ends of the ameloblasts. Calcium levels were reduced near the distal ends of the cells following fluoride and cobalt injections, while magnesium levels were increased markedly in the same region. This multi-method approach showed correlated calcium localization in specific regions of this cell in relation to changes in function. The study thus provides additional evidence for active involvement of the ameloblasts in enamel mineralization.