Electron microprobe investigations into the process of hard tissue formation

The electron microprobe microanalyser has been used to measure the concentrations of Ca, P and S in the predentine of young rat incisors. The specimens were prepared as alcohol embedded ultrathin sections, unfixed vacuum embedded dry cut ultrathin sections and as thin cryostat sections. The results show the influence of preparation on the measured compositions and indicate that Ca is tightly bound to the matrix, whereas P can be easily washed out. Measurements along the dentine-predentine border demonstrated zones of Ca enrichment, the average size of which suggests that the zones could be the prestages of calcospherites. A mineralisation mechanism is discussed in which the high Ca concentration activates pyrophosphosphatase or ATPase before the onset of nucleation.