Studies on dentinogenesis in the rat

Three-day-old rats were fixed by perfusion with glutaraldehyde and thin slices were cut of the first molar germs. The slices were treated with EDTA and activated with buffered solutions containing Mg²⁺, Ca²⁺ or Zn²⁺. Incubation was carried out in buffered solutions (pH 8.5) containing inorganic pyrophosphate and Pb²⁺. In the Mg²⁺-activated specimens incubation products were localized to the plasma membranes in the stratum intermedium and the subodontoblastic area. Lead deposits were found on the periphery of the dentinal globules. Incubation products were more randomly distributed in Ca²⁺-activated specimens whereas those activated with Zn²⁺ displayed a deposition of lead precipitates mainly corresponding to that seen after activation with Mg²⁺. The findings are discussed in reference to the localization of alkaline phosphatase in the dentin-producing tissues and it is proposed that the results are indicative of the presence of an inorganic pyrophosphatase in these tissues.