Ultrastructural observations on the intraodontoblastic collagen fibrils of the mouse tooth germs

We examined electron-microscopically and histochemically the ultrastructural features of the intraodontoblastic collagen fibrils of the mouse. These collagen fibrils were most common in secreting odontoblasts (pre-odontoblasts) of the maturating stages. In such cells they were most numerous at the peripheral zone of the Golgi apparatus, and were sometimes seen in odontoblastic processes. Intraodontoblastic collagen fibrils also had morphological variations including a banded structure enclosed by limiting membranes of vacuoles, fusion with primary lysosomes, and an electron-dense material covering with a structure that was not banded. Study of acid phosphatase activity showed that these structural changes were caused by the degradation of intraodontoblastic collagen fibrils by lysosomes. The results of studies of the permeation of lanthanum nitrate and the alkaline phosphatase reaction showed that these collagen fibrils were separate from the extracellular matrix and that there was no phagocytosis of the odontoblasts.