The Formation of Collagen Fibrils in the Dental Pulp

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Abstract
Eighty molar buds from newborn hamsters were fixed in either KMnO4 or OsO4, embedded in methacrylate, sectioned on a Porter-Blum microtome, and studied under the electron microscope. The KMnO4 fixation was far superior to OSO4 for the study of the membranes of fibroblasts and fibril formation in young pulp. The fibroblasts in young pulp had an outer cell membrane completely enclosing the cytoplasm. Therefore, they do not form a true syncytium but establish contact with each other by means of intercellular attachments. The cytoplasmic characteristics of fibroblasts in young pulp appeared somewhat different from those of fibroblasts found in connective tissue in adult animals. A lesser amount of endoplasmic reticulum was found, and the mitochondria in the young cells had fewer cristae mitochondriales. The electron density of the cytoplasm of the cell body was similar to that of its processes. Intra-cellular location of collagen fibrils was observed but was believed to be artifactual and caused by sectioning through infolding membrane or oblique sectioning of the outer cell membrane. Many collagen fibrils measuring 100-300A in diameter and having a periodicity of 458A were observed near, or in contact with, the outer cell membrane of the fibroblast. Other collagen fibrils measuring 200-400A in diameter were noted farther from the cell surface. It is believed that the fibroblasts of the dental pulp function in the production of collagen fibrils on or within the outer membrane of the cell.