The Formation of Collagen Fibrils in the Dental Pulp

In the last twenty years, because of the application of the electron microscope, there has been a considerable increase in knowledge concerning the origin and mechanism of formation of collagen. Since the work of Schmitt, Hall, and Jakus' in 1942 illustrated that collagen was composed of a unit structure of fibrils, renewed interest has appeared in this area. Porter2 in 1952 and Wasserman3 in 1956 have reviewed the extensive work in this area and pointed out that the two controversial viewpoints of intracellular versus intercellular origin of collagen -still persist. Fleming,4 Mall,5 Ferguson,6 and Lewis7 promoted the theory that collagen was formed within the cell. These beliefs were later supported by Jackson,8 Jackson and Smith,9 and Wasserman3 10 by the observation of submicroscopic filaments or primary fibrils within the cytoplasm. On the other hand, Baitsell,"-13 Baitsell and Mason,14 Maximow,'5 Nageotte and Guyon,"6 Levi-Montalcini and Sacerdote,17 and more recently, Stearns'18 19 and Kajikawa and Sumita20 point out that collagen is formed outside the cell in the ground substance. Studnicka,21 Porter,2 and Porter and Pappas22 have arrived at perhaps a third viewpoint in their belief that the collagen fibril components are developed extracellularly but at, or on the surface of, the fibroblast. Jackson23 and Jackson and Smith24 now support the theory that fibrogenesis is intimately associated with the surface of osteoblasts and chondroblasts, as does Wasserman,'0 who observed bundles of primary fibrils at the surface of fibroblasts. Bradbury and Meek25 have recently illustrated collagen fibrils in the covering on the surface of fibroblasts in the leech. Weiss and Ferris26 and Kemp27' 28 came to a similar conclusion that procollagen units are derived from the fibroblasts. The majority of the recent evidence supports the premise that collagen is formed near, or in close conjunction with, the cell surface and that precursor substances are formed within the cell. The tooth pulp has been described as being composed of a specialized connective tissue syncytium of stellate-appearing fibroblasts.29' 30 There have been few electronmicroscope studies of the pulp except those describing the fine structure of nerve fibers by Arwill,31 Matthews, Dorman, and Bishop,32 Uchizomo and Homma,33 and Engstrom and Ohman.34 To the authors' knowledge there have been no descriptions of where the collagen fibrils of the pulp arise. The present study was designed to obtain information about the morphologic characteristics of the pulp fibroblast and to gain some insight into the origin of the collagen fibrils of the pulp.