2. Gingival connective tissue
a. Gingival fibers - Collagen
Fig. 26: Transmission electron micrograph of gingival connective tissue showing the intercellular junctions (ICJ) between cytoplasmic strands from adjacent fibroblasts. The fibroblasts form an interconnected network of cells, the intercellular spaces of which are filled with fibers and ground substance, the jelly-like material in which the fibers are embedded. The fibroblasts are responsible for the production of the fibers and ground substance. They are also capable of removing fibers and ground substance during remodeling of the gingival tissues.
Most of the fibers in gingival connective tissue are composed of collagen
. The bulk of the collagen is type I collagen, the most abundant form of collagen in the human body. The structural unit of type I collagen is a typically striated fibril with a characteristic banding pattern that repeats every 64 nm. The banding results from the packing arrangement of the collagen molecules that make up the individual fibril (Fig. 27).
Fig. 27: Transmission electron micrograph of type I collagen fibrils shown in cross-sections (A) as well as longitudinal sections (B). The typical banding of type I collagen is readily detectable in longitudinally sectioned fibrils.
Type I collagen fibrils are normally organized into bundles of fibrils, or fibers. They are found throughout the lamina propria
. Type III collagen fibers are thinner than the type I fibers and tend to be found close to basal laminas of vascular channels and epithelial tissues. They stain readily with silver stains and probably account for most of the argyrophilic (silver stained) fibers seen in silver-stained sections. They are also known as reticular fibers
Fig. 28 (From unknown source): Diagrammatic representation of reticular fibers (top) and typical type I collagen fibers (bottom). Each fiber type consists of a bundle of fibrils, the structural unit of the fibers. The fibrils in reticular fibers are fewer and thinner (diam. ~40 nm) than those in typical type I collagen fibers (diam. ~80-90 nm). Collagen fibers may contain as many as several hundred fibrils and reach a diameter of several micrometers.