Fibril diameters in the extracellular matrix of the periodontal connective tissues of the rat.

The diameters of collagen fibrils were measured in three varieties of periodontal connective tissue in the rat mandible (incisor periodontal ligament, incisor enamel-related connective tissue and molar periodontal ligament). Despite structural and functional differences between the tissues, a similar range of collagen fibril diameters was seen in each (average 45 nm). Variation between animals and between adjacent fiber bundles in any given tissue was observed. Even within any single fiber bundle, the fibrils had a variety of diameters. Although it has been claimed that collagen fibrils have diameters which are multiples of 8 nm, such a relationship could not be discerned for periodontal collagen fibrils. It was estimated that about 65 per cent of a periodontal collagen fiber bundle or sheet is composed of ground substance. Despite reports of abundant oxytalan fibers in periodontal tissues at the light microscope level, only one fiber having characteristics of oxytalan was observed in this electron microscopic study. Some aspects of the functional significance of the findings are discussed.