Ultrastructural quantification of collagen fibrils in the central region of the articular disc of the temporomandibular joint of the cat and the guinea pig.

This quantitative ultrastructural analysis was made on articular discs from four guinea pigs and four cats. Mean diameters of collagen fibrils were small (approximately 45 nm) and showed unimodal distributions. These features are consistent for connective tissues subjected to compressional forces. The relatively high percentage volume of the extracellular matrix occupied by collagen in the articular disc of the guinea pig (approximately 60 per cent) and the presence of crimping is, however, more typical of a connective tissue subjected to tension. Two differences were discernible between the collagen in the articular discs of the guinea pig and cat. First, the percentage volume occupied by collagen for the guinea pig disc was significantly higher than for the cat. Second, the frequency distribution of collagen fibril diameters for the cat, although unimodal, was skewed. These differences possibly reflect the different types of movement at the temporomandibular joints in the two species.