Ultrastructural alteration of cartilaginous fibril arrangement in the rat mandibular condyle as revealed by high‐resolution scanning electron microscopy

Three‐dimensional alteration of fibrillar matrix in the rat mandibular condylar cartilage was investigated with a high‐resolution scanning electron microscope (SEM) and it was determined whether alterations correlate with developing occlusion and advancing age. Two important SEM techniques of DMSO freeze‐cracking and treatment with trypsin and hyaluronidase were employed to remove interfibrillar proteoglycans and disclose fibril arrangement. Our SEM investigation demonstrated that collagen fibrils in the fibrous zone covering hyaline‐cartilaginous area in the condyle are thicker (50 to 80 nm in diameter) than the fibrils (30 to 50 nm in diameter) that predominantly constituted an interterritorial fibrillar matrix (IFM) in the area. While the thick fibrils had a distinct striation of about 55 nm periodicity, the thin fibrils had no distinguishable striation. The thick fibrils having a periodic striation of about 60 nm was found along with the thin fibrils, also in the IFM in the aged rats and in the deep IFM, but were considerably less than the thin fibrils. The fibrils in the fibrous zone and IFM were disorderly arranged at 19‐day‐insemination age. In 1‐week‐old rats whose incisors erupted, the fibrils constituting the fibrous zone altered from disordered to ordered arragement. The IFM in these rats took the form of a network. Incorporation of small fibrillar bundles into the fibrillar network was seen in 2‐week‐old rats whose upper and lower first molars erupted. In 8‐week‐old rats whose molars had erupted completely, the IFM completely occupied by regularly oriented fibrils appeared additionally. The structural alteration that occurred in both individual fibrils and fibril arrangement probably correlates with increasing stress due to developing occlusion and aging of the condylar cartilage.© Willey‐Liss, Inc.