Aging Changes in the Articular Disk of the Temporomandibular Joint in the Guinea Pig

The development of cartilage cells was in-vestigated in the articular disks of the tem-poromandibular joint (TMJ disk) from two groups of guinea pigs age I month and 2 years old. There is strong evidence that the presence of chondrocytes in the TMJ disks of the older group of guinea pigs is the re-sult of a biological aging phenomenon and is not related to pathologically induced changes. Although the structure of the temporoman-dibular (TMJ) disk in the human has been extensively discussed in the literature, there are still certain debatable points. Among them is the problem of the existence and significance of chondrocytes in the central portion of the disk. It is widely accepted that the intra-articular disk, which is always present in the eutherian mammals, is com-posed of dense fibrous tissue.1,2 However, textbooks of animal anatomy3,4 use mainly the term fibrocartilage for the histologic picture of the TMJ disk in various mam-mals. Searching the literature, we were un-able to find specific observations concerning the type of and structural aging changes of the cells in the TMJ disk in the various mammals. Between connective tissue and cartilage there are intermediate kinds of tissue called chondroid tissue. This is an undeveloped condition of cartilage composed of closely adjacent vesicular cells, provided with thin capsules and with collagenous fibers in its interstitial substance. Chondroid tissue may remain throughout life in certain parts of the bodies of higher organisms; it occurs often in lower vertebrates and is still more common in invertebrates.5 Received for publication January 22, 1975. Accepted for publication August 5, 1975