The behaviour of collagen fibres in stress relaxation and stress distribution in the jaw-joint disc of rabbits.

The physical properties of the temporomandibular joint disc are largely attributable to its collagen fibre and proteoglycan composition and organization. Structural and stress relaxation data were obtained from the discs of six rabbits. Two stainless-steel balls, 4.8 mm dia, were used to load the disc surfaces in compression. Stress relaxation tests were performed at loads of 0.8-1.4 kg, and the disc was then placed in fixative while still in the loading apparatus in order to preserve its deformed state at equilibrium stress. After overnight fixation the discs were sectioned and assessed by means of a polarizing microscope with a rotating universal stage. This allowed measurement of three-dimensional changes in collagen fibre waviness and alignment as the result of loading. The data showed that despite significant stress relaxation and strains, only minor changes in fibre waviness and alignment occurred within the disc, reflecting its effectiveness as a tough but compliant structure, well suited to distribute load in the temporomandibular joint.

An animal model for studying mechanisms in human temporomandibular joint disc derangement.

PURPOSE: A method for producing disc displacement is presented in which remodeling events in the disc and posterior attachment (PA) are similar to those occurring in patients suffering from disc displacement (DD). METHOD: Thirty-three adult New Zealand White rabbits were used in this study. A unilateral anterior DD was surgically induced in 18 animals. Six animals were sham operated and nine animals served as controls. RESULTS: Macroscopically, DD was associated with gross thickening of the posterior band (PB), shortening of the disc anteroposteriorly, flexure of the intermediate zone (IZ), and loss of the biconcave shape. Microscopically, dramatic internal structural changes were observed in displaced discs, including extensive collagenous fiber reorganization and changes in cell morphology associated with a generalized loss of metachromatic staining. As in humans, the disc displacement caused abnormal loading of the PA and remodeling of this tissue into a disc-like structure characterized by the appearance of coarse collagenous fiber bundles and scattered chondrocytes surrounded by a matrix-containing cartilage-like glycosaminoglycans (GAGs). CONCLUSION: These pathoanatomic changes bear a remarkable similarity to those described in human disc derangements and support the use of this method as an experimental model for the study of remodeling events in human DD arthropathies.

Morphologic, microscopic, and immunohistochemical investigations into the function of the primate TMJ disc.

The distribution and arrangement of extracellular matrix proteins were examined in the primate temporomandibular joint disc and posterior attachment using a combination of light microscopic, immunohistochemical, and biochemical techniques. The band areas of the disc contain a complex collagenous (type I) fiber network consisting of a mediolaterally directed fiber bundle system that interlaces or becomes continuous with an anteroposteriorly directed collagenous fiber array that runs through the intermediate zone. Thin, branching, elastic fibers are a significant component of the disc and are generally oriented parallel to the collagenous fiber network. Interfibrillar spaces in band areas contain numerous chondrocytes encased within a matrix that is rich in a high molecular weight, predominantly chondroitin-sulfate proteoglycan and type II collagen. The intermediate zone appears tendinous in its construction and is composed of anteroposteriorly oriented elastic and collagenous fibers, scattered chondrocytes, and reduced amounts of chondroitin-sulfate proteoglycan and type II collagen. The posterior attachment is composed of fibrocytes, larger caliber elastic fibers, loosely organized type I collagenous fibers, and low molecular weight dermatan-sulfate proteoglycan. These results indicate that the primate temporomandibular joint disc is a microheterogenous tissue with distinct regional specializations.

The posterior attachment: its structure, function, and appearance in TMJ imaging studies. Part 1.

The posterior attachment of the temporomandibular joint disc is a highly compliant tissue, capable of large volumetric fluctuations. Its structure and volume at any moment are a function of condylar position. The posterior attachment appears to function as a device for rearrangement of liquids. The liquids are blood, tissue fluid, and synovial fluid.

The posterior attachment: its structure, function, and appearance in TMJ imaging studies. Part 2.

The anatomy of the posterior attachment was described in the first part of this paper (J Craniomandib Disord Facial Oral Pain 1991;5:83-95). In part 2, the appearance of the posterior attachment in imaging studies and inferences on its function are discussed.

Animal model for disk displacement.

This paper describes the soft-tissue changes associated with surgically created, nonreducing disk displacements in the New Zealand white rabbit. Four rabbits, one control and three experimental, were used. The disk of the control animal had thick posterior and anterior bands separated by a thinner intermediate zone. The disk in the one animal sacrificed immediately after surgical disk displacement was buckled downward at the intermediate zone, with the posterior band lying inferior to the anterior band. The disks in the two animals sacrificed 2 months after surgical disk displacement were grossly deformed and clearly had abnormal internal architecture. Tissue reactions seem to be similar to those observed in human disk displacement specimens, namely disk remodeling and degenerative joint disease. This animal model will aid in the understanding of the progression of this disorder.

Remodeling of the temporomandibular joint disk and posterior attachment in disk displacement specimens in relation to glycosaminoglycan content.

In meniscus displacement pathosis, the anterior part of the posterior attachment is subjected to abnormal compressive loading. This study presents evidence that the loaded tissue is capable of producing glycosaminoglycans of the sort that are found in the disk and articular surfaces of the articular eminence and mandibular condyle.

A cinephotographic study of the role of the canine in limiting lateral jaw movement in Macaca fascicularis.

Three specimens of Macaca fascicularis were examined to test the hypothesis that the canines do not restrict lateral masticatory movements in these animals. The animals were filmed while chewing freely before, shortly after, and seven weeks after canine removal. Facial markers, viewed from the lateral plane, allowed for computer tracings of all mandibular movements. The maximal lateral movement of the mandible was assessed for each chewing cycle, and means were calculated for each test condition and animal. These means were compared intra-animal for statistically significant differences in lateral jaw movement before and after canine removal. No significant long-term increase in lateral movement was found in any animal after the removal of its canine teeth. We conclude that, in accordance with our hypothesis, the lateral movement during mastication did not increase significantly after removal of the canine teeth in three specimens of Macaca fascicularis. Therefore, the use of the macaque as a human model for masticatory studies requires further assessment. This study reveals that the canine teeth are not as important as previously assumed in affecting the form of the masticatory cycle in the macaque.

Histopathology associated with malposition of the human temporomandibular joint disc.

Anterior displacement of the temporomandibular joint disc is associated with a general remodeling of the joint's soft tissues. The anterior part of the posterior attachment becomes fibrotic. The external shape and the internal architecture of the disc change in characteristic ways. The disc appears to overlie more of the lateral pterygoid muscle than is normal. The capsule connecting the anterior band of the disc to the condyle appears to be elongated.

Secondary cartilages in growth and development of the symphysis menti in the hamster.

The early growth and development of the symphyseal joint and pertinent adjacent regions of the mandible in the hamster, Mesocricetus auratus, are described. The joint is patent throughout life and in adults contains a large fibrocartilage which mediates mandibular movements. Evidence is presented to show that this cartilage is formed by the fusion of Meckel's cartilage with two secondary cartilages that appear within the joint space. Evidence is also presented which suggests that cells of the symphyseal cartilage have the capacity to produce bone.