Further ultrastructural studies on the temporomandibular joint of the guinea pig

Age changes in the cells of the intra-articular disc of the temporomandibular joints of rats and marmosets

Cells in the intra-articular disc of the temporomandibular joint were studied ultrastructurally at three different ages to investigate any age changes. Rats aged 2, 15.5 months, and 2.5 years, and marmosets aged 21 months, 7 years, and between 10.5 and 14 years were studied. In the first two age groups of the rat and the first of the marmoset, the cells were generally rounded and had moderate amounts of rough endoplasmic reticulum and other organelles associated with protein synthesis and secretion. Many cells had conspicuous amounts of microfilamentous material and cell membranes were closely applied to the collagen fibrils of the extracellular matrix. Occasionally, a narrow, irregular space containing microfilamentous material lay adjacent to the cell membrane. In the 2.5-year-old rats and the two older age groups of marmosets, cells with chondrocyte-like morphology were present. These cells were surrounded by a conspicuous pericellular matrix devoid of collagen fibrils and composed of microfilamentous material embedded in an amorphous ground substance. They resembled cells described in fibrocartilage from other sites, but differed from chondrocytes in hyaline cartilage by lacking a pericellular capsule. Thus, rats and marmosets both show cellular age changes in the intra-articular disc of the mandibular joint, which can be considered as changing from fibrous to fibrocartilaginous with age, a condition similar to that reported in humans.

Repair of temporomandibular joint disc perforation using a synovial membrane flap in Macaca fascicularis monkeys: light and electron microscopy studies

Previous studies have demonstrated that experimentally produced perforations in the discs of Macaca fascicularis monkeys lead to osteoarthrosis. Synovial membrane hyperplasia also was demonstrated in monkey and human joints with disc perforations. The hypothesis was advanced that a synovial flap obtained from within the affected joint would be the most appropriate tissue to repair chronic disc perforation. To test this hypothesis, four adult M fascicularis monkeys were anesthetized and 4- to 6-mm perforations were made in the posterolateral aspects of the avascular discs bilaterally. The wounds were sutured leaving the perforations open, and the animals were fed their normal diet. After 4 weeks, one joint in each monkey was reopened and a repair was performed using a double-layered flap from the synovial lining of the superior and inferior recesses. Four weeks after repair, the animals were killed and the temporomandibular joints (TMJs) were removed en bloc and decalcified. The joints were sectioned into lateral, middle, and medial sections and were photographed using a stereomicroscope and then processed for light and electron microscopy. The same processing was done to four intact joints that were used as controls. Eight weeks following perforation, the joint components showed degenerative changes consistent with osteoarthritis. Close to the perforations the disc showed loss of collagen, vacuolation of extracellular matrix, accumulation of dense proteoglycan-like material, and the appearance within the disc of type A or macrophage-like cells of the synovium. The discal tissue away from the perforation showed high cellularity and vascularity. The temporal and condylar surfaces showed denudation, fibrillation, osteophytes, and chondrocytic clustering, all characteristics of osteoarthrosis. The surgically repaired discs were intact and the articular surfaces showed no degenerative changes. Discal collagen was restored and appearance of myofibroblasts and elastogenesis were a consistent feature of the repaired disc. The vascularity of the condylar cartilage of the repaired joints appeared similar to that of embryonic cartilage. The reversibility of the degenerative alterations following discal repair in this experimental model should provide the basis for a rational and useful method for surgical repair of TMJ disc perforation using intraarticular synovial tissue.

The effect of growth on collagen and glycosaminoglycans in the articular disc of the rat temporomandibular joint

Newly synthesized collagen and glycosaminoglycans (GAG) were studied in the temporomandibular discs of male Sprague-Dawley rats of 3-13 weeks of age. Each age group had eight animals and [14C]glycine or [3H]glucosamine were used to determine the proportion of newly synthesized type III to type I collagens or the proportion of different types of newly synthesized GAGs during 4 h of labelling in organ culture. Separation of newly synthesized collagen bands from rat disc by sodium dodecyl sulphate-polyacrylamide gel electrophoresis showed a peak in type III at the ages of 7 and 8 weeks. Type III collagen synthesis and the rate of mandibular growth were strongly related through all ages studied. GAG chains were separated by cellulose-acetate electrophoresis. Calculation of disintegrations/min per mg of wet disc tissue for each GAG peak showed that hyaluronic acid (HA), chondroitin-6-sulphate and keratan sulphate/chondroitin-4-sulphate (KS/C4S) were the predominant molecules synthesized in the disc. There was also a steady increase in newly synthesized HA and C6S synthesis up to 6 and 7 weeks respectively. Proportions of newly synthesized C4S/KS, HA and C6S were significantly higher than those of other GAGs with respect to ageing. From these observations it appears that the articular disc shows more of the characteristics of cartilage, as evidenced by the increased amounts of C6S and KS/C4S during the mandibular growth spurt at the ages of 6 and 7 weeks, similar to that of type III collagen. There were also increased amounts of HA, suggesting that during 5-7 weeks of age the rat disc is undergoing more active remodelling. This study provides baseline data for further analysis of the effects of mechanical loading and trauma on articular disc responses.

Ultrastructural quantification of collagen in the articular disc of the temporomandibular joint of the rabbit

Collagen fibril diameters were quantified in two regions of the articular disc of this joint. One region was the thinner, translucent central part of the disc; the other was from the thicker, opaque peripheral part more anteriorly. Mean collagen fibril diameters in the thicker zone were small and had a unimodal distribution. In contrast, mean collagen fibril diameters in the thinner central region were larger and with a much wider range of values, as indicated by the larger standard deviations. It was concluded that regional variations exist in the collagen of the rabbit articular disc and may reflect the mechanical loads to which the disc is subjected.

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.

Vascular collagen fibril morphology in type IV Ehlers-Danlos syndrome

Morphometric analysis of transmission electron micrographs of blood vessel, skin and dura mater collagen fibers were performed on postmortem tissues taken from 28-year-old female with Ehlers-Danlos type IV syndrome (EDS IV). Vascular tissue from this patient was compared to 5 age- and sex-matched controls (age range 26-28 years). Our study revealed significant variation in collagen fibril diameter in the walls of almost all the vessels studied. In general, the EDS IV tissue showed a net decrease in average collagen fibril cross sectional area in arterial wall samples. This decrease was significant (p less than .05) across the entire wall of the renal artery, in the media of the carotid artery, and in the media and adventitia of the common iliac artery. Samples from the vena cava show significant increases in collagen fibril cross sectional area across the vessel wall (p less than .005). The only areas studied which did not show significant changes were the intimal and adventitial regions of the common carotid artery. The observed changes may be contributory to the decreased arterial wall strength typical of the syndrome.

Distribution of elastic fibres in the developing rabbit craniomandibular joint

The biomechanical properties of the CMJ disc depend upon the composition and organization of the extracellular matrix. Elastic fibres are important elements of the matrix and may be in part responsible for the resilience of the disc during jaw movements. Elastic fibres first appeared after the establishment of a miniature CMJ at 23 days of prenatal development. The first elastic fibres appeared in the antero-inferior and postero-inferior attachment regions of the disc. In the newborn rabbit there were elastic fibres in the articulating surfaces of the joint and by one week fibres could be seen in the intermediate zone portion of the disc. At two weeks, when the animals were beginning to experiment with solid food, the disc band areas showed accumulations of elastic fibres and proteoglycans. The findings suggest that the elastic elements of the disc, squamosal and condylar articulations may have a resilience function which develops in response to functional loads placed upon the joint as the rabbit grows and changes diet.

Light and electron microscopic morphology of the temporomandibular joint in growing and mature crab-eating monkeys (Macaca fascicularis): the condylar articular layer

In an attempt to establish maturational alterations in the morphology of the articular tissue layer, mandibular condyles of four immature and four mature male monkeys (Macaca fascicularis) were studied using light microscopy as well as scanning and transmission electron microscopy. Specimens were fixed in situ by perfusion in the presence of ruthenium red to stabilize proteoglycans. Preparations intended for observation in the scanning electron microscope were first dehydrated and sputtered for the examination of articular surfaces, and afterwards treated with trypsin to expose the spatial arrangement of collagen fibrils. Gross anatomical relations between joint components indicated that the anterior and central, but not the posterior region of the condylar articular surface can be subject to compressional load. Load-bearing and non-load-bearing regions differed with respect to the morphology of the articular layer. Load-bearing surfaces were covered by a prominent articular surface lamina similar to that observed on articular cartilage. This lamina seemed to constitute an integral part of the articular layer, distinct from the lining of synovial fluid, and to be composed largely of proteoglycans. It was unaffected by maturation. The subjacent, load-bearing articular layer differed markedly in structure, both from articular cartilage, and between immature and mature animals. Articular cells of immature animals were classified as fibroblastlike, but unlike typical fibroblasts, were surrounded by a thin, often incomplete halo of fibril-free pericellular matrix, presumably consisting of proteoglycans. In mature animals, articular cells closely resembled chondrocytes, but exhibited prominent nuclear fibrous laminae, which usually are found only in fibroblasts. Thus, the load-bearing part of the articular layer seems to undergo a maturation-dependent metaplastic conversion, from a dense connective tissue with some features of fibrocartilage, to a fibrocartilage-like tissue containing chondrocyte-like cells with some features of fibroblasts. This conversion might reflect an adaptation to a maturation-associated increase in articular stress.

Morphological and biochemical evidence for elastic fibres in the Syrian hamster temporomandibular joint disc

Elastic fibres are considered to be important for the normal biomechanical functions of the TMJ. The objective here was to correlate morphological evidence for the presence of elastic fibres in discal tissues with biochemical evidence for elastin. For light microscopy, the joints were removed en bloc, processed for paraffin embedding, sectioned and stained with resorcin-fuchsin. For biochemical study, a radioimmunoassay for desmosine was used to estimate the amount of elastin in excised articular discs. The histological preparations showed that numerous elastic fibres were present in various areas of the disc and in some of the discal attachments to surrounding bone. Radioimmunoassay also indicated that elastin was present in these tissues. Therefore, the biochemical findings support the morphological in suggesting that elastic fibres are present in the articular disc of the hamster TMJ.

Ultrastructure of the articular cartilage of the mandibular condyle: aging and degeneration

To obtain more insight into the pathogenesis of osteoarthrosis of the temporomandibular joint, we examined the ultrastructure of articular cartilage of six healthy and sixteen osteoarthrotic human mandibular condyles. Ultrastructural changes due to aging and osteoarthrosis are described and compared with the findings of other ultrastructural studies of articular cartilage of synovial joints. Aging was accompanied by some slight degenerative signs. Osteoarthrotic hyaline cartilage and fibrocartilage showed a striking similarity. The only ultrastructural difference was the presence of elastic fibers in the latter. Therefore, both seem to have the same pathogenesis. Several current statements on the pathogenesis of osteoarthrosis are discussed.

The microscopic structure of fibrous articular surfaces: a review

The present knowledge of the microscopic structure of fibrous articulating surface is reviewed. The influence of dissection, postmortem change, fixation, and dehydration on the microscopic appearances of these surfaces is considered. The results of those studies of surface morphology that investigate intact, supported specimens and that are controlled by surveys of fresh, unfixed, or frozen material are advantageous. New information on the effects of alterations in intermaxillary relationship on the morphology of fibrous articulating surfaces is presented. There is need for further work in this field of research.