Chronic inflammation deteriorates structure and function of collagen fibril in rat temporomandibular joint disc.

Collagen is the building component of temporomandibular joint (TMJ) discs and is often affected by inflammation in temporomandibular disorders. The macromechanical properties of collagen are deteriorated by chronic inflammation. However, the mechanism by which inflammation influences disc function remains unknown. The relationship between the ultrastructure and nanomechanical properties of collagen in inflamed discs should be clarified. Seven-week-old female Sprague-Dawley rats were randomly divided into two groups. Chronic TMJ inflammation was induced by intra-articular injection of complete Freund's adjuvant, and samples were harvested after 5 weeks. Picrosirius staining revealed multiple colours under polarized light, which represented alternative collagen bundles in inflamed discs. Using atomic force microscopy scanning, the magnitude of Young's modulus was reduced significantly accompanied with disordered collagen fibril arrangement with porous architecture of inflamed discs. Transmission electron microscopy scanning revealed a non-uniform distribution of collagen fibres, and oversized collagen fibrils were observed in inflamed discs. Fourier transform infrared microspectroscopy revealed a decrease in 1 338 cm-1/amide II area ratio of collagen in different regions. The peak positions of amide I and amide II bands were altered in inflamed discs, indicating collagen unfolding. Our results suggest that sustained inflammation deteriorates collagen structures, resulting in the deterioration of the ultrastructure and nanomechanical properties of rat TMJ discs.

Structure-Function Relationships of Temporomandibular Retrodiscal Tissue.

It is estimated that 2% to 4% of the US population will seek treatment for temporomandibular joint (TMJ) symptoms, typically occurring with anterior disc displacement. The temporomandibular retrodiscal tissue (RDT) has been postulated to restrict pathologic disc displacement. To elucidate RDT function, understanding regional RDT biomechanics and ultrastructure is required. No prior biomechanical analysis has determined regional variations in RDT properties or associated biomechanical outcomes with regional variations in collagen and elastin organization. The purpose of this study was to determine direction- and region-dependent tensile biomechanical characteristics and regional fibrillar arrangement of porcine RDT. Incremental stress relaxation experiments were performed on 20 porcine RDT specimens, with strain increments from 5% to 50%, a ramp-strain rate of 2% per second, and relaxation periods of 2.5 min. Tensile characteristics were determined between temporal and condylar regions and anteroposterior and mediolateral directions. RDT preparations were imaged using second-harmonic generation (SHG) microscopy for both collagen and elastin. Young's modulus showed significant differences by region ( P < 0.001) and strain ( P < 0.001). Young's modulus was <1 MPa from 5% to 20% strain, before increasing from 20% to 50% strain to a maximum of 2.9 MPa. Young's modulus trended higher in the temporal region and mediolateral direction. Instantaneous and relaxed moduli showed no significant difference by region or direction. Collagen arrangement was most organized near the disc boundary, with disorganization increasing posteriorly. Elastin was present at the disc boundary and RDT mid-body. Porcine RDT demonstrated region- and strain-dependent variations in tensile moduli, associated with regional differences in collagen and elastin. The small tensile moduli suggest that the RDT is not resistive to pathologic disc displacement. Further biomechanical analysis of the RDT is required to fully define RDT functional roles. Understanding regional variations in tissue stiffness and ultrastructure for TMJ components is critical to understanding joint function and for the long-term goal of improving TMJ disorder treatment strategies.

The Yucatan Minipig Temporomandibular Joint Disc Structure-Function Relationships Support Its Suitability for Human Comparative Studies.

Frequent involvement of the disc in temporomandibular joint (TMJ) disorders warrants attempts to tissue engineer TMJ disc replacements. Physiologically, a great degree of similarity is seen between humans and farm pigs (FPs), but the pig's rapid growth confers a significant challenge for in vivo experiments. Minipigs have a slower growth rate and are smaller than FPs, but minipig TMJ discs have yet to be fully characterized. The objective of this study was to determine the suitability of the minipig for TMJ studies by extensive structural and functional characterization. The properties of minipig TMJ discs closely reproduced previously reported morphological, biochemical, and biomechanical values of human and FP discs. The width/length dimension ratio of the minipig TMJ disc was 1.95 (1.69 for human and 1.94 for FP). The biochemical evaluation revealed, on average per wet weight, 24.3% collagen (22.8% for human and 24.9% for FP); 0.8% glycosaminoglycan (GAG; 0.5% for human and 0.4% for FP); and 0.03% DNA (0.008% for human and 0.02% for FP). Biomechanical testing revealed, on average, compressive relaxation modulus of 50 kPa (37 kPa for human and 32 kPa for FP), compressive instantaneous modulus of 1121 kPa (1315 kPa for human and 1134 kPa for FP), and coefficient of viscosity of 13 MPa·s (9 MPa·s for human and 3 MPa·s for FP) at 20% strain. These properties also varied topographically in accordance to those of human and FP TMJ discs. Anisotropy, quantified by bidirectional tensile testing and histology, again was analogous among minipig, human, and FP TMJ discs. The minipig TMJ's ginglymoarthrodial nature was verified through cone beam computer tomography. Collectively, the similarities between minipig and human TMJ discs support the use of minipig as a relevant model for TMJ research; considering the practical advantages conferred by its growth rate and size, the minipig may be a preferred model over FP.

Deterioration of mechanical properties of discs in chronically inflamed TMJ.

Temporomandibular joint (TMJ) discs frequently undergo degenerative changes in arthritis. However, the biomechanical properties of pathogenic discs remain to be explored. In this study, we evaluated the effects of chronic inflammation on the biomechanical properties of TMJ discs in rats. Chronic inflammation of TMJs was induced by double intra-articular injections of complete Freund's adjuvant for 5 weeks, and biomechanical properties and ultrastructure of the discs were examined by mechanical testing, scanning electron microscopy, and transmission electron microscopy. The instantaneous compressive moduli of the anterior and posterior bands of discs in inflamed TMJs were decreased significantly compared with those in the control group. The instantaneous tensile moduli of the discs of inflamed TMJs also showed significant decreases in both the anterior-posterior and mesial-lateral directions. The relaxation moduli of the discs of inflamed TMJs showed nearly the same tendency as the instantaneous moduli. The surfaces of the discs of inflamed TMJs became rough and porous due to the loss of the superficial gel-like stratum, with many collagen fibers exposed and degradation of the sub-superficial collagen fibrils. Our results suggested that chronic inflammation of TMJ could lead to deterioration of mechanical properties and alteration of disc ultrastructure, which might contribute to TMJ disc displacement.

Network of telocytes in the temporomandibular joint disc of rats.

The phenotypes of the temporomandibular joint (TMJ) disc cells range from fibroblasts to chondrocytes. There are relatively few reported studies using transmission electron microscopy (TEM) to determine the ultrastructural features of these cells. It was hypothesized that at least a subpopulation of TMJ stromal cells could be represented by the telocytes, cells with telopodes. In this regard a TEM study was performed on rat TMJ samples. Collagen-embedded networks were found built-up by cells with telopodes with subplasmalemmal caveolae, moderate content in matrix secretory organelles and well-represented intermediate filaments. Appositions of cell bodies were found. Prolongations of such cells were closely related to nerves and microvessels. Our study indicates that the TMJ disc attachment seems equipped with telocytes capable of stromal signaling. However, further studies are needed to assess whether the telocytes belong to a renewed cell population derived from circulating precursors.

Relationship between anisotropic diffusion properties and tissue morphology in porcine TMJ disc.

OBJECTIVE: To investigate the relationship between anisotropic solute diffusion properties and tissue morphology in porcine temporomandibular joint (TMJ) discs. DESIGN: TMJ discs from eleven pigs aged 6-8 months were divided into five regions: anterior, intermediate, posterior, lateral, and medial. The transport properties and tissue morphology were investigated in three orthogonal orientations: anteroposterior (AP), mediolateral (ML), and superoinferior (SI). The anisotropic diffusivity of fluorescein (332 Da) in the right discs was determined by the fluorescence recovery after photobleaching (FRAP) protocols. The tissue morphology in the left discs was quantified by scanning electron microscopy. RESULTS: The diffusivities of fluorescein in the TMJ disc were significantly anisotropic, except for the anterior region. In the medial, intermediate, and lateral regions, the diffusion along the fiber orientation (i.e., AP direction) was significantly faster than the diffusion in ML and SI directions. In the posterior region, the diffusion along the fiber orientation (i.e., ML direction) was significantly faster than the diffusion in AP and SI directions. The diffusion in the anterior region was mostly isotropic with the lowest degree of diffusion anisotropy, as well as collagen fiber alignment, likely due to the multi-directional fiber arrangement. The anterior region had the highest mean diffusivity [65.6 (49.3-81.8) µm(2)/s] in the disc, likely due to its high water content. The overall average diffusivity of fluorescein across the TMJ disc was 57.0 (43.0-71.0) µm(2)/s. CONCLUSIONS: The solute diffusion in porcine TMJ discs was strongly anisotropic and inhomogeneous, which associated with tissue structure (i.e., collagen fiber alignment) and composition (e.g., water content).

Modificación del líquido sinovial en diferentes afecciones articulares de la rodilla / Changes in synovial fluid in different knee-joint diseases

Objetivo. Analizar las modificaciones del líquido sinovial (LS) en las afecciones articulares más frecuentes de la rodilla y establecer una relación en función de su concentración. Material y métodos. Se analizaron 62 muestras de LS de rodillas con afección meniscal (32), rotura del ligamento cruzado anterior (LCA) (17) y lesión condral aislada (13). De cada muestra se realizó un estudio cuantitativo y cualitativo de las citocinas (IL-1, IL-2, IL-6, IL-10, TNF-alfa) y factores de crecimiento (IGF-1, TGF-Beta). Resultados. En la lesión del LCA, el ambiente del LS fue predominantemente anabólico e inflamatorio, con niveles elevados de IL1, IL6, significativos de TGF-Beta (p=0,02 y p=0,004), IL-10 (p=0,046 y p=0,047) y significativamente disminuidos de TNF-alfa (p=0,02 y p=0,004). En la afección condral y meniscal, predominó un ambiente catabólico, con elevación significativa del TNF-alfa y disminución significativa del TGF-Beta (p=0,02 y p=0,004). Las diferencias fueron mayores en el caso de la lesión condral aislada. Conclusión. Los cambios observados señalan que en la lesión articular, además de la alteración biomecánica, el LS influye negativamente en la homeostasis articular, variando su composición según el tipo de afección (AU)

Objective. To analyse the changes in synovial fluid (SF) in the most common knees joint diseases, and to establish a relationship according to its concentration. Material and methods. A total of 62 synovial fluids were analysed from knees with, meniscus disease (32), anterior cruciate ligament (ACL) (17) and isolated chondral injury (13). A quantitative and quality study was performed on each sample, which included cytokines IL-1, IL-2, IL-6, IL-10, TNF-alfa and growth factors, IGF-1 and TGF-Beta). Results. The SF environment in the ACL injury was mainly anabolic and inflammatory, with increased levels of IL1, IL6, significant levels of TGF-Beta (P=.02 and P=.004), IL-10 (P=.046 and P=.047) and significantly decreased levels of TNF-alfa (P=.02 and P=.004). There was mainly a catabolic environment in chondral and meniscal disease, with a significant increase in TNF-alfa and a significant decrease in TGF-Beta (P=.02 and P=.004). The differences were greater in the case of isolated chondral injury. Conclusion. The changes observed show that, as well as the biomechanical changes, the SF has a negative effect on joint homeostasis, it composition varying depending on the type of pathology (AU)

Psychological stress induces alterations in temporomandibular joint ultrastructure in a rat model of temporomandibular disorder.

OBJECTIVE: The objective of this study was to investigate the effects of psychological stress on temporomandibular disorder (TMD). STUDY DESIGN: A communication box was used to induce psychological stress (PS) in rats. Then, the ultrastructure of temporomandibular was observed using scanning electron microscopy. Interleukin-1 (IL-1) and IL-6 were measured with reverse transcription polymerase chain reaction. RESULTS: The PS group showed evidence of ultrastructural changes in the condyle and articular disk after stimulation, i.e., incomplete gelatinlike material was observed on the condyle after 1 week of PS, wider waves on the articular disk and exposed condylar collagen were observed after 3 weeks of PS, and cracks were apparent on the surface of the condyle. The expression of IL-1 and IL-6 in the condyle cartilage significantly increased after exposure to psychological stress. CONCLUSIONS: These results indicate that psychological stress induces ultrastructure alterations in the temporomandibular joint and plays an important role in TMD.

Phenotypes of articular disc cells in the rat temporomandibular joint as demonstrated by immunohistochemistry for nestin and GFAP.

The articular disc is a dense collagenous tissue containing disc cells that are phenotypically described as chondrocyte-like cells or fibrochondrocytes. Despite the possible existence of these phenotypes in systemic joints, little is known about the detailed classification of the articular disc cells in the temporomandibular joint. In this immunocytochemical study we examined the localization and distribution patterns of nestin and glial fibrillary acidic protein (GFAP) in the articular disc of the rat temporomandibular joint at postnatal day 1, and weeks 1, 2, 4 and 8, based on the status of tooth eruption and occlusion. Nestin and GFAP are intermediate filament proteins whose expression patterns are closely related to cell differentiation and cell migration. Both types of immunopositive cell greatly increased postnatally to a stable level after postnatal week 4, but they showed different distribution patterns and cell morphologies. Nestin-reactive disc cells, which were characterized by a meagre cytoplasm and thin cytoplasmic processes, were scattered in the articular disc, whereas GFAP-positive cells, characterized by broader processes, existed exclusively in the deeper area. In mature discs, the major proportion of articular disc cells exhibited GFAP immunoreactivity. Furthermore, a double-immunostaining demonstrated that the nestin-negative cells, consisting of GFAP-positive and -negative cells, exhibited immunoreactions for heat shock protein 25. These findings indicate that the articular disc cells comprise at least three types in the rat temporomandibular joint and suggest that their expressions closely relate to mechanical loading forces within the joint, including occlusal force, as observed through postnatal development.

A mechanical evaluation of three decellularization methods in the design of a xenogeneic scaffold for tissue engineering the temporomandibular joint disc.

Tissue-engineered temporomandibular joint (TMJ) discs offer a viable treatment option for patients with severe joint internal derangement. To date, only a handful of TMJ tissue engineering studies have been carried out and all have incorporated the use of synthetic scaffold materials. These current scaffolds have shown limited success in recapitulating morphological and functional aspects of the native disc tissue. The present study is the first to investigate the potential of a xenogeneic scaffold for use in tissue engineering the TMJ disc. The effects of decellularization agents on the disc's mechanical properties were assessed using three common decellularization protocols: Triton X-100, sodium dodecyl sulfate (SDS) and an acetone/ethanol solution. Decellularized scaffolds were subsequently characterized through cyclic mechanical testing at physiologically relevant frequencies to determine which chemical agent most accurately preserved the native tissue properties. Results have shown that porcine discs treated with SDS most closely matched the energy dissipation capabilities and resistance to deformation of the native tissue. Treatments using Triton X-100 caused the resultant tissue to become relatively softer with inferior energy dissipation capabilities, while treatment using acetone/ethanol led to a significantly stiffer and dehydrated material. These findings support the potential of a porcine-derived scaffold decellularized by SDS as a xenograft for TMJ disc reconstruction.

Matrix metalloproteinase and its inhibitor in temporomandibular joint osteoarthrosis after indirect trauma in young goats.

Our aim was to examine the change in expression of matrix metalloproteinases (MMP-13), matrix metalloproteinases-3 (MMP-3), and tissue inhibitor of matrix metalloproteinase-1 (TIMP-1) in the articular cartilage of goats with experimentally-induced osteoarthrosis of the temporomandibular joint (TMJ) at various times. Osteoarthrosis was induced in 20 goats in the bilateral TMJ and 5 goats acted as controls. There were 5 goats in each group, and a group was killed at 7 days, and 1, 3, and 6 months postoperatively. The samples were collected, and the joints evaluated histologically. Immunofluorescence was used to detect the presence of MMPs and TIMP-1 in the articular disc and condylar cartilage. The ultrastructure of the articular disc and condylar surface at 1 month was examined with scanning electron microscopy (SEM). Osteoarthrosis of the TMJ progressed gradually over time. MMP-13, MMP-3, and TIMP-1 were expressed strongly in the TMJ soon after injury; MMP-13 became gradually weakened, and MMP-3 strengthened later. None of these were expressed in the normal condyle. After a month the surface of the arthrotic condyle was uneven, and the underlying collagen fibrils were exposed in irregular fissures on the surface. The secretion of TIMP-1 was related closely to the changes of MMPs during osteoarthrosis of the TMJ. The unbalanced ratio between them caused degradation of the matrix of the cartilage and might be the cause of osteoarthrosis of the TMJ.

Ultrastructural study of the temporomandibular joint after unilateral meniscectomy in Wistar rats.

Meniscectomy of the temporomandibular joint (TMJ) was frequently performed until a few years ago but now is seldom employed. This procedure induces important articular modifications but the complete extent of ultrastructural changes is still unknown. Twenty-one Wistar rats were submitted to unilateral meniscectomy. Animals were randomly divided into three groups and followed for 15, 35 or 60 days. After killing both meniscectomized and contralateral TMJ specimens were sectioned sagittally and prepared for light and scanning electron microscopy studies. Normal TMJs are characterized by glenoid fossa and condylar process with distinct conjunctive layers in which regularly arranged type 1 collagen fibres predominate. Meniscectomized animals initially exhibit a different tissue covering the eroded articular surface of the condyle with the prevalence of type 3 collagen fibres but type 1 fibres predominate in the late postoperative period. Subchondral cysts are clearly visible. A complex remodelling process of the TMJ after meniscectomy is evident with important ultrastructural modifications that may correlate to unsatisfactory clinical results. The dynamic nature of this process is also observed when specimens from different postoperative periods are compared. Surgeons should always bear in mind these alterations when indicating this procedure.

Biomechanical responses of human temporomandibular joint disc under tension and compression.

The purpose of this study was to observe the microscopic changes in the temporomandibular joint (TMJ) disc in response to tension and compression, and to study the mechanism of disc failure when subjected to mechanical stresses. The scanning electron microscope was used to observe topographic characteristics of TMJ disc samples obtained from 13 cadavers before and during biomechanical experiments. The stress relaxation experiments were conducted at different strain levels (2, 3, 4 and 6%). The uniaxial tensile experiments were carried out at a constant strain rate (0.05 mm/s). The confined compression tests were performed with 3 different indenters (2, 3 and 4mm in diameter) for 150 s and 3 h. The maximal tensile strain of the disc was 5% (nearly equal to 0.22 MPa of tensile stress) in the mediolaterally tensile direction. Typical wavelike structure of the collagen fibrils of the disc was present at 2-4% strain ranges. Tensile and shear damage to local collagen fibrils was observed in specimens of the intermediate zone and the posterior band at 6% strain level. Changes in the collagen network from a wavelike structure to distortion observed on the surface of the testing samples were reversible in the 150-s indentation, but severe, irreversible breakdown and deformation of the collagen-proteoglycan network occurred in those specimens that had been compressed for 3h. Persistent and prolonged compression inevitably resulted in irrecoverable disc failure. Mechanical stress is a crucial factor in breakdown of the TMJ disc.

Cell type and distribution in the porcine temporomandibular joint disc.

PURPOSE: Surprisingly little is known about the cellular composition of the temporomandibular joint (TMJ) disc, which is a crucial piece of the puzzle in tissue engineering efforts. Toward this end, cell types were identified and quantified regionally in the TMJ disc. MATERIALS AND METHODS: Porcine TMJ discs were examined by histology, electron microscopy, and immunohistochemistry. Histology consisted of hematoxylin and eosin staining to identify regional variation of cell type and cell numbers. Transmission electron microscopy was used to elucidate differences in organelle content and pericellular matrix between TMJ disc cells and chondrocytes from hyaline cartilage. Immunohistochemistry was used to assess the presence of smooth and skeletal muscle character in the TMJ disc. RESULTS: The overall ratio of fibroblasts to chondrocyte-like cells in the TMJ disc was approximately 2.35 to 1, with the highest relative number of chondrocyte-like cells in the intermediate zone. Electron microscopy revealed distinct differences between TMJ disc chondrocyte-like cells and chondrocytes from hyaline cartilage with respect to organelles and the pericellular region. Immunostaining identified smooth muscle in the form of vessels, which were most prominent in the anterior band. Skeletal muscle was not observed. CONCLUSION: The cells of the TMJ disc are distinctly different from cells of hyaline cartilage, and consequently should not be referred to as chondrocytes. TMJ disc cells are comprised of heterogeneously distributed subpopulations, with fibroblasts predominating over fibrochondrocytes.

Ultrastructure of the human intra-articular disc of the temporomandibular joint.

The ultrastructural appearance of the human intra-articular disc (IAD) was investigated in three discs that had been surgically removed due to disease from three female patients aged 47, 50, and 54 years of age. Regions of the IAD were selected from central areas that appeared to be least affected by disease. Sections were fixed in 2.5 per cent glutaraldehyde in 0.1 M phosphate buffer, pH 7.3 immediately after surgery. The regions examined showed no obvious signs of inflammation. The cells showed moderate amounts of the intracellular organelles associated with protein synthesis and secretion, and possessed considerable amounts of microfilamentous material, thus resembling those described in other mammals. Despite the large number of cells examined, only one cell showed evidence of a chondrocyte-like morphology in that it possessed an incomplete pericellular zone of microfilamentous material separating the cell membrane from the adjacent collagen bundles of the extracellular matrix (ECM). Thus, on morphological grounds, fibrocartilage was virtually non-existent in the specimens examined. The mean collagen fibril diameter was 43.9 nm and the fibril diameter distribution was not unimodal. Although the majority of fibrils had a relatively small diameter, two of the three specimens possessed many fibrils with diameters of over 100 nm, this being consistent with tissue subjected to tension. The mean area of a fibre bundle occupied by collagen (as opposed to the ground substance) was approximately 56 per cent.

The structure of the bilaminar zone in the human temporomandibular joint: a light and scanning electron microscopy study in young and elderly subjects.

The bilaminar zone (BZ) in the human temporomandibular joint (TMJ) of toothed adults (GI) and toothless, elderly humans (GII) were analysed using light and scanning electron microscopy (SEM). In both groups the BZ consists of an upper and a lower stratum of connective tissue separated by a vascularized middle region. The superior stratum contains bundles of collagen fibres disposed in different directions. The fibres are fairly thick and transversely oriented immediately posterior to the TMJ disc. The initial part of the inferior stratum contains curved bundles of collagen fibres oriented anterio-posteriorly. From the middle to the posterior part of the inferior stratum, the fibres are right-aligned in GI and clearly sinuous in nature in GII. In both groups, the middle and posterior portions of the middle region are distinguished by the presence of vessels and vascular spaces. Loosely arranged connective and adipose tissues are also evident. The vascular spaces are wider in GII than in GI. The predominance of type I collagen fibres is clear in all regions of the BZ in both groups. The elastic fibres lie parallel to the collagen fibres in both groups and they are thicker and more abundant in GI, apparently decreasing in GII.

The microanatomy of the rhesus monkey temporomandibular joint.

PURPOSE: The objective of this study was to describe and compare the histology of the rhesus monkey temporomandibular joint (TMJ) with that of the human joint. MATERIALS AND METHODS: Seventeen rhesus monkeys (Macaca mulatta) with an age range from 4 to 11 years were used. Both TMJs of the first animal and the left TMJs of the remaining 16 animals were used for this study. The joint specimens were sectioned sagittally and processed for light and electron microscopic studies. RESULTS: The rhesus monkey TMJ consists of the condylar, glenoid fossa, and articular disc components. The histology of these components is described at the light and electron microscopic level. CONCLUSIONS: The monkey TMJ was found to be anatomically similar to the human joint. It was concluded that the rhesus monkey is one of the most suitable animal models for studies involving the TMJ.

Ultrastructure of collagen fibers and distribution of extracellular matrix in the temporomandibular disk of the human fetus and adult.

We quantitatively examined the distribution of these differences in extracellular matrices (collagen types I, III, and fibronectin) and elastic fibers under confocal laser scanning microscopy and electron scanning microscopy in terms of their contribution to the mechanics of the TMJ during development and in adults. Elastic fibers were found in the anterior and posterior bands in adults aged 40 years, and a few elastic fibers in the anterior band of the disk in adults aged 80 to 90 years. The extracellular matrix contents of the TMJ disk are shown in various detected levels in the anterior, intermediate, posterior bands of TMJ disk. During development, collagen fibers are arranged in a complex fashion from 28 weeks' gestation. These ultrastructures of the embryonic TMJ are resembled to that of adults aged the 40s, however the difference in extracellular matrix distribution found in embryonic stages and adults. They might reflect the differences in function between mastication and sucking or the changes in shape and form as results of functional disorders of the TMJ.

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.

Crimping of collagen in the intra-articular disc of the temporomandibular joint: a comparative study.

Very occasional reference is made to the presence of collagen crimps in the fibre bundles of the intra-articular disc (IAD) of the temporomandibular joint (TMJ). As the crimp structure may confer important biomechanical properties on the IAD, the present study was undertaken to determine its distribution in a variety of mammals, including humans. IADs from the rat, rabbit, guinea pig, ferret, sheep, marmoset and human were either sectioned or examined as whole mount preparations with polarized light. Apart from the guinea pig, where fibre bundles in the central region of the disc showed considerable overlap and masking of the crimp structure, the anteroposterior aligned fibres in the central region of all remaining animals showed the conspicuous presence of crimps. The periodicity of the crimp distance varied between about 10 and 30 microm. There was variation of the crimp periodicity between animals and between regions of the same disc. The crimping was associated with undulations along the length of the collagen fibres visible at the light microscope level using routine staining. The possible significance of crimping in association with internal derangement is discussed.