Spatial arrangement of collagen fibrils in the articular cartilage of the mandibular condyle: a light microscopic and scanning electron microscopic study

Distribution of pericellular matrix molecules in the temporomandibular joint and their chondroprotective effects against inflammation

The objectives of this study were to (1) determine the distribution and synthesis of pericellular matrix (PCM) molecules (collagen VI, collagen IV and laminin) in rat temporomandibular joint (TMJ) and (2) investigate the effects of PCM molecules on chondrocytes against inflammation in osteoarthritis. Four zones (fibrous, proliferating, mature and hypertrophic) of condylar cartilage and three bands (anterior, intermediate and posterior) of disc were analysed by immunohistochemistry for the presence of PCM molecules in rat TMJs. Isolated chondrocytes were pre-treated with PCM molecules before being subjected to interleukin (IL)-1β treatment to stimulate inflammation. The responses of the chondrocytes were analysed using gene expression, nitric oxide release and matrix metalloproteinase (MMP)-13 production measures. Histomorphometric analyses revealed that the highest areal deposition of collagen VI (67.4%), collagen IV (45.7%) and laminin (52.4%) was in the proliferating zone of TMJ condylar cartilage. No significant difference in the distribution of PCM molecules was noted among the three bands of the TMJ disc. All three PCM molecules were expressed intracellularly by chondrocytes cultured in the monolayer. Among the PCM molecules, pre-treatment with collagen VI enhanced cellular proliferation, ameliorated IL-1β-induced MMP-3, MMP-9, MMP-13 and inducible nitric oxide synthase gene expression, and attenuated the downregulation of cartilage matrix genes, including collagen I, aggrecan and cartilage oligomeric matrix protein (COMP). Concurrently, collagen VI pretreatment inhibited nitric oxide and MMP-13 production. Our study demonstrates for the first time the distribution and role of PCM molecules, particularly collagen VI, in the protection of chondrocytes against inflammation.

Mandibular Cartilage Collagen Network Nanostructure: Insights for Regeneration

BACKGROUND

Mandibular condyle cartilage (MCC) has a unique structure among articular cartilages; however, little is known about its nanoscale collagen network architecture, hampering design of regeneration therapies and rigorous evaluation of regeneration experiment outcomes in preclinical research. Helium ion microscopy is a novel technology with a long depth of field that is uniquely suited to imaging open 3D collagen networks at multiple scales without obscuring conductive coatings.

OBJECTIVE

The objective of this research was to image, at the micro- and nanoscales, the depth-dependent MCC collagen network architecture.

DESIGN

MCC was collected from New Zealand white rabbits. Images of MCC zones were acquired using helium ion, transmission electron, and light microscopy. Network fibril and canal diameters were measured.

RESULTS

For the first time, the MCC was visualized as a 3D collagen fibril structure at the nanoscale, the length scale of network assembly. Fibril diameters ranged from 7 to 110 nm and varied by zone. The articular surface was composed of a fine mesh that was woven through thin layers of larger fibrils. The fibrous zone was composed of approximately orthogonal lamellae of aligned fibrils. Fibrocyte processes surrounded collagen bundles forming extracellular compartments. The proliferative, mature, and hypertrophic zones were composed of a branched network that was progressively remodeled to accommodate chondrocyte hypertrophy. Osteoid fibrils were woven around osteoblast cytoplasmic processes to create numerous canals similar in size to canaliculi of mature bone.

CONCLUSION

This multiscale investigation advances our foundational understanding of the complex, layered 3D architecture of the MCC collagen network.

The trends and challenges in orthopaedic simulation

Generally, in some universities of medicine, orthopaedic training procedures represent a difficult task due to the inadequacies of the systems, the resources, and the use of technologies. This article explains the challenges and the needs for more research in the issue of orthopaedic simulation around the world.

Temporomandibular disorders: a review of etiology, clinical management, and tissue engineering strategies

Temporomandibular disorders (TMD) are a class of degenerative musculoskeletal conditions associated with morphologic and functional deformities that affect up to 25% of the population, but their etiology and progression are poorly understood and, as a result, treatment options are limited. In up to 70% of cases, TMD are accompanied by malpositioning of the temporomandibular joint (TMJ) disc, termed "internal derangement." Although the onset is not well characterized, correlations between internal derangement and osteoarthritic change have been identified. Because of the complex and unique nature of each TMD case, diagnosis requires patient-specific analysis accompanied by various diagnostic modalities. Likewise, treatment requires customized plans to address the specific characteristics of each patient's disease. In the mechanically demanding and biochemically active environment of the TMJ, therapeutic approaches that can restore joint functionality while responding to changes in the joint have become a necessity. One such approach, tissue engineering, which may be capable of integration and adaptation in the TMJ, carries significant potential for the development of repair and replacement tissues. The following review presents a synopsis of etiology, current treatment methods, and the future of tissue engineering for repairing and/or replacing diseased joint components, specifically the mandibular condyle and TMJ disc. An analysis of native tissue characterization to assist clinicians in identifying tissue engineering objectives and validation metrics for restoring healthy and functional structures of the TMJ is followed by a discussion of current trends in tissue engineering.

Dynamic compressive properties of articular cartilages in the porcine temporomandibular joint

The mandibular condylar and temporal cartilages in the temporomandibular joint (TMJ) play an important role as a stress absorber during function. However, relatively little information is available on its viscoelastic properties in dynamic compression, particularly in a physiological range of frequencies. We hypothesized that these properties are region-specific and depend on loading frequency. To characterize the viscoelastic properties of both cartilages, we performed dynamic indentation tests over a wide range of loading frequencies. Nine porcine TMJs were used; the articular surface was divided into five regions: anterior; central; posterior; medial and lateral. Sinusoidal compressive strain was applied with an amplitude of 1.0% and a frequency range between 0.01 and 10 Hz. In both cartilages, the dynamic storage modulus increased with frequency, and the value was the highest in the lateral region. These values of E' in the temporal cartilage were smaller than those in the mandibular condylar cartilage in all five regions except the lateral region. The Loss tangent values were higher in the temporal cartilage (0.35-0.65) than in the mandibular condylar one (0.2-0.45), which means that the temporal cartilage presents higher viscosity. The present results suggest that the dynamic compressive moduli in both cartilages are region-specific and dependent on the loading frequency, which might have important implications for the transmission of load in the TMJ.

Biomechanical and biochemical characteristics of the mandibular condylar cartilage

The human masticatory system consists of a mandible which is able to move with respect to the skull at its bilateral temporomandibular joint (TMJ) through contractions of the masticatory muscles. Like other synovial joints, the TMJ is loaded mechanically during function. The articular surface of the mandibular condyle is covered with cartilage that is composed mainly of collagen fibers and proteoglycans. This construction results in a viscoelastic response to loading and enables the cartilage to play an important role as a stress absorber during function. To understand its mechanical functions properly, and to assess its limitations, detailed information about the viscoelastic behavior of the mandibular condylar cartilage is required. The purpose of this paper is to review the fundamental concepts of the biomechanical behavior of the mandibular condylar cartilage. This review consists of four parts. Part 1 is a brief introduction of the structure and function of the mandibular condylar cartilage. In Part 2, the biochemical composition of the mandibular condylar cartilage is summarized. Part 3 explores the biomechanical properties of the mandibular condylar cartilage. Finally, Part 4 relates this behavior to the breakdown mechanism of the mandibular condylar cartilage which is associated with the progression of osteoarthritis in the TMJ.

Biomechanical properties of the mandibular condylar cartilage and their relevance to the TMJ disc

Mandibular condylar cartilage plays a crucial role in temporomandibular joint (TMJ) function, which includes facilitating articulation with the TMJ disc, reducing loads on the underlying bone, and contributing to bone remodeling. To improve our understanding of the TMJ function in normal and pathological situations, accurate and validated three-dimensional (3-D) finite element models (FEMs) of the human TMJ may serve as valuable diagnostic tools as well as predictors of thresholds for tissue damage resulting from parafunctional activities and trauma. In this context, development of reliable biomechanical standards for condylar cartilage is crucial. Moreover, biomechanical characteristics of the native tissue are important design parameters for creating functional tissue-engineered replacements. Towards these goals, biomechanical characteristics of the condylar cartilage have been reviewed here, highlighting the structure-function correlations. Structurally, condylar cartilage, like the TMJ disc, exhibits zonal and topographical heterogeneity. Early structural investigations of the condylar cartilage have suggested that the tissue possesses a somewhat transversely isotropic orientation of collagen fibers in the fibrous zone. However, recent tensile and shear evaluations have reported a higher stiffness of the tissue in the anteroposterior direction than in the mediolateral direction, corresponding to an anisotropic fiber orientation comparable to the TMJ disc. In a few investigations, condylar cartilage under compression was found to be stiffer anteriorly than posteriorly. As with the TMJ disc, further compressive characterization is warranted. To draw inferences for human tissue using animal models, establishing stiffness-thickness correlations and regional evaluation of proteoglycan/glycosaminoglycan content may be essential. Efforts directed from the biomechanics community for the characterization of TMJ tissues will facilitate the development of reliable and accurate 3-D FEMs of the human TMJ.

Tensile properties of the mandibular condylar cartilage

Mandibular condylar cartilage plays a crucial role in temporomandibular joint (TMJ) function, which includes facilitating articulation with the temporomandibular joint disc and reducing loads on the underlying bone. The cartilage experiences considerable tensile forces due to direct compression and shear. However, only scarce information is available about its tensile properties. The present study aims to quantify the biomechanical characteristics of the mandibular condylar cartilage to aid future three-dimensional finite element modeling and tissue engineering studies. Porcine condylar cartilage was tested under uniaxial tension in two directions, anteroposterior and mediolateral, with three regions per direction. Stress relaxation behavior was modeled using the Kelvin model and a second-order generalized Kelvin model, and collagen fiber orientation was determined by polarized light microscopy. The stress relaxation behavior of the tissue was biexponential in nature. The tissue exhibited greater stiffness in the anteroposterior direction than in the mediolateral direction as reflected by higher Young's (2.4 times), instantaneous (1.9 times), and relaxed (1.9 times) moduli. No significant differences were observed among the regional properties in either direction. The predominantly anteroposterior macroscopic fiber orientation in the fibrous zone of condylar cartilage correlated well with the biomechanical findings. The condylar cartilage appears to be less stiff and less anisotropic under tension than the anatomically and functionally related TMJ disc. The anisotropy of the condylar cartilage, as evidenced by tensile behavior and collagen fiber orientation, suggests that the shear environment of the TMJ exposes the condylar cartilage to predominantly but not exclusively anteroposterior loading.

Lubrication of the temporomandibular joint

Although tissue engineering of the temporomandibular joint (TMJ) structures is in its infancy, tissue engineering provides the revolutionary possibility for treatment of temporomandibular disorders (TMDs). Recently, several reviews have provided a summary of knowledge of TMJ structure and function at the biochemical, cellular, or mechanical level for tissue engineering of mandibular cartilage, bone and the TMJ disc. As the TMJ enables large relative movements, joint lubrication can be considered of great importance for an understanding of the dynamics of the TMJ. The tribological characteristics of the TMJ are essential for reconstruction and tissue engineering of the joint. The purpose of this review is to provide a summary of advances relevant to the tribological characteristics of the TMJ and to serve as a reference for future research in this field. This review consists of four parts. Part 1 is a brief review of the anatomy and function of the TMJ articular components. In Part 2, the biomechanical and biochemical factors associated with joint lubrication are described: the articular surface topology with microscopic surface roughness and the biomechanical loading during jaw movements. Part 3 includes lubrication theories and possible mechanisms for breakdown of joint lubrication. Finally, in Part 4, the requirement and possibility of tissue engineering for treatment of TMDs with degenerative changes as a future treatment regimen will be discussed in a tribological context.

Tissue Engineering the Mandibular Condyle

Tissue engineering provides the revolutionary possibility for curing temporomandibular joint (TMJ) disorders. Although characterization of the mandibular condyle has been extensively studied, tissue engineering of the mandibular condyle is still in an inchoate stage. The purpose of this review is to provide a summary of advances relevant to tissue engineering of mandibular cartilage and bone, and to serve as a reference for future research in this field. A concise anatomical overview of the mandibular condyle is provided, and the structure and function of the mandibular condyle are reviewed, including the cell types, extracellular matrix (ECM) composition, and biomechanical properties. Collagens and proteoglycans are distributed heterogeneously (topographically and zonally). The complexity of collagen types (including types I, II, III, and X) and cell types (including fibroblast-like cells, mesenchymal cells, and differentiated chondrocytes) indicates that mandibular cartilage is an intermediate between fibrocartilage and hyaline cartilage. The fibrocartilaginous fibrous zone at the surface is separated from hyaline-like mature and hypertrophic zones below by a thin and highly cellular proliferative zone. Mechanically, the mandibular condylar cartilage is anisotropic under tension (stiffer anteroposteriorly) and heterogeneous under compression (anterior region stiffer than posterior). Tissue engineering of mandibular condylar cartilage and bone is reviewed, consisting of cell culture, growth factors, scaffolds, and bioreactors. Ideal engineered constructs for mandibular condyle regeneration must involve two distinct yet integrated stratified layers in a single osteochondral construct to meet the different demands for the regeneration of cartilage and bone tissues. We conclude this review with a brief discussion of tissue engineering strategies, along with future directions for tissue engineering the mandibular condyle.

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.

Cell surface receptors transmit sufficient force to bend collagen fibrils

To better understand the dynamic interaction of cells with their surrounding extracellular matrix, chondrocytes and rat embryo fibroblasts were overlaid with individual collagen fibrils and observed with high-resolution video-enhanced differential interference contrast microscopy. Although the cells had a polygonal shape characteristic of nonmotile cells, they used processes usually associated with cell locomotion to acquire the collagen fibrils. Instead of being transported in a retrograde direction, fibrils on the dorsal cell surface were bent, and regions of the bent fibrils were shifted in diverse directions. A blocking antibody to the beta1 integrin subunit significantly inhibited collagen fibril acquisition and bending. Enhanced actin assembly was only occasionally associated with fibrils undergoing rearrangement. Considering that the relatively stiff collagen fibrils require the application of force to be bent, this study shows that cells with a polygonal morphology (as opposed to a polarized, motile shape) are capable of exerting force through the beta1 integrins on the dorsal surface of the cell. Analysis of the bending patterns indicates that fibril buckling was induced by retrograde force combined with regions held stationary and/or the fibrils were bent by forces acting in opposing directions.

Frequency and distribution of articular tissue features in adult human mandibular condyles: a semiquantitative light microscopic study

BACKGROUND

The adult mandibular condyle is reported to be covered by fibrocartilage that develops from growth cartilage present earlier in life. Available data on the organization of condylar fibrocartilage are entirely descriptive or have been derived from young adult individuals. In order to examine the variability in normal appearance, condyles from a representative sample of adult humans were analyzed semiquantitatively.

METHODS

With a light microscope, features of the superficial, intermediate, and deep tissue zones subjacent to small contiguous sectors of the articular surface were recorded. The distribution of each feature relative to the total surface was then calculated and respective data obtained from nine predetermined condylar regions and from males and females were compared using analysis of variance.

RESULTS

The organization of the articular tissue varied significantly in the anteroposterior direction only. Unlike during growth, the superficial and deep zones in anterior and superior regions mostly contained fibrocartilage, although of markedly different appearance. Furthermore, the intermediate zone along about half of its anteroposterior extension lacked a distinctly visible layer, because the cell density was low and there was dense fibrous tissue or fibrocartilage similar to that of the superficial or deep zone, respectively. In these situations, zonation of the articular tissue was revealed only by the arrangement of collagen fibers.

CONCLUSIONS

The appearance of adult condylar articular tissue, in addition to varying considerably within and between putative load-bearing and nonload-bearing regions, bears only a vague resemblance to the layered organization of the growing condyle. Current terminology that refers to that organization, therefore, is inappropriate. It is proposed to designate impartially the three articular tissue zones of the adult condyle as "superficial," "intermediate," and "deep."

Microanatomy of the moose temporomandibular joint (Alces alces; Linnaeus, 1758)

Temporomandibular joint (TMJ) histology was investigated in 8 female Scandinavian moose. 5 were 1-year-old with a carcass weight (cw) of 125-140 kg, and 3 were 2-years-old (160-175 kg cw). The condylar articular surface consisted of a connective tissue lining with parallel collagen fibres. Numerous blood vessels were observed adjacent to the joint chamber. Below the fibrous layer, a proliferative cellular zone of undifferentiated mesenchymal cells was situated. These cells differentiated into chondroblasts and hypertrophied chondrocytes. Further down, an endochondral ossification process was initiated. Vertically directed invaginations were observed. A similar cellular organization was identified in the temporal component. However, the undifferentiated mesenchymal cell layer was discontinuous. The disc showed dense collagen bundles without main alignment. Vessels were identified throughout the entire disc. The results indicate that the cellular organization of the moose TMJ is similar to the TMJ histology found in other mammals but differences do occur.

Normal cartilage structure, biochemistry, and metabolism: a review of the literature

PURPOSE

To understand the possible significance of the presence of proteases, cytokines, growth factors, and arachidonic acid metabolites in the osteoarthritic temporomandibular joint (TMJ), a review of the normal physiologic processes and participating factors in the normal TMJ is established, based on knowledge of structure, biochemistry and metabolism of normal cartilage in general.

Metabolic turnover of sulfated glycosaminoglycans and proteoglycans in rabbit temporomandibular joint cartilages with experimentally induced osteoarthrosis

Osteoarthrosis-like changes were induced by means of experimental disk perforation in the right temporomandibular joint of rabbits. The turnover of proteoglycans and glycosaminoglycans was studied 16 weeks later, using 35SO4. Tissues were sampled 1 day and 7 days after injection of the sulfate. The corresponding tissues from the left untreated joint were used as controls. After isolation of the glycosaminoglycans the incorporation of 35SO4 was estimated by scintillating counting. The extracted proteoglycans were analyzed, using gel electrophoresis, and the distribution of radioactivity was determined by autoradiography, followed by densitometry. Both the synthesis and rate of degradation of the proteoglycans were increased in the experimental disk, compared with those of the control. The net result of these metabolic changes seemed to be losses of small proteoglycans, whereas a slow increase in the number of larger ones may have occurred. The turnover rates of 4- and 6-sulfate increased, although their ratio remained unchanged at this stage of the osteoarthrosis-like process. In the condylar cartilage the turnover of large and small proteoglycans was also increased. The increase was most marked among those containing 6-sulfated galactosaminoglycans. The results concerning the experimental condylar cartilage indicated a decrease in the largest proteoglycan population, whereas the proportion of small proteoglycans was increased.

Calcified cartilage zone and its dimensional relationship to the articular cartilage in the human temporomandibular joint of elderly individuals

The aim was to describe the appearance of the calcified cartilage zone (CCZ) and to determine its dimensional relationship to the articular cartilage thickness in the normal human temporomandibular joint. An autopsy material comprising 21 joints from 12 elderly individuals was examined microscopically. The appearance of the CCZ was examined, and the thickness of the CCZ and of the total articular cartilage was measured in 18 different positions in each joint. The CCZ was outlined by a flat or gently undulating tidemark and an irregular osteochondral junction. The cellularity of the CCZ varied extensively. The cells were numerous in the CCZ when the overlying articular cartilage displayed high cellularity. Statistical analysis of the measurements demonstrated a relationship (p < 0.001) between the thickness of the CCZ and of the articular cartilage. Our findings, both qualitative and quantitative, indicate a close relationship between the physiology of the CCZ and of the overlying articular cartilage.

Surface structure of the temporomandibular joint in normal and steroid-treated rats: a scanning electron microscopic study

The aim was to study the ultrastructure of the surface of the temporomandibular joint (TMJ) in mature rats. The TMJs from control rats and rats given corticosteroids for 10 days or 38 days were examined. In three joints from the control rats the disk was detached from the condyle before preparation and analysis. Scanning electron microscopy was performed on the condyle, the disk, and the temporal component. Generally, the surface of the three components was predominantly smooth, although the condyle exhibited a more even surface than the disk and the temporal component. In the fossa a pitted or ridged appearance was observed in some areas. There was a striking difference between the surface structure of disks attached to, and that of disks detached from, the condyle during preparation. A prominent undulation of surface was evident in disks detached from the condyle. Below the surface layer of the articular cartilage, a network of collagen fibers and fibrils running in all directions could be observed in all three components. In limited areas there was fibrillation and shallow defects of the surface layer. These changes were seen in all rats given corticosteroids for 38 days but also in some rats given corticosteroids for 10 days and in a few control rats.

Pathology of temporomandibular joint internal derangement and osteoarthrosis

Temporomandibular joint (TMJ) osteoarthrosis and disk displacement seem to be strongly related, but they may also represent mutually independent temporomandibular disorders. This paper presents relevant aspects of normal physiology and degeneration of synovial joints, aspects of normal temporomandibular articular disk physiology and of displacement of the disk, the relationship between TMJ osteoarthrosis and disk displacement, and a general classification of temporomandibular disorders.

Tissue responses to degenerative changes in the temporomandibular joint: a review

The articular cartilage covering of the mandibular condyle and the articular eminence, as well as the tissue of the articular disc, may be affected by degenerative changes associated with osteoarthrosis. Degenerative changes of cartilage alter its physical properties and, as a result, affect its ability to withstand compressive and shearing stresses. Increased friction between the articular surfaces may impair joint movement and may elicit compensatory or pathologic responses of the cartilage and the adjacent tissues, such as capsule and ligaments, synovial membrane, subchondral bone, and associated musculature. In this review, these structural changes are described and related to common signs and symptoms of craniomandibular dysfunction, such as clicking, locking and instability, pain and tenderness, restricted ranges of mandibular motion, crepitation, deformity, muscle wasting, and changes of occlusion.

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.

The effect of shear fatigue on bovine articular cartilage

The objective of this study was to investigate the effects of mechanical fatigue in the form of cyclic shear strain on articular cartilage. Three millimeter diameter full-thickness plugs were cored from the lateral aspect of bovine tibial plateaus. Sinusoidal shear strains of +/- 5, +/- 10, and +/- 15% were applied to the specimens at 100 Hz for 3 h (a total of 108 x 10(4) cycles). The mechanical shear properties of the tissue (loss and storage moduli) were determined as a function of the number of applied strain cycles. A rapid, irreversible decrease of approximately 35% of initial modulus was found to occur in both loss and storage modulus during application of the first 90,000 cycles. Further decay in the moduli was found to occur from 90 x 10(3) to 108 x 10(4) cycles, but was of considerably smaller magnitude than the initial decrease. The moduli remained relatively constant beyond application of 108 x 10(4) cycles. No consistent change in proteoglycan content was found to be associated with the fatigue process when comparing tested specimens with fresh, untested tissue, and with experimental controls. In addition, no structural defects in the mechanically altered tissue were revealed by scanning electron microscopy.

Osteoarthrosis as the cause of craniomandibular pain and dysfunction: a unifying concept

It has been demonstrated that osteoarthrotic changes in the temporomandibular joint (TMJ) and in other synovial joints show a similar course, both clinically and (ultra)microscopically. Initially, cartilage changes and possibly also changes in the synovial membrane set up a vicious cycle of cartilage breakdown accompanied by attempts at repair. When the degradative process exceeds the response of repair, the osteoarthrotic disorder progresses into clinically detectable stages. Frequently, the gliding capacity of the articular disc is also impaired, giving rise to an internal derangement. In this article, a concept is presented in which it is suggested that in many cases of craniomandibular pain and dysfunction TMJ osteoarthrosis is the basic disorder.

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.

Osteoarthritis of the temporomandibular joint: a light microscopic and scanning electron microscopic study of the articular cartilage of the mandibular condyle

The aim of this study was to investigate the organization of collagen fibrils and the histopathologic alterations as well as the morphologic aspects of osteoarthritic articular cartilage of the human mandibular condyle. Nine osteoarthritic condyles, three obtained at necropsy and the other six during surgery, were examined by light microscopy and scanning electron microscopy. Light microscopic observations revealed features of progressive and regressive remodeling and the presence of clefts. Scanning electron microscopic observations showed the presence of thick, coiled fibrils at the joint surface and numerous osmiophilic lipid globules scattered between the collagen fibrils. The collagen fibrils were disordered. It was concluded that collagen fiber network disintegration and fatty degeneration comprise the osteoarthritic changes of the articular cartilage of the human mandibular condyle.