Shox2-deficiency leads to dysplasia and ankylosis of the temporomandibular joint in mice

The temporomandibular joint (TMJ) is a unique synovial joint whose development differs from the formation of other synovial joints. Mutations have been associated with the developmental defects of the TMJ only in a few genes. In this study, we report the expression of the homeobox gene Shox2 in the cranial neural crest derived mesenchymal cells of the maxilla-mandibular junction and later in the progenitor cells and undifferentiated chondrocytes of the condyle as well as the glenoid fossa of the developing TMJ. A conditional inactivation of Shox2 in the cranial neural crest-derived cells causes developmental abnormalities in the TMJ, including dysplasia of the condyle and glenoid fossa. The articulating disc forms but fuses with the fibrous layers of the condyle and glenoid fossa, clinically known as TMJ ankylosis. Histological examination indicates a delay in development in the mutant TMJ, accompanied by a significantly reduced rate of cell proliferation. In situ hybridization further demonstrates an altered expression of several key osteogenic genes and a delayed expression of the osteogenic differentiation markers. Shox2 appears to regulate the expression of osteogenic genes and is essential for the development and function of the TMJ. The Shox2 conditional mutant thus provides a unique animal model of TMJ ankylosis.     

Tensile properties of the porcine temporomandibular joint disc

Despite the significant morbidity associated with the temporomandibular joint (TMJ), little is known about the pathophysiology of this complex joint. TMJ disc degeneration plays a central role in the progression of TMJ disorders, and therefore disc regeneration would be a crucial treatment modality. Unfortunately, scarce information about the structural and functional characteristics of the TMJ disc is available. The current study aims to provide a standard for the biomechanical behavior of the TMJ disc for future tissue engineering studies. The disc was loaded under uniaxial tension in two directions, mediolateral and anteroposterior, and in three locations per direction. In the mediolateral direction, the posterior band was 2.5 times stiffer, 2.4 times tougher (energy to maximum stress), and 2.2 times stronger than the anterior band, which was in turn 16 times stiffer and 5.7 times stronger than the intermediate zone. In the anteroposterior direction, the central and medial regions were 74% and 35% stiffer and 56% and 59% stronger than the lateral region, respectively, although similar to each other in strength and stiffness. There was no significant difference in toughness between regions in the anteroposterior direction. These results correlated qualitatively with collagen fiber orientation and fiber size obtained using polarized light microscopy.     

Age-related osteo-arthrotic degeneration of the temporomandibular joint in the mouse

The light-microscopic and ultrastructural characteristics of the temporomandibular joints (TMJs) of female STR/IN mice, aged from 3 to 12 months, were studied. Every TMJ of an adult mouse starts to degenerate in early adulthood and subsequently suffers from osteo-arthrosis. Ageing of the TMJ is characterized by thinning out of its cartilaginous components. The chondrocytes are no longer distributed regularly in the ground substance but form clusters. Cracks and fissures invade the condylar cartilage and lead to the formation of cartilage islands, which finally become loose as free bodies in the lower joint chamber and joint capsule. The lower joint chamber diminishes, but no ankylosis is observed. Ultrastructurally, the number of vesicles around the degenerated chondrocytes increases. Aged chondrocytes contain more lysosomes. The condylar surface becomes irregular and reveals microscars. Its surface is covered by an electron-dense fine granular material, considered to be built up by proteoglycans. Compared to the male ICR mouse, the osteo-arthrotic destruction of the cartilage, the subchondral sclerosis and the deformation of the underlying bone exhibit only minor states in the female STR/IN mouse. Concerning the aetiology and pathogenesis, the very early degeneration of the mostly unloaded TMJ seems to be based on a genetically altered composition of the articular cartilage, possibly due to failing articular chondrocyte responses to stimuli connected with degeneration and repair.     

Expression of lumican related to CD34 and VEGF in the articular disc of the human temporomandibular joint

Lumican belongs to the small leucine-rich repeat proteoglycan (SLRP) gene family and has been reported to exist in the cornea, intervertebral disc and tendon. Lumican plays a significant role in the assembly and regulation of collagen fibres. The human temporomandibular joint (TMJ) disc is made up of fibrocartilage with an extracellular matrix (ECM) composed of collagen and proteoglycans. The existence and behaviour of lumican have not been studied in the human TMJ disc. Therefore, we used immunohistochemical methods to detect lumican, CD34 and vascular endothelial growth factor (VEGF) and histochemical staining with toluidine blue in 13 human TMJ specimens (10 surgically removed and 3 obtained from autopsy). In both normal and deformed discs we observed staining with toluidine blue. We found that the area of metachromasia inside the deformed disc was uneven and expression of lumican was strong in the areas negative for metachromasia. Staining of VEGF and CD34 inside the deformed disc was seen. We confirmed the expression of lumican in the human TMJ disc and showed that a large number of fibroblast-like cells existed in the area of strong lumican expression. These new findings about the behaviour of lumican suggest that it may play a key role in the generation of a new collagen network by fibroblast-like cells.Key words: TMJ disc, lumican, CD34, VEGF, immunohistochemistry, metachromasia.     

Histochemistry for studying structure and function of the articular disc of the human temporomandibular joint

The articular disc of the temporomandibular joint (TMJ) is composed of fibrocartilage, and the extracellular matrix of this disc is composed mainly of collagen, glycosaminoglycan and proteoglycans. Research on the changes that occur in the composition of the articular disc of the TMJ is necessary for understanding the basis of the pathological process of internal derangement (ID), and a number of reports have been published in recent years on the application of refined histochemical techniques to investigate the structure and function of the TMJ. The direction of future TMJ disc studies should be towards obtaining more evidence to support previous results, and should hopefully be of practical use in terms of prevention and cure of ID.     

The regional contribution of glycosaminoglycans to temporomandibular joint disc compressive properties

Understanding structure-function relationships in the temporomandibular joint (TMJ) disc is a critical first step toward creating functional tissue replacements for the large population of patients suffering from TMJ disc disorders. While many of these relationships have been identified for the collagenous fraction of the disc, this same understanding is lacking for the next most abundant extracellular matrix component, sulfated glycosaminoglycans (GAGs). Though GAGs are known to play a major role in maintaining compressive integrity in GAG-rich tissues such as articular cartilage, their role in fibrocartilaginous tissues in which GAGs are much less abundant is not clearly defined. Therefore, this study investigates the contribution of GAGs to the regional viscoelastic compressive properties of the temporomandibular joint (TMJ) disc. Chondroitinase ABC (C-ABC) was used to deplete GAGs in five different disc regions, and the time course for >95% GAG removal was defined. The compressive properties of GAG depleted regional specimens were then compared to non-treated controls using an unconfined compression stress-relaxation test. Additionally, treated and non-treated specimens were assayed biochemically and histologically to confirm GAG removal. Compared to untreated controls, the only regions affected by GAG removal in terms of biomechanical properties were in the intermediate zone, the most GAG-rich portion of the disc. Without GAGs, all intermediate zone regions showed decreased tissue viscosity, and the intermediate zone lateral region also showed a 12.5% decrease in modulus of relaxation. However, in the anterior and posterior band regions, no change in compressive properties was observed following GAG depletion, though these regions showed the highest compressive properties overall. Although GAGs are not the major extracellular matrix molecule of the TMJ disc, they are responsible for some of the viscoelastic compressive properties of the tissue. Furthermore, the mechanical role of sulfated GAGs in the disc varies regionally in the tissue, and GAG abundance does not always correlate with higher compressive properties. Overall, this study found that sulfated GAGs are important to TMJ disc mechanics in the intermediate zone, an important finding for establishing design characteristics for future tissue engineering efforts.     

Morphological study of lectin binding in the rabbit temporomandibular joint disc

Summary Glycoconjugates of the extracellular matrix are important for the normal mechanical functions of connective tissue structures such as the temporomandibular joint disc. Since lectins are known to bind to sugar residues with high affinity, a variety of lectins were used to study the presence and distribution of glycoconjugates in the temporomandibular joint disc. Discs were removed from 6 to 8-month-old rabbits and either sectioned in a cryostat and processed for light microscopy or fixed in 2% glutaraldehyde and processed for electron microscopy. The frozen sections were incubated with fluorescein- or peroxidaseconjugated lectin solutions. Ultrathin sections mounted on grids were incubated with lectins combined with a colloidal gold marker system for electron microscopical study. Our results indicate thatCanavalia ensiformis agglutinin (ConA) showed little or no binding to the discal tissue.Triticum vulgaris agglutinin (WGA) andMacluras pomifera (MPA) were bound strongly to both the synovium and the extracellular matrix and WGA also bound to the territorial matrix of chondrocyte-like cells.Glycine max andArachis hypogoea agglutinins (SBA and PNA), were localized in the synovium and extracellular matrix but to a lesser degree than WGA and MPA. WGA, MPA,Griffonia simplicifolia II andUlex europaeus were bound by discal fibroblasts. WGA was also localized in lysosomes of synovial A-cells (macrophages). The electron microscopical studies with lectins and colloidal gold marker systems indicated that some areas of the disc may be fibrocartilagenous as had been suggested by earlier immunohistochemical studies using monoclonal antibodies to characteristic glycosaminoglycans (GAGs) in cartilage.     

Tenascin in the human intervertebral disc: alterations with aging and disc degeneration

Our objective for this study was to determine the presence and distribution of tenascin in the human intervertebral disc. The tenascins are a family of extracellular matrix proteins with repeated structural domains homologous to epidermal growth factor, fibronectin type III and the fibrinogens. Little is known about the presence of this protein in the disc. Ten normal human discs donated from subjects newborn to 15 years old, 10 control discs from adult donors aged 24-41 years, and 11 surgical disc specimens from patients aged 26-76 years were examined for immunolocalization of tenascin. In young discs, tenascin was localized throughout the annulus; in the nucleus, localization was confined to pericellular matrix. In adult control and degenerating disc specimens, tenascin in the annulus was localized primarily in pericellular matrix regions encircling either single cells or clusters of disc cells; in rare instances localization was more diffuse in the intraterritorial matrix. In young, healthy disc, tenascin was abundant throughout the annulus. In contrast, degenerating discs in adults showed a localization restricted to the pericellular, and rarely, more restricted intraterritorial matrix. These observations indicate that changes in the amount and distribution of tenascin may have a role in disc aging and degeneration, possibly by modulating fibronectin-disc-cell interactions, and causing alterations in the shape of disc cells.     

HMGB1‐induced angiogenesis in perforated disc cells of human temporomandibular joint

High mobility group 1 protein (HMGB1), a highly conserved nuclear DNA‐binding protein and inflammatory mediator, has been recently found to be involved in angiogenesis. Our previous study has demonstrated the elevation of HMGB1 in the tissue of perforated disc of temporomandibular joint (TMJ). Here, we investigated a novel mediator of HMGB1 in regulating hypoxia‐inducible factor‐1α (HIF‐1α) and vascular endothelial growth factor (VEGF) to mediate angiogenesis in perforated disc cells of TMJ. HMGB1 increased the expression of HIF‐1α and VEGF in a dose‐ and time‐dependent manner in these cells. Moreover, immunofluorescence assay exhibits that the HIF‐1α were activated by HMGB1. In addition, HMGB1 activated extracellular signal‐related kinase 1/2 (Erk1/2), Jun N‐terminal kinase (JNK), but not P38 in these cells. Furthermore, both U0126 (ErK inhibitor) and SP600125 (JNK inhibitor) significantly suppressed the enhanced production of HIF‐1α and VEGF induced by HMGB1. Tube formation of human umbilical vein endothelial cells (HUVECs) was significantly increased by exposure to conditioned medium derived from HMGB1‐stimulated perforated disc cells, while attenuated with pre‐treatment of inhibitors for VEGF, HIF‐1α, Erk and JNK, individually. Therefore, abundance of HMGB1 mediates activation of HIF‐1α in disc cells via Erk and JNK pathway and then, initiates VEGF secretion, thereby leading to disc angiogenesis and accelerating degenerative change of the perforated disc.     

Immunohistochemical expression of types I and III collagen antibodies in the temporomandibular joint disc of human foetuses

The objective was to study the morphology of the articular disc and analyse the immunohistochemical expression of types I and III collagen markers in the temporomandibular joint (TMJ) disc of human foetuses of different gestational ages. Twenty TMJ from human foetuses supplied by Universidade Federal de Uberaba with gestational ages from 17 to 24 weeks were studied. The gestational age of the foetuses was determined by measuring the crown-rump (CR) length. Macroscopically, the foetuses were fixed in 10% formalin solution and dissected by removing the skin and subcutaneous tissue and exposing the deep structures. Immunohistochemical markers of type I and III were used to characterize the existence of collagen fibres. Analysis of the immunohistochemical markers of types I and III collagen revealed the presence of heterotypical fibril networks.     

Regional and disease-related differences in properties of the equine temporomandibular joint disc

Temporomandibular joint (TMJ) disorders affect up to 12% of the human population, and naturally occurring TMJ diseases are increasingly recognized in animals. The TMJ disc plays a major role in TMJ disorders in people, but little is known about its role in TMJ pathology in animals. This study characterizes differences in properties of equine TMJ discs associated with age, disc region, and presence of TMJ osteoarthritis (OA). Discs were dissected from both TMJ’s of sixteen horses euthanized for reasons unrelated to this study. Each joint was grossly evaluated and scored as normal, mild OA, or severe OA. Samples from the rostral, caudal, lateral, central, and medial regions of the disc were subject to compressive testing, quantitative biochemistry, and histology. Samples from the lateral, central, and medial region were tested for tensile properties in the rostrocaudal and mediolateral directions. We found that the equine TMJ disc is highly anisotropic, and its glycosaminoglycan (GAG) content and compressive stiffness vary between disc regions. The disc also exhibits increasing GAG content and compressive stiffness with increasing age. While equine TMJ disc properties are generally similar to other herbivores, greater compressive stiffness throughout the disc and greater GAG content in its rostral region suggest that mechanical demands on the TMJ disc differ between horses and other species. Importantly, a region-specific decrease in compressive stiffness was observed associated with joint disease and corresponded to cartilage erosions in the underlying condylar surface.     

Effects of intraoral splint wear on proteoglycans in the temporomandibular joint disc

Intraoral splints are a common dental treatment for dysfunctions of the temporomandibular joint (TMJ), but their effects on the structures of the joint, specifically the disc, have not been well investigated. This study examined proteoglycans (PGs) of the TMJ disc of the miniature pig and tested for alterations resulting from intraoral splint wear. Sixteen female pigs were divided into three groups: control (C), control splint (CS), and protrusive splint (PS). Splinted groups received chrome-cobalt ramp splints which were worn continuously for 2 months. PG content within various disc locations was determined by colorimeteric assay. PG synthesis and type were examined by labeling with (35)S-sulfate and SDS-PAGE analysis. Average water content of the disc was 77.1%, which places it at the high end of the normal range for collagenous biomaterials (60-80%). PGs migrating to the positions typical of aggrecan, biglycan, and decorin on SDS-PAGE were present in all locations of all groups. The highest content and synthesis of PGs were always found in the intermediate band of the disc regardless of group (P < 0.05), supporting the notion that this band encounters heavy compressive loading during function. The joints of animals from both splinted groups showed a high frequency of gross pathology. Biglycan synthesis was increased in both splinted groups (P < 0.05). Newly synthesized biglycan had a shorter migration distance in the intermediate bands of the CS group, suggesting increased hydrodynamic size. These findings suggest that intraoral splint wear may cause disc damage or remodeling.     

Viscoelastic characterization of the porcine temporomandibular joint disc under unconfined compression

Pathophysiology of the temporomandibular joint (TMJ) disc is central to many orofacial disorders; however, mechanical characterization of this tissue is incomplete. In this study, we identified surface-regional mechanical variations in the porcine TMJ disc under unconfined compression. The intermediate zone, posterior, anterior, lateral, and medial regions of eight TMJ discs were sectioned into inferior and superior surface samples. Surface-regional sections were then subjected to incremental stress relaxation tests. Single strain step (SSS) and final deformation (FD) viscoelastic models were fit to experimental data. Both models represented the experimental data with a high degree of accuracy (R(2)=0.93). The instantaneous modulus and relaxation modulus for the TMJ disc sections were approximately 500 kPa and 80 kPa, respectively; the coefficient of viscosity was approximately 3.5 MPa-s. Strain dependent material properties were observed across the disc's surface-regions. Regional variations in stiffness were observed in both models. The relaxation modulus was largest in the inferior-medial parts of the disc. The instantaneous modulus was largest in the posterior and anterior regions of the disc. Surface-to-surface variations were observed in the relaxation modulus for only the FD model; the inferior surface was found to be more resistant to compression than the superior surface. The results of this study imply the stiffness of the TMJ disc may change as strain is applied. Furthermore, the lateral region exhibited a lower viscosity and stiffness compared to other disc regions. Both findings may have important implications on the TMJ disc's role in jaw motion and function.     

The effect of collagen reinforcement in the behaviour of the temporomandibular joint disc

In this paper, the influence of collagen fibres in the behaviour of the temporomandibular joint disc is studied. A three-dimensional finite element model of the joint is developed from a set of medical images. The model comprises the mandible, part of the cranium and both temporomandibular joints. Joints have been considered to be composed of the articular discs and the temporomandibular ligaments. A fibre-reinforced porohyperelastic model was used to study the response under clenching of the fibrocartilage that composes the articular disc. This was divided in an intermediate zone, and two bands, an anterior and other posterior, in order to define the orientation of collagen fibres. The study demonstrates that the introduction of collagen fibres in the biphasic behaviour of the articular disc implies for a prescribed displacement not only an increase of the pressurization in the tissue, but also higher stresses in the anterior and posterior bands, as well as in the lateral zone of the disc. Thus, modelling the disc as an isotropic solid matrix leads in this case to an overestimation of the stresses in the intermediate zone, an underestimation of the pore pressure in this area, and an underestimation of the stresses in the rest of the disc.     

Size and location of the human temporomandibular joint

The literature abounds with conflicting data on various morphometric aspects of the temporomandibular joint (TMJ). The purpose of this study was to observe the effects of sex, ethnic group, and edentulism on TMJ osseous morphology and to define possible factors which might influence variation in this structure. TMJs and related craniofacial structures were measured directly on 229 dry skulls and matching mandibles. Analysis of variance, principal component analysis, and cluster analysis were performed. Our results indicate that 1) the anteroposterior-related TMJ dimensions are independent of sex, ethnic group, and edentulism; 2) the transverse TMJ dimension is related to cranial breadth measures; and 3) the projected distance, along a midsagittal plane, between the TMJ and foramen magnum is independent of sex, ethnicity, and edentulism. It is our assertion that the TMJ must not be considered as a single morphological structure but rather viewed as a functional unit with component parts which are subordinate to completely different sets of influences. © 1996 Wiley-Liss, Inc.