Glycosaminoglycans in normal and osteoarthrotic human temporomandibular joint disks

Reduction of osteoarthritis severity in the temporomandibular joint of rabbits treated with chondroitin sulfate and glucosamine

Osteoarthritis is a degenerative disease that causes substantial changes in joint tissues, such as cartilage degeneration and subchondral bone sclerosis. Chondroitin sulfate and glucosamine are commonly used products for the symptomatic treatment of osteoarthritis. The aim of the present study was to investigate the effects of these products when used as structure-modifying drugs on the progression of osteoarthritis in the rabbit temporomandibular joint. Thirty-six New Zealand rabbits were divided into 3 groups (n = 12/group): control (no disease); osteoarthritis (disease induction); and treatment (disease induction and administration of chondroitin sulfate and glucosamine). Osteoarthritis was induced by intra-articular injection of monosodium iodoacetate. Animals were killed at 30 and 90 days after initiation of therapy. The treatment was effective in reducing disease severity, with late effects and changes in the concentration of glycosaminoglycans in the articular disc. The results indicate that chondroitin sulfate and glucosamine may have a structure-modifying effect on the tissues of rabbit temporomandibular joints altered by osteoarthritis.

Estrogen signaling impacts temporomandibular joint and periodontal disease pathology

Women experience a higher incidence of oral diseases including periodontal diseases and temporomandibular joint disease (TMD) implicating the role of estrogen signaling in disease pathology. Fluctuating levels of estrogen during childbearing age potentiates facial pain, high estrogen levels during pregnancy promote gingivitis, and low levels of estrogen during menopause predisposes the TMJ to degeneration and increases alveolar bone loss. In this review, an overview of estrogen signaling pathways in vitro and in vivo that regulate pregnancy-related gingivitis, TMJ homeostasis, and alveolar bone remodeling is provided. Deciphering the specific estrogen signaling pathways for individual oral diseases is crucial for potential new drug therapies to promote and maintain healthy tissue.

Fibro/chondrogenic differentiation of dental stem cells into chitosan/alginate scaffolds towards temporomandibular joint disc regeneration

Tissue engineering (TE) may provide effective alternative treatment for challenging temporomandibular joint (TMJ) pathologies associated with disc malpositioning or degeneration and leading to severe masticatory dysfunction. Aim of this study was to evaluate the potential of chitosan/alginate (Ch/Alg) scaffolds to promote fibro/chondrogenic differentiation of dental pulp stem cells (DPSCs) and production of fibrocartilage tissue, serving as a replacement of the natural TMJ disc. Ch/Alg scaffolds were fabricated by crosslinking with CaCl2 combined or not with glutaraldehyde, resulting in two scaffold types that were physicochemically characterized, seeded with DPSCs or human nucleus pulposus cells (hNPCs) used as control and evaluated for cell attachment, viability, and proliferation. The DPSCs/scaffold constructs were incubated for up to 8 weeks and assessed for extracellular matrix production by means of histology, immunofluorescence, and thermomechanical analysis. Both Ch/Alg scaffold types with a mass ratio of 1:1 presented a gel-like structure with interconnected pores. Scaffolds supported cell adhesion and long-term viability/proliferation of DPSCs and hNPCs. DPSCs cultured into Ch/Alg scaffolds demonstrated a significant increase of gene expression of fibrocartilaginous markers (COLI, COL X, SOX9, COM, ACAN) after up to 3 weeks in culture. Dynamic thermomechanical analysis revealed that scaffolds loaded with DPSCs significantly increased storage modulus and elastic response compared to cell-free scaffolds, obtaining values similar to those of native TMJ disc. Histological data and immunochemical staining for aggrecan after 4 to 8 weeks indicated that the scaffolds support abundant fibrocartilaginous tissue formation, thus providing a promising strategy for TMJ disc TE-based replacement.

The identification of proteoglycans and glycosaminoglycans in archaeological human bones and teeth

Bone tissue is mineralized dense connective tissue consisting mainly of a mineral component (hydroxyapatite) and an organic matrix comprised of collagens, non-collagenous proteins and proteoglycans (PGs). Extracellular matrix proteins and PGs bind tightly to hydroxyapatite which would protect these molecules from the destructive effects of temperature and chemical agents after death. DNA and proteins have been successfully extracted from archaeological skeletons from which valuable information has been obtained; however, to date neither PGs nor glycosaminoglycan (GAG) chains have been studied in archaeological skeletons. PGs and GAGs play a major role in bone morphogenesis, homeostasis and degenerative bone disease. The ability to isolate and characterize PG and GAG content from archaeological skeletons would unveil valuable paleontological information. We therefore optimized methods for the extraction of both PGs and GAGs from archaeological human skeletons. PGs and GAGs were successfully extracted from both archaeological human bones and teeth, and characterized by their electrophoretic mobility in agarose gel, degradation by specific enzymes and HPLC. The GAG populations isolated were chondroitin sulfate (CS) and hyaluronic acid (HA). In addition, a CSPG was detected. The localization of CS, HA, three small leucine rich PGs (biglycan, decorin and fibromodulin) and glypican was analyzed in archaeological human bone slices. Staining patterns were different for juvenile and adult bones, whilst adolescent bones had a similar staining pattern to adult bones. The finding that significant quantities of PGs and GAGs persist in archaeological bones and teeth opens novel venues for the field of Paleontology.

The temporomandibular joint of California sea lions (Zalophus californianus): part 1 - characterisation in health and disease

OBJECTIVES

This study aimed to characterise the histologic, biomechanical and biochemical properties of the temporomandibular joint (TMJ) of California sea lions. In addition, we sought to identify structure-function relationships and to characterise TMJ lesions found in this species.

DESIGN

Temporomandibular joints from fresh cadaver heads (n=14) of California sea lions acquired from strandings were examined macroscopically and microscopically. The specimens were also evaluated for their mechanical and biochemical properties. Furthermore, if TMJ arthritic changes were present, joint characteristics were described and compared to healthy joints.

RESULTS

Five male and 9 female specimens demonstrated macroscopically normal fibrocartilaginous articular surfaces and fibrous discs in the TMJ. Out of the 9 female specimens, 4 specimens had TMJ lesions were seen either in the articular surface or the disc. Histologically, these pathologic specimens demonstrated subchondral bone defects, cartilage irregularities and inflammatory cell infiltrates. The normal TMJ discs did not exhibit significant direction dependence in tensile stiffness or strength in the rostrocaudal direction compared with the mediolateral direction among normal discs or discs from affected joints. The TMJ discs were not found to be anisotropic in tensile properties. This feature was further supported by randomly oriented collagen fibres as seen by electron microscopy. Furthermore, no significant differences were detected in biochemical composition of the discs dependent upon population.

CONCLUSION

The TMJ and its disc of the California sea lion exhibit similarities but also differences compared to other mammals with regards to structure-function relationships. A fibrous TMJ disc rich in collagen with minimal glycosaminoglycan content was characterised, and random fibre organisation was associated with isotropic mechanical properties in the central region of the disc.

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.

Comparison of the T2 relaxation time of the temporomandibular joint articular disk between patients with temporomandibular disorders and asymptomatic volunteers

BACKGROUND AND PURPOSE

T2 relaxation time is a quantitative MR imaging parameter used to detect degenerated cartilage in the knee and lumbar intervertebral disks. We measured the T2 relaxation time of the articular disk of the temporomandibular joint in patients with temporomandibular disorders and asymptomatic volunteers to demonstrate an association between T2 relaxation time and temporomandibular disorder MR imaging findings.

MATERIALS AND METHODS

One hundred forty-four patients with temporomandibular disorders and 17 volunteers were enrolled in this study. An 8-echo spin-echo sequence for measuring the T2 relaxation times was performed in the closed mouth position, and the T2 relaxation time of the entire articular disk was measured. Patients were classified according to the articular disk location and function, articular disk configuration, presence of joint effusion, osteoarthritis, and bone marrow abnormalities.

RESULTS

The T2 relaxation time of the entire articular disk was 29.3 ± 3.8 ms in the volunteer group and 30.7 ± 5.1 ms in the patient group (P = .177). When subgroups were analyzed, however, the T2 relaxation times of the entire articular disk in the anterior disk displacement without reduction group, the marked or extensive joint effusion group, the osteoarthritis-positive group, and the bone marrow abnormality-positive group were significantly longer than those in the volunteer group (P < .05).

CONCLUSIONS

The T2 relaxation times of the articular disk of the temporomandibular joint in patients with progressive temporomandibular disorders were longer than those of healthy volunteers.

Detection of osteoarthritis in knee and hip joints by fast field-cycling NMR

It is known that in the early stages of osteoarthritis, the concentration of glycan proteins decreases in articular cartilage. This phenomenon is under active research to develop a means to characterize osteoarthritis accurately in the early stages of the disease, when still reversible. However, no method of quantification has yet shown clear success in this area. In this article, we propose a novel approach to detect glycan depletion using fast field-cycling NMR. This technique was previously reported to allow noninvasive measurement of protein concentration via the (14)N quadrupolar relaxation in certain amide groups. We have demonstrated that the articular cartilage exhibits clear quadrupolar peaks that can be measured by a benchtop fast field-cycling NMR device and which changes significantly between normal and diseased tissues (P < 0.01). This signal is probably glycan specific. The method may have potential for early evaluation of osteoarthritis in patients on fast field-cycling-MRI scanners currently under evaluation in the authors' laboratory.

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.

Design characteristics for temporomandibular joint disc tissue engineering: learning from tendon and articular cartilage

Tissue engineering of chondrocytic or fibroblastic musculoskeletal tissues has been relatively well studied compared with that of the temporomandibular joint (TMJ) disc. Early attempts at tissue engineering the disc have been misguided owing to a lack of understanding of the composition and function of the TMJ disc. The objective of this review is to compare the TMJ disc with a chondrocytic tissue (hyaline articular cartilage) and a fibroblastic tissue (tendon) to understand better the properties of this fibrocartilaginous tissue. The TMJ disc has 25 times more glycosaminoglycan (GAG) per dry weight than tendon but half that of articular cartilage. The disc's tensile modulus is six times more than cartilage but orders less than tendon. The GAG content and tensile modulus suggest that the TMJ disc is characterized as a tissue between hyaline cartilage and tendon, but the disc appears more tendon like when considering its collagen make-up and cell content. Like tendon, the TMJ disc contains primarily collagen type I at 85 per cent per dry weight, while articular cartilage has 30 per cent less collagen, which is type II. Knowledge of quantitative comparisons between joint tissues can give extensive insight into how to improve tissue engineering of the TMJ disc.

Disc derangements of the temporomandibular joint

Disc-related derangement of the temporomandibular joint is common and epidemiological research has found that about 20% of the population may be affected. Although very few of these people have the more prominent symptoms, recent data indicate that the numbers who need treatment is increasing. The two clinical variants of disc derangement, reciprocal clicking and closed lock, have long been recognized, but the association between them and their aetiology and pathogenesis is still unclear. As a consequence, there is still uncertainty on how to treat the conditions, and this is even more evident when surgery is involved. This paper describes new tissue research related to disc derangement. A simplified scheme is presented and implications for surgical treatment are discussed.

Cartilage tissue engineering and bioreactor systems for the cultivation and stimulation of chondrocytes

Damage to and degeneration of articular cartilage is a major health issue in industrialized nations. Articular cartilage has a particularly limited capacity for auto regeneration. At present, there is no established therapy for a sufficiently reliable and durable replacement of damaged articular cartilage. In this, as well as in other areas of regenerative medicine, tissue engineering methods are considered to be a promising therapeutic component. Nevertheless, there remain obstacles to the establishment of tissue-engineered cartilage as a part of the routine therapy for cartilage defects. One necessary aspect of potential tissue engineering-based therapies for cartilage damage that requires both elucidation and progress toward practical solutions is the reliable, cost effective cultivation of suitable tissue. Bioreactors and associated methods and equipment are the tools with which it is hoped that such a supply of tissue-engineered cartilage can be provided. The fact that in vivo adaptive physical stimulation influences chondrocyte function by affecting mechanotransduction leads to the development of specifically designed bioreactor devices that transmit forces like shear, hydrostatic pressure, compression, and combinations thereof to articular and artificial cartilage in vitro. This review summarizes the basic knowledge of chondrocyte biology and cartilage dynamics together with the exploration of the various biophysical principles of cause and effect that have been integrated into bioreactor systems for the cultivation and stimulation of chondrocytes.

Mechanical work during stress-field translation in the human TMJ

The pathomechanics of degenerative joint disease of the temporomandibular joint (TMJ) may involve fatigue produced by mechanical work on the articulating tissues. This study tested the hypotheses that mechanical work in the TMJ (i) varies with the type of mandibular activity, and (ii) is evenly distributed over TMJ surfaces. Ten healthy human participants were recorded with Magnetic Resonance Imaging (MRI) and jaw tracking. The data were used to reconstruct and animate TMJ activity. Aspect ratios, instantaneous velocities, and distances of stress-fields translation were used to calculate work (mJ). The results were analyzed by least-squares polynomial regression and ANOVA. Work magnitudes were related to peak velocity (R(2) = 0.92) and distance of stress-field translation (R(2) = 0.83), and were distributed over the joint surfaces (p < 0.03). During mandibular laterotrusion, average mechanical work was 1.5 times greater in the contralateral joint. Peak magnitudes of work (> 3000 mJ) were 4 times that previously reported.

Tissue Engineering of the TMJ disc: a review

The potential impact of a tissue-engineered temporomandibular joint (TMJ) disc is immense. Currently, patients suffering from a severely dysfunctional TMJ have few options. Facing the general lack of safe, effective TMJ disc implants, many patients undergo discectomy, a procedure that removes the injured TMJ disc in hopes of reducing debilitating symptoms associated with severe TMJ disorders. This procedure may not be ideal as the TMJ is left without an important functional component. Tissue engineering is a promising approach for the creation of viable, effective implants. The first attempt to investigate TMJ disc cells on a biomaterial was conducted in 1991. The first TMJ tissue-engineered constructs to be tested biochemically and biomechanically were formed in 1994; however, in examining this study in retrospect, it is clear how little TMJ knowledge was available at that time. Within the last 10 to 15 years, multiple studies have investigated critical TMJ disc characteristics, and while this characterization is not complete, these data have created a solid foundation for tissue-engineering research. Thus, the last 5 years have yielded core studies investigating the principal elements of tissue engineering: scaffold, cell source, and biological/biomechanical stimuli. Although TMJ disc tissue engineering is still in its formative years, its future is quite promising. Key studies are now being conducted that will assist in the establishment of a solid TMJ disc tissue-engineering approach. As the challenges of tissue engineering are faced and met, the ultimate goal of creating a functional biological implant nears.

Spatiotemporal distribution of heparan sulfate epitopes during murine cartilage growth plate development

Heparan sulfate proteoglycans (HSPGs) are abundant in the pericellular matrix of both developing and mature cartilage. Increasing evidence suggests the action of numerous chondroregulatory molecules depends on HSPGs. In addition to specific functions attributed to their core protein, the complexity of heparan sulfate (HS) synthesis provides extraordinary structural and functional heterogeneity. Understanding the interactions of chondroregulatory molecules with HSPGs and their subsequent outcomes has been limited by the absence of a detailed analysis of HS species in cartilage. In this study, we characterize the distribution and variety of HS species in developing cartilage of normal mice. Cryo-sections of femur and tibia from normal mouse embryos were evaluated using immunostaining techniques. A panel of unique phage display antibodies specific to particular HS species were employed and visualized with secondary antibodies conjugated to Alexa-fluor dyes. Confocal microscopy demonstrates that HS species are dynamic structures within developing growth plate cartilage and the perichondrium. GlcNS6S-IdoUA2S-GlcNS6S species are down regulated and localization of GlcNS6S-IdoUA-GlcNS6S species within the hypertrophic zone of the growth plate is lost during normal development. Regional differences in HS structures are present within developing growth plates, implying that interactions with and responses to HS-binding proteins also may display regional specialization.

Biochemical analysis of the porcine temporomandibular joint disc

Tissue engineering can be a boon in treating lesions of the disc in the temporomandibular joint (TMJ). Unfortunately, little is known about its biochemical content, so we analysed the discs of six slaughtered pigs. We measured the content and distribution of total DNA, glycosaminoglycan, and collagen. The mean (S.D.) content of DNA was 0.14% (0.08%) of the dry weight, of glycosaminoglycan 0.96% (0.39%), and of collagen 68.2% (14.5%). There were no significant differences from top to bottom, but from front to back the smallest concentration of glycosaminoglycan was in the posterior band, and the highest concentration of collagen was in the intermediate zone. The concentrations of DNA and glycosaminoglycan were higher in the medial than in the lateral area of the disc.

Pathogenesis of degenerative temporomandibular joint arthritides

Over the past decade, remarkable progress has been made in the study of molecular mechanisms involved in degenerative temporomandibular joint arthritides. Based on recent findings, models of degenerative temporomandibular joint disease predict that mechanical loads trigger a cascade of molecular events leading to disease in susceptible individuals. These events involve the production or release of free radicals, cytokines, fatty acid catabolites, neuropeptides, and matrix-degrading enzymes. Under normal circumstances, these molecules may be involved in the remodeling of articular tissues in response to changing functional demands. However, if functional demands exceed the adaptive capacity of the temporomandibular joint or if the affected individual is susceptible to maladaptive responses, then a disease state will ensue. An individual's susceptibility to degenerative temporomandibular joint disease may be determined by several factors, including genetic backdrop, sex, age, and nutritional status. It is hoped that, by furthering our understanding of the molecular events that underlie degenerative temporomandibular joint diseases, improved diagnostics and effective therapies for these debilitating conditions will be developed.

Effects of Initial Cell Seeding Density for the Tissue Engineering of the Temporomandibular Joint Disc

Tissue engineering may provide a better treatment modality for postoperative discectomy patients. The TMJ disc is an ideal candidate for tissue engineering approaches because of its lack of an intrinsic regenerative ability. Unfortunately, basic knowledge related to TMJ disc tissue engineering is still at an infancy level and not on par to that related to articular cartilage tissue engineering. The objective of this study was to examine the effects of initial cell density of TMJ disc cells seeded in nonwoven poly-glycolic acid (PGA) scaffolds on the biochemical and biomechanical properties of constructs examined at 0, 3, and 6 weeks after seeding. Low, medium, and high seeding densities were chosen to be 15, 30, and 120 million cells per ml of scaffold, which were seeded using a spinner flask. Significant differences were found temporally and as a function of seeding density in morphology, total collagen, GAG content, and permeability of the constructs, but not in aggregate modulus. The high seeding density group outperformed the low and medium groups in collagen and GAG content at all time points measured. The high-density group produced a total of 55.37 +/- 3.56 microg of collagen per construct, maintained 15.77 +/- 1.86 microg of GAG per construct, and only shrunk to 50% of the original scaffold size. Permeability of the constructs at 6 weeks was decreased by 70% compared to 0 weeks.

Quantitative analysis and comparative regional investigation of the extracellular matrix of the porcine temporomandibular joint disc

Characterization of the extracellular matrix of the temporomandibular joint (TMJ) disc is crucial to advancing efforts in tissue engineering the disc. However, the current literature is incomplete and often contradictory in its attempts to describe the nature of the TMJ disc matrix. The aim of this study was to identify the variation of key matrix components along the three axes of the porcine disc using ELISAs to quantify these matrix components, immunohistochemistry to identify their regional distribution, and SEM to examine collagen fiber diameter and orientation. The overall GAG content of the TMJ disc (including the dermatan sulfate proteoglycans) was 5.3+/-1.2% of the dry weight. Chondroitin sulfate, which comprised 74% of this total GAG content, was 4.4, 8.2, and 164 times more abundant than dermatan sulfate proteoglycan, keratan sulfate, and hyaluronic acid, respectively. In general, these GAGs were most concentrated in the intermediate zone of the TMJ disc, appearing in dense clusters, and least concentrated in the posterior band. Additionally, chondroitin sulfate was more abundant medially than laterally. Collagen II was discovered in trace amounts, with higher relative amounts in the intermediate zone. Collagen fibers were observed to run primarily in a ring-like fashion around the periphery of the disc and anteroposteriorly through the intermediate zone, with a mean fiber diameter of 18+/-9 mum. Characterization studies of the TMJ disc, including prior biomechanical and cell studies along with the current study of the extracellular matrix, collectively reveal a distinct character of the intermediate zone of the disc compared to its anterior and posterior bands.

Motivation, characterization, and strategy for tissue engineering the temporomandibular joint disc

The purpose of this review is to serve as the standard point of reference in guiding researchers investigating the tissue engineering of the temporomandibular joint (TMJ) disc. Tissue engineering of the TMJ disc is in its infancy, and currently there exists a gap between the tissue engineering community and the TMJ characterization community. The primary goal is to help bridge that gap by consolidating the characterization studies here as a reference to researchers attempting to tissue engineer the TMJ disc. A brief review of TMJ anatomy is provided, along with a description of relevant pathology, current treatment, and a rationale for engineering the TMJ disc. The biochemical composition and organization of the disc are reviewed, including glycosaminoglycan (GAG) and collagen content. The collagen of the disc is almost exclusively type I and primarily runs anteroposteriorly through the center and in a ringlike fashion around the periphery. The GAG content is approximately an order of magnitude less than that of hyaline cartilage, and although the distribution is not entirely clear, it seems as though chondroitin and dermatan sulfate are by far the primary GAGs. Cellular characterization and mechanical properties under compression, tension, and shear are reviewed as well. The cells of the disc are not chondrocytes, but rather resemble fibrocytes and fibrochondrocytes and may be of the same lineage. Mechanically, the disc is certainly anisotropic and nonhomogeneous. Finally, a review of efforts in tissue engineering and cell culture studies of the disc is provided and we close with a description of the direction we envision/propose for successful tissue engineering of the TMJ disc.

Matrix glycosaminoglycans in the temporomandibular joint in patients with painful clicking and chronic closed lock

The aim was to investigate the content of 4- and 6-sulphated glycosaminoglycans (GAGs) in specimens from temporomandibular joint disc and posterior disc attachment in patients with painful clicking and chronic closed lock. Nineteen patients (19 joints) with a clinical diagnosis of painful clicking were compared with 22 patients (22 joints) with a clinical diagnosis of chronic closed lock. Specimens were obtained from the disc and the posterior disc attachment, and their content of glycosaminoglycans analysed by means of capillary zone electrophoresis. These were significant differences in the amount of glycosaminoglycans between the two groups, values in patients with painful clicking being comparable to those of normal individuals, while patients having chronic closed lock showed significantly reduced values. Both groups showed higher values in the posterior disc attachment when compared to the disc and similar pattern of glycosaminoglycan sulphation. The results suggest that these two patient groups have distinctly different patterns of tissue reactions. In patients with chronic closed lock there was an altered composition of matrix, this change involving both disc and posterior disc attachment.

Structure and function of the temporomandibular joint disc: implications for tissue engineering

The temporomandibular joint (TMJ) disc is a little understood structure that, unfortunately, exhibits a plethora of pathologic disorders. Tissue engineering approaches may be warranted to address TMJ disc pathophysiology, but first a clear understanding of structure-function relationships needs to be developed, especially as they relate to the regenerative potential of the tissue. In this review, we correlate the biochemical content of the TMJ disc to its mechanical behavior and discuss what this correlation infers for tissue engineering studies of the TMJ disc. The disc of the TMJ exhibits a somewhat biconcave shape, being thicker in the anterior and posterior bands and thinner in the intermediate zone. The disc, which is certainly an anisotropic and nonhomogeneous tissue, consists almost entirely of type I collagen with trace amounts of type II and other types. In general, collagen fibers in the intermediate zone appear to run primarily in an anteroposterior direction and in a ringlike fashion around the periphery. Collagen orientation is reflected in higher tensile stiffness and strength in the center anteroposteriorly than mediolaterally and in the anterior and posterior bands than the intermediate zone mediolaterally. Tensile tests have shown the disc is stiffer and stronger in the direction of the collagen fibers. Elastin fibers in general appear along the collagen fibers and most likely function in restoring and retaining disc form after loading. The 2 primary glycosaminoglycans of the disc by far are chondroitin sulfate and dermatan sulfate, although their distribution is not clear. Compression studies are conflicting, but evidence suggests the disc is compressively stiffest in the center. Only a few tissue engineering studies of the TMJ disc have been performed to date. Tissue engineering studies must take advantage of existing information for experimental design and construct validation, and more research is necessary to characterize the disc to create a clearer picture of our goals in tissue engineering the TMJ disc.

Experimental induction of anterior disk displacement of the rabbit craniomandibular joint: an immuno-electron microscopic study of collagen and proteoglycan occurrence in the condylar cartilage

BACKGROUND

Results from our previous studies suggest that surgical induction of anterior disk displacement (ADD) in the rabbit craniomandibular joint (CMJ) leads to histopathological alterations consistent with osteoarthritis. In addition, molecular changes in collagens and glycosaminoglycans (GAGs) were observed using immunohistochemistry. The purpose of the present study was to further characterize those molecular changes in collagens and GAGs using immuno-electron microscopy.

METHODS

The right joint of 15 rabbits was exposed surgically and all discal attachments were cut except for the posterior attachment (the bilaminar zone). The disc was then repositioned anteriorly and sutured to the zygomatic arch. The left joint was used as a sham-operated control. Ten additional joints were used as non-operated controls. Mandibular condyles were removed 2 weeks following surgery and processed for light and immuno-electron microscopy using colloidal gold-labeled antibodies against collagen type I, II, VI and IX and against keratan sulfate, chondroitin-4 and -6-sulfate, and link protein.

RESULTS

Light microscopic results showed osteoarthritic changes. Immuno-electron microscopy of osteoarthritic cartilage demonstrated a decline in type II collagen, the abnormal presence of type I collagen and loss of type VI and IX collagens. Quantitative colloidal gold immuno-electron microscopy confirmed the depletion of keratan sulfate, chondroitin-4 and -6-sulfate, and link protein in osteoarthritic cartilage.

CONCLUSION

Anterior disk displacement leads to molecular alterations in both the collagen and the proteoglycans of rabbit condylar cartilage characteristic of osteoarthritis in other synovial joints. These alterations are consistent with loss of the shock absorber function of the cartilage and injury of the underlying bone.

Utility of frequency-selective fat saturation T2-weighted MR images for the detection of joint effusion in the temporomandibular joint

OBJECTIVES

To evaluate joint effusion in the temporomandibular joint (TMJ) using frequency-selective fat saturation (FS) T2-weighted images and assess this technique. To investigate whether bone marrow abnormalities and magnetic resonance imaging (MRI) findings of internal derangement may be linked to joint effusion in the TMJ in patients with pain.

METHODS

TMJ effusion was sought on FS T2-weighted images and conventional T2-weighted images in 400 joints from 200 patients with TMJ-related pain. Self-reported pain records were obtained from patients immediately before MRI and images assessed by the amount of TMJ fluid graded bilaterally using reference films by two radiologists. Other parameters recorded included disk displacement categories and condyle marrow abnormalities. The association between the recorded parameters and TMJ effusion judged by FS-sequences or conventional sequences was analysed using chi-square and Kappa tests.

RESULTS

The detection rate of TMJ effusion by FS-sequences was significantly greater than by conventional methods, and the results showed a significant relationship between MRI interpretation of TMJ effusion using FS-sequences or conventional methods and the presence of pain. The correlation between TMJ effusion on FS-sequences and pain was significantly stronger than the conventional method. Kappa test indicated good agreement between pain and MRI TMJ effusion by FS-sequences (kappa = 0.66), but not by conventional sequences (kappa = 0.56). The other parameters showed a similar trend for TMJ-related pain.

CONCLUSIONS

FS T2-weighted imaging is useful for detection of TMJ effusion, without known causes and confirms the importance of TMJ effusion as an indicator in patients with TMJ-related pain, bone abnormalities, and disk displacement.

Tomographic assessment of temporomandibular joint osseous articular surface contour and spatial relationships associated with disc displacement and disc length

The objective of this retrospective study was to determine whether associations exist between osseous temporomandibular joint (TMJ) characteristics and TMJ internal derangement (disc position and deformation) in an adolescent population. Magnetic resonance imaging (MRI) was used to quantitatively determine disc position and length in 335 TMJs in 175 subjects (106 female and 69 male) between the ages of 7.27 and 20.0 years (mean age, 13.08 years). Nine tomographic variables were measured from pretreatment tomograms. Tomographic data were cross-referenced with MRI data. Male and female samples were evaluated separately. Stepwise linear regression identified associations between disc displacement and reduced superior joint space, increased posterior joint space, increased anterior joint space, and reduced articular eminence convexity (male R(2) value, 0.41; female R(2) value, 0.38). Associations between reduced disc length and condylar position and eminence flattening were weaker (male R(2) value, 0.16; female R(2) value, 0.32). This study demonstrates that TMJ internal derangement is associated with functional osseous adaptation within the joint.

Viscoelastic properties of the human temporomandibular joint disc in patients with internal derangement

PURPOSE

This study investigated the viscoelastic properties of human temporomandibular joint (TMJ) discs in patients with severe internal derangement (ID).

PATIENTS AND METHODS

TMJ discs obtained from 5 patients with severe TMJ internal derangement were analyzed. Normal discs derived from 2 fresh cadavers and 4 patients without ID served as the controls. The viscoelastic responses of the discs to tensile forces were evaluated by means of stress-strain analyses.

RESULTS

The discs in both groups exhibited a nonlinear stress-strain relationship that was represented by a power function of the strain. However, after stress relaxation, the ID discs were likely to exhibit a linear stress-strain relationship. The instantaneous elastic moduli were almost the same in both discs, but the relaxed elastic modulus of the ID discs was significantly greater than that of the controls in lower strain range of less than 2%.

CONCLUSIONS

ID discs are more rigid than normal discs. These findings suggest that the changes in viscoelastic property of the discs in patients with ID are somewhat different from those that occur with aging.

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.

Male adolescent facial pattern associated with TMJ disk displacement and reduction in disk length: Part II

Dental practitioners continually strive to understand and determine which factors influence craniofacial morphology and how these factors may be controlled to provide the best treatment outcome for patients. Recently, an association between internal derangement of the TMJ and altered facial morphology was shown in an adolescent female sample by means of multiple regression techniques. The present study aims to determine whether similar associations are present between facial patterns exhibited by a preorthodontic male sample (n = 70) and varying degrees of TMJ internal derangement as assessed by magnetic resonance imaging. Multiple regression techniques were used to test the associations in 5 facial regions. Associations between internal derangement and craniofacial morphology differed in 3 of the facial regions when males and females were compared. However, associations between internal derangement and alteration in mandibular morphology and positioning were consistent in both gender groups.

Female adolescent facial pattern associated with TMJ disk displacement and reduction in disk length: part I

The aim of this study was to determine whether associations exist between temporomandibular joint (TMJ) disk displacement, and craniofacial morphology in an adolescent sample. Craniofacial lateral cephalometric radiographs and magnetic resonance images of the TMJs were obtained of 119 females between the ages of 10 and 17 years. Once the effects of age had been considered, associations between TMJ internal derangement and craniofacial morphology were studied in 5 facial regions making use of 5 separate multiple regression analyses. In females, associations between altered facial morphology and altered disk position were present within each of the facial regions investigated; the mandibular regions showed the strongest associations. This study shows that functional alteration in TMJ disk dynamics may be another factor to consider when craniofacial growth is forecasted for orthodontic treatment planning.

Discectomy of the temporomandibular joint: an experimental study in monkeys

Postoperative changes have been observed in the temporomandibular joint (TMJ) after discectomies. Animal models have often shown that interventions in the TMJ may heal uneventfully. Discectomies were performed on 14 Macaca fascicularis and macroscopic and microscopic examination performed after sacrifice of the animals. Two of the animals did not show any apparent macroscopic or microscopic changes. The remaining 12 joints showed minor to major changes. The most serious changes were seen in three joints with fibrous ankylosis and five joints showed marked destruction of the articular cartilage.

Synovial inflammation in arthroscopically obtained biopsy specimens from the temporomandibular joint: a review of the literature and a proposed histologic grading system

Data indicate that the synovial lining of the temporomandibular joint (TMJ) in some respects differs from other joints. The normal variation in morphology of the synovial lining of the TMJ is quite great, whereas the variation in pattern of pathologic changes appears to be relatively small (ie, synovial inflammation is not of the severity as that in other joints). In the current review, a system for histologic grading of synovial inflammation is proposed. The system is based on semiquantitative evaluation of the following set of parameters: 1) synovial lining cell layers; 2) vascularity (number or size of vascular profiles); and 3) Inflammatory cell infiltrate (commonly lymphocytes).

Quantitative assessment of temporomandibular joint disk status

The purpose of this study was to quantify temporomandibular joint disk-slice information produced by magnetic resonance imaging by means of a stepwise discriminant analysis. One hundred ninety-four adolescents consented to magnetic resonance imaging evaluation of their temporomandibular joints. Sagittal magnetic resonance imaging slices of each joint were assigned to one of six subjective categories of disk position by an experienced maxillofacial radiologist. Standardized reference planes transferred to each magnetic resonance image from corresponding lateral cephalometric radiographics facilitated the measurement of disk length and disk displacement and the computation of ratio values of these measurements. Discriminant analysis revealed that all three quantitative variables were descriptive and discriminant for grouping slice data into pre-established subjective categories. Cross-validation and misclassification error calculations showed a 69.3% agreement between subjective and discriminant classification. Therefore quantification of disk displacement can be used in place of subjective evaluation. In addition, discriminant analysis disclosed a reduction in disk length associated with increased severity of disk displacement.

Chondroitin sulfate isomers in synovial fluid of healthy and diseased human temporomandibular joints

Synovial fluid was collected from the superior articular cavity of the temporomandibular joint in patients with unilateral internal derangement and joint pain whose contralateral joint was healthy. Glycosaminoglycans were liberated by digestion with pronase E, and precipitated with cetylpyridinium chloride and ethanol. Unsaturated disaccharide isomers of chondroitin sulfate, obtained following chondroitinase ACII digestion, were analyzed by high-performance liquid chromatography. Analytic data indicated that deltaDi-0S and deltaDi-6S were often found in chondroitin sulfate from the fluid of the diseased joints. The amounts of deltaDi-0S and deltaDi-6S differed significantly between synovial fluid samples from the diseased and healthy joints. Comparison of the relative proportions of the unsaturated disaccharides in the synovial fluid with previously reported values for several tissues, indicated that the chondroitin sulfate originated from articular cartilage, with possibly some contributions from soft connective tissues and serum present in the synovial fluid. These results suggest that chondroitin sulfate in the synovial fluid provides a useful indicator of the degree of internal derangement of the temporomandibular joint.

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

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

Histochemical and immunohistochemical studies of the effects of experimental anterior disc displacement on sulfated glycosaminoglycans, hyaluronic acid, and link protein of the rabbit craniomandibular joint

PURPOSE

The purpose of this study was to determine the effects of surgically induced anterior disc displacement (ADD) on sulfated glycosaminoglycans (GAGs) such as keratan sulfate (KS), chondroitin-4-sulfate (C4S), and chondroitin-6-sulfate (C6S), hyaluronic acid (HA), and link protein (LP) of the rabbit craniomandibular joint (CMJ) using histochemical and immunohistochemical techniques.

MATERIALS AND METHODS

The right joint of 20 rabbits was exposed surgically, and all discal attachments were severed except for the posterior attachment. The disc was then repositioned anteriorly and sutured to the zygomatic arch. The left joint served as a sham-operated control. Ten additional joints were used as nonoperated controls. Deeply anesthetized rabbits were perfused with 2% buffered formalin 2 weeks (10 rabbits) or 6 weeks (10 rabbits) after surgery. Discs, bilaminar zones, condyles, and articular eminences were excised. Condyles and articular eminences were decalcified in ethylenediaminetetraacetic acid (EDTA). All tissues were sectioned at 10 microns in a cryostat. Sections were incubated with alcian blue and monoclonal antibodies directed against KS, C4S, C6S, HA, or LP. After incubation in the appropriate fluorescein isothiocyanate (FITC)-labeled secondary antibodies, tissue sections were studied under the fluorescence microscope.

RESULTS

The results showed a reduction in alcian blue staining and KS, C4S, C6S, HA, and LP immunostaining in the disc and articular surfaces at 2 weeks after induction of ADD. This reduction was followed by an increase in their immunostaining at 6 weeks. Also, there was a progressive increase in alcian blue staining, and KS, C4S, C6S, and HA immunostaining in the bilaminar zone at 2 and 6 weeks.

CONCLUSION

It was concluded that surgical induction of ADD in the rabbit CMJ leads to alterations in KS, C4S, C6S, HA, and LP content, consistent with similar changes accompanying osteoarthritis of other synovial joints.

Age changes in the rat temporomandibular joint articular disc: a biochemical study on glycosaminoglycan content

The temporomandibular joint (TMJ) articular discs were removed from female Sprague-Dawley rats 3, 5, 10, 32, 90 and 130 weeks of age. Glycosaminoglycans (GAGs) were extracted from the discs by heat treatment, alkali treatment and digestion with Pronase E, and purified by precipitation with cetylpyridinium chloride and ethanol. The concentration of total GAG was highest in the 3 week extracts and tended to decrease with age. Dermatan sulphate was the predominant GAG detected in all age groups along with chondroitin sulphate, hyaluronic acid and heparan sulphate. The disaccharides obtained from chondroitin sulphate were delta Di-4S, delta Di-6S and delta Di-0S, with delta Di-4S being the predominant isomer followed by delta Di-6S for all ages of all the GAG examined. The concentration of chondroitin sulphate showed a decrease with age. Quantitative changes of GAG with age may be related to functional changes in TMJ discs.

Pathogenesis of degenerative joint disease in the human temporomandibular joint

The wide range of disease prevalences reported in epidemiological studies of temporomandibular degenerative joint disease reflects the fact that diagnoses are frequently guided by the presence or absence of non-specific signs and symptoms. Treatment is aimed at alleviating the disease symptoms rather than being guided by an understanding of the underlying disease processes. Much of our current understanding of disease processes in the temporomandibular joint is based on the study of other articular joints. Although it is likely that the molecular basis of pathogenesis is similar to that of other joints, additional study of the temporomandibular joint is required due to its unique structure and function. This review summarizes the unique structural and molecular features of the temporomandibular joint and the epidemiology of degenerative temporomandibular joint disease. As is discussed in this review, recent research has provided a better understanding of the molecular basis of degenerative joint disease processes, including insights into: the regulation of cytokine expression and activation, arachidonic acid metabolism, neural contributions to inflammation, mechanisms of extracellular matrix degradation, modulation of cell adhesion in inflammatory states, and the roles of free radicals and heat shock proteins in degenerative joint disease. Finally, the multiple cellular and molecular mechanisms involved in disease initiation and progression, along with factors that may modify the adaptive capacity of the joint, are presented as the basis for the rational design of new and more effective therapy.

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

PURPOSE

A method for producing disc displacement is presented in which remodeling events in the disc and posterior attachment (PA) are similar to those occurring in patients suffering from disc displacement (DD).

METHOD

Thirty-three adult New Zealand White rabbits were used in this study. A unilateral anterior DD was surgically induced in 18 animals. Six animals were sham operated and nine animals served as controls.

RESULTS

Macroscopically, DD was associated with gross thickening of the posterior band (PB), shortening of the disc anteroposteriorly, flexure of the intermediate zone (IZ), and loss of the biconcave shape. Microscopically, dramatic internal structural changes were observed in displaced discs, including extensive collagenous fiber reorganization and changes in cell morphology associated with a generalized loss of metachromatic staining. As in humans, the disc displacement caused abnormal loading of the PA and remodeling of this tissue into a disc-like structure characterized by the appearance of coarse collagenous fiber bundles and scattered chondrocytes surrounded by a matrix-containing cartilage-like glycosaminoglycans (GAGs).

CONCLUSION

These pathoanatomic changes bear a remarkable similarity to those described in human disc derangements and support the use of this method as an experimental model for the study of remodeling events in human DD arthropathies.

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.

An experimental model of osteoarthrosis in the temporomandibular joint of the rabbit

Degenerative changes in the temporomandibular joint were induced in 24 rabbits by surgical perforation of the disk. The incongruence obtained between the joint surfaces caused a gradual increase in macroscopic and microscopic changes, including gross remodeling, loss of tissue volume, and altered cell morphology within a 16-week observation period. These changes occurred concurrently with major alterations in the composition of the matrix, as demonstrated by increase in the glycosaminoglycan content of both condylar cartilage and disk and by loss of hydroxyproline in the disk. The lesions in the disk tissue were clearly discernible, whereas those in the condylar cartilage were less extensive. The described method is concluded to give alterations in the temporomandibular tissues, as seen in degenerative joint disease of an early stage.