Histologic evaluation of temporomandibular arthritis induced by mild mechanical loading in rabbits

Appropriate cyclic tensile strain promotes biological changes of cranial base synchondrosis chondrocytes

OBJECTIVES

This study was designed to clarify biological changes of cranial base synchondrosis chondrocytes (CBSCs) upon cyclic tensile strain (CTS) loading which simulated orthopaedic mechanical protraction on cranial base synchondroses (CBS).

MATERIAL AND METHODS

A two-step digestion method was used to isolate CBSCs obtained from 1-week-old Sprague Dawley rats. Immunohistochemical staining of type II collagen and Sox9 was conducted to identify chondrocytes. A CTS of 1 Hz and 10% elongation was applied to the second passage of CBSCs by FX-5000™ Tension System for 24 hours. The control group kept static at the same time. The expression levels of extracellular matrix (Acan, Col1a1, Col2a1 and Col10a1) and key regulatory factors (Sox9, Ihh and PTHrP) were detected by quantitative real-time RT-PCR.

RESULTS

Positive staining of type II collagen and Sox9 was detected in the isolated CBSCs. The relative expression level of Acan, Col2a1, Col10a1, Sox9 and Ihh in the CTS-loading group was 1.85-fold, 2.19-fold, 1.53-fold, 6.62-fold, and 1.39-fold, respectively, as much as that in the control group, which had statistical significance (P<.05). There was no statistical difference (P>.05) in the expression of Col1a1 and PTHrP.

CONCLUSIONS

A CTS of 1 Hz and 10% elongation for 24 hours had positive effects on chondrocyte proliferation, phenotype maintenance and cartilage matrix synthesis.

Dietary variation and mechanical properties of articular cartilage in the temporomandibular joint: implications for the role of plasticity in mechanobiology and pathobiology

Due to their nature as tissue composites, skeletal joints pose an additional challenge in terms of evaluating the functional significance of morphological variation in their bony and cartilaginous components in response to altered loading conditions. Arguably, this complexity requires more direct means of investigating joint plasticity and performance than typically employed to analyze macro- and micro-anatomical phenomena. To address a significant gap in our understanding of the plasticity of the mammalian temporomandibular joint (TMJ), we investigated the histology and mechanical properties of condylar articular cartilage in rabbits subjected to long-term variation in diet-induced masticatory stresses, specifically cyclical loading. Three cohorts of male weanlings were raised for six months on different diets until adulthood. Following euthanasia, the TMJ condyles on one side were dissected away, fixed, decalcified, dehydrated, embedded and sectioned. Safranin O staining was employed to identify variation in proteoglycan content, which in turn was used to predict patterns of articular cartilage stiffness in contralateral condylar specimens for each treatment group. Hematoxylin and eosin staining was used to quantify diet-induced changes in chondrocyte hypertrophy and cellularity. Mechanical tests document significant decreases in articular cartilage stiffness corresponding to patterns of extracellular matrix relative protein abundance in rabbits subjected to greater cyclical loading. This indicates that TMJs routinely subjected to higher masticatory stresses due to a challenging diet eventually develop postnatal decreases in the ability to counter compressive loads during postcanine biting and chewing. These findings provide novel information regarding TMJ performance, with broader implications about the costs and benefits of phenotypic plasticity as well as implications for how such biological processes affect connective tissue mechanobiology and pathobiology.

Effect of mechanical loading on the metabolic activity of cells in the temporomandibular joint: a systematic review

OBJECTIVES

The purpose of this systematic review was to elucidate how different modalities and intensities of mechanical loading affect the metabolic activity of cells within the fibro-cartilage of the temporomandibular joint (TMJ).

MATERIALS AND METHODS

A systematic review was conducted according to PRISMA guidelines using PubMed, Embase, and Web of Science databases. The articles were selected following a priori formulated inclusion criteria (viz., in vivo and in vitro studies, mechanical loading experiments on TMJ, and the response of the TMJ). A total of 254 records were identified. After removal of duplicates, 234 records were screened by assessing eligibility criteria for inclusion. Forty-nine articles were selected for full-text assessment. Of those, 23 were excluded because they presented high risk of bias or were reviews. Twenty-six experimental studies were included in this systematic review: 15 in vivo studies and 11 in vitro ones.

CONCLUSION

The studies showed that dynamic mechanical loading is an important stimulus for mandibular growth and for the homeostasis of TMJ cartilage. When this loading is applied at a low intensity, it prevents breakdown of inflamed cartilage. Yet, frequent overloading at excessive levels induces accelerated cell death and an increased cartilage degradation.

CLINICAL SIGNIFICANCE

Knowledge about the way temporomandibular joint (TMJ) fibrocartilage responds to different types and intensities of mechanical loading is important to improve existing treatment protocols of degenerative joint disease of the TMJ, and also to better understand the regenerative pathway of this particular type of cartilage.

Immunohistochemical evaluation of neuroreceptors in healthy and pathological temporo-mandibular joint

AIM

A study was performed on the articular disk and periarticular tissues of the temporo-mandibular joint (TMJ) with immunohistochemical techniques to give evidence to the presence of neuroreceptors (NRec) in these sites.

METHODS

The study was carried out on tissue samples obtained from 10 subjects without TMJ disease and from 7 patients with severe TMJ arthritis and arthrosis. We use antibodies directed against following antigens: Gliofibrillary Acidic Protein (GFAP), Leu-7, Myelin Basic Protein (MBP), Neurofilaments 68 kD (NF), Neuron Specific Enolase (NSE), S-100 protein (S-100) and Synaptophysin (SYN).

RESULTS

This study revealed that Ruffini's-like, Pacini's-like and Golgi's-like receptors can be demonstrated in TMJ periarticular tissues and that free nervous endings are present in the subsynovial tissues but not within the articular disk. We observed elongated cytoplamic processes of chondrocytes that demonstrated strong S-100 immunoreactivity but they were unreactive with all other antibodies. These cytoplamic processes were more abundant and thicker in the samples obtained from patients with disease TMJ.

CONCLUSION

The results of this study confirm that different Nrec are detectable in TMJ periarticular tissues but they are absent within the articular disk. In the latter site, only condrocytic processes are evident, especially in diseased TMJ, and they might have been confused with nervous endings in previous morphological studies. Nevertheless the absence of immunoreactivity for NF, NSE and SYN proves that they are not of neural origin.

Histomorphometric analysis of the temporal bone after change of direction of force vector of mandible: an experimental study in rabbits

Objectives

The present study aimed at performing a histological evaluation of the response of temporal bone tissue to a change of direction of the force vector of the mandible in relation to the base of the skull.

Material and methods

Adult rabbits were assigned into four groups with two control and four experimental animals in each group. Experimental animals underwent surgery, which resulted in a change of direction of the force vector on the right temporomandibular joint. Samples were collected after 15, 30, 60 and 90 days for histological analysis.

Results

In the two-way analysis of variance, the effect of group and time was statistically significant (p<0.001). Additionally, a statistically significant interaction between group and time was observed (p<0.001). Control animals showed normal growth and development of the temporal region. In the experimental group, the change in direction of the force vector of the mandible induced significant changes in the temporal bone, with a bone modeling process, which suggests growth of this cranial structure.

Conclusions

The methodology used in this experiment allows us to conclude that the change in direction of the force vector of the mandible in relation to the skull base induces remodeling and modeling processes in the temporal bone. The resumption of normal oral functions after bone healing of the mandibular fracture appears to increase cell activation in the remodeling and modeling of the temporal bone structure. The observation of areas of temporal bone modeling shows the relevance of further investigation on the correlation between the joint structures and craniofacial growth and development.

Alterations in intermediate filaments expression in disc cells from the rat temporomandibular joint following exposure to continuous compressive force

The articular disc in the temporomandibular joint (TMJ) that serves in load relief and stabilizing in jaw movements is a dense collagenous tissue consisting of extracellular matrices and disc cells. The various morphological configurations of the disc cells have given us diverse names, such as fibroblasts, chondrocyte-like cells and fibrochondrocytes; however, the characteristics of these cells have remained to be elucidated in detail. The disc cells have been reported to exhibit heterogeneous immunoreaction patterns for intermediate filaments including glial fibrillary acidic protein (GFAP), nestin and vimentin in the adult rat TMJ. Because these intermediate filaments accumulate in the disc cells as tooth eruption proceeds during postnatal development, it might be surmised that the expression of these intermediate filaments in the disc cells closely relates to mechanical stress. The present study was therefore undertaken to examine the effect of a continuous compressive force on the immunoexpression of these intermediate filaments and an additional intermediate filament - muscle-specific desmin - in the disc cells of the TMJ disc using a rat experimental model. The rats wore an appliance that exerts a continuous compressive load on the TMJ. The experimental period with the appliance was 5 days as determined by previous studies, after which some experimental animals were allowed to survive another 5 days after removal of the appliance. Histological observations demonstrated that the compressive force provoked a remarkable acellular region and a decrease in the thickness of the condylar cartilage of the mandible, and a sparse collagen fiber distribution in the articular disc. The articular disc showed a significant increase in the number of desmin-positive cells as compared with the controls. In contrast, immunopositive cells for GFAP, nestin and vimentin remained unchanged in number as well as intensity. At 5 days after removal of the appliance, both the disc and cartilage exhibited immunohistological and histological features in a recovery process. These findings indicate that the mature articular cells are capable of producing desmin instead of the other intermediate filaments against mechanical stress. The desmin-positive disc cells lacked α-smooth muscle actin (α-SMA) in this study, even though desmin usually co-exists with α-SMA in the vascular smooth muscle cells or pericytes. Because the precursor of a pericyte has such an immunoexpression pattern during angiogenesis, there is a further possibility that the formation of new vessels commenced in response to the extraordinary compressive force.

Pathophysiology of TMD pain--basic mechanisms and their implications for pharmacotherapy

This article discusses the pathophysiology of temporomandibular disorders (TMD)-related pain and its treatment with analgesic drugs. Temporomandibular disorders are comprised of a group of conditions that result in temporomandibular joint pain (arthralgia, arthritis) and/or masticatory muscle pain (myofascial TMD). In at least some patients with TMD, a peripheral mechanism contributes to this pain. However, there is often a poor correlation between the severity of TMD-related pain complaints and evidence of definitive tissue pathology. This has led to the concept that pain in some patients with TMD may result from altered central nervous system pain processing and further that this altered pain processing may be attributable to specific genes that are heritable. Psychosocial stressors are also thought to contribute to the development of TMD-related pain, particularly masticatory muscle pain. Finally, substantially more women suffer from TMD than men. Although there are arguably multiple reasons for sex-related differences in the prevalence of TMD, one candidate for the increased occurrence of this disorder in women has been suggested to be the female sex hormone oestrogen. Analgesic drugs are an integral part of the primary treatment for TMD-related pain and dysfunction with more that 90% of treatment recommendations involving use of medications. The most commonly used agents include non-steroidal anti-inflammatory drugs, corticosteroids, muscle relaxants, anxiolytics, opiates and tricyclic antidepressants, however, evidence in support of the effectiveness of these drugs is lacking. Continued research into the pathophysiology of TMD-related pain and the effectiveness of analgesic treatments for this pain is required.

Short-term efficacy of physical therapy compared to splint therapy in treatment of arthrogenous TMD

A prospective randomized study was carried out to evaluate the efficacy of physical therapy in addition to splint therapy on treatment outcome in patients with temporomandibular disorders (TMD) with respect to objective and subjective parameters. Twenty-six patients suffering from an arthrogenic TMD and exhibiting a painfully restricted jaw opening were randomized in two groups. Thirteen patients were treated solely with Michigan splint (group I), 13 patients received supplementary physical therapy (group II). Before treatment a clinical examination and electronic recording of jaw movements were performed and subjective pain level was evaluated by visual analogue scales. After 3 months of therapy maintenance of improvement was evaluated. Within treatment groups comparison of data before and after treatment was analysed using Wilcoxon test. Groups were compared by Mann-Withney-U test. A P-value < 0.05 was considered significant. Compared with the baseline, in both groups mandibular movement capacity increased significantly after treatment, whereas subjective pain decreased significantly (P < 0.05). Active jaw opening increased from 28.6 +/- 5.8 to 35.9 +/- 4.8 mm in group I and from 30.1 +/- 5.4 to 40.8 +/- 4.1 mm in group II. After therapy the difference of active jaw opening between groups was significant (P < 0.05). Physical therapy also gave a supplementary improvement of protrusive mandibular movement capacity during electronic registration and subjective pain level. For none of these parameters this difference between groups was significant. Physical therapy seems to have a positive effect on treatment outcome of patients with TMD.

Pushing the limit: masticatory stress and adaptive plasticity in mammalian craniomandibular joints

Excessive, repetitive and altered loading have been implicated in the initiation of a series of soft- and hard-tissue responses or ;functional adaptations' of masticatory and locomotor elements. Such adaptive plasticity in tissue types appears designed to maintain a sufficient safety factor, and thus the integrity of given element or system, for a predominant loading environment(s). Employing a mammalian species for which considerable in vivo data on masticatory behaviors are available, genetically similar domestic white rabbits were raised on diets of different mechanical properties so as to develop an experimental model of joint function in a normal range of physiological loads. These integrative experiments are used to unravel the dynamic inter-relationships among mechanical loading, tissue adaptive plasticity, norms of reaction and performance in two cranial joint systems: the mandibular symphysis and temporomandibular joint (TMJ). Here, we argue that a critical component of current and future research on adaptive plasticity in the skull, and especially cranial joints, should employ a multifaceted characterization of a functional system, one that incorporates data on myriad tissues so as to evaluate the role of altered load versus differential tissue response on the anatomical, cellular and molecular processes that contribute to the strength of such composite structures. Our study also suggests that the short-term duration of earlier analyses of cranial joint tissues may offer a limited notion of the complex process of developmental plasticity, especially as it relates to the effects of long-term variation in mechanical loads, when a joint is increasingly characterized by adaptive and degradative changes in tissue structure and composition. Indeed, it is likely that a component of the adaptive increases in rabbit TMJ and symphyseal proportions and biomineralization represent a compensatory mechanism to cartilage degradation that serves to maintain the overall functional integrity of each joint system. Therefore, while variation in cranial joint anatomy and performance among sister taxa is, in part, an epiphenomenon of interspecific differences in diet-induced masticatory stresses characterizing the individual ontogenies of the members of a species, this behavioral signal may be increasingly mitigated in over-loaded and perhaps older organisms by the interplay between adaptive and degradative tissue responses.

Pivot appliances ? is there a distractive effect on the temporomandibular joint?

The purpose of this study was to investigate the distractive effect of posterior occlusal pivots on the temporomandibular joint. The study comprised 23 healthy subjects. None of them had a third molar and none of them had a missing tooth or showed tooth mobility. All subjects clenched (i) on 1 mm tin foil positioned between the teeth 17/47 and 27/37; (ii) on a stiff bite registration material of 1 mm thickness that prevented protrusion because of its bold occlusal relief. During clenching on the tin foil and on the protrusion preventing bite registration material, respectively, the vertical and horizontal condylar position was measured using a 6 d.f. ultrasonic motion analyser. Clenching with maximal force on the tin foil lead to a noticeable anterior downward directed movement of the condyle. Clenching on the protrusion preventing pivot, however, caused a statistically significant upward condylar movement of about 0.3 mm. These results indicate that occlusal pivots have no distractive effect on the temporomandibular joint but can lead to unwanted joint compression, if they are designed in a way that is preventing protrusion.

Electrophoretically separation of the synovial fluid proteins in rabbit temporomandibular arthritis induced by mechanical loading

BACKGROUND

The concentration of protein in synovial fluid (SF) of temporomandibular joints (TMJs) with disorders tends to be increased. We investigated the protein composition of SF of rabbits in which arthritis of the TMJ was induced.

METHOD

Arthritis was induced in six TMJs in six rabbits by exertion of a load for 4 weeks. Six non-loaded TMJs in six rabbits served as controls. The protein concentration and content in TMJ SF of the two groups were compared.

RESULTS

The mean protein concentration was higher in the SF of the loaded group than in that of the non-loaded group (1824 microg/ml vs. 398 microg/ml, P = 0.002). Proteins with molecular weights of more than 95 kDa were abundant in the loaded group (P < 0.05).

CONCLUSION

Temporomandibular arthritis induced by mechanical loading in rabbit is accompanied by an increase in the abundance of relatively high molecular weight proteins in SF.