Cyclic Tensile Strain Reduces TNF-α Induced Expression of MMP-13 by Condylar Temporomandibular Joint Cells

Mechanisms Underlying Sex Differences in Temporomandibular Disorders and Their Comorbidity with Migraine

Sexual dimorphism in temporomandibular disorders (TMDs) and their comorbidity with migraine are important phenomena observed in clinics. TMDs are the most prevalent orofacial pain conditions with jaw joint and masseter muscle dysfunction. Migraine is the predominant headache commonly associated with TMDs. Women much more often suffer from this orofacial pain than men. However, currently, there is no gender-specific therapy for such pain conditions. Understanding the pathophysiological mechanisms behind sex differences in TMDs as well as their comorbidity with migraines is essential for developing novel approaches for gender-specific treatment of TMDs and related orofacial pain comorbidity. In this review, we summarize recent research progress regarding sex differences in TMDs, focusing on the underlying mechanisms including craniofacial anatomy, hormonal regulation, and roles of opioids, transient receptor potential channels, and endocannabinoid systems. We also discuss the mechanisms of comorbid TMDs and migraine. The information covered in this review will provide mechanistic insights into sex differences in TMDs and their comorbidity with migraine, which could aid in developing effective treatment strategies for the overlapping orofacial pain condition.

Critical signaling molecules in the temporomandibular joint osteoarthritis under different magnitudes of mechanical stimulation

The mechanical stress environment in the temporomandibular joint (TMJ) is constantly changing due to daily mandibular movements. Therefore, TMJ tissues, such as condylar cartilage, the synovial membrane and discs, are influenced by different magnitudes of mechanical stimulation. Moderate mechanical stimulation is beneficial for maintaining homeostasis, whereas abnormal mechanical stimulation leads to degeneration and ultimately contributes to the development of temporomandibular joint osteoarthritis (TMJOA), which involves changes in critical signaling molecules. Under abnormal mechanical stimulation, compensatory molecules may prevent degenerative changes while decompensatory molecules aggravate. In this review, we summarize the critical signaling molecules that are stimulated by moderate or abnormal mechanical loading in TMJ tissues, mainly in condylar cartilage. Furthermore, we classify abnormal mechanical stimulation-induced molecules into compensatory or decompensatory molecules. Our aim is to understand the pathophysiological mechanism of TMJ dysfunction more deeply in the ever-changing mechanical environment, and then provide new ideas for discovering effective diagnostic and therapeutic targets in TMJOA.

Impact of physiotherapy on orofacial manifestations of juvenile idiopathic arthritis

BACKGROUND

Physiotherapy appears as a promising therapy option for patients with Juvenile Idiopathic Arthritis (JIA) [1, 2], but the effects of physiotherapy and jaw exercises on JIA-related orofacial symptoms remain unknown [3]. The aim of this proof-of-concept study was to assess the impact of orofacial physiotherapy and home-exercise programs in patients with JIA and temporomandibular joint (TMJ) involvement.

METHODS

Twelve patients with JIA and TMJ involvement received a treatment of physiotherapy, complemented by prescribed home exercises spanning over eight weeks. Orofacial symptoms and dysfunction were monitored pre-treatment, during treatment, after treatment, and at a three-months follow-up.

RESULTS

Orofacial pain frequency and intensity significantly decreased during the course of the treatment (p = 0.009 and p = 0.006), with further reductions observed at the three-month follow-up (p = 0.007 and p = 0.002). During treatment, the mandibular function improved significantly in terms of maximal mouth opening capacity, laterotrusion, and protrusion.

CONCLUSIONS

This proof-of-concept study shows favourable effects of physiotherapy and home excercises in the management of JIA-related orofacial symptoms and dysfunctions.

The Role of TNF-α in the Pathogenesis of Temporomandibular Disorders

Temporomandibular disorder (TMD) is an oral dentofacial disease that is related to multiple factors such as disordered dental occlusion, emotional stress, and immune responses. In the past decades, tumor necrosis factor-alpha (TNF-α), a pleiotropic cytokine, has provided valuable insight into the pathogenesis of TMD, particularly in settings associated with inflammation. It is thought that TNF-α participates in the pathogenesis of TMD by triggering immune responses, deteriorating bone and cartilage, and mediating pain in the temporomandibular joint (TMJ). Initially, TNF-α plays the role of "master regulator" in the complex immune network by increasing or decreasing the production of other inflammatory cytokines. Then, the effects of TNF-α on cells, particularly on chondrocytes and synovial fibroblasts, result in pathologic cartilage degradation in TMD. Additionally, multiple downstream cytokines induced by TNF-α and neuropeptides can regulate central sensitization and inflammatory pain in TMD. Previous studies have also found some therapies target TMD by reducing the production of TNF-α or blocking TNF-α-induced pathways. All this evidence highlights the numerous associations between TNF-α and TMD; however, they are currently not fully understood and further investigations are still required for specific mechanisms and treatments targeting specific pathways. Therefore, in this review, we explored general mechanisms of TNF-α, with a focus on molecules in TNF-α-mediated pathways and their potential roles in TMD treatment. In view of the high clinical prevalence rate of TMD and damage to patients' QOL, this review provides adequate evidence for studying links between inflammation and TMD in further research and investigation.

Interdisciplinary Management of Dentofacial Deformity in Juvenile Idiopathic Arthritis

Temporomandibular joint (TMJ) arthritis impacts mandibular growth and development. This can result in skeletal deformity, such as facial asymmetry and/or malocclusion asymmetry. This article reviews the unique properties of TMJ and dentofacial growth and development in the setting of juvenile idiopathic arthritis (JIA). Specific orthopedic/orthodontic and surgical management of children with JIA and TMJ arthritis is discussed. The importance of interdisciplinary collaboration is highlighted.

IL-1β Damages Fibrocartilage and Upregulates MMP-13 Expression in Fibrochondrocytes in the Condyle of the Temporomandibular Joint

The temporomandibular joint (TMJ), which differs anatomically and biochemically from hyaline cartilage-covered joints, is an under-recognized joint in arthritic disease, even though TMJ damage can have deleterious effects on physical appearance, pain and function. Here, we analyzed the effect of IL-1β, a cytokine highly expressed in arthritic joints, on TMJ fibrocartilage-derived cells, and we investigated the modulatory effect of mechanical loading on IL-1β-induced expression of catabolic enzymes. TMJ cartilage degradation was analyzed in 8–11-week-old mice deficient for IL-1 receptor antagonist (IL-1RA^−/−) and wild-type controls. Cells were isolated from the juvenile porcine condyle, fossa, and disc, grown in agarose gels, and subjected to IL-1β (0.1–10 ng/mL) for 6 or 24 h. Expression of catabolic enzymes (ADAMTS and MMPs) was quantified by RT-qPCR and immunohistochemistry. Porcine condylar cells were stimulated with IL-1β for 12 h with IL-1β, followed by 8 h of 6% dynamic mechanical (tensile) strain, and gene expression of MMPs was quantified. Early signs of condylar cartilage damage were apparent in IL-1RA^−/− mice. In porcine cells, IL-1β strongly increased expression of the aggrecanases ADAMTS4 and ADAMTS5 by fibrochondrocytes from the fossa (13-fold and 7-fold) and enhanced the number of MMP-13 protein-expressing condylar cells (8-fold). Mechanical loading significantly lowered (3-fold) IL-1β-induced MMP-13 gene expression by condylar fibrochondrocytes. IL-1β induces TMJ condylar cartilage damage, possibly by enhancing MMP-13 production. Mechanical loading reduces IL-1β-induced MMP-13 gene expression, suggesting that mechanical stimuli may prevent cartilage damage of the TMJ in arthritic patients.

The many faces of genetic contributions to temporomandibular joint disorder: An updated review

OBJECTIVES

The aim was to review the literature regarding genetic contributions to temporomandibular joint disorder (TMD) after our 2008 publication.

SETTING AND SAMPLE POPULATION

Literature review.

MATERIAL AND METHODS

PubMed and MEDLINE were used to obtain literature in any language regarding genes and TMD, using the keywords "temporomandibular joint disorder" and "temporomandibular joint dysfunction" for studies published from 2009 to 2017.

RESULTS

In our search, 274 studies were found. We excluded 76 studies from animal models, 22 studies that were in vitro and 120 reports that were not cohort or case-control studies. Of the 274 results, 56 articles were selected for this review. Genes that are suggested to contribute to TMD included the ones related to disc and bone alterations as well as pain sensation.

CONCLUSION

Currently, no evidence of associated genetic variants, which can determine the development of TMD in individuals, could be translated to novel clinical management and public health strategies for patients suffering from TMD.

Relationship between arthroscopic findings of synovitis and levels of tumour necrosis factor-alpha and matrix metalloproteinases in synovial lavage fluid from patients with unilateral high mandibular condyle fractures

Arthrocentesis has an effect of washing out inflammatory products that accumulate in the joint compartment of a dysfunctional temporomandibular joint (TMJ). The procedure removes inflammatory cytokines, which are pain-causing substances, for early reduction of TMJ pain and quick recovery of jaw function, thus increasing the possibility of a successful rehabilitation. The aim of this study was to investigate the relationship between arthroscopy synovitis grade in patients with unilateral high condylar fractures and concentrations of the pro-inflammatory cytokines tumour necrosis factor (TNF)-alpha as well as of matrix metalloproteinases (MMPs) in washed-out synovial fluid (SF) samples obtained from those patients. A total of 26 patients with unilateral high condylar fractures who underwent arthrocentesis for a therapeutic purpose were examined. SF samples were collected before performing arthroscopy to determine synovitis grade. The detection rates and concentrations of TNF-alpha and MMPs were determined, and their association with synovitis grade was analysed. TNF-alpha was detected in 23 and MMP-3 in 22 of the TMJs. There was a correlation between synovitis grade and concentration of TNF-alpha in the fracture group. Furthermore, the concentrations of TNF-alpha and MMP-3 were significantly higher as compared to the control group, comprised of TMJs on the non-fracture side of the same patients, while a correlation was also noted between TNF-alpha concentration and synovitis grade in the fracture group. The present findings may provide a biological/biochemical rationale for arthrocentesis as a reasonable treatment modality for high condylar fractures.

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.