Temporomandibular Joint Hypofunction Secondary to Unilateral Partial Discectomy Attenuates Degeneration in Murine Mandibular Condylar Cartilage

Post-traumatic osteoarthritic-mediated changes in condylar shape do not covary with changes in the internal microstructure of the bone

Post-traumatic osteoarthritis (PTOA) in the temporomandibular joint (TMJ) is associated with remodeling of the subchondral bone. This remodeling changes both the external appearance of the condylar bone and the internal bony microstructure. The external geometry can be quantified using shape, a multivariate mathematical measurement that contains all of the structure's geometric information with location, scale, and rotation effects removed. There is an important gap in knowledge related to how TMJ PTOA affects the shape of the mandible and if the external shape covaries with the internal bony microstructure. To evaluate these gaps, TMJ PTOA was induced in male and female skeletally mature mice using a surgical destabilization procedure. After four weeks, tissues were collected and characterized using a high-resolution μCT scanner. Shape was calculated from surface reconstructions of the mandibular condyle, and the internal bony microstructure was characterized by the region of interest including the subchondral trabeculae. The covariance of shape with and without corrections for allometric scaling and internal bony microstructure was calculated using a Procrustes ANOVA. The data illustrate that PTOA significantly alters the shape of the condyle in a sex-independent manner. PTOA does alter some aspects of the internal bony microstructure in a sex-dependent manner. Allometric scaling was a significant factor in the variance of shape. Shape including the effects of allometric scaling significantly covaries with some internal bony microstructure variables in both sexes. Shape scaled to remove the effects of allometric scaling does not covary with internal bony microstructure in either sex. These findings indicate that PTOA progression is associated with changes in the size and shape of the condyle but variance in trabecular bone remodeling is only associated with size related shape change. Thus, the allostatic response of subchondral bone is multimodal, coordinating two independent biological processes controlling size and shape. Since subchondral bone participates in and guides the progression of PTOA, these findings have implications for identifying select and specific mechanisms contributing to the progression and pathophysiology of the PTOA in the TMJ.

The Kinematics of Proal Chewing in Rats

Chewing kinematics are well-documented in several mammal species with fused mandibular symphyses, but relatively understudied in mammals with an unfused symphysis, despite the fact that more than half of extant Mammalia have an unfused mandibular symphysis. The Wistar brown rat (Rattus norvegicus) is widely used in human health research, including studies of mastication or neurological studies where mastication is the output behavior. These animals are known to have unfused mandibular symphyses and proal jaw (rostrocaudal) motion during occlusion, but the lack of high resolution, 3-dimensional analysis of rat chewing leaves the functional significance of symphyseal mobility unknown. We used biplanar fluoroscopy and the X-ray reconstruction of moving morphology workflow to quantify chewing kinematics in 3 brown rats, quantifying overall jaw kinematics, including motions about the temporomandibular joint and unfused mandibular symphysis. During occlusion, the teeth and the mandibular condyle translate almost exclusively anteriorly (proal) during occlusion, with little motion in any other degrees of freedom. At the symphysis, we observed minimal flexion throughout the chew cycle. Overall, there are fundamental differences in jaw kinematics between rats and other mammals and therefore rats are not an appropriate proxy for ancestral mammal jaw mechanics. Additionally, differences between humans and rat chewing kinematics must be considered when using rats as a clinical model for pathological feeding research.

Analysis of risk factors and interactions for pain in temporomandibular disorder: A cross-sectional study

BACKGROUND

Risk factors for temporomandibular disorder (TMD) pain remain unclear.

OBJECTIVES

This study aimed to identify risk factors for TMD pain using a biopsychosocial model and to investigate interactions between potential risk factors-oral behaviours (OBs), psychological factors and sleep quality-and their direct and indirect effects on TMD pain.

METHODS

This was a cross-sectional study of 488 patients with TMDs (422 women; 30.8 ± 9.4 years). Pain was assessed using the Numerical Rating Scale. Demographic, behavioural, psychological and biomedical data were collected through clinical examination, face-to-face interviews and questionnaires. Multiple linear regression analysis was used to identify factors associated with TMD pain. Mediation and moderation analysis were used to evaluate interactions between variables. Significant mediation ('0' not included in the 95% confidence interval (CI)) and moderation (p < .05) effects on TMD pain were identified.

RESULTS

Marital status, diagnosis subgroup, previous medication use, depression and sleep quality were significant risk factors for TMD pain (p < .05). Significant mediation effects were observed as follows: depression and sleep quality mediated the association between OBs and pain; sleep quality mediated the association between somatization, depression, anxiety and pain; and depression mediated the association between sleep quality and pain (all 95% CI did not contain '0').

CONCLUSIONS

(1) Marital status, diagnosis subgroup, previous medication use, depression and sleep quality were associated with TMD pain. (2) OBs can exacerbate pain by promoting depression and reducing sleep quality. Psychological factors and sleep quality can interact to exacerbate pain.

Association between chewing side preference and MRI characteristics in patients with anterior disc displacement of the temporomandibular joint

OBJECTIVE

To compare the magnetic resonance imaging (MRI) characteristics in the anterior disc displacement (ADD) patients with and without chewing side preference (CSP).

METHODS

The MRI characteristics of the bilateral temporomandibular joint (TMJ) in 111 patients with ADD were retrospectively analysed. Based on the presence of CSP, all subjects were divided into the non-CSP group (NC group, N = 40) and CSP group (C group, N = 71). Based on the preferred chewing side in the C group, the patients were divided into ipsilateral and contralateral sides. The morphology, length, disc-condyle angle, and coordinate position of the disc and condyle of the bilateral TMJ were compared.

RESULTS

MRI examination showed a significant difference between ipsilateral and contralateral joint displacement in patients with CSP (P<0.05). In CSP patients, the disc length of the same side in the ipsilateral side was significantly shorter than the contralateral side (P<0.05). A significant difference in the Y-axis coordinates of the ipsilateral and contralateral discs was also found in patients with CSP (P<0.05). The disc displacement grade, morphology of the articular disc, ipsilateral disc length, and ipsilateral disc-condyle Y-axis distance were positively correlated with CSP (P<0.05).

CONCLUSION

CSP is related to the shape of the articular disc and disc-condyle position in patients with ADD. CSP may aggravate the development of ADD.

Disrupting mechanical homeostasis promotes matrix metalloproteinase-13 mediated processing of neuron glial antigen 2 in mandibular condylar cartilage

Post-traumatic osteoarthritis in the temporomandibular joint (TMJ OA) is associated dysfunctional cellmatrix mediated signalling resulting from changes in the pericellular microenvironment after injury. Matrix metalloproteinase (MMP)-13 is a critical enzyme in biomineralisation and the progression of OA that can both degrade the extracellular matrix and modify extracellular receptors. This study focused on MMP-13 mediated changes in a transmembrane proteoglycan, Neuron Glial antigen 2 (NG2/CSPG4). NG2/CSPG4 is a receptor for type VI collagen and a known substrate for MMP-13. In healthy articular layer chondrocytes, NG2/CSPG4 is membrane bound but becomes internalised during TMJ OA. The objective of this study was to determine if MMP-13 contributed to the cleavage and internalisation of NG2/CSPG4 during mechanical loading and OA progression. Using preclinical and clinical samples, it was shown that MMP-13 was present in a spatiotemporally consistent pattern with NG2/CSPG4 internalisation during TMJ OA. In vitro, it was illustrated that inhibiting MMP-13 prevented retention of the NG2/CSPG4 ectodomain in the extracellular matrix. Inhibiting MMP-13 promoted the accumulation of membrane-associated NG2/CSPG4 but did not affect the formation of mechanical-loading dependent variant specific fragments of the ectodomain. MMP- 13 mediated cleavage of NG2/CSPG4 is necessary to initiate clathrin-mediated internalisation of the NG2/ CSPG4 intracellular domain following mechanical loading. This mechanically sensitive MMP-13-NG2/CSPG4 axis affected the expression of key mineralisation and OA genes including bone morphogenetic protein 2, and parathyroid hormone-related protein. Together, these findings implicated MMP-13 mediated cleavage of NG2/CSPG4 in the mechanical homeostasis of mandibular condylar cartilage during the progression of degenerative arthropathies such as OA.

Osteoarthritis of the Temporomandibular Joint: A Narrative Overview

Background and Objectives: This study reviewed the literature to summarize the current and recent knowledge of temporomandibular joint osteoarthritis (TMJOA). Methods: Through a literature review, this work summarizes many concepts related to TMJOA. Results: Although many signaling pathways have been investigated, the etiopathogenesis of TMJOA remains unclear. Some clinical signs are suggestive of TMJOA; however, diagnosis is mainly based on radiological findings. Treatment options include noninvasive, minimally invasive, and surgical techniques. Several study models have been used in TMJOA studies because there is no gold standard model. Conclusion: More research is needed to develop curative treatments for TMJOA, which could be tested with reliable in vitro models, and to explore tissue engineering to regenerate damaged temporomandibular joints.

NG2/CSPG4 regulates cartilage degeneration during TMJ osteoarthritis

Changes in the mechanical homeostasis of the temporomandibular joint (TMJ) can lead to the initiation and progression of degenerative arthropathies such as osteoarthritis (OA). Cells sense and engage with their mechanical microenvironment through interactions with the extracellular matrix. In the mandibular condylar cartilage, the pericellular microenvironment is composed of type VI collagen. NG2/CSPG4 is a transmembrane proteoglycan that binds with type VI collagen, and has been implicated in the cell stress response through mechanical loading-sensitive signaling networks including ERK 1/2. The objective of this study is to define the role of NG2/CSPG4 in the initiation and progression of TMJ OA and to determine if NG2/CSPG4 engages ERK 1/2 in a mechanical loading dependent manner. In vivo, we induced TMJ OA in control and NG2/CSPG4 knockout mice using a surgical destabilization approach. In control mice, NG2/CSPG4 is depleted during the early stages of TMJ OA and NG2/CSPG4 knockout mice have more severe cartilage degeneration, elevated expression of key OA proteases, and suppression of OA matrix synthesis genes. In vitro, we characterized the transcriptome and protein from control and NG2/CSPG4 knockout cells and found significant dysregulation of the ERK 1/2 signaling axis. To characterize the mechanobiological response of NG2/CSPG4, we applied mechanical loads on cell-agarose-collagen scaffolds using a compression bioreactor and illustrate that NG2/CSPG4 knockout cells fail to mechanically activate ERK 1/2 and are associated with changes in the expression of the same key OA biomarkers measured in vivo. Together, these findings implicate NG2/CSPG4 in the mechanical homeostasis of TMJ cartilage and in the progression of degenerative arthropathies including OA.

Mechanical Loading Disrupts Focal Adhesion Kinase Activation in Mandibular Fibrochondrocytes During Murine Temporomandibular Joint Osteoarthritis

PURPOSE

Mechanical overloading is a key initiating condition for temporomandibular joint (TMJ) osteoarthritis (OA). The integrin-focal adhesion kinase (FAK) signaling axis is implicated in the mechanobiological response of cells through phosphorylation at Tyr397 (pFAK) but poorly defined in TMJ health and disease. We hypothesize that mechanical overloading disrupts TMJ homeostasis through dysregulation of FAK signaling.

MATERIALS AND METHODS

To assess if FAK and pFAK are viable clinical targets for TMJ OA, peri-articular tissues were collected from patients with TMJ OA receiving a total TMJ replacement. To compare clinical samples with preclinical in vivo studies of TMJ OA, the joints of c57/bl6 mice were surgically destabilized and treated with and without inhibitor of pFAK (iFAK). FAK signaling and TMJ OA progression was evaluated and compared using RT-PCR, western blot, immunohistochemistry, and histomorphometry. To evaluate mechanical overloading in vitro, primary murine mandibular fibrochondrocytes were seeded in a 4% agarose-collagen scaffold and loaded in a compression bioreactor with and without iFAK.

RESULTS

FAK/pFAK was mostly absent from the articular cartilage layer in the clinical sample and suppressed on the central condyle and elevated on the lateral and medial condyle in murine TMJ OA. In vitro, compressive loading lowered FAK/pFAK levels and elevated the expression of TGFβ, NG2, and MMP-13. iFAK treatment suppressed MMP13 and Col6 and elevated TGFβ, NG2, and ACAN in a load independent manner. In vivo, iFAK treatment moderately attenuated OA progression and increased collagen maturation.

CONCLUSION

These data illustrate that FAK/pFAK is implicated in the signaled dysfunction of excessive mechanical loading during TMJ OA and that iFAK treatment can moderately attenuate the progression of cartilage degeneration in the mandibular condyle.