Experimental Methods to Inform Diagnostic Approaches for Painful TMJ Osteoarthritis

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.

Role of Trace Cadmium Exposure on the Development of Occlusal Traumatic Temporomandibular Arthritis

OBJECTIVE

To investigate whether heavy metal cadmium acts as a risk factor for temporomandibular joint disorder disease and to study its pathogenic mechanism.

METHODS

A total of 57 rats were allocated into 6 distinct groups, distinguished by 2 interventions: occlusal elevation and cadmium water gavage. These groups included a blank control group, occlusal elevation group, occlusal elevation + 0.42 mg/mL cadmium water gavage group, occlusal elevation + 4.2 mg/mL cadmium water gavage group, no occlusal elevation + 0.42 mg/mL cadmium water gavage group, and no occlusal elevation + 4.2 mg/mL cadmium water gavage group. The impact of cadmium exposure on cartilage oxidative stress was evaluated through the assessment of SOD, CAT, GST, and GSH-Px enzyme activities. In addition, the influence of cadmium exposure on alterations in the extracellular matrix and inflammatory mediators was examined by analyzing the expression levels of type II collagen, protein aggregation polysaccharide, glycosaminoglycan, IL1β, IL-6, and TNF-α. Histologic examination of the condylar process cartilage of rats in the occlusal elevation + cadmium water gavage group was conducted to ascertain the occurrence of osteoarthritis.

RESULTS

The variance in the expression levels of inflammatory factors did not demonstrate statistical significance between the occlusal elevation group and the blank control group; however, statistical significance was observed between the occlusal elevation + cadmium water gavage group and both the control and occlusal elevation groups.

CONCLUSION

The severity of inflammation and condylar lesions correlates directly with the concentration of cadmium.

Excessive load promotes temporomandibular joint chondrocyte apoptosis via Piezo1/endoplasmic reticulum stress pathway

Excessive load on the temporomandibular joint (TMJ) is a significant factor in the development of TMJ osteoarthritis, contributing to cartilage degeneration. The specific mechanism through which excessive load induces TMJ osteoarthritis is not fully understood; however, mechanically-activated (MA) ion channels play a crucial role. Among these channels, Piezo1 has been identified as a mediator of chondrocyte catabolic responses and is markedly increased in osteoarthritis. Our observations indicate that, under excessive load conditions, endoplasmic reticulum stress in chondrocytes results in apoptosis of the TMJ chondrocytes. Importantly, using the Piezo1 inhibitor GsMTx4 demonstrates its potential to alleviate this condition. Furthermore, Piezo1 mediates endoplasmic reticulum stress in chondrocytes by inducing calcium ion influx. Our research substantiates the role of Piezo1 as a pivotal ion channel in mediating chondrocyte overload. It elucidates the link between excessive load, cell apoptosis, and calcium ion influx through Piezo1. The findings underscore Piezo1 as a key player in the pathogenesis of TMJ osteoarthritis, shedding light on potential therapeutic interventions for this condition.

A comprehensive patient-specific prediction model for temporomandibular joint osteoarthritis progression

Temporomandibular joint osteoarthritis (TMJ OA) is a prevalent degenerative disease characterized by chronic pain and impaired jaw function. The complexity of TMJ OA has hindered the development of prognostic tools, posing a significant challenge in timely, patient-specific management. Addressing this gap, our research employs a comprehensive, multidimensional approach to advance TMJ OA prognostication. We conducted a prospective study with 106 subjects, 74 of whom were followed up after 2 to 3 y of conservative treatment. Central to our methodology is the development of an innovative, open-source predictive modeling framework, the Ensemble via Hierarchical Predictions through Nested cross-validation tool (EHPN). This framework synergistically integrates 18 feature selection, statistical, and machine learning methods to yield an accuracy of 0.87, with an area under the ROC curve of 0.72 and an F1 score of 0.82. Our study, beyond technical advancements, emphasizes the global impact of TMJ OA, recognizing its unique demographic occurrence. We highlight key factors influencing TMJ OA progression. Using SHAP analysis, we identified personalized prognostic predictors: lower values of headache, lower back pain, restless sleep, condyle high gray level-GL-run emphasis, articular fossa GL nonuniformity, and long-run low GL emphasis; and higher values of superior joint space, mouth opening, saliva Vascular-endothelium-growth-factor, Matrix-metalloproteinase-7, serum Epithelial-neutrophil-activating-peptide, and age indicate recovery likelihood. Our multidimensional and multimodal EHPN tool enhances clinicians' decision-making, offering a transformative translational infrastructure. The EHPN model stands as a significant contribution to precision medicine, offering a paradigm shift in the management of temporomandibular disorders and potentially influencing broader applications in personalized healthcare.

Forced mouth opening induces post-traumatic hyperalgesia and associated peripheral sensitization after temporomandibular joints injury in mice

Temporomandibular disorder (TMD) is the most prevalent painful condition in the craniofacial area. The pathophysiology of TMD is not fully understood, and it is necessary to understand pathophysiology underlying painful TMD conditions to develop more effective treatment methods. Recent studies suggested that external or intrinsic trauma to TMJ is associated with chronic TMD in patients. Here, we investigated the effects of the TMJ trauma through forced-mouth opening (FMO) in mice to determine pain behaviors and peripheral sensitization of trigeminal nociceptors. FMO increased mechanical hyperalgesia assessed by von Frey test, spontaneous pain-like behaviors assessed by mouse grimace scale, and anxiety-like behaviors assessed by open-field test. In vivo GCaMP Ca 2+ imaging of intact trigeminal ganglia (TG) showed increased spontaneous Ca 2+ activity and mechanical hypersensitivity of TG neurons in the FMO compared to the sham group. Ca 2+ responses evoked by cold, heat, and capsaicin stimuli were also increased. FMO-induced hyperalgesia and neuronal hyperactivities were not sex dependent. TG neurons sensitized following FMO were primarily small to medium-sized nociceptive afferents. Consistently, most TMJ afferents in the TG were small-sized peptidergic neurons expressing calcitonin gene-related peptides, whereas nonpeptidergic TMJ afferents were relatively low. FMO-induced intraneural inflammation in the surrounding tissues of the TMJ indicates potentially novel mechanisms of peripheral sensitization following TMJ injury. These results suggest that the TMJ injury leads to persistent post-traumatic hyperalgesia associated with peripheral sensitization of trigeminal nociceptors.

Orthodontics and Temporomandibular Disorders: An Overview

The relationship between orthodontics and temporomandibular disorders (TMDs) constitutes a subject of paramount significance in dental and craniofacial health. This abstract embarks upon an in-depth examination of the intricate connection between orthodontic practices and TMD, primarily focusing on evaluating the impact of orthodontic treatment modalities on the health and functionality of the temporomandibular joint (TMJ). This exploration elucidates the multifaceted interplay between orthodontic interventions and TMD by traversing a landscape of scholarly research and empirical investigations. The review draws from a broad spectrum of studies to analyze the potential influence of orthodontic treatments, which encompass occlusal adjustments and alterations in jaw positioning, on the development and management of TMD symptoms. The inquiry delves into the diverse range of TMD conditions, considering the implications of orthodontic techniques on occlusal stability, condylar alignment, and overall TMJ function. Through a comprehensive synthesis of the available body of knowledge, this abstract aspires to equip dental practitioners, orthodontists, and researchers with a nuanced understanding of the complex dynamics that govern the relationship between orthodontics and TMD. This knowledge, in turn, offers a foundation for informed clinical decision-making and the formulation of effective treatment strategies for patients presenting with TMD symptoms. By shedding light on the intricate interactions between orthodontic procedures and TMJ health, this abstract contributes to the advancement of clinical practices, promoting improved patient outcomes and well-being in the context of both orthodontics and TMDs.

GLX351322, a Novel NADPH Oxidase 4 Inhibitor, Attenuates TMJ Osteoarthritis by Inhibiting the ROS/MAPK/NF-κB Signaling Pathways

As a degenerative disease in joints, temporomandibular joint osteoarthritis (TMJOA) is characterized by progressive cartilage degradation, subchondral bone remodeling, and chronic synovitis, severely undermining functions and quality of life in patients. NADPH oxidase 4 (NOX4) contributes to reactive oxygen species (ROS) production and inflammatory pathway activation in osteoarthritis, which has attracted increasing attention in research in recent years. GLX351322 (GLX), a novel NOX4 inhibitor, exerts a protective effect on chondrocytes. However, whether it has a therapeutic effect on ROS production and inflammatory responses in synovial macrophages remains to be evaluated. In this study, we examined the effect of GLX on LPS-induced ROS production and inflammatory responses in vitro and on complete Freund's adjuvant (CFA)-induced TMJ inflammation in vivo. We found that GLX could depress LPS-induced intracellular ROS production and inflammatory response without cytotoxicity by inhibiting the ROS/MAPK/NF-κB signaling pathways. In line with in vitro observations, GLX markedly attenuated the synovial inflammatory reaction in the TMJ, thus protecting the condylar structure from severe damage. Taken together, our results suggest that GLX intervention or NOX4 inhibition is a promising curative strategy for TMJOA and other inflammatory diseases.

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.

MicroRNA-26b regulates BMSC osteogenic differentiation of TMJ subchondral bone through β-catenin in osteoarthritis

Temporomandibular joint osteoarthritis (TMJ-OA) is a degenerative disease of the joint. The early manifestations of TMJ-OA are abnormal remodeling of condylar subchondral bone. In bone tissue, bone marrow mesenchymal stem cells (BMSCs) and osteoblasts play important roles in the differentiation and maturation of most hematopoietic cells. MicroRNA-26b (miR-26b) is upregulated during the osteogenesis of BMSCs, and miR-26b overexpression leads to the activation of β-catenin and the enhancement of osteogenesis and cartilage formation. However, the pathologic mechanism remains unclear. In the present study, we used a rat model with OA-like changes in the TMJ induced by experimental unilateral anterior crossbite (UAC) and found that the level of miR-26b was markedly lower in BMSCs from the subchondral bones of UAC rats than in those from sham control rats. MiR-26b overexpression by agomiR-26b increased condylar subchondral bone osteogenesis in UAC rats. Notably, although agomiR-26b primarily affected miR-26b levels in the subchondral bone (but not in cartilage or the synovium), the overexpression of miR-26b in BMSCs in UAC rats largely rescued OA-like cartilage degradation, while the inhibition of miR-26b in BMSCs exacerbated cartilage degradation in UAC rats. We measured the expression levels of β-catenin and related osteogenic and osteoclastic factors after using miR-26b mimics and inhibitors in vivo. Moreover, BMSCs were treated with the β-catenin blocker Wnt-C59 and then transfected with miR-26b mimics or inhibitors. Then, we examined the expression of β-catenin as the direct target of miR-26b. The results of the present study indicate that miR-26b may modulate subchondral bone loss induced by abnormal occlusion and influence the osteogenic differentiation of subchondral BMSCs through β-catenin in the context of TMJ-OA progression.

MMPs in tissues retrieved during surgery from patients with TMJ disorders relate to pain more than to radiological damage score

Orofacial pain is among the most common chronic pain conditions and can result from temporomandibular disorders (TMDs) of the temporomandibular joint (TMJ). Matrix metalloproteinases (MMPs) drive degeneration of TMJ tissues and likely mediate pain in TMJ disorders given their role in nociception. However, few studies have assessed MMPs in the TMJ innervated tissues nor in the context of pain. This study defined the extent of MMP-1, MMP-9, and MMP-2 in TMJ tissues from patients undergoing total joint replacement (TJR) or arthroplasty discectomy for painful TMJ disorders. Protein expression was probed by Western blot in TMJ disc and capsular ligaments taken during TJR (n = 6) or discectomy (n = 3) for osteoarthritis or internal derangement in an IRB-approved study. Pro- and active MMP-1, active MMP-9, and pro- and active MMP-2 are detectable. MMP-1 and MMP-9 correlate positively to each other (Kendall's τ = 0.63; p = 0.01), strengthening the hypothesis that they are mechanistically related in regulatory cascades. Active MMP-1 and active MMP-9 correlate positively with self-reported pain scores (τ ≥ 0.51; p ≤ 0.04), suggesting their involvement in peripheral nociception. Overall, neither MMPs nor pain correlate with the functional vertical opening of the jaw. MMP-1 varies with the observed stage of degeneration during surgery (p = 0.04). Neither overall MMPs nor pain correlate with the overall magnetic resonance imaging scores, corroborating the longstanding, but confounding, clinical observation that pain and radiological evidence of joint damage are not always related. Clinical significance: These findings suggest that MMPs mediate pain in innervated soft tissues and may be targets for diagnosing disease stage and treatments in painful TMJ disorders.

An Update on Mesenchymal Stem Cell-Centered Therapies in Temporomandibular Joint Osteoarthritis

Temporomandibular joint osteoarthritis (TMJOA) is a degenerative disease characterized by cartilage degeneration, disrupted subchondral bone remodeling, and synovitis, seriously affecting the quality of life of patients with chronic pain and functional disabilities. Current treatments for TMJOA are mainly symptomatic therapies without reliable long-term efficacy, due to the limited self-renewal capability of the condyle and the poorly elucidated pathogenesis of TMJOA. Recently, there has been increased interest in cellular therapies for osteoarthritis and TMJ regeneration. Mesenchymal stem cells (MSCs), self-renewing and multipotent progenitor cells, play a promising role in TMJOA treatment. Derived from a variety of tissues, MSCs exert therapeutic effects through diverse mechanisms, including chondrogenic differentiation; fibrocartilage regeneration; and trophic, immunomodulatory, and anti-inflammatory effects. Here, we provide an overview of the therapeutic roles of various tissue-specific MSCs in osteoarthritic TMJ or TMJ regenerative tissue engineering, with an additional focus on joint-resident stem cells and other cellular therapies, such as exosomes and adipose-derived stromal vascular fraction (SVF). Additionally, we summarized the updated pathogenesis of TMJOA to provide a better understanding of the pathological mechanisms of cellular therapies. Although limitations exist, MSC-centered therapies still provide novel, innovative approaches for TMJOA treatment.

A Systematic Review of Rat Models With Temporomandibular Osteoarthritis Suitable for the Study of Emerging Prolonged Intra-Articular Drug Delivery Systems

PURPOSE

Development of minimally invasive therapies for temporomandibular joint osteoarthritis (TMJOA) has focused on drug intra-articular injections to avoid the systemic adverse effects experienced when these substances are administered orally. Therefore, we performed a systematic review to answer the question "Which method of induction of a TMJOA-related pain model in rats leads to prolonged painful symptoms, allowing the best assessment of a sustained drug delivery system?"

MATERIALS AND METHODS

Following the PRISMA guidelines, we searched MEDLINE for papers published from 1994 to July 2020 on a TMJ arthritis model using rats. We identified the means of pain induction and of nociception assessment. We assessed protocol bias using an adaptation of the QUADAS-2 tool. Animal selection, the reference standard method of pain assessment, applicability of a statistical assessment, and flow and timing were assessed.

RESULTS

Of the 59 full papers we reviewed, 41 performed no pain assessment after the first 7 days following induction of the TMJ-related pain model. We eventually identified 18 long-term TMJOA-related pain models. Pain was induced by injection of toxic substances, most commonly Freund's complete adjuvant (50 μg per 50 μl), formalin at various concentrations, or monosodium iodoacetate (0,5 mg per 50 μl), into the TMJ, or by physical methods. Few studies reported data on pain after 21 days of follow-up. Heterogeneity of induction methods, pain assessment methods, and flow and timing biases precluded a meta-analysis.

CONCLUSIONS

Given that pain is 1 of the main symptoms of TMJOA, experimental study protocols should include long-term pain assessment.

TMJ arthroscopy with hyaluronic acid: A 12-month randomized clinical trial

OBJECTIVES

To determine the effects of hyaluronic acid (HA) as an adjunct to temporomandibular joint (TMJ) arthroscopy, relative to standard TMJ arthroscopy, in Wilkes stage-III and stage-IV patients.

METHODS

A randomized clinical trial design was utilized (ClinicalTrials.gov NCT04110587). 51 patients were allocated to a TMJ arthroscopy (n = 25) or a TMJ arthroscopy plus HA (n = 26) group. Visual analog scale joint pain scores, maximum mouth opening (MMO), and muscle pain were measured at baseline, and at 3, 6, 9, and 12 months. Disk position on magnetic resonance imaging was evaluated at baseline and 12 months. Oral health-related quality of life (OHRQoL) was assessed at baseline, and at 6 and 12 months.

RESULTS

No group differences were observed in clinical or radiographic measurements (p ≥ .05). The results do not indicate any benefit of HA as an adjuvant therapy to arthroscopy during follow-up months 3-12. TMJ arthroscopy improved OHRQoL at 6 and 12 months (Oral Health Impact Profile-14 questionnaire scores of -14.59 and -14.27, 95% confidence intervals = -17.55 to -11.63 and -17.27 to -11.27) respectively, as well as pain and MMO, at all follow-up time points (p < .001).

CONCLUSIONS

A beneficial effect of HA injection during TMJ arthroscopy after the 3-month follow-up was not observed.

Repeated Live Imaging in the Temporomandibular Joint of an Anterior Crossbite Mouse Model Using a 7T Magnetic Resonance Device

BACKGROUND/AIM

Few studies have performed magnetic resonance (MR) imaging on live animals. The aim of this study was to perform 7T MR microimaging of the temporomandibular joint (TMJ) multiple times in the same living mice with malocclusion, and to compare between MR imaging and histopathological findings.

MATERIALS AND METHODS

Mice were examined by MR imaging at 3-4, 6 and 12 weeks following the attachment of a metal tube on the left mandibular incisor. Histopathological examination was done at 3, 6 and 12 weeks.

RESULTS

The detailed structure of the TMJ was evident from MR microimaging. The histopathological examination showed some changes in the cartilage, but no changes in the bone structure of these mice.

CONCLUSION

We successfully performed multiple 7T MR imaging in living mice. Even if the TMJ showed no obvious changes on MR images, minute changes may be present in the cartilage.