Pain Mechanisms and Centralized Pain in Temporomandibular Disorders

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.

Effectiveness of intra-articular infiltration of platelet concentrates for the treatment of painful joint disorders in the temporomandibular joint: a systematic review

BACKGROUND

The role of Platelet-rich Plasma injections as a complementary therapy, together with other minimally invasive procedures, has been analyzed previously, however, there are no articles that evaluate the effects of intra-articular infiltration in the Temporomandibular Joint by itself. The aim of this article is to evaluate the effectiveness of intra-articular infiltration with Platelet-rich Plasma, as a single procedure, to both reduce pain and improve clinical parameters in painful joint disorders.

MATERIAL AND METHODS

A systematic search was performed using the terms "Temporomandibular Joint Disorders" and "Platelet-rich plasma" in May 2021. Only the Clinical Trials found in the Pubmed/Medline, Embase, Cochrane Library/Cochrane CENTRAL, Google Scholar, and LILACS databases were selected.

RESULTS

Only four articles were selected for full-text review. Statistically significant differences were found in pain reduction Platelet-rich Plasma-based interventions with respect to preoperative measurements up to six months. Only two studies found significant intergroup differences favoring Platelet-rich Plasma over other interventions. In relation to maximum mouth opening, three studies reported an increase compared to the preoperative measurements.

CONCLUSIONS

Platelet-rich Plasma might potentially be effective in reducing pain levels and improving clinical parameters such as interincisal distance. However, studies with better methodological quality, larger sample sizes, and lower risk of bias are required to assess the real value of this intervention in the management of painful joint disorders.

Prediction of duloxetine efficacy in addition to self-management in painful temporomandibular disorders: A randomised, placebo-controlled clinical trial

BACKGROUND

Conditioned pain modulation (CPM) is a potential predictor of treatment response that has not been studied in temporomandibular disorders (TMD).

OBJECTIVES

We conducted a randomised, double-blind, placebo-controlled trial (RCT) of duloxetine in addition to self-management (SM) strategies to investigate its efficacy to reduce pain intensity in painful TMD patients. Moreover, we investigated whether baseline CPM would predict the duloxetine efficacy to reduce TMD pain intensity.

METHODS

Eighty participants were randomised to duloxetine 60 mg or placebo for 12 weeks. The primary outcomes were the change in the pain intensity from baseline to week-12 and CPM-sequential paradigm at baseline. Safety, physical and emotional functioning outcomes were also evaluated.

RESULTS

Of 80 participants randomised, 78 were included in intention-to-treat analysis. Pain intensity decreased for SM-duloxetine and SM-placebo but did not differ between groups (p = .82). A more efficient CPM was associated with a greater pain intensity reduction regardless of the treatment group (p = .035). Physical and emotional functioning did not differ between groups, but adverse events (p = .014), sleep impairment (p = .003) and catastrophizing symptoms (p = .001) were more prevalent in SM-duloxetine group.

CONCLUSION

This study failed to provide evidence of a beneficial effect of adding duloxetine to SM strategies for treatment of painful TMD. Nonetheless, this RCT has shown the feasibility of applying pain modulation assessment to predict short-term treatment response in painful TMD patients, which confirms previous finds that CPM evaluation may serve a step forward in individualising pain treatment.

Neuroimaging and artificial intelligence for assessment of chronic painful temporomandibular disorders-a comprehensive review

Chronic Painful Temporomandibular Disorders (TMD) are challenging to diagnose and manage due to their complexity and lack of understanding of brain mechanism. In the past few decades' neural mechanisms of pain regulation and perception have been clarified by neuroimaging research. Advances in the neuroimaging have bridged the gap between brain activity and the subjective experience of pain. Neuroimaging has also made strides toward separating the neural mechanisms underlying the chronic painful TMD. Recently, Artificial Intelligence (AI) is transforming various sectors by automating tasks that previously required humans' intelligence to complete. AI has started to contribute to the recognition, assessment, and understanding of painful TMD. The application of AI and neuroimaging in understanding the pathophysiology and diagnosis of chronic painful TMD are still in its early stages. The objective of the present review is to identify the contemporary neuroimaging approaches such as structural, functional, and molecular techniques that have been used to investigate the brain of chronic painful TMD individuals. Furthermore, this review guides practitioners on relevant aspects of AI and how AI and neuroimaging methods can revolutionize our understanding on the mechanisms of painful TMD and aid in both diagnosis and management to enhance patient outcomes.

Mitochondria-targeting nanozyme alleviating temporomandibular joint pain by inhibiting the TNFα/NF-κB/NEAT1 pathway

Inflammatory cytokines that are secreted into the spinal trigeminal nucleus caudalis (Sp5C) may augment inflammation and cause pain associated with temporomandibular joint disorders (TMD). In a two-step process, we attached triphenylphosphonium (TPP) to the surface of a cubic liposome metal-organic framework (MOF) loaded with ruthenium (Ru) nanozyme. The design targeted mitochondria and was designated Mito-Ru MOF. This structure scavenges free radicals and reactive oxygen species (ROS) and alleviates oxidative stress. The present study aimed to investigate the effects and mechanisms by which Mito-Ru MOF ameliorates TMD pain. Intra-temporomandibular joint (TMJ) injections of complete Freund's adjuvant (CFA) induced inflammatory pain for ≥10 d in the skin areas innervated by the trigeminal nerve. Tumor necrosis factor-alpha (TNF-α), nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), long non-coding RNA nuclear paraspeckle assembly transcript 1 (lncRNA NEAT1), and ROS also have been proved to be significantly upregulated in the Sp5C of TMD mice. Moreover, a single Mito-Ru MOF treatment alleviated TMD pain for 3 d and downregulated TNF-α, NF-κB, lncRNA NEAT1, and ROS. NF-κB knockdown downregulated NEAT1 in the TMD mice. Hence, Mito-Ru MOF inhibited the production of ROS and alleviated CFA-induced TMD pain via the TNF-α/NF-κB/NEAT1 pathway. Therefore, Mito-Ru MOF could effectively treat the pain related to TMD and other conditions associated with severe acute inflammatory activation.

Evaluated periodontal tissues and oxidative stress in rats with neuropathic pain-like behavior

BACKGROUND

Oxidative stress has a critical effect on both persistent pain states and periodontal disease. Voltage-gated sodium NaV1.7 (SCN9A), and transient receptor potential ankyrin 1 (TRPA1) are pain genes. The goal of this study was to investigate oxidative stress markers, periodontal status, SCN9A, and TRPA1 channel expression in periodontal tissues of rats with paclitaxel-induced neuropathic pain-like behavior (NPLB).

METHODS AND RESULTS

Totally 16 male Sprague Dawley rats were used: control (n = 8) and paclitaxel-induced pain (PTX) (n = 8). The alveolar bone loss and 8-hydroxy-2-deoxyguanosine (8-OHdG) levels were analyzed histometrically and immunohistochemically. Gingival superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) activities (spectrophotometric assay) were measured. The relative TRPA1 and SCN9A genes expression levels were evaluated using quantitative real-time PCR (qPCR) in the tissues of gingiva and brain. The PTX group had significantly higher alveolar bone loss and 8-OHdG compared to the control. The PTX group had significantly lower gingival SOD, GPx and CAT activity than the control groups. The PTX group had significantly higher relative gene expression of SCN9A (p = 0.0002) and TRPA1 (p = 0.0002) than the control in gingival tissues. Increased nociceptive susceptibility may affect the increase in oxidative stress and periodontal destruction.

CONCLUSIONS

Chronic pain conditions may increase TRPA1 and SCN9A gene expression in the periodontium. The data of the current study may help develop novel approaches both to maintain periodontal health and alleviate pain in patients suffering from orofacial pain.

Gut-Brain Crosstalk and the Central Mechanisms of Orofacial Pain

Accumulated evidence has demonstrated that the gut microbiome can contribute to pain modulation through the microbiome-gut-brain axis. Various relevant microbiome metabolites in the gut are involved in the regulation of pain signaling in the central nervous system. In this review, we summarize recent advances in gut-brain interactions by which the microbiome metabolites modulate pain, with a focus on orofacial pain, and we further discuss the role of gut-brain crosstalk in the central mechanisms of orofacial pain whereby the gut microbiome modulates orofacial pain via the vagus nerve-mediated direct pathway and the gut metabolites/molecules-mediated indirect pathway. The direct and indirect pathways both contribute to the central regulation of orofacial pain through different brain structures (such as the nucleus tractus solitarius and the parabrachial nucleus) and signaling transmission across the blood-brain barrier, respectively. Understanding the gut microbiome-regulated pain mechanisms in the brain could help us to develop non-opioid novel therapies for orofacial pain.

Quantitative Sensory Testing to Characterize Sensory Changes in Hidradenitis Suppurativa Skin Lesions

Importance

Pain is the most impactful symptom in patients with hidradenitis suppurativa (HS). Characterization of sensory profiles may improve understanding of pain mechanisms in HS and facilitate identification of effective pain management strategies.

Objective

To characterize somatosensory profiles in patients with HS at clinically affected and nonaffected sites compared with pain-free reference data.

Design, Setting, and Participants

This cross-sectional study was conducted at the Emory University Dermatology Clinic. It was hypothesized (1) that patients with HS would demonstrate hypersensitivity to pain in HS lesions and (2) that some patients would have sensory profiles consistent with complex pain mechanisms. Therefore, adults with dermatologist-diagnosed HS and at least 1 painful HS lesion at the time of testing were enrolled between September 10, 2020, and March 21, 2022. Patients with other diagnoses contributing to pain or neuropathy were excluded. Data analysis was conducted between March and April 2022.

Exposure

Quantitative sensory testing was performed on HS lesions and control skin according to a standardized protocol.

Main Outcomes and Measures

Quantitative sensory testing outcomes included innocuous thermal and mechanical sensitivity (cold, warmth, and light touch detection thresholds), noxious thermal and mechanical sensitivity (cold, heat, pinprick, and deep pressure pain thresholds and suprathreshold pinprick sensitivity), temporal summation of pinprick, paradoxical thermal sensations, and dynamic mechanical allodynia (pain upon light stroking of the skin). Sensitivity in HS lesions was compared with sensitivity in a control location (the hand) and in pain-free controls using t tests.

Results

This study included 20 participants with a median age of 35.5 (IQR, 30.0-46.5) years, the majority of whom were women (15 [75%]). In terms of race and ethnicity, 2 participants (10%) self-identified as Asian, 11 (55%) as Black, 6 (30%) as White, and 1 (5%) as more than 1 race or ethnicity. Compared with site-specific reference values from healthy, pain-free control participants, HS lesions were insensitive to innocuous cold and warmth, noxious heat, and light touch (t = -5.69, -10.20, -3.84, and 4.46, respectively; all P < .001). In contrast, HS lesions also demonstrated significant hypersensitivity to deep pressure pain (t = 8.36; P < .001) and cutaneous pinprick (t = 2.07; P = .046). Hypersensitivity to deep pressure pain was also observed in the control site (t = 5.85; P < .001). A subset of patients with HS displayed changes in pain processing that are often seen in neuropathic and nociplastic pain conditions, including hypersensitivity to repetitive pinprick (5 [26%]), paradoxical thermal sensations (3 [15%]), and pain upon light stroking of the skin (10 [50%]).

Conclusions and Relevance

The findings of this cross-sectional study suggest that HS involves local changes in the skin or its free nerve endings, possibly leading to peripheral neuropathy and alterations in the transduction of innocuous and noxious thermal and mechanical stimuli. For some patients, central nervous system changes in somatosensory processing may also occur, but confirmatory evidence is needed. Better understanding of neuropathic and nociplastic mechanisms in HS pain could lead to individually tailored treatments.

Multimodal hypersensitivity derived from quantitative sensory testing predicts pelvic pain outcome: an observational cohort study

ABSTRACT

Multimodal hypersensitivity (MMH)-greater sensitivity across multiple sensory modalities (eg, light, sound, temperature, pressure)-is associated with the development of chronic pain. However, previous MMH studies are restricted given their reliance on self-reported questionnaires, narrow use of multimodal sensory testing, or limited follow-up. We conducted multimodal sensory testing on an observational cohort of 200 reproductive-aged women, including those at elevated risk for chronic pelvic pain conditions and pain-free controls. Multimodal sensory testing included visual, auditory, and bodily pressure, pelvic pressure, thermal, and bladder pain testing. Self-reported pelvic pain was examined over 4 years. A principal component analysis of sensory testing measures resulted in 3 orthogonal factors that explained 43% of the variance: MMH, pressure pain stimulus response, and bladder hypersensitivity. The MMH and bladder hypersensitivity factors correlated with baseline self-reported menstrual pain, genitourinary symptoms, depression, anxiety, and health. Over time, MMH increasingly predicted pelvic pain and was the only component to predict outcome 4 years later, even when adjusted for baseline pelvic pain. Multimodal hypersensitivity was a better predictor of pelvic pain outcome than a questionnaire-based assessment of generalized sensory sensitivity. These results suggest that MMHs overarching neural mechanisms convey more substantial long-term risk for pelvic pain than variation in individual sensory modalities. Further research on the modifiability of MMH could inform future treatment developments in chronic pain.

Involvement of Oxidative Stress and Nutrition in the Anatomy of Orofacial Pain

Pain is a very important problem of our existence, and the attempt to understand it is one the oldest challenges in the history of medicine. In this review, we summarize what has been known about pain, its pathophysiology, and neuronal transmission. We focus on orofacial pain and its classification and features, knowing that is sometimes purely subjective and not well defined. We consider the physiology of orofacial pain, evaluating the findings on the main neurotransmitters; in particular, we describe the roles of glutamate as approximately 30-80% of total peripheric neurons associated with the trigeminal ganglia are glutamatergic. Moreover, we describe the important role of oxidative stress and its association with inflammation in the etiogenesis and modulation of pain in orofacial regions. We also explore the warning and protective function of orofacial pain and the possible action of antioxidant molecules, such as melatonin, and the potential influence of nutrition and diet on its pathophysiology. Hopefully, this will provide a solid background for future studies that would allow better treatment of noxious stimuli and for opening new avenues in the management of pain.

Orofacial Pain Management: An Overview of the Potential Benefits of Palmitoylethanolamide and Other Natural Agents

Pain is the most common symptom that dentists are confronted with, whether acute (pulpitis, acute periodontitis, post-surgery, etc.) or chronic diseases, such as periodontitis, muscle pain, temporomandibular joint (TMJ) disorders, burning mouth syndrome (BMS), oral lichen planus (OLP) and others. The success of therapy depends on the reduction in and management of pain through specific drugs, hence the need to analyze new pain medications with specific activity, which are suitable for long-term use, with a low risk of side effects and interactions with other drugs, and capable of leading to a reduction in orofacial pain. Palmitoylethanolamide (PEA) is a bioactive lipid mediator, which is synthesized in all tissues of the body as a protective pro-homeostatic response to tissue damage and has aroused considerable interest in the dental field due to its anti-inflammatory, analgesic, antimicrobial, antipyretic, antiepileptic, immunomodulatory and neuroprotective activities. It has been observed that PEA could play a role in the management of the pain of orofacial origin, including BMS, OLP, periodontal disease, tongue a la carte and temporomandibular disorders (TMDs), as well as in the treatment of postoperative pain. However, actual clinical data on the use of PEA in the clinical management of patients with orofacial pain are still lacking. Therefore, the main objective of the present study is to provide an overview of orofacial pain in its many manifestations and an updated analysis of the molecular pain-relieving and anti-inflammatory properties of PEA to understand its beneficial effects in the management of patients with orofacial pain, both neuropathic and nociceptive in nature. The aim is also to direct research toward the testing and use of other natural agents that have already been shown to have anti-inflammatory, antioxidant and pain-relieving actions and could offer important support in the treatment of orofacial pain.

Emerging role of microglia and astrocyte in the affective-motivational response induced by a rat model of persistent orofacial pain

Few studies are approaching the neural basis underlying the aggregation of emotional disorders in orofacial pain despite the stress, depression, and anxiety are some of the most commonly reported risk factors. Using a persistent orofacial pain rat model induced by complete Freund's adjuvant (CFA) injection into the temporomandibular joint, we have investigated the plasticity astrocytes and microglia key brain regions for the affective-emotional component of pain. We measured the expression and morphologic pattern of reactivation of glial fibrillary acidic protein (GFAP, astrocyte marker) and Iba-1 (microglial marker) by western blotting and immunohistochemistry analysis. The results showed no alterations on motor activity during inflammatory pain, indicating an exclusive effect of nociceptive behavior on the plasticity of limbic regions. CFA-induced temporomandibular inflammation changed GFAP and Iba-1 expression in distinct regions related to emotional behavior in a time-dependent manner. A significant increase in GFAP and Iba-1 expression was observed in the central nucleus of the amygdala, hippocampus and periaqueductal grey matter from day 3 to day 10 post-CFA injection. Moreover, a positive correlation between GFAP and Iba-1 upregulation and an increased mechanical hypersensitivity was observed. Conversely, no change on GFAP and Iba-1 expression was observed in the hypothalamus and colliculus during orofacial inflammatory pain. Our data suggest an important role for glial cells in the affective-motivational dimension of orofacial pain beyond their well-explored role in the traditional nociceptive transmission circuits.

Psychosocial factors associated with pain outcomes in patients with painful temporomandibular disorders and headaches

The objective of this study was to assess the association between psychosocial factors (in terms of anxiety, somatization, depression, and optimism) and pain (in terms of headache pain intensity and pain-related disability), in patients with a painful temporomandibular disorder (TMD) and one of the following headache types: migraine, tension-type headache (TTH), or headache attributed to TMD, corrected for the influence of bruxism. A retrospective study was conducted at an orofacial pain and dysfunction (OPD) clinic. Inclusion criteria were painful TMD, with migraine, TTH, and/or headache attributed to TMD. Linear regressions were performed to assess the influence of psychosocial variables on pain intensity and on pain-related disability, stratified per headache type. The regression models were corrected for bruxism and the presence of multiple headache types. A total of 323 patients (61% female; mean age 42.9, SD 14.4 years) were included. Headache pain intensity only had significant associations in TMD-pain patients with headache attributed to TMD, and anxiety showed the strongest relation (β = 0.353) with pain intensity. Pain-related disability was most strongly associated with depression in TMD-pain patients with TTH (β = 0.444), and with somatization in patients with headache attributed to TMD (β = 0.399). In conclusion, the influence of psychosocial factors on headache pain intensity and pain-related disability depends on the headache type presenting.

Characterization of visual processing in temporomandibular disorders using functional magnetic resonance imaging

BACKGROUND AND PURPOSE

Many patients with chronic pain report hypersensitivity not only to noxious stimuli, but also to other modalities including innocuous touch, sound, and light, possibly due to differences in the processing of these stimuli. The goal of this study was to characterize functional connectivity (FC) differences between subjects with temporomandibular disorders (TMD) and pain-free controls during a visual functional magnetic resonance imaging (fMRI) task that included an unpleasant, strobing visual stimulus. We hypothesized the TMD cohort would exhibit maladaptations in brain networks consistent with multisensory hypersensitivities observed in TMD patients.

METHODS

This pilot study included 16 subjects, 10 with TMD and 6 pain-free controls. Clinical pain was characterized using self-reported questionnaires. Visual task-based fMRI data were collected on a 3T MR scanner and used to determine differences in FC via group independent component analysis.

RESULTS

Compared to controls, subjects with TMD exhibited abnormally increased FC between the default mode network and lateral prefrontal areas involved in attention and executive function, and impaired FC between the frontoparietal network and higher order visual processing areas.

CONCLUSIONS

The results indicate maladaptation of brain functional networks, likely due to deficits in multisensory integration, default mode network function, and visual attention and engendered by chronic pain mechanisms.

Investigation of temporomandibular disorders in patients with fibromyalgia syndrome: A case-control study

INTRODUCTION

The aim of this study is to compare the frequency of temporomandibular disorders and to examine the temporomandibular pain and functionality levels between healthy female participants and female patients diagnosed with fibromyalgia.

MATERIALS AND METHODS

Our study included 300 participants. Patients were evaluated according to the Diagnostic Criteria for Temporomandibular Disorders: Assessment Instruments (DC/TMD). While evaluating the patients using DC/TMD, TMD Pain Screener and Symptom questionnaire were used within the scope of Axis I, and Graded Chronic Pain Scale, Jaw Functional Limitation Scale-8 (JFLS-8), Patient Health Questionnaire (PHQ-4) and Oral Behaviors Checklist were applied.

RESULTS

Bruxism, tooth grinding and masseter hypertrophy were found to be significantly higher in fibromyalgia patients compared to healthy volunteers (p<0.001). The pain screener, JFLS-8, PHQ-4 and OBC scores and GCPS levels were found to be increased in the fibromyalgia group compared to healthy individuals (p<0.001). Considering the post-examination diagnoses of the participants, the diagnoses of myalgia (p=0.022) and disc displacement with reduction (p<0.001) were significantly higher than healthy individuals.

CONCLUSIONS

Fibromyalgia is a common pathology, therefore, TMD symptoms, which are more difficult to diagnose and often missed, should be questioned in fibromyalgia patients and should be kept in mind in the management of fibromyalgia patients.

Accurate Diagnosis and Treatment of Painful Temporomandibular Disorders: A Literature Review Supplemented by Own Clinical Experience

Introduction

Temporomandibular disorders (TMD) is a multifactorial group of musculoskeletal disorders often with combined etiologies that demand different treatment plans. While pain is the most common reason why patients decide to seek help, TMD is not always painful. Pain is often described by patients as a headache, prompting patients to seek the help of neurologists, surgeons, and ultimately dentists. Due to the unique characteristics of this anatomical area, appropriate diagnostic tools are needed, as well as therapeutic regimens to alleviate and/or eliminate the pain experienced by patients. Aim of the Study. The aim of this study is to collect and organize information on the diagnosis and treatment of pain in TMD, through a review of the literature supplemented by our own clinical experience. Material and Methods. The study was conducted by searching scientific databases PubMed, Scopus, and Google Scholar for documents published from 2002-2022. The following keywords were used to build the full list of references: TMD, pain, temporomandibular joint (TMJ), TMJ disorders, occlusal splint, relaxing splints, physiotherapy TMD, pharmacology TMD, natural therapy TMD, diagnostic criteria for TMD, and DC/TMD. The literature review included 168 selected manuscripts, the content of which was important for pain diagnosis and clinical treatment of TMD.

Results

An accurate diagnosis of TMD is the foundation of appropriate treatment. The most commonly described treatments include physiotherapy, occlusal splints therapy, and pharmacological treatment tailored to the type of TMD.

Conclusions

Based on the literature review and their own experience, the authors concluded that there is no single ideal form of pain therapy for TMD. Treatment of TMD should be based on a thorough diagnostic process, including the DC/TMD examination protocol, psychological evaluation, and cone beam computer tomography (CBCT) imaging. Following the diagnostic process, once a diagnosis is established, a treatment plan can be constructed to address the patient's complaints.

Topical review - salivary biomarkers in chronic muscle pain

BACKGROUND AND AIMS

Muscle related temporomandibular disorders (myogenous TMD), one of the most common orofacial pain conditions, is characterized by facial pain and often accompanied by jaw movement limitations. Although the underlying biological mechanisms are still unclear, a cluster of proteins and peptides is assumed to be involved in the pathophysiology. These proteins and peptides may be measured in a simple non-invasive saliva sample. This work investigated whether saliva can be used to sample algogenic substances that can serve as molecular biomarkers for TMD myalgia.

METHODS

Saliva and blood samples were collected from healthy individuals (n=69) and patients diagnosed with TMD myalgia (n=39) according to the Diagnostic Criteria for TMD. Unstimulated and stimulated whole, parotid, and sublingual saliva were analysed. The protein profiles were investigated using two-dimensional gel electrophoresis followed by identification with liquid chromatography tandem mass spectrometry. Levels of nerve growth factor (NGF), calcitonin gene-related peptide (CGRP), and brain derived neuro-tropic factor (BDNF) were determined using western blotting based technology and multiplex electro-chemiluminescence assay panel. Glutamate, serotonin, and substance p (SP) were determined using commercially available methods.

RESULTS

Different saliva collection approaches resulted in significant differences in the protein profile as well as in the expression of NGF, BDNF, CGRP, SP, and glutamate. Stimulated whole saliva showed least variability in protein concentration (35%) and was correlated to plasma levels of glutamate. Unlike SP and glutamate, NGF and BDNF expressed a rhythmic variation in salivary expression with higher levels in the morning (p<0.05). Patients with a diagnosis of TMD myalgia had significantly higher levels of salivary glutamate but lower salivary NGF and BDNF compared to controls; in addition, the lower NGF and BDNF levels correlated to psychological dysfunction. The quantitative proteomics data revealed 20 proteins that were significantly altered in patients compared to controls. The identified proteins are involved in metabolic processes, immune response, and stress response. Dissimilarities in protein profile and clinical variables were observed between TMD myalgia and myofascial pain.

CONCLUSIONS

The work highlights the importance of consistency in saliva collection approaches, including the timing of the collection. It displayed significant changes in pain specific mediators and protein profile in TMD myalgia and furthermore dissimilarities between subclasses indicating different pathophysiology. After extensive validation, potential salivary biomarkers can be combined with clinical features to better understand and diagnose TMD myalgia.

Cannabis Bioactive Compound-Based Formulations: New Perspectives for the Management of Orofacial Pain

The management of orofacial pain to alleviate the quality of life of affected patients is becoming increasingly challenging for scientific research and healthcare professionals. From this perspective, in addition to conventional therapies, new alternatives are being sought, increasingly looking at the use of both natural and synthetic products. Cannabis sativa L. represents an interesting source of bioactive compounds, including non-psychoactive cannabinoids, flavonoids, and terpenes, many of which are effective in improving pain intensity. Here, we aim to analyze the possible mechanisms of action of the bioactive natural and synthetic hemp-derived compounds responsible for the modulatory effects on pain-related pathways. The ability of these compounds to act on multiple mechanisms through a synergistic effect, reducing both the release of inflammatory mediators and regulating the response of the endocannabinoid system, makes them interesting agents for alternative formulations to be used in orofacial pain.

Effectiveness of conservative therapeutic modalities for temporomandibular disorders-related pain: a systematic review

PURPOSE

The aim of this systematic review was to evaluate the effectiveness of conservative different therapeutic modalities for temporomandibular disorders (TMD) pain.

MATERIALS AND METHODS

An electronic systematic search was conducted in the MEDLINE (PubMed) database to identify the randomized clinical trials (RCTs) published between 2001 and 2021. The following, simple or multiple conjunctions, search keywords were selected: TMD pain, TMD management or conservative treatment or treatment strategies and TMD pain, therapeutic modalities or interventions and TMD. Studies included must have patients older than 18 years, with painful TMD, which diagnosis was performed by Research Diagnostic Criteria for TMD or Diagnostic Criteria for TMD. Outcome variables were pain relief and post treatment pain intensity reduction. Data were analysed with non-parametric tests and the level of significance was set at p<.05.

RESULTS

Out of 1599 articles obtained, 28 RCTs fulfilled all selection criteria and were included. The results of this study show that there was a significant decrease in short-term post-treatment TMD pain with the use of occlusal splint alone or in combination with other therapeutic modalities when compared with the control group. Statistically significant differences were also detected between laser and photobiomodulation group and the control, in short-term treatment TMD-related pain.

CONCLUSIONS

The primary findings of the present systematic review showed that the occlusal splint alone or combined with other therapeutic intervention presented positive effect on short-term TMD pain reduction. Secondary outcome suggests that laser and photobiomodulation therapy had, also, a significant role in short term pain relief.

Oral health-related quality of life in patients with osteoarthritis of the temporomandibular joint-Results of a systematic review

OBJECTIVES

The aim of this systematic review was to assess the oral health-related quality of life (OHRQoL) of patients with osteoarthritis (OA) of the temporomandibular joint (TMJ).

METHODS

This systematic literature search applied the search terms "oral health-related quality of life AND osteoarthritis of jaw OR arthritis of temporomandibular joint AND oral health-related quality of life" in PubMed, Medline, Web of Science and Scopus. Eligibility criteria were publication until 31 August 2021, examination of children or adults with OA of TMJ, reporting of any OHRQoL measurement and a full text in English language. Two different, independent and experienced reviewers performed this systematic literature search. The analysis of respective data was qualitative. For quality appraisal, the available checklist from the Agency for Healthcare Research and Quality (AHRQ) was applied.

RESULTS

Out of 102 findings, eight studies were included in qualitative analysis. Seven clinical investigations were performed in adults aged between 34 and 43 years. The other included study was performed on children. The quality of two studies was moderate, and six studies were evaluated as of high quality. Most studies applied the 14-item short form of the oral health impact profile (OHIP 14) for assessment of OHRQoL. OHIP 14 ranged between 9.24 and 38.86 points in means of sum score. Comparison with healthy individuals revealed worse OHRQoL of OA patients in two studies. Associations between OHRQoL with either oral health, general quality of life or disease-related parameters were rarely reported and heterogeneous. Five of the included studies reported subscales of OHIP 14, showing an impairment in all subscales.

CONCLUSIONS

There are hints that patients with OA of the TMJ show a reduced OHRQoL. More studies are needed, especially regarding oral health, disease-related parameters and pain intensity and its potential influence on OHRQoL.

Topology of pain networks in patients with temporomandibular disorder and pain-free controls with and without concurrent experimental pain: A pilot study

Temporomandibular disorders (TMD) involve chronic pain in the masticatory muscles and jaw joints, but the mechanisms underlying the pain are heterogenous and vary across individuals. In some cases, structural, functional, and metabolic changes in the brain may underlie the condition. In the present study, we evaluated the functional connectivity between 86 regions of interest (ROIs), which were chosen based on previously reported neuroimaging studies of pain and differences in brain morphology identified in an initial surface-based morphometry analysis. Our main objectives were to investigate the topology of the network formed by these ROIs and how it differs between individuals with TMD and chronic pain (n = 16) and pain-free control participants (n = 12). In addition to a true resting state functional connectivity scan, we also measured functional connectivity during a 6-min application of a noxious cuff stimulus applied to the left leg. Our principal finding is individuals with TMD exhibit more suprathreshold correlations (higher nodal degree) among all ROIs but fewer "hub" nodes (i.e., decreased betweenness centrality) across conditions and across all pain pathways. These results suggest is this pain-related network of nodes may be "over-wired" in individuals with TMD and chronic pain compared to controls, both at rest and during experimental pain.

Increased nociceptive sensitivity is associated with periodontal inflammation and expression of chronic pain genes in gingival tissues of male rats

OBJECTIVE

This study aimed to evaluate the inflammatory response, hyperpolarization-activated cyclic nucleotide-gated 2 (HCN2), and voltage-gated potassium (Kv) 9.1 channel expression in rats with paclitaxel-induced neuropathic pain-like behavior.

METHODS

Sixteen male Sprague Dawley rats were divided equally into two groups: control and paclitaxel-induced pain (PTX). The attachment loss and inflammatory cell infiltrate levels were analyzed histometrically and immunohistochemically. The gene expression of HCN2 and KCNS1 was analyzed by qPCR in the brain and gingival tissues.

RESULTS

The attachment loss and prominent infiltration of inflammatory cells were significantly higher in the PTX group than in the control groups. In gingival tissues; the expression levels of HCN2 (p = 0,0011) were significantly higher and KCNS1 (p = 0,0003) were significantly lower in the PTX group than in the control groups.

CONCLUSION

Increased nociceptive sensitivity, may play a role in periodontal inflammation. KCNS1 may decrease and HCN2 expression may increase in periodontium in permanent chronic pain states. The results of the present study may be helpful in developing new approaches to alleviate pain and maintain periodontal health in patients suffering from orofacial pain.

Masticatory Myoelectric Side Modular Ratio Asymmetry during Maximal Biting in Women with and without Temporomandibular Disorders

There is no consensus on the role of electromyographic analysis in detecting and characterizing the asymmetries of jaw muscle excitation in patients with temporomandibular disorders (TMD). To analyze the TMD patients (n = 72) in comparison with the healthy controls (n = 30), the surface electromyography (sEMG) of the temporalis anterior muscle (TA) and masseter muscle (M) was recorded while a maximal biting task was performed. The differences in the asymmetry of the relationship between the masseter muscles were assessed in a module to determine the sensitivity (Sn) of binomial logistic models, based on the dominance of the TA or the M muscle, in accurately predicting the presence of TMD. All assumptions were met, and comparisons between the groups showed significant differences for the TA muscle ratio (p = 0.007), but not for the M muscle ratio (p = 0.13). The left side was predominant over the right side in the TMD group for both the TA (p = 0.02) and M muscles (p = 0.001), while the non-TMD group had a higher frequency of the right side. Binary logistic regression showed a significant model (χ² = 9.53; p = 0.002) for the TA muscle with Sn = 0.843. The model for the M muscle also showed significance (χ² = 8.03; p = 0.005) with Sn = 0.837. The TMD patients showed an increased TA muscle ratio and asymmetry of left dominance, compared to the healthy subjects. Both of the binomial logistic models, based on muscle dominance TA or M, were moderately sensitive for predicting the presence of TMD.

The Role of Pain Inflexibility and Acceptance among Headache and Temporomandibular Disorders Patients

Temporomandibular disorders (TMD) and headache are complex. This study aims to assess the association between TMD, headache, and psychological dimensions such as psychological inflexibility and pain acceptance. The sample consisted of 120 participants following a non-probabilistic convenience sampling strategy through a direct invitation to the patients attending our facilities and their relatives (n = 61 diagnosed with headache, n = 34 diagnosed with TMD-headache, n = 25 control group). Diagnostic Criteria for Temporomandibular Disorders (DC-TMD), International Classification of Headache Disorders (ICHD-3 beta version), Chronic Pain Acceptance Questionnaire (CPAQ-8), and Psychological Inflexibility in Pain Scale (PIPS) were used as assessment tools. One-way ANOVA, multiple regression analysis (MRA), and the Johnson-Neyman approach were run by IBM SPSS, version 27 (IBM^® Company, Chicago, IL, USA). The significance level was 0.05. One third of our sample presented with headache with TMD. Females were predominant. Males with headache, no systemic disease, less pain severity but higher frequency, living longer with the disease and having sensitive changes, showed higher pain acceptance. When headache occurs with TMD, women with higher education, no headache family history, less pain, and no motor changes showed higher pain acceptance. Patients with both conditions are more liable to have chronic pain and pain inflexibility. Pain intensity and willingness explain 50% of the psychological inflexibility in the headache group. In our sample, individuals suffering from both conditions show greater pain inflexibility, implicating more vivid suffering experiences, leading to altered daily decisions and actions. However, further studies are needed to highlight this possible association.

Back and neck pain: A comparison between acute and chronic pain-related Temporomandibular Disorders

Background

Temporomandibular disorders (TMDs) are common and cause persistent pain. Comorbidities are associated with TMDs and can affect the effectiveness of their treatments. The literature is lacking enough evidence on the difference between acute and chronic pain, particularly in TMDs. Investigating this difference could highlight potential risk factors for the transition from acute to chronic pain–related TMDs.

Aim

To compare the likelihood of back and neck pain (BP, NP) between acute and chronic pain–related TMDs (AP-TMD, CP-TMD) as defined by pain duration and pain-related disability.‎

Methods

Participants with AP-TMDs (≤3 months) and CP-TMDs (>3 months) were recruited according to the diagnostic criteria and research diagnostic criteria of TMD. BP and NP were assessed using a self-reported checklist. CP-TMDs defined by disability (chronic disability) and depression and anxiety symptoms were assessed using validated instruments. Logistic regression analyses were employed.

Results

This study enrolled 487 adults with AP-TMD (n = 118) and CP-TMD (n = 369). Relative to AP-TMD, participants with CP-TMD had twice the odds of reporting NP (odds ratio [OR] = 2.17‎, 95% CI 1.27–3.71) but not BP ‎‎(OR = 0.96, 95% CI 0.57–1.64). Participants with chronic disability were twice as likely to report NP ‎(OR = 1.95‎, 95% CI 1.20–3.17‎) but not BP (OR = 1.13, 95% CI 0.69–1.82)‎ compared to those without. All analyses were adjusted for age, sex, and anxiety and depression symptoms.

Conclusions

Within the limitations of this study, results suggest that central dysregulation or trigeminocervical convergence mechanisms are implicated in the process of pain-related TMD chronification and highlight the relevance of considering disability when defining CP-TMDs.

Dry needling and upper cervical spinal manipulation in patients with temporomandibular disorder: A multi-center randomized clinical trial

OBJECTIVE

To compare the effects of dry needling and upper cervical spinal manipulation with interocclusal splint therapy, diclofenac, and temporomandibular joint (TMJ) mobilization in patients with temporomandibular disorder (TMD).

METHODS

One hundred-twenty patients with TMD were randomized to receive six treatment sessions of dry needling plus upper cervical spinal manipulation (n = 62) or interocclusal splint therapy, diclofenac, and joint mobilization to the TMJ (n = 58).

RESULTS

Patients receiving dry needling and upper cervical spinal manipulation experienced significantly greater reductions in jaw pain intensity over the last 7 days (VAS: F = 23.696; p < 0.001) and active pain-free mouth opening (F = 29.902; p < 0.001) than those receiving interocclusal splint therapy, diclofenac, and TMJ mobilization at the 3-month follow-up.

CONCLUSION

Dry needling and upper cervical spinal manipulation was more effective than interocclusal splint therapy, diclofenac, and TMJ mobilization in patients with TMD.

Which symptoms best distinguish fibromyalgia patients from those with other chronic pain disorders?

RATIONALE, AIMS AND OBJECTIVES

The primary purpose of this study was to test both classic and novel FM pain and non-pain symptoms to determine their practical efficacy in aiding clinicians to distinguish FM pain from other chronic pain disorders.

METHODS

158 pain patients from two primary care clinics were evaluated with history, physical exam, chart review, and a questionnaire containing 26 exploratory symptoms (10 from the Symptom Impact Questionnaire (SIQR) and 16 from the FM literature)). The symptoms were rated on a 0-10 VAS for severity by those patients reporting pain over the past week. Somers' D and mean severity differences between FM and chronic pain patients without FM were used to rank the discriminatory and diagnostic contributions of symptoms.

RESULTS

Fifty patients (14.2%) carried a chart diagnosis of FM, 108 (30.7%) had pain but not FM, and 192 (54.5%) who had neither pain nor FM. Comparing means between the two pain groups, the 5 best differentiating symptoms (all, P < .0001) were: a persistent deep aching over most of my body, poor balance (7.4 vs 3.1), environmental sensitivity (6.8 vs 3.0), tenderness to touch (6.8 vs 3.6) and pain after exercise (8.1 vs 4.1). Notably, VAS pain though significantly higher for FM was least discriminatory (6.5 vs 5.1, P < .001). The five best symptoms generated a ROC = 0.85 and Somers' D = 0.69, an accuracy of 81%, and an odd's ratio of 14.4.

CONCLUSIONS

Our results herein suggest that clinicians may be well-served to consider symptoms in addition to those contained in current diagnostic criteria when recognizing FM in their chronic pain patients.

Relationship between cervical angle and temporomandibular disorders in young and middle-aged population

OBJECTIVE

To verify temporomandibular disorders (TMDs) and cervical angles in a young and middle-aged population.

METHODS

Ninety participants were included, 45 of whom had TMDs. The participants were diagnosed according to the Research Diagnostic Criteria for TMDs. Lateral cervical radiographs were taken, and relevant cervical angles were measured. The general characteristics of the TMD group and control group were analyzed using chi-square analysis, and the relationship between cervical angles and TMDs was evaluated using the unpaired t-test.

RESULTS

The decrease in C2-C7 Cobb and increase in the posterior occipitocervical angle (POCA) were associated with the incidence of TMDs (p < 0.0001).

CONCLUSION

This study revealed that the cervical angle was related to TMDs. People with a long-time habit of head bending posture had a decrease in C2-C7 Cobb and an increase in the POCA. This group of people was more likely to develop TMDs.

The prevalence of comorbid chronic pain conditions among patients with temporomandibular disorders: A systematic review

BACKGROUND

This systematic review was designed to evaluate the presence of comorbid conditions among patients with temporomandibular disorders (TMDs).

TYPES OF STUDIES REVIEWED

The authors reviewed studies that reported the prevalence or incidence of chronic pain conditions or psychiatric disorders (anxiety, mood, personality disorders) among patients with any type of TMD. The authors calculated sample size-weighted prevalence estimates when data were reported in 2 or more studies for the same comorbid condition.

RESULTS

A total of 9 prevalence studies and no incidence studies were eligible for review; 8 of the studies examined chronic pain comorbidities. Weighted estimates showed high prevalence of pain comorbidities across studies, including current chronic back pain (66%), myofascial syndrome (50%), chronic stomach pain (50%), chronic migraine headache (40%), irritable bowel syndrome (19%), and fibromyalgia (14%). A single study examined psychiatric disorders and found that current depression was the most prevalent disorder identified (17.5%).

CONCLUSIONS AND PRACTICAL IMPLICATIONS

There is a high prevalence of comorbid chronic pain conditions among patients with TMDs, with more than 50% of patients reporting chronic back pain, myofascial syndrome, and chronic stomach pain. Psychiatric disorders among patients with different types of TMDs were studied less commonly in this pain population. Knowledge of the distribution of these and other comorbid disease conditions among patients with different types of TMDs can help dentists and other health care providers to identify personalized treatment strategies, including the coordination of care across medical specialties.

Influence of increased pain sensitivity on patient-reported outcomes following total knee arthroplasty

PURPOSE

The purpose of this study was to discover whether increased pain sensitivity was associated with postoperative pain and patient-reported outcome measures (PROMs) after total knee arthroplasty (TKA).

METHODS

Pain sensitivity was evaluated preoperatively using a pain sensitivity questionnaire (PSQ). Resting, walking, nighttime, and average pain visual analog scale (VAS) were measured before surgery and 6 weeks, 3 months, 6 months, and 1 year after surgery. PROMs were also evaluated based on the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) score and patient satisfaction. The association between pain VAS average score, WOMAC total score, and PSQ score (minor, moderate, and total score) was assessed at each stage.

RESULTS

There were 59 patients with a high PSQ score (≥ 5.2) and 53 with a low PSQ score (< 5.2). Up to 1 year postoperatively, the group with high PSQ scores had higher resting, walking, nighttime, and average pain VAS scores than the group with low scores (all p < 0.05). Worse preoperative WOMAC pain, function, and total scores continued until 1 year after surgery in the high-scoring PSQ group (all p < 0.05). The group with low PSQ scores was more satisfied with surgery than the group with high scores (p = 0.027). There was a positive correlation between preoperative PSQ score and pain VAS average score at all time points (all p < 0.05). A relationship between PSQ score and WOMAC total score was also observed (all p < 0.05).

CONCLUSION

Increased pain sensitivity is a factor related to higher postoperative pain levels and inferior PROMs in patients undergoing primary TKA.

LEVEL OF EVIDENCE

Case-controlled study, III.

Temporomandibular disorders cases with high-impact pain are more likely to experience short-term pain fluctuations

Temporomandibular disorders (TMD) patients can present clinically significant jaw pain fluctuations which can be debilitating and lead to poor global health. The Graded Chronic Pain Scale evaluates pain-related disability and its dichotomous grading (high/low impact pain) can determine patient care pathways and in general high-impact pain patients have worse treatment outcomes. Individuals with low-impact TMD pain are thought to have better psychosocial functioning, more favorable disease course, and better ability to control pain, while individuals with high-impact pain can present with higher levels of physical and psychological symptoms. Thereby, there is reason to believe that individuals with low- and high-impact TMD pain could experience different pain trajectories over time. Our primary objective was to determine if short-term jaw pain fluctuations serve as a clinical marker for the impact status of TMD pain. To this end, we estimated the association between high/low impact pain status and jaw pain fluctuations over three visits (≤ 21-day-period) in 30 TMD cases. Secondarily, we measured the association between jaw pain intensity and pressure pain thresholds (PPT) over the face and hand, the latter measurements compared to matched pain-free controls (n = 17). Jaw pain fluctuations were more frequent among high-impact pain cases (n = 15) than low-impact pain cases (n = 15) (OR 5.5; 95% CI 1.2, 26.4; p value = 0.033). Jaw pain ratings were not associated with PPT ratings (p value > 0.220), suggesting different mechanisms for clinical versus experimental pain. Results from this proof-of-concept study suggest that targeted treatments to reduce short-term pain fluctuations in high-impact TMD pain is a potential strategy to achieve improved patient perception of clinical pain management outcomes.

Oxytocin inhibits hindpaw hyperalgesia induced by orofacial inflammation combined with stress

Oxytocin (OT) is recognized as a critical neuropeptide in pain-related disorders. Chronic pain caused by the comorbidity of temporomandibular disorder (TMD) and fibromyalgia syndrome (FMS) is common, but whether OT plays an analgesic role in the comorbidity of TMD and FMS is unknown. Female rats with masseter muscle inflammation combined with 3-day forced swim (FS) stress developed somatic hypersensitivity, which modeled the comorbidity of TMD and FMS. Using this model, the effects of spinal OT administration on mechanical allodynia and thermal hyperalgesia in hindpaws were examined. Furthermore, the protein levels of OT receptors and 5-HT2A receptors in the L4-L5 spinal dorsal horn were analyzed by Western blot. The OT receptor antagonist atosiban and 5-HT2A receptor antagonist ritanserin were intrathecally injected prior to OT injection in the separate groups. Intrathecal injection of 0.125 μg and 0.5 μg OT attenuated the hindpaw hyperalgesia. The expression of OT receptors and 5-HT2A receptors in the L4-L5 spinal dorsal horn significantly increased following intrathecal injection of 0.5 μg OT. Intrathecal administration of either the OT receptor antagonist atosiban or 5-HT2A receptor antagonist ritanserin blocked the analgesic effect of OT. These results suggest that OT may inhibit hindpaw hyperalgesia evoked by orofacial inflammation combined with stress through OT receptors and/or 5-HT2A receptors, thus providing a therapeutic prospect for drugs targeting the OT system and for patients with comorbidity of TMD and FMS.

Acute and Chronic Temporomandibular Disorder Pain: A critical review of differentiating factors and predictors of acute to chronic pain transition

AIMS

The aims of this critical review were to: (i) assess the factors that differentiate acute from chronic temporomandibular disorders (TMD) pain; (ii) assess the risk factors associated with the transition from acute to chronic TMD pain; and (iii) summarize and appraise the studies.

METHOD

The databases used were MEDLINE, Embase, and Cochrane Database of Systematic Reviews. Eligible studies included articles comparing acute to chronic TMD pain, and cohort studies assessing the risk factors implicated in the transition from acute to chronic TMD pain.

RESULTS

Seven articles were selected: one case-control study, three cross-sectional studies, and three cohort studies. These studies found that psychological factors were more common in chronic than acute TMD pain patients; however, these factors did not increase the transition risk in the multivariable model. Myofascial and baseline pain intensity were associated with the transition from acute to chronic TMD pain at a 6-month follow-up. Due to methodological weaknesses in the available literature, more research is required to establish the risk factors implicated in the transition from acute to chronic TMD pain.

CONCLUSION

This review found some evidence that myofascial pain is associated with the transition risk from acute to chronic TMD pain at a 6-month follow-up and that pain intensity at baseline is associated with more intense TMD pain 6 months later. There is insufficient evidence to draw conclusions about the role of demographics and psychological disorders as independent risk factors.

Painful and non-painful comorbidities associated with short- and long-term painful temporomandibular disorders: A cross-sectional study among adolescents from Brazil, Canada, and France

BACKGROUND

Temporomandibular disorder (TMD) pain is common among adolescents. The association between painful TMD and other comorbidities has been demonstrated. However, the difference between short-term (<6 months) and long-term (≥ 6 months) painful TMD is not yet clear.

OBJECTIVE

The aim of this study was to assess the association between comorbidities and short- and long-term painful TMD among adolescents.

METHODS

In this cross-sectional study, adolescents were recruited from Montreal (Canada), Nice (France), and Arceburgo (Brazil). Self-reported painful TMD, comorbidities, school absence, and analgesic intake were assessed using reliable instruments. Multivariable logistic regression analyses were conducted to assess the study aims.

RESULTS

The prevalence of short- and long-term painful TMD was estimated at 22.29% and 9.93%, respectively. The number of comorbidities was associated with short- (OR = 1.71, 95%CI = 1.53-1.90) and long-term painful TMD (OR = 1.79, 95%CI = 1.55-2.08) compared to controls. Frequent headaches (OR_short-term = 4.39, 95%CI = 3.23-5.98, OR_long-term = 3.69, 95%CI = 2.45-5.57) and back pain (OR_short-term = 1.46, 95%CI=1.06-2.03, OR_long-term  = 1.69, 95%CI = 1.11-2.59) were associated with both painful TMD groups. Frequent neck pain (OR = 2.23, 95%CI = 1.53-3.26) and allergies were only associated with short-term painful TMD (OR = 1.54, 95%CI = 1.13-2.10). Frequent stomach pain was related to long-term (OR = 2.01, 95%CI = 1.35-3.26), and it was the only comorbidity significantly more frequent among the long than short-term TMD (OR = 1.82, 95%CI: 1.14-2.90). These analyses were adjusted by sex, age, and city.

CONCLUSION

In this multi-center study, both short- and long-term painful TMD are associated with frequent headaches and back pain, whereas frequent neck pain and allergies are related to only short-term, and frequent stomach pain with long-term painful TMD.

Electroacupuncture for Temporomandibular Disorders: A Systematic Review of Randomized Controlled Trials

Although electroacupuncture (EA) is an effective treatment for pain relief, there has been no systematic review of EA treatment for temporomandibular disorder TMD. This systematic review aimed to evaluate the efficacy and safety of EA in TMD management. We searched 14 databases until April 2021 for randomized controlled trials (RCTs) evaluating the effects of EA on TMDs. Eleven RCTs with 667 patients that used three acupuncture points (ST6, ST7, and LI4) were included. Two RCTs reported significant effects of EA plus microwave treatment compared with EA treatment alone on the total effectiveness rate (TER) for TMD. Further, two studies reported that compared with ultrashort wave alone, EA plus ultrashort wave had a significant effect on the TER for TMD and visual analog scale. All RCTs did not report adverse events. Our findings demonstrated the positive potential of EA in TMD management. However, there was weak evidence regarding EA use for TMD management given the poor quality and small sample sizes of the included studies. In the future, well-designed RCTs are required. It is necessary to investigate clinical trials and systematic reviews to compare the effectiveness and safety of EA and acupuncture for TMD.

Central sensitization in burning mouth syndrome: a practical approach using questionnaires

OBJECTIVES

Some experts have suggested that burning mouth syndrome (BMS) should be included in the family of central sensitivity syndromes, a group of similar medical disorders linked by the central sensitization (CS) mechanism. Our objective is to assess the presence of CS in patients with BMS by performing a clinical examination and administering questionnaires to measure the generalized extent of pain, the presence of associated symptoms, and the number of other concurrent chronic pain conditions.

STUDY DESIGN

We conducted a case-control study in 82 subjects (40 patients with BMS and 42 controls). Patients with BMS were diagnosed using The International Classification of Headache Disorders 3rd edition, beta version (ICHD-IIIβ) criteria. The Widespread Pain Index (WPI) and Symptom Severity (SS) Score questionnaires were used to determine the degree of central sensitivity. The number of other concurrent chronic pain conditions was determined with the Neblett inventory.

RESULTS

Data indicative of CS show a statistically significant association with BMS. Both SS Score and Widespread Pain Index scores higher in patients with BMS. Additionally, patients with BMS reported a significantly higher number of other central sensitivity syndromes.

CONCLUSIONS

Patients with BMS could present a CS component as well as other chronic pain conditions. The use of questionnaires may be useful to determine the degree of central sensitivity in patients with BMS.

Occlusal Trauma Induces Neuroimmune Crosstalk for a Pain State

Temporomandibular joint (TMJ) disorder caused by occlusal trauma is one of the most controversial topics in dentistry. Experimental traumatic occlusion (ETO) induced by metal crowns cemented to mandibular first molars in rats causes a long-lasting nociceptive response. This study aimed to elucidate whether ETO generates an increase in inflammatory mediators in the TMJ. In addition, the impact of ETO on trigeminal ganglia, neurotransmitter release, and satellite glial cell (SGC) activation was investigated. ELISA revealed enhanced inflammatory mediators, including TNF-α, IL-1β, IL-6, CX3CL1, and ADAM-17 by Western blotting, in periarticular TMJ tissue after 28 d of ETO. In the trigeminal ganglia, ETO groups increased the release of the neurotransmitters substance P and glutamate. Overexpression of the AMPA receptor and upregulation of NMDA were observed in the 0.4- and 0.7-mm ETO groups, respectively, highlighting enhanced neuronal excitation. Increased IL-1β and COX-2 mRNA levels in the 0.7-mm ETO group confirmed trigeminal ganglia SGC activation. Immunofluorescence and electrophoresis of SGC revealed increased pERK expression in the 0.7-mm ETO group. ERK phosphorylation was shown to be nociceptive specific, with its upregulation occurring in cases of chronic inflammatory pain. Increased PKA mRNA levels were observed in the 0.4-mm ETO group, while CREB mRNA levels were upregulated for both ETO groups. Electrophoresis showed overexpression of sodium channel Nav 1.7 in the 0.7-mm ETO group, while immunofluorescence revealed that Nav 1.7 is expressed in sensory trigeminal ganglia cells. The results of this study suggest that occlusal trauma induces neuroimmune crosstalk, with synthesis of proinflammatory/pronociceptive mediators, which increases neuronal activity in trigeminal ganglia via the activation of an inflammatory response cascade to develop a persistent neuroinflammatory state that leads to central sensitization.

The expression of Netrin-1 in the MIA-induced osteoarthritic temporomandibular joint in mice

Subchondral bone degeneration is the main pathological change during temporomandibular joint (TMJ) osteoarthritis (OA) development. Netrin-1, an axon-guiding factor, might play roles in OA development and pain. The purpose of this study was to investigate the expression of Netrin-1 in TMJ OA and its possible role in the progression of TMJ OA and pain. The synovial fluids of temporomandibular joint disorders (TMDs) patients were collected for Netrin-1 by enzyme linked immunosorbent assay (ELISA). TMJ OA model was built by MIA joint injection, and then the von Frey test, hematoxylin & eosin (H&E) staining, toluidine blue (TB) staining, immunohistochemical (IHC) staining and micro-CT were performed. After induction of osteoclast differentiation of raw264.7 cells, immunofluorescence (IF) was used to detect the Netrin-1 and its receptors on osteoclast membrane. The concentration of Netrin-1 increased in the synovial fluid of TMJ OA patients. After MIA injection to TMJ, the head withdrawal threshold (HWT) was significantly decreased. Microscopically, the structural disorder of subchondral bone was the most obvious at the 2nd week after MIA injection. In addition, Netrin-1 expression increased in the subchondral bone at the 2nd week after MIA injection. In vitro, the expressions of Netrin-1 and its receptor Unc5B were upregulated on the osteoclast membrane. Netrin-1 might be an important regulator during bone degeneration and pain in the process of TMJ OA.

Occlusal disharmony and chronic oro-facial pain: from clinical observation to animal study

BACKGROUND

Occlusion can be viewed as the most sensitive susceptor of the central nervous system in the oro-facial region. Its inalienable relationships to the temporomandibular joint, the muscles, the stomatognathic system and even the central nervous system are self-evident. Almost all the dental treatments inevitably change the occlusion, potentially or actually, locally or extensively, and immediately or gradually.

OBJECTIVE

The objective of this study was to present a narrative literature on occlusal disharmony and chronic oro-facial pain.

METHODS

Literature reviews focusing on clinical studies about the relationship between occlusal disharmony and myofascial oro-facial pain, and related preclinical studies about the animal models of, as well as the peripheral and central mechanisms underlying this condition related to, occlusal disharmony were used as starting point and guidelines to describe the topics mentioned. A search of the PubMed database was performed mainly with the following search terms: "occlusion," "occlusal interference," "occlusal disharmony," "occlusal change," "oro-facial pain" and "myofascial pain."

RESULTS

Relevant literature from the past 70 years until the present day was meticulously studied. The literature review together with three related characteristic clinical cases revealed an intimate association between occlusal disharmony and chronic oro-facial pain, involving pathological changes, extending from the peripheral tissues to the central nervous system. The patients suffered from psychological distress, sleep disturbance and poor life quality.

CONCLUSION

Occlusal disharmony-related oro-facial pain is a clinical problem that deserves attention, although there are no universally accepted clinical protocols. The existing literature provides some constructive suggestions, but further research is needed.

Neuroimmune interactions in painful TMD: Mechanisms and treatment implications

The underlying mechanisms and treatment of painful temporomandibular disorders (TMDs) are important but understudied topics in craniofacial research. As a group of musculoskeletal diseases, the onset of painful TMD is proved to be a result of disturbance of multiple systems. Recently, emerging evidence has revealed the involvement of neuroimmune interactions in painful TMD. Inflammatory factors play an important role in peripheral sensitization of temporomandibular joint (TMJ), and neurogenic inflammation in turn enhances TMJs dysfunction in TMD. Furthermore, centralized neuroimmune communications contribute to neuron excitability amplification, leading to pain sensitization, and is also responsible for chronic TMD pain and other CNS symptoms. Therapeutics targeting neuroimmune interactions may shed light on new approaches for treating TMD. In this review, we will discuss the role of neuroimmune interactions in the onset of painful TMD from the peripheral and centralized perspectives, and how understanding this mechanism could provide new treatment options. Insights into the neuroimmune interactions within TMJs and painful TMD would broaden the knowledge of mechanisms and treatments of this multifactorial disease.

Comorbid Conditions in Temporomandibular Disorders Myalgia and Myofascial Pain Compared to Fibromyalgia

The impact of comorbidities in fibromyalgia (FM) and temporomandibular disorders (TMD) have been well documented, but whether TMD sub-diagnoses myalgia (MYA) and myofascial pain with referral (MFP) differ regarding comorbidity is unclear. We aimed to elucidate this by studying the presence and associations of comorbidities in FM, MFP and MYA. An extended version of the Diagnostic Criteria for TMD axis II questionnaire was used to examine demographics, pain and comorbidities in 81 patients with FM, 80 with MYA, and 81 with MFP. Patients with MFP and FM reported a higher percentage of irritable bowel syndrome (IBS), depression, anxiety, somatic symptoms, perceived stress, and insomnia compared to MYA. Patients with FM had more IBS, depression, and somatic symptom disorder versus MFP. After adjusting for confounding variables, participants with anxiety, somatic symptoms disorder, pain catastrophizing, and perceived stress, as well as a greater number of comorbidities, were more likely to have MFP than MYA, whereas FM participants were more associated with IBS, somatic symptoms and insomnia compared to MFP. The number of comorbidities was significantly associated with widespread pain but not pain duration, body mass index or being on sick leave. In conclusion, patients with MFP were more similar to those with FM regarding comorbidity and should be differentiated from MYA in clinical settings and pain management.

Disturbed sleep may be a core risk factor for jaw functional limitation in patients with painful temporomandibular disorders

BACKGROUND

Pain related to temporomandibular disorder (TMD) usually affects jaw function. In patients with TMD, little is known about the biopsychosocial relevance to jaw functional limitations.

OBJECTIVE

This study explored the impact of biopsychosocial risk factors on jaw functional limitation in patients with painful TMD.

METHODS

A comprehensive set of patient-reported outcomes (PROs), consisting of pain severity (Brief Pain Inventory), psychological stress (Symptom Checklist-90-Revised), catastrophising thought (Pain Catastrophizing Scale), kinesiophobia (Tampa Scale for Kinesiophobia-TMD), sleep quality (Pittsburgh Sleep Quality Index) and jaw functional limitation (Jaw Functional Limitation Scale-20), were administered, and clinical examinations were performed in patients with TMD.

RESULTS

This study included the data obtained from 131 patients with painful TMD. In the logistic regression analysis, biomedical factors (age, sex, pain duration and TMD phenotype) were not associated with jaw functional limitation. Correlations were higher in the order of sleep quality (ρ = 0.946), pain severity (ρ = 0.582), pain catastrophising (ρ = 0.535), kinesiophobia (ρ = 0.486) and emotional distress (ρ = 0.268). Multiple regression analysis demonstrated three predictors, including pain severity (p = .001), kinesiophobia (p = .023) and sleep quality (p < .001) for jaw functional limitation. In the mediation analysis, the indirect effect of pain severity on the association between sleep and limitation was significant (p < .0001).

CONCLUSION

Jaw functional limitation is associated with biopsychosocial factors. In particular, sleep may be a core risk factor for functional limitation in patients with painful TMD.

Role of Photobiomodulation Therapy in Modulating Oxidative Stress in Temporomandibular Disorders. A Systematic Review and Meta-Analysis of Human Randomised Controlled Trials

This systematic review and meta-analysis (PROSPERO registration; ref CRD 42020198921) aimed to govern photobiomodulation therapy (PBMT) efficacy in temporomandibular disorder (TMD). PRISMA guidelines and Cochrane Collaboration recommendations were followed. Differences in pain reduction assessment by qualitative measurement with visual analogue scale pain (VAS), pressure threshold (PPT) and maximum mouth opening (MMO) were calculated with 95% confidence intervals and pooled in a random effects model with a subgroup analysis, evaluating the role of follow-up duration. Heterogeneity was analysed using Q and I² tests. Publication bias was assessed by visual examination of funnel plot symmetry. Qualitative analysis revealed 46% of the 44 included studies showed a high risk of bias. Meta-analysis on 32 out of 44 studies revealed statistically significant intergroup differences (SSID) for VAS (SMD = -0.55; 95% CI = -0.82 to -0.27; Z = 3.90 (p < 0.001)), PPT (SMD = -0.45; 95% CI = -0.89 to 0.00; Z = 1.97 (p = 0.05)) and MMO (SMD = -0.45; 95% CI = -0.89 to 0.00; Z = 1.97 (p = 0.05)), favouring PBMT compared to control treatment strategies. Sensitivity analysis revealed SSID (SMD = -0.53; 95% CI = -0.73 to -0.32; Z = 5.02 (p < 0.0001)) with low heterogeneity (Τ² = 0.02; χ² = 16.03 (p = 0.31); I² = 13%). Hence, this review, for first time, proposed suggested recommendations for PBMT protocols and methodology for future extensive TMD research.

Animal Models of Temporomandibular Disorder

Temporomandibular disorders (TMD) are a group of diseases in the oral and maxillofacial region that can manifest as acute or chronic persistent pain, affecting millions of people worldwide. Although hundreds of studies have explored mechanisms and treatments underlying TMD, multiple pathogenic factors and diverse clinical manifestations make it still poorly managed. Appropriate animal models are helpful to study the pathogenesis of TMD and explore effective treatment measures. At present, due to the high cost of obtaining large animals, rodents and rabbits are often used to prepare TMD animal models. Over the past decade, various animal models have been intensively developed to understand neurobiological and molecular mechanisms of TMD, and seek effective treatments. Although these models cannot carry out all clinical features, they are valuable in revealing the mechanisms of TMD and creating curative access. Currently, there are multitudinous animal models of TMD research. They can be constructed in different means and summarized into four ways according to the various causes and symptoms, including chemical induction (intra-articular injection of ovalbumin, collagenase, formalin, vascular endothelial growth factor, intramuscular injection of complete Freund’s adjuvant, etc.), mechanical stress stimulation (passive mouth opening, change of chewing load), surgical operation (partial disc resection, joint disc perforation) and psychological stress induction. Here, we summarize and discuss different approaches of animal models for determining neurophysiological and mechanical mechanisms of TMD and assess their advantages and limitations, respectively.

Effect of Manual Therapy and Therapeutic Exercise Applied to the Cervical Region on Pain and Pressure Pain Sensitivity in Patients with Temporomandibular Disorders: A Systematic Review and Meta-analysis

OBJECTIVE

To assess the effectiveness of cervical manual therapy (MT) on patients with temporomandibular disorders (TMDs) and to compare cervico-craniomandibular MT vs cervical MT.

DESIGN

Systematic review and meta-analysis (MA).

METHODS

A search in PubMed, EMBASE, PEDro, and Google Scholar was conducted with an end date of February 2019. Two independent reviewers performed the data analysis, assessing the relevance of the randomized clinical trials regarding the studies' objectives. The qualitative analysis was based on classifying the results into levels of evidence according to the Grading of Recommendations, Assessment, Development and Evaluation (GRADE).

RESULTS

Regarding cervical MT, MA included three studies and showed statistically significant differences in pain intensity reduction and an increase in masseter pressure pain thresholds (PPTs), with a large clinical effect. In addition, the results showed an increase in temporalis PPT, with a moderate clinical effect. MA included two studies on cervical MT vs cervico-craniomandibular MT interventions and showed statistically significant differences in pain intensity reduction and pain-free maximal mouth opening, with a large clinical effect.

CONCLUSIONS

Cervical MT treatment is more effective in decreasing pain intensity than placebo MT or minimal intervention, with moderate evidence. Cervico-craniomandibular interventions achieved greater short-term reductions in pain intensity and increased pain-free MMO over cervical intervention alone in TMD and headache, with low evidence.

Digital pain drawings are a useful and reliable tool for assessing patients with temporomandibular disorders

BACKGROUND

Temporomandibular disorders (TMD) are characterised by complex symptomatology and their assessment can be enhanced using pain drawings (PD).

OBJECTIVES

To evaluate the location and extent of pain in people TMD using digital PD, and to explore their association with clinical features. Reliability of pain extent and pain location using PD was also assessed.

METHODS

Forty volunteers with TMD completed two consecutive digital PDs. Clinical features were captured from self-reported questionnaire. Additionally, secondary hyperalgesia was measured using the pressure pain threshold (PPT). The correlation between pain extent and clinical features was investigated using Spearman rank correlation coefficients. Reliability of pain extent was evaluated using intraclass correlation coefficient (ICC) and Bland-Altman plots. The Jaccard index was computed to assess the reliability of pain location.

RESULTS

Analysis of the PDs indicated that people with TMD commonly experience pain in other body regions including the neck, the shoulder and the low back. Except for PPT and pain catastrophising, all other clinical features were significantly correlated with pain extent. The ICCs of pain extent for all body charts were very high (ICCs 95% CI from 0.73 to 0.96), and Bland-Altman plots showed mean biases close to zero with narrow limits of agreement. The reliability of pain location was also supported by Jaccard index mean scores above 0.68.

CONCLUSIONS

People with TMD showed widespread pain, and pain extent was associated with pain intensity, neck and headache-related disability, depression, anxiety, hyperventilation and central sensitivity. The reliability of measuring pain extent and pain location was confirmed.

Impact of Fibromyalgia Phenotype in Temporomandibular Disorders

BACKGROUND

Mounting evidence suggests that central nervous system amplification, similar to that seen in fibromyalgia (FM), contributes to the pain experience in a subset of patients with temporomandibular disorders (TMD).

METHODS

In this prospective observational study, patients with TMD completed the 2011 FM survey questionnaire, a surrogate measure of "centralized" pain. The influence of centralized pain on TMD pain, dysfunction, and disability was assessed dichotomously by determining the incidence of FM-positive cases in the sample and by using FM survey scores as a continuous measure of "fibromyalgia-ness" ("FM-ness").

RESULTS

The patients meeting criteria for FM diagnosis (17 of 89) had significantly more disease burden on numerous measures. FM-ness was positively associated with pain at rest, negative mood, tenderness to palpation, perceived jaw functional limitation, and pain-related disability, and it was negatively associated with comfortable pain-free jaw opening. The impact of FM-ness on perceived jaw functional limitation and disability was mediated by levels of spontaneous, ongoing pain in the orofacial region. Importantly, this pattern of findings was still present even in those not meeting the criteria for FM diagnosis.

CONCLUSION

Together, these results imply that higher FM-ness increases TMD patient burden by amplifying spontaneous pain and further hampering painless jaw function, even in patients who do not meet criteria for FM diagnosis. These results are highly relevant for the clinical management of TMD, as they imply that targeting the central nervous system in the treatment of patients with TMD with evidence of pain centralization may help ameliorate both pain and jaw dysfunction.

Aberrant Brain Signal Variability and COMT Genotype in Chronic TMD Patients

The analysis of brain signal variability is a promising approach to understand pathological brain function related to chronic pain. This study investigates whether blood-oxygen-level-dependent signal variability (BOLD_SV) in specific frequency bands is altered in temporomandibular disorder (TMD) and correlated to its clinical features. Twelve patients with chronic myofascial TMD and 24 healthy controls (HCs) underwent resting-state functional magnetic resonance imaging. The BOLD_SV was measured as the standard deviation of the BOLD time series at each voxel and compared between groups. We also examined the potential relationship between the BOLD_SV and the catechol-O-methyltransferase (COMT) Val¹⁵⁸Met polymorphism. We assessed sensory-discriminative pain in the craniofacial region, pain sensitivity to sustained masseteric pain challenge, and TMD pain frequency for clinical correlation. Patients displayed reduced BOLD_SV in the dorsolateral prefrontal cortex (dlPFC) as compared with HC in all frequency bands. In the slow-3 band, patients also showed reduced BOLD_SV in the medial dorsal thalamus, primary motor cortex (M1), and primary somatosensory cortex (S1) and heightened BOLD_SV in the temporal pole. Notably, we found a significant correlation between lower BOLD_SV (slow-3) in the orofacial M1/S1 regions and higher clinical pain (intensity/area) and higher sensitivity of the masseter muscle pain. Moreover, lower BOLD_SV (slow-3) in the dlPFC and ventrolateral PFC was associated with a higher TMD pain frequency. Participants who had the COMT ¹⁵⁸Met substitution exhibited lower BOLD_SV in the dlPFC and higher BOLD_SV in the temporal pole as compared with participants without the COMT ¹⁵⁸Met substitution. An increasing number of Met alleles was associated with lower dlPFC and greater temporal pole BOLD_SV in both HC and TMD groups. Together, we demonstrated that chronic TMD patients exhibit aberrant BOLD_SV in the top-down pain modulatory and sensorimotor circuits associated with their pain frequency and severity. COMT Val¹⁵⁸Met polymorphism might affect clinical symptoms in association with regional brain signal variability, specifically involved in cognitive and emotional regulation of pain.