Somatosensory assessment and conditioned pain modulation in temporomandibular disorders pain patients

Temporomandibular Joint Disorder: An integrated study of the pathophysiology, neural mechanisms, and therapeutic strategies

OBJECTIVE

The study aims to investigate Temporomandibular Joint Disorder (TMJD) through a interdisciplinary lens, integrating insights from neuroscience, dentistry, and psychology to dissect its complex pathophysiology and neural mechanisms. It focuses on exploring the neurobiological underpinnings of TMJD, emphasizing the role of pain perception, modulation, and the impact of neurophysiological changes on the disorder.

DESIGN

This is a comprehensive narrative review of the literature.

RESULTS

Research findings pinpoint altered pain perception and modulation processes as central neural mechanisms contributing to TMJD, highlighting the importance of personalized treatment approaches due to the disorder's complexity and patient variability. The study recognizes advances in neuroscience offering new treatment avenues, such as neuromodulation and biofeedback, which provide non-invasive and personalized options. However, it also addresses the challenges in TMJD research, such as the multifaceted nature of the disorder and the need for more comprehensive, interdisciplinary strategies in research and clinical practice.

CONCLUSIONS

TMJD is a multifaceted disorder requiring an interdisciplinary approach for effective management. The study stresses the crucial role of neuroscience in understanding and treating TMJD, facilitating the development of innovative treatment strategies. It emphasizes the need for further research, advocating an integrated approach that combines neuroscience, dentistry, and psychology to address TMJD's complexities comprehensively and improve patient care, thereby enhancing the quality of life for affected individuals.

Influence of psychometric and sleep quality features on painful mechanical sensitivity and pain modulation in patients with temporomandibular disorders

Investigating the collective impact of psychometric properties and sleep quality on pain sensitivity in temporomandibular disorder (TMD) patients could improve clinical management strategies.

OBJECTIVE

Assessing whether combined psychometric properties and sleep quality impact painful mechanical sensitivity and pain modulation in TMD patients.

MATERIALS AND METHODS

A cross-sectional study using secondary data analysis of 77 TMD patients and 101 controls. All participants completed questionnaires characterizing their psychometric profile (anxiety, depression, stress and catastrophizing) and sleep quality, alongside psychophysical tests for painful mechanical sensory (mechanical pain threshold (MPT), pressure pain threshold (PPT), and wind-up ratio (WUR)) and conditioned pain modulation (CPM). Participants were grouped into "High distress" or "Low distress" categories based on psychometric properties and sleep quality using hierarchical cluster and k-means analyses. Multiple linear regression evaluated the influence of TMD, age, and the distress cluster on MPT, WUR, PPT, and CPM in masseter and thenar muscles. Differences were statistically significant when p < 0.05.

RESULTS

The presence of TMD was the strongest predictor of mechanical painful sensitivity in the trigeminal region (MPT[F(3,174) = 51.902;p < .001;R2 = .463]; TMD presence (β = -.682) / PPT[F(3,174) = 15.573;p < .001;R2 = .198] TMD presence (β = -.452), and extra-trigeminal (MPT[F(3,174) = 35.897;p < .001;R2 = .382] TMD (β = -.647) / CPM [F(3,174) = 4.106;p < .05;R2 = .050] TMD presence (β = .197). Furthermore, neither the high distress group nor the low distress group were able to significantly influence the variation of the values of any of the psychophysical variables evaluated (p > .05).

CONCLUSIONS

There is not a significant influence of impairment clusters based on psychological variables and sleep quality on painful mechanical sensitivity and pain modulation, regardless of the presence of TMD.

CLINICAL RELEVANCE

This outcome suggests that psychosocial factors and sleep quality may not play a decisive role in the sensory-discriminative aspect of pain, particularly concerning painful TMD.

Visual psychosocial profiling of Chinese temporomandibular disorder pain patients and correlations with somatosensory function

BACKGROUND

Psychosocial function of Chinese temporomandibular disorders (TMD) pain patients and the correlation with somatosensory function has not been sufficiently studied.

OBJECTIVE

The study aims at assessing the psychosocial function of Chinese TMD pain patients by visualisation method and evaluating the correlations with somatosensory function quantitatively.

METHODS

The Symptom Checklist 90 (SCL-90) questionnaire and standardised quantitative sensory testing (QST) were administered to 70 Chinese TMD pain patients and age- and gender-matched healthy controls (HCs). Of these, 40 TMD arthralgia patients received QST before and after medication. Psychosocial and somatosensory parameters were transformed into standardised scores. Differences within groups were assessed through t tests. Correlations between psychosocial and somatosensory profiles were explored through correlation analyses with Bonferroni correction for multiple comparisons.

RESULTS

100% of the Chinese TMD pain patients exhibited psychosocial distress in contrast to HCs. Anger and hostility showed negative correlation with the thermal nonnociceptive parameter (thermal sensory limen, p =.002) and nociceptive parameters (cold pain threshold and pain pressure threshold, p<.001). Correlation analysis indicated that cold detection threshold was negatively correlated with somatization and mechanical pain sensitivity had a negative correlation with anger and hostility through medical treatment (p <.001).

CONCLUSIONS

Visual psychosocial profiles provided an easy overview of psychosocial function in Chinese TMD pain patients. Anger and hostility was associated with increased thermal nonnociceptive and nociceptive sensitivity to stimuli. Psychosocial distress might be negatively associated with TMD treatment response which indicated a possible need for psychological intervention during treatment.

Could painful temporomandibular disorders be nociplastic in nature? A critical review and new proposal

Classification of temporomandibular disorders (TMD) and, indeed, all types of orofacial pains has significantly progressed in the last decade based on international consensus work and operationalized clustering of signs and symptoms. A challenging gap nevertheless continues to exist in terms of understanding the underlying pain mechanisms and link to management. Recently, a novel mechanistic descriptor 'nociplastic pain' was introduced, and diagnostic algorithms and characteristic features were proposed. This narrative and critical review aim to discuss to what extent could painful TMD conditions fit into this category. Moreover, a number of less common types of orofacial pain could possibly also reflect nociplastic pain mechanisms. A model to differentiate TMD pain mechanisms is proposed, and the implications for management are discussed. The purpose of this review is to stimulate original and novel research into mechanisms of orofacial pain and hopefully thereby improve management of the individual patient.

Quantification of stimulus-evoked tactile allodynia in free moving mice by the chainmail sensitivity test

Chronic pain occurs at epidemic levels throughout the population. Hypersensitivity to touch, is a cardinal symptom of chronic pain. Despite dedicated research for over a century, quantifying this hypersensitivity has remained impossible at scale. To address these issues, we developed the Chainmail Sensitivity Test (CST). Our results show that control mice spend significantly more time on the chainmail portion of the device than mice subject to neuropathy. Treatment with gabapentin abolishes this difference. CST-derived data correlate well with von Frey measurements and quantify hypersensitivity due to inflammation. Our study demonstrates the potential of the CST as a standardized tool for assessing mechanical hypersensitivity in mice with minimal operator input.

Clinical features of chronic primary pain in individuals presenting painful temporomandibular disorder and comorbidities

BACKGROUND

The diagnosis of chronic primary pain (CPP), according to the recently released International Classification of Disease (ICD-11) criteria, refers to conditions with complex aetiologies. CPP is characterized by specific clinical features such as generalized sensory hypersensitivity and widespread pain, and is associated with functional disability and emotional distress.

OBJECTIVE

This study investigated clinical features of CPP in individuals with painful temporomandibular disorders (TMD) and comorbidities (fibromyalgia, migraine and/or tension-type headache).

METHODS

This cross-sectional study was conducted with a sample of 129 individuals. Painful TMD, fibromyalgia and primary headaches were evaluated based on well-established international criteria. Generalized sensory hypersensitivity was assessed using psychophysical tests. Symptoms of anxiety and depression were assessed by the Generalized Anxiety Disorder-7 and Patient Health Questionnaire-9. The Central Sensitization Inventory was applied to assess central sensitization-related symptoms and the Pittsburg Sleep Quality Index to evaluate the quality of sleep. The presence of widespread pain was assessed using a body map. The sample was stratified into three groups: control (n = 25), TMD-painful TMD only (n = 35) and TMD + Cm-painful TMD and comorbidities (n = 69). Statistical analysis was performed using one-way ANOVA, chi-squared test and ANCOVA, considering gender as a covariate (α = .05).

RESULTS

Compared to controls, individuals presenting painful TMD and comorbidities showed lower pressure pain thresholds in all evaluated areas (p ≤ .012) and a higher number of painful areas in the body (p = .001). They presented more symptoms of anxiety (p = .040) and depression (p = .018), and a higher score in the Central Sensitization Inventory (p ≤ .006) than the other groups.

CONCLUSION

Individuals with painful TMD and comorbidities presented more clinical features of CPP compared to those affected by TMD only.

Insomnia is associated with symptoms of central sensitization in patients with painful temporomandibular disorders

BACKGROUND

Central sensitization (CS) and temporomandibular disorder (TMD) are both associated with insomnia. Therefore, the authors aimed to investigate whether insomnia was associated with more symptoms of CS in patients with TMD.

METHODS

In 82 volunteers with TMD, insomnia was clinically assessed, allowing sample stratification according to its presence. The Central Sensitization Inventory questionnaire was self-applied to assess the clinical symptoms of CS.

RESULTS

Participants with insomnia had significantly higher mean (SD) scores of CS according to the Central Sensitization Inventory than participants without insomnia (43.10 [12.57] vs 26.59 [13.66]; P = < .001).

CONCLUSIONS

Insomnia was associated with higher scores of CS symptoms in patients with TMD.

PRACTICAL IMPLICATIONS

Insomnia influences TMD as well as its relationship with CS, and, therefore, it is critical to the clinical management of TMD.

Referred sensations in the orofacial region are associated with a decreased descending pain inhibition and modulated by remote noxious stimuli and local anesthesia

ABSTRACT

Referred sensation (RS) as a specific clinical phenomenon has been known for a long time, although the underlying mechanisms remain unclear. The aims of this study were to assess if (1) healthy individuals who experienced RS had a less active endogenous pain system when compared with those who did not; (2) activation of descending pain inhibition mechanisms can modulate RS parameters; and finally, (3) a transient decrease in peripheral afferent input because of a local anesthetic (LA) block in the masseter muscle can modulate RS parameters. To assess these, 50 healthy participants were assessed in 3 different sessions. In the first session, conditioned pain modulation (CPM) as well as mechanical sensitivity and RS at the masseter muscle were assessed. In the same session, participants who experienced RS had their mechanical sensitivity and RS assessed again while undergoing a CPM protocol. In the second and third sessions, participants had their mechanical sensitivity and RS assessed before and after receiving an injection of 2 mL of LA and isotonic saline into the masseter muscle. The main findings of this study were (1) participants who experienced RS during standardized palpation exhibited increased mechanical sensitivity ( P < 0.05, Tukey post hoc test) and decreased CPM ( P < 0.05, Tukey post hoc test) when compared with those who did not; RS incidence ( P < 0.05, Cochran Q test), frequency ( P < 0.05; Friedman test), intensity ( P < 0.05, Tukey post hoc test), and area ( P < 0.05, Tukey post hoc test) were all significantly reduced when assessed (2) during a painful conditioning stimulus and (3) after LA block. These novel findings highlight that RS in the orofacial region are strongly modified by both peripheral and central nervous system factors.

Are central sensitization symptoms and psychosocial alterations interfering in the association between painful TMD, migraine, and headache attributed to TMD?

OBJECTIVE

To determine if somatosensory function and symptoms related to central sensitization (CS) differed in individuals with painful temporomandibular disorders (TMD) according to the presence of migraine (MIG) or MIG + headache attributed to TMD (HAT).

MATERIALS AND METHODS

This study evaluated 92 adults (20-65 years), presenting painful TMD. Standard diagnostic criteria were applied to classification of painful TMD, MIG, and HAT. CS was assessed through the central sensitization inventory (CSI), wind-up ratio (WUR), pressure pain thresholds (PPT), and the conditioned pain modulation test (CPM). Psychosocial factors were evaluated by validated instruments.

RESULTS

There was a significant difference regarding gender, with more women in the group TMD + MIG + HAT (p = 0.028). TMD + MIG and TMD + MIG + HAT had significantly lower PPTs than the TMD group. No group differences were found for the WUR, CPM, or CSI. TMD + MIG + HAT had higher chronic pain intensity (p = 0.001), disability points (p = 0.045), graded chronic pain scale (p = 0.007), and higher somatization (NSPS) scores (p = 0.012), compared to the other groups.

CONCLUSION

Mechanical hyperalgesia was more pronounced in the group with the highest pain and somatization scores, while CPM and WUR did not differ between groups. Altered somatosensory function and CS may partially underlie the pathophysiology of overlapping TMD pain conditions, pointing towards additive effects of comorbid head pains.

CLINICAL RELEVANCE

Our results demonstrate the importance of considering the association of primary and secondary headaches during TMD assessment and its implications for maintaining the signs and symptoms of CS. This can influence the conduct of treatment, which must be multidisciplinary, and must include management of mechanisms related to CS.

Enhanced pain facilitation rather than impaired pain inhibition in burning mouth syndrome female patients

Background

Deficient endogenous pain modulation has been implicated in the development and exacerbation of chronic orofacial pain. To date, relatively little is known regarding the function of the endogenous pain modulation in patients with burning mouth syndrome (BMS). This case–control study investigated endogenous pain modulation in women with BMS.

Methods

Conditioned pain modulation (CPM) was assessed upon temporal summation (TSP) of thermal pain. Forty female subjects, 20 BMS patients and 20 age-matched control subjects, were included in a 2 session-protocol. Mechanical and thermal pain thresholds were measured on the forearm and hand. TSP was obtained using repetitive laser-evoked thermal stimuli applied on the non-dominant hand, at an intensity yielding to moderate pain. During TSP, CPM was produced by immersing the contralateral foot in a water bath at painful cold (8 °C) temperature. In control conditions, the foot was immersed in a water bath at not painful (30 °C) temperature.

Results

BMS was not associated with any impairment in thermal as well as mechanical extracephalic pain thresholds. TSP and CPM efficacy were similar in BMS patients and control subjects. However, BMS patients exhibited enhanced extracephalic heat hyperalgesia.

Conclusion

This study reveals that there is no impairment of endogenous pain inhibition mechanisms in BMS patients, but rather an increase in pain facilitation.

Temporal Summation and Aftersensations of Second Pain in Women with Myofascial Temporomandibular Disorder Differ by Presence of Temporomandibular Joint Pain

Purpose

Mechanisms underlying myofascial temporomandibular disorder (mTMD) are poorly understood. One theory is dysfunction in the central mediation of pain, specifically in enhanced facilitatory pain modulation. Because mechanisms leading to central sensitization may differ for joint and muscle pain, this study of mTMD addressed phenotypic heterogeneity by temporomandibular (TM) joint pain in the examination of quantitative sensory testing (QST).

Patients and Methods

The stimulus dependent increase in second pain (temporal summation (TS)) and associated aftersensations (AS) were examined across groups of women with mTMD with TM joint pain and without, and a demographically matched control group.

Results

TS was slightly more evident in mTMD without joint pain vs with (p = 0.035), but AS were most robustly persistent in the group with joint pain vs without (p < 0.002).

Conclusion

While both subgroups demonstrated evidence of central sensitization relative to controls on one of two measures, differences in QST results, if replicated, may point to possible differences in the mechanisms that yield central sensitization. Alternatively, it may represent methodological artifacts that need to be addressed. Therefore, greater consideration should be given to symptom-based phenotypes in studies examining TS and AS.

Evidence for alterations to dynamic quantitative sensory tests in patients with chronic temporomandibular myalgia: a systematic review of observational studies with meta-analysis

BACKGROUND

Conflicting results exist between somatosensory profiles of patients with temporomandibular myalgia (TMDm). The objective of this review was to examine whether adults with TMDm show altered responses to dynamic quantitative sensory tests compared with healthy controls.

METHODS

We searched five electronic databases for studies, excluding those without suitable controls or where TMDm was associated with confounding non-musculoskeletal disorders. Risk of bias was assessed with the SIGN case-control study checklist. Findings were structured around dynamic quantitative sensory tests and their localization. Where possible, we performed meta-analysis with a random inverse variance model to compare patients with TMDm and healthy controls. Statistical heterogeneity was estimated with Chi² test and inconsistency index, I².

RESULTS

We extracted data from 23 studies comprising 1284 adults with chronic TMDm and 2791 healthy controls. Risk of bias was assessed as high for 20 studies. Mechanical temporal summation, the most studied phenomenon (14 studies), is increased in the upper limb of patients with TMDm (SMD = .43; 95% CI: .11 to .75; p = .0001) but not in the jaw area (p = .09) or in the cervical area (p = .29). Very little evidence for altered thermal temporal summation (five studies), conditioned pain modulation (seven studies), exercise-induced hypoalgesia (two studies), placebo analgesia (two studies), stress-induced hypoalgesia (one study) and offset analgesia (one study) was found.

DISCUSSION

A major limitation of this review was the risk of bias of included studies. Future studies would benefit from following methodological guidelines and consideration of confounding factors.

A comprehensive review on biomarkers associated with painful temporomandibular disorders

Pain of the orofacial region is the primary complaint for which patients seek treatment. Of all the orofacial pain conditions, one condition that possess a significant global health problem is temporomandibular disorder (TMD). Patients with TMD typically frequently complaints of pain as a symptom. TMD can occur due to complex interplay between peripheral and central sensitization, endogenous modulatory pathways, and cortical processing. For diagnosis of TMD pain a descriptive history, clinical assessment, and imaging is needed. However, due to the complex nature of pain an additional step is needed to render a definitive TMD diagnosis. In this review we explicate the role of different biomarkers involved in painful TMD. In painful TMD conditions, the role of biomarkers is still elusive. We believe that the identification of biomarkers associated with painful TMD may stimulate researchers and clinician to understand the mechanism underlying the pathogenesis of TMD and help them in developing newer methods for the diagnosis and management of TMD. Therefore, to understand the potential relationship of biomarkers, and painful TMD we categorize the biomarkers as molecular biomarkers, neuroimaging biomarkers and sensory biomarkers. In addition, we will briefly discuss pain genetics and the role of potential microRNA (miRNA) involved in TMD pain.

Psychophysical evaluation of somatosensory function in oro-facial pain: achievements and challenges

AIM

This critical review describes key methodological aspects for a successful oro-facial psychophysical evaluation of the somatosensory system and highlights the diagnostic value of somatosensory assessment and management perspectives based on somatosensory profiling.

METHODS

This topical review was based on a non-systematic search for studies about somatosensory evaluation in oro-facial pain in PubMed and Embase.

RESULTS

The recent progress regarding the psychophysical evaluation of somatosensory function was largely possible due to the development and application of valid, reliable and standardised psychophysical methods. Qualitative sensory testing may be useful as a screening tool to rule out relevant somatosensory abnormalities. Nevertheless, the patient should preferably be referred to a more comprehensive assessment with the quantitative sensory testing battery if confirmation of somatosensory abnormalities is necessary. Moreover, the identification of relevant somatosensory alterations in chronic pain disorders that do not fulfil the current criteria to be regarded as neuropathic has also increased the usefulness of somatosensory evaluation as a feasible method to better characterise the patients and perhaps elucidate some underpinnings of the so-called 'nociplastic' pain disorders. Finally, an additional benefit of oro-facial pain treatment based on somatosensory profiling still needs to be demonstrated and convincing evidence of somatosensory findings as predictors of treatment efficacy in chronic oro-facial pain awaits further studies.

CONCLUSION

Psychophysical evaluation of somatosensory function in oro-facial pain is still in its infancy but with a clear potential to continue to improve the assessment, diagnosis and management of oro-facial pain patients.

Ultrasound is Effective to Treat Temporomandibular Joint Disorder

Background

Temporomandibular joint disorder (TMD) affects millions of people. It is unclear if low intensity ultrasound (US) is effective to treat TMD.

Methods

A total of 160 patients with TMD were enrolled in this study. The subjects were randomized into two groups to receive US therapy or no therapy. Patients in the US group were given US therapy once a day for 5 days per week for 2 consecutive weeks. Before and 4 weeks and 6 months after the treatments, the patients were assessed for pain using visual analog scale (VAS) and the maximum pain-free inter-incisal distance (IID). In addition, mandibular movement (MM), jaw noise (JN), disability index (DI) and craniomandibular index (CMI) were also assessed.

Results

Compared with the patients before the therapy, VAS, IID, MM, JN, DI and CMI in the US group were significantly improved 4 weeks and 6 months after therapy. However, 6 months after the therapy, US group had a recurrence rate of 2.63%.

Conclusion

US therapy can significantly reduce the pain, and improve the functionality of the temporomandibular joint and mouth opening limit for TMD patients, and is therefore recommended for TMD patients.

Phenotyping peripheral neuropathic pain in male and female adolescents: pain descriptors, somatosensory profiles, conditioned pain modulation, and child-parent reported disability

ABSTRACT

Neuropathic pain (NeuP) can be difficult to diagnose and manage in children. Data regarding prevalence and sex-dependent differences are limited, and more detailed phenotyping is needed. This observational cohort study recruited adolescents (10-17 years) with NeuP or complex regional pain syndrome (CRPS). After pain history and NeuP questionnaires, quantitative sensory testing was performed. Individual z-score plots were calculated with body-region control measures and matched to mechanism-related sensory profiles (sensory loss, thermal hyperalgesia, and mechanical hyperalgesia). Conditioned pain modulation was assessed with pressure pain threshold and a contralateral cold conditioning stimulus, and meaningful conditioned pain modulation defined as twice the standard error of measurement. Patients and parents completed validated questionnaires for child quality of life (QoL), pain catastrophizing, and self-reported anxiety/depression. Males (n = 23) and females (n = 43) with NeuP (n = 52) or CRPS (n = 14) reported moderate-severe pain with neuropathic sensory descriptors. Mixed patterns of sensory gain/loss at pain sites were not sex-dependent. Thermal hyperalgesia was common in both NeuP and CRPS, whereas sensory loss occurred only with NeuP and in a smaller proportion than adult cohorts. Conditioned pain modulation was inhibitory in 54%, facilitatory in 14%, and nonresponders had variable cold conditioning sensitivity. Males and females reported marked impairment of QoL, increased emotional distress, and pain catastrophising. Child-parent QoL scores correlated, but catastrophizing scores were discordant when parents or adolescents reported higher anxiety/depression. NeuP in adolescents is associated with significant pain, physical impairment, and psychosocial impairment. Quantifying alterations in somatosensory profiles, descending modulation, child and parent psychological function will inform individualized therapy and stratification for future clinical trials.

Assessment of Pain Modulatory and Somatosensory Profiles in Chronic Tension-Type Headache Patients

Objective

The aim of this study was to thoroughly phenotype a group of chronic tension-type headache (CTTH) patients.

Methods

Fifteen CTTH patients diagnosed according to the International Classification of Headache Disorders–3 and 15 healthy controls were included in this study. Furthermore, 70 healthy controls were included to establish normative values. Quantitative sensory testing (QST), including temporal summation of pain (TSP), conditioned pain modulation (CPM), and psychological and sleep variables, was assessed in a single session. TSP and CPM were then combined to build pain modulation profiles (PMP) for each individual.

Results

No difference was found between groups for PMP, TSP, and CPM. However, 10 CTTH patients showed a pronociceptive PMP, with 8 related to a deficient CPM and 2 to both a deficient CPM and increased TSP. Increased cold detection thresholds were the most common sensory disturbance found in CTTH patients. Significant differences were seen between groups for pain catastrophizing, depression, and sleep quality although not all patient’s scores were above the clinically meaningful cutoffs.

Conclusions

In summary, CTTH patients presented with different PMP. These PMP may be related to increased TSP, deficient CPM, alterations in thermal detection that may be related to autonomic dysregulation, or a combination of all three. Overall, this suggests that due to their heterogeneous pathophysiology, CTTH patients should be managed according to their underlying pathophysiology and not with a one-size-fits-all approach.

Lack of correlation between central sensitization inventory and psychophysical measures of central sensitization in individuals with painful temporomandibular disorder

OBJECTIVE

To assess the correlation between the Central Sensitization Inventory (CSI) scores and the results of psychophysical tests and psychosocial questionnaires according to the presence of painful temporomandibular disorder (TMD).

DESIGN

It was a cross-sectional study involving 146 participants, aged 20-65 years. Painful TMD was classified using the Research Diagnostic Criteria for Temporomandibular Disorders. CSI was applied to assess "central sensitization-related symptoms", as has been suggested. Wind-up ratio, pressure pain threshold and conditioned pain modulation were used as psychophysical tests to evaluate signs and symptoms of central sensitization. Psychosocial factors were assessed by the presence of non-specific physical symptoms, depressive and anxiety symptoms. The sample was divided into two groups: Control (n = 31); Painful TMD (n = 115). Descriptive statistics characterized the sample. Correlation analysis were performed using Pearson's and Spearman's correlation coefficients (α = 5%).

RESULTS

Of the total sample, 78.8 % presented painful TMD, and the mean (standard deviation) age was 37.4 (±11.5) years. Anxiety symptoms (p = 0.028) and non-specific physical symptoms (p < 0.001) were more frequent in the painful TMD group than in controls. Painful TMD patients presented higher scores of the CSI (p < 0.001) and lower pressure pain thresholds (p ≤ 0.020) compared to controls. CSI scores were significantly correlated with psychosocial measures (p < 0.001) but not with psychophysical tests (p ≥ 0.089).

CONCLUSION

The CSI scores did not correlate with psychophysical measures of central sensitization but were positively correlated with the results of psychosocial questionnaires.

Increased somatosensory amplification is associated with decreased pressure pain thresholds at both trigeminal and extra-trigeminal locations in healthy individuals

BACKGROUND

The diagnosis of temporomandibular disorders (TMD) is based on patient history and physical examination, and may require medical imaging. Masticatory muscle palpation is essential to make a diagnosis of TMD. However, the response of masticatory muscles to mechanical pressure stimuli depends on many physical and psychological factors.

OBJECTIVE

This study aimed at determining the impact of somatosensory amplification (SSA)-an estimate of somatic awareness and bodily hypervigilance-on pressure pain thresholds (PPTs) measured at both trigeminal and extra-trigeminal locations in healthy individuals.

METHODS

PPTs were measured at the right anterior temporalis and superficial masseter, and the thenar eminence of the right hand in one hundred healhty individuals (69F, 31M), divided in three groups based on their SSA scores: low (N = 32), intermediate (N = 34) and high (N = 34). General linear models were used to test between-group differences in PPTs including sex as a covariate. The level of significance was set at P < .05.

RESULTS

Individuals with high SSA had lower PPTs at the anterior temporalis than individuals with low (P = .006) and intermediate (P = .001) SSA. No significant between-group differences were found in PPTs measured at the masseter (P = .372). PPTs measured at the thenar eminence were significantly lower in the high than the low SSA group (P = .009). Females had lower PPTs at the masseter than males (P = .021) but not at other muscle locations (all P > .05).

CONCLUSION

Increased somatosensory amplification is associated with decreased pressure pain thresholds at both trigeminal and extra-trigeminal locations in healthy individuals. SSA could be a potential confounder while diagnosing TMD and evaluating treatment outcomes.

Assessment of somatosensory changes in Chinese temporomandibular disorders arthralgia patients by quantitative sensory testing

BACKGROUND

Somatosensory changes in Chinese temporomandibular disorders (TMD) arthralgia patients have not been fully studied by the latest technologies.

OBJECTIVE

This study aims at assessing somatosensory changes in Chinese TMD arthralgia patients quantitatively.

METHODS

Standardised quantitative sensory testing (QST) was performed on the pain sites and contralateral sites of 40 patients diagnosed with TMD arthralgia according to the Diagnostic Criteria for Temporomandibular Disorders (DC/TMD) before and after medication; similar measures were taken in 40 age- and gender-matched healthy controls. Differences within and between groups were assessed through Z-scores, two-way ANOVA and loss/gain coding system.

RESULTS

The pain sites of patients presented increased sensitivity to thermal stimuli and mechanical pain stimuli together with decreased sensitivity to mechanical tactile stimuli before medication (P < .001). Before treatment, 100% of patients had somatosensory abnormalities at the pain sites; the most frequent abnormalities were somatosensory gain to cold nociceptive, pinprick and pressure stimuli, and the most frequent loss/gain score was L0G3 (no somatosensory loss with a gain of thermal and mechanical somatosensory function; 70.0%). After treatment, although the clinical symptoms and signs of 40 patients disappeared, 80.0% of the patients' pain sites still showed multiple phenotype abnormalities. The most frequent loss/gain score was L0G2 (no somatosensory loss with a gain of mechanical somatosensory function; 35.0%).

CONCLUSIONS

Multiple phenotypes of facial somatosensory abnormalities were detected in Chinese TMD arthralgia patients before and after treatment, despite the disappearance of clinical signs and symptoms. Individual variations indicate a possible need for subgroup classification, individualised management and mechanism-based treatment.

Treatment of Temporomandibular Joint Disorders by Ultrashort Wave and Extracorporeal Shock Wave: A Comparative Study

Background

This study was carried out to compare the therapeutic efficacy of extracorporeal shock wave (ESW) and ultrashort wave (UW) for temporomandibular joint disorder (TMD).

Material/Methods

A total of 80 patients with myofascial pain and TMD were enrolled in this study. The subjects were randomized to receive ESW or UW treatments. Patients in the ESW group received 1 ESW treatment for 4 weeks and patients in the US group were given US treatment once a day for 5 days per week for 4 weeks. The pain was measured using visual analog scale (VAS) and mouth opening was determined as pain-free maximum mouth opening (MMO) before and 4 weeks after the treatments. Other parameters assessed included functional indexes of temporomandibular joint such as mandibular movement (MM), joint noise (JN), joint press (JP), and disability index (DI).

Results

After therapy, VAS, MMO, MM, JN, JP, and DI in ESW group, and VAS in UW group were significantly improved (P<0.05) as compared to before therapy. VAS, MMO, and the functional indexes of temporomandibular joint in the ESW group were significantly better than those in the UW group (1.79 vs. 2.00, 3.23 vs. 2.03, 1.79 vs. 2.41, 1.45 vs. 2.27, 1.55 vs. 2.59, and 3.30 vs. 4.79, respectively. P<0.05).

Conclusions

ESW significantly reduces pain and improves the functional indexes of temporomandibular joint and mouth opening limit for TMD patients as compared with UW therapy.

Quantitative sensory testing of periauricular skin in healthy adults

The aim of this study was to investigate the test-retest reliability of quantitative sensory testing (QST) and mechanical sensitivity mapping of the periauricular skin. Twenty volunteers (10 men, 10 women) participated in two sessions at intervals of one week. Cold and warm detection threshold (CDT&WDT), cold and heat pain threshold (CPT&HPT), mechanical detection and pain threshold (MDT&MPT), pressure pain threshold (PPT) and two-point discrimination (2PD) were measured at five sites: bilateral subauricular and postauricular sites (LA, RA, LB, RB) and the dorsum of left hand (control). Pressure stimulation was applied at each of the four periauricular test sites. The test-retest reliability of the QST data implied fair to excellent agreement as evaluated by the intra-class correlation coefficients (ICC; all >0.4) for different days. There was no difference between each side in the QST parameters and mechanical sensitivity mapping (P ≥ 0.057). Significant differences between subauricular and postauricular sites were shown for WDT and PPT (P ≤ 0.028). NRS scores of mechanical sensitivity mapping showed significant effects of gender, site and point (P ≤ 0.040). QST and mechanical sensitivity mapping can be considered to be a reliable technique to assess somatosensory function of the periauricular skin.

Biomarkers in Temporomandibular Disorder and Trigeminal Neuralgia: A Conceptual Framework for Understanding Chronic Pain

In this review, we will explore the use of biomarkers in chronic pain, using the examples of two prototypical facial pain conditions: trigeminal neuralgia and temporomandibular disorder. We will discuss the main categories of biomarkers and identify various genetic/genomic, molecular, neuroradiological, and psychophysical biomarkers in both facial pain conditions, using them to compare and contrast features of neuropathic, nonneuropathic, and mixed pain. By using two distinct model facial pain conditions to explore pain biomarkers, we aim to familiarize readers with different types of biomarkers currently being studied in chronic pain and explore how these biomarkers may be used to develop new precision medicine approaches to pain diagnosis, prognosis, and management.

Somatosensory changes in Chinese patients after coronectomy vs. total extraction of mandibular third molar: a prospective study

Objectives

This study aimed to quantitatively compare the somatosensory function changes of inferior alveolar nerve (IAN) after mandibular third molar extraction with a surgery protocol of coronectomy, as opposed to the conventional method.

Materials and methods

Patients with a lower third molar directly contacting IAN were recruited and assigned either to a test group (coronectomy group) or a control group (conventional extraction). A standardized quantitative sensory testing (QST) battery was performed for four times: one week before surgery and the second, seventh, and 28th days after surgery. Z-scores and the loss/gain coding system were applied for each participant.

Results

A total of 140 molars (test group: n = 91, control group: n = 49) were enrolled. The sensitivity of the mechanical detection threshold (MDT) and pressure pain threshold (PPT) significantly increased after surgery more than before surgery in both groups (P ≤ 0.001). After the surgery, the sensitivities of the cold detection threshold (CDT), cold pain threshold (CPT), and heat pain threshold (HPT) were significantly higher in the test group than in the control group (P ≤ 0.027). The risk of IANI was significantly larger (P = 0.041) in the test group than in the control group.

Conclusions

QST was a sensitive way to detect somatosensory abnormalities even with no subjective complaint caused by surgery. Coronectomy had less influence on IAN function than conventional total extraction.

Clinical relevance

The somatosensory function changes after mandibular third molar extraction were quantitatively studied, and coronectomy was proved a reliable alternation to reduce IAN injury rate.

The association between back muscle characteristics and pressure pain sensitivity in low back pain patients

BACKGROUND AND AIMS

Some low back pain (LBP) patients recover after every pain episode whereas others develop chronicity. Research indicates that the amount of atrophy and fat infiltration differs between patients with LBP. Also enhanced pain sensitivity is present only in a subgroup of LBP patients. The relationship between pain sensitivity and muscular deformations in LBP, is however unexplored. This study examined the association between pressure pain sensitivity and the structural characteristics of the lumbar muscles in three different groups of non-specific LBP patients.

METHODS

This cross-sectional study examined the total cross-sectional area (CSA), fat CSA, muscle CSA and muscle fat index (MFI) of the lumbar multifidus (MF) and erector spinae (ES) at level L4 by magnetic resonance imaging in 54 patients with non-specific LBP (23 recurrent LBP, 15 non-continuous chronic LBP and 16 continuous chronic LBP). Pressure pain thresholds were measured at four locations (lower back, neck, hand and leg) by a manual pressure algometer and combined into one "pain sensitivity" variable. As a primary outcome measure, the association between pain sensitivity and muscle structure characteristics was investigated by multiple independent general linear regression models. Secondly, the influence of body mass index (BMI) and age on muscle characteristics was examined.

RESULTS

A positive association was found between pain sensitivity and the total CSA of the MF (p=0.006) and ES (p=0.001), and the muscle CSA of the MF (p=0.003) and ES (p=0.001), irrespective of the LBP group. No association was found between pain sensitivity and fat CSA or MFI (p>0.01). Furthermore, a positive association was found between BMI and the fat CSA of the MF (p=0.004) and ES (p=0.006), and the MFI of the MF (p<0.01) and ES (p=0.003). Finally, a positive association was found between age with the fat CSA of the MF (p=0.008) but not with the fat CSA of the ES (p>0.01), nor the MFI of the MF (p>0.01) and ES (p>0.01).

CONCLUSIONS

A higher pain sensitivity is associated with a smaller total and muscle CSA in the lumbar MF and ES, and vice versa, but results are independent from the LBP subgroup. On the other hand, the amount of fat infiltration in the lumbar muscles is not associated with pain sensitivity. Instead, a higher BMI is associated with more lumbar fat infiltration. Finally, older patients with LBP are associated with higher fat infiltration in the MF but not in the ES muscle.

IMPLICATIONS

These results imply that reconditioning muscular tissues might possibly decrease the pain sensitivity of LBP patients. Vice versa, therapy focusing on enhancement of pain sensitivity might also positively influence the CSA and that way contribute to the recovery of LBP. Furthermore, the amount of lumbar muscle fat seems not susceptible to pain sensitivity or vice versa, but instead a decrease in BMI might decrease the fat infiltration in the lumbar muscles and therefore improve the muscle structure quality in LBP. These hypothesis apply for all non-specific LBP patients, despite the type of LBP.

Characterization and predictive mechanisms of experimentally induced tension-type headache

Objective

Studies have shown it is possible to elicit a tension-type headache episode in 15 to 30% of healthy individuals following a tooth-clenching or stress-inducing task. Despite this, no studies have attempted to understand why some healthy individuals develop a headache episode while others do not.

Methods

The present randomized, single-blind, controlled study recruited 60 healthy participants who participated in a 30-minute tooth-clenching task and 10 participants who participated in a control task. Before the tasks, participants had their pericranial tenderness and pain modulation profiles (wind-up ratio and conditioned pain modulation) assessed. Two hours later, pericranial tenderness and pressure pain thresholds were assessed as well as any developing temporomandibular disorders. Pain diaries were kept for 24 hours to register any developing pain or headache.

Results

Participants with a decrease in pericranial tenderness after the tooth-clenching task were less likely to develop headache when compared to participants without. Pain modulation profiles could not predict who developed headache and who did not. Finally, no difference was found between groups for developing temporomandibular disorders. No difference in frequency of participants who developed headache was found between the tooth-clenching and the control task.

Conclusions

In conclusion, it was shown that increased pericranial tenderness was not required to trigger an episode of tension-type headache in healthy participants. Furthermore, pain modulation profiles could not predict who developed headache and who did not. Finally, activation of descending inhibitory pathways, as assessed by decreases in pericranial tenderness, was protective against the development of headache. These findings provide new insights into the pathophysiology of experimentally-induced tension-type headache.

Somatosensory profiles of patients with chronic myogenic temporomandibular disorders in relation to their painDETECT score

BACKGROUND

The purpose of this study was to characterize patients with chronic temporomandibular disorders (TMD) in terms of existing hyperalgesia against cold, heat and pressure.

METHODS

The extent of hyperalgesia for pressure and thermal sensation in TMD patients was determined by the use of the painDETECT questionnaire ("Is cold or heat in this area occasionally painful?" "Does slight pressure in this area, e.g., with a finger, trigger pain?") and experimental somatosensory testing against thermal and pressure stimuli (Quantitative Sensory Testing; QST). In addition, we explored psychological comorbidity among the chronic TMD patients (hospital anxiety and depression scale, HADS-D and coping strategies questionnaire, CSQ).

RESULTS

Nineteen patients with chronic TMD and 38 healthy subjects participated in the study. N = 12 patients had a painDETECT score ≤ 12, n = 3 patients had a painDETECT score of 13-18 and n = 4 patients had a painDETECT score ≥ 19. TMD patients with painDETECT scores ≥19 had moderately, strong or very strong enhancement of thermal and pressure pain perception, whereas patients with painDETECT scores 13-18 and ≤ 12 responded these questions with "never", "hardly noticed" or "slightly painful" (p < 0.05-0.01). With increasing painDETECT scores we found increased hyperalgesia for pressure (p < 0.01) and thermal stimuli (p < 0.05) in QST. The patients with a painDETECT score ≥ 19 showed increased signs of anxiety (p < 0.05), depression (p < 0.01), praying and hoping (p < 0.05).

CONCLUSION

The present study has shown that the PainDETECT questionnaire can be a helpful additional diagnostic tool. Together with QST, the PainDETECT questionnaire detected hyperalgesia for pressure and thermal sensation. Therefore the PainDETECT questionnaire is helpful to decide which TMD patients should undergo QST.

Experimental evidence for weaker endogenous inhibition of trigeminal pain than extra-trigeminal pain in healthy individuals

Background and objectives The prevalence of pain syndromes that affect the territories innervated by the trigeminal nerve, such as headaches, is one of the highest and ranks second only to low back pain. A potential mechanism underlying this high prevalence may be a relatively weak endogenous pain modulation of trigeminal pain. Here, we sought to systematically compare endogenous pain modulation capabilities in the trigeminal region to those of extra-trigeminal regions in healthy subjects. Methods Healthy, pain free subjects (n = 17) underwent a battery of quantitative sensory testing to assess endogenous pain inhibition and pain enhancement efficiencies within and outside the trigeminal innervated region. Measurements included conditioned pain modulation (CPM), temporal summation of pain (TSP) and spatial summation of pain (SSP). Results Testing configurations that included trigeminal-innervated body regions displayed significantly weaker CPM when compared to extra-trigeminal innervated areas. SSP magnitude was smaller in the ophthalmic trigeminal innervation when compared to other body regions. TSP magnitude was not different between the different body regions tested. Conclusions Our findings point to regional differences in endogenous pain inhibition and suggest that in otherwise healthy individuals, the trigeminal innervation is subjected to a weaker inhibitory pain control than other body regions. Such weaker endogenous pain control could play, at least in part, a role in mediating the high prevalence of trigeminal-related pain syndromes, including primary headaches and TMD pain.

Pain threshold and temporomandibular function in systemic sclerosis: comparison with psoriatic arthritis

The aim of the study was to evaluate whether a reduced pain threshold is associated with increased temporomandibular dysfunction in systemic sclerosis (SSc) compared to psoriatic arthritis (PsA) and healthy controls. Ninety subjects participated in the study (30 SSc, 30 PsA, and 30 healthy controls). The Helkimo index was used to evaluate temporomandibular dysfunction. Digital palpation was performed at the temporomandibular joint (TMJ) surface and at the superficial masseter muscle (SMM) and pain intensity was recorded on a visual analog scale (VAS), while pain pressure threshold (PPT) was measured at the same sites through a pressure algometer. PPT scores were lower in SSc patients compared to PsA patients and controls. In addition, the average Helkimo index score, measuring the degree of TMJ dysfunction, was higher in SSc compared to PsA and controls. A significant inverse correlation was observed between every PPT score, and both Helkimo index and VAS palpation in SSc and PsA. Both the range of motion and all the other pain-related subdomains of the Helkimo index score (pain on movement, pain palpation TMJ and pain palpation muscle) were significantly worse in SSc compared to PsA, while no significant differences were observed in the TMJ function subdomain. In SSc patients, the skin score was directly associated with the range of motion subdomain of the Helkimo index. Our results confirm that TMJ function is impaired in SSc; further longitudinal studies are needed to assess the role of pain threshold in the assessment of limitations in TMJ function and to identify an objective marker of therapeutic response.

Do patients with chronic unilateral orofacial pain due to a temporomandibular disorder show increased attending to somatosensory input at the painful side of the jaw?

BACKGROUND

Patients with chronic orofacial pain due to temporomandibular disorders (TMD) display alterations in somatosensory processing at the jaw, such as amplified perception of tactile stimuli, but the underlying mechanisms remain unclear. This study investigated one possible explanation, namely hypervigilance, and tested if TMD patients with unilateral pain showed increased attending to somatosensory input at the painful side of the jaw.

METHODS

TMD patients with chronic unilateral orofacial pain (n = 20) and matched healthy volunteers (n = 20) performed a temporal order judgment (TOJ) task indicated which one of two tactile stimuli, presented on each side of the jaw, they had perceived first. TOJ methodology allows examining spatial bias in somatosensory processing speed. Furthermore, after each block of trials, the participants rated the perceived intensity of tactile stimuli separately for both sides of the jaw. Finally, questionnaires assessing pain catastrophizing, fear-avoidance beliefs, and pain vigilance, were completed.

RESULTS

TMD patients tended to perceive tactile stimuli at the painful jaw side as occurring earlier in time than stimuli at the non-painful side but this effect did not reach conventional levels of significance (p = .07). In the control group, tactile stimuli were perceived as occurring simultaneously. Secondary analyses indicated that the magnitude of spatial bias in the TMD group is positively associated with the extent of fear-avoidance beliefs. Overall, intensity ratings of tactile stimuli were significantly higher in the TMD group than in the control group, but there was no significant difference between the painful and non-painful jaw side in the TMD patients.

DISCUSSION

The hypothesis that TMD patients with chronic unilateral orofacial pain preferentially attend to somatosensory information at the painful side of the jaw was not statistically supported, although lack of power could not be ruled out as a reason for this. The findings are discussed within recent theories of pain-related attention.

Quantitative sensory testing (QST) in the orofacial region of healthy Chinese: influence of site, gender and age

OBJECTIVE

To establish a preliminary thermal and mechanical somatosensory profile using a standardized quantitative sensory testing (QST) to investigate site, gender and age differences in healthy Chinese.

MATERIALS AND METHODS

Twenty younger (age: 20-40 years, 10 men, 10 women) and twenty older (age: 41-61 years, 10 men, 10 women) healthy participants completed the study. Cold detection threshold (CDT), warm detection threshold (WDT), cold pain threshold (CPT), heat pain threshold (HPT), mechanical detection threshold (MDT) and mechanical pain threshold (MPT) were measured at five sites: Left hand, bilaterally at the mental area, tip of tongue and the lower lip mucosa. Mixed model ANOVAs with repeated measures were used to analyze the data.

RESULTS

MDT(p < .001) and MPT (p < .05) were significantly higher on the hand compared to the mental areas. The CDT ( p = .006) was significantly higher and WDT (p < .001) was significantly lower at the tongue compared to lip mucosa and CDT (p < .001) was higher at the tongue mucosa than at the mental areas. WDT (p < .001) and HPT (p < .05) were significantly higher at the tip of the tongue and the lower lip mucosa compared to the mental areas. Significantly lower sensitivity for WDT (p < .001) and CDT (p = .004) were found in the older group compared to the younger group. Significant gender differences were found with less sensitivity for WDT (p = .024) and MDT (p = .003) in men compared to women.

CONCLUSIONS

Application of standardized QST can provide valuable information of orofacial somatosensory phenotypes in a Chinese population. Age, gender and site are mandatory to control for.

Does conditioned pain modulation predict the magnitude of placebo effects in patients with neuropathic pain?

BACKGROUND

Conditioned pain modulation (CPM) is a validated measure of the function of endogenous pain inhibitory pathways. Placebo effects reflect top-down inhibitory modulation of pain. CPM and placebo effects are both influenced by expectations, albeit to varying degrees, and are related to neurotransmitter systems such as the endogenous opioid system, and it can be speculated that CPM responses are positively associated with the magnitude of placebo effects. Yet, no studies have tested this.

METHODS

The study included 19 patients with neuropathic pain. CPM was quantified as the difference in pressure pain threshold (PPT) as measured at the middle deltoid muscle before and after 5-min exposure to the cold pressor test (CPT) (conditioning pain stimulus). Placebo effects were tested via open and hidden applications of the pain-relieving agent lidocaine (2 mL) using a disinfection napkin controlled for no treatment.

RESULTS

The mean (SD) PPT was 668.7 (295.7) kPa before and 742.3 (370.8) kPa after the CPT. The mean (SD) CPM response was -73.6 (214.0) kPa corresponding to an 11% increase in PPT, reflecting a normally functioning endogenous pain modulatory system. Large and significant placebo effects were observed in ongoing neuropathic pain intensity (p = 0.002). The CPM response did not predict the magnitude of the placebo effect (p = 0.765). Moreover, there were no interaction effects for the moderator variables: clinical pain level (p = 0.136), age (p = 0.347) and gender (p = 0.691).

CONCLUSIONS

Conditioned pain modulation and placebo effects do not seem to be associated in patients with neuropathic pain.

SIGNIFICANCE

Conditioned pain modulation and placebo effects are endogenous pain-modulating phenomena that are influenced by some of the same mechanisms. This study suggests that CPM and placebo effects in neuropathic pain are independent phenomena that may be mediated by different mechanisms.

Temporomandibular disorders: Old ideas and new concepts

Background Temporomandibular disorders (TMD) is an umbrella term for pain and dysfunction involving the masticatory muscles and the temporomandibular joints (TMJs). TMD is the most common orofacial pain condition. Its prominent features include regional pain in the face and preauricular area, limitations in jaw movement, and noise from the TMJs during jaw movements. TMD affects up to 15% of adults and 7% of adolescents. Chronic pain is the overwhelming reason that patients with TMD seek treatment. TMD can associate with impaired general health, depression, and other psychological disabilities, and may affect the quality of life of the patient. Assessment Evaluations indicate that the recently published Diagnostic Criteria for TMD (DC/TMD) are reliable and valid. These criteria cover the most common types of TMD, which include pain-related disorders (e.g., myalgia, headache attributable to TMD, and arthralgia) as well as disorders associated with the TMJ (primarily disc displacements and degenerative disease). As peripheral mechanisms most likely play a role in the onset of TMD, a detailed muscle examination is recommended. The persistence of pain involves more central factors, such as sensitization of the supraspinal neurons and second-order neurons at the level of the spinal dorsal horn/trigeminal nucleus, imbalanced antinociceptive activity, and strong genetic predisposition, which also is included in DC/TMD. Conclusion The etiology is complex and still not clearly understood, but several biological and psychosocial risk factors for TMD have been identified. Several studies indicate that patients with TMD improve with a combination of noninvasive therapies, including behavior therapy, pharmacotherapy, physical therapy, and occlusal appliances. More stringently designed studies, however, are needed to assess treatment efficacy and how to tailor treatment to the individual patient.

Pain profiling of patients with temporomandibular joint arthralgia and osteoarthritis diagnosed with different imaging techniques

Background

Clinical differentiation between pain mechanisms of temporomandibular joint (TMJ) arthralgia and osteoarthritis (OA) is challenging. The aims were to compare somatosensory function at the TMJs and conditioned pain modulation (CPM) effects between TMJ arthralgia and OA patients diagnosed clinically and based on different imaging techniques and age- and gender-matched healthy controls (n = 41).

Methods

Patients (n = 58) underwent standard clinical examination and three different TMJ imaging modalities. After each examination, they were classified into arthralgia or OA based on the findings. TMJ region somatosensory testing was performed in all participants. Z-scores were calculated for patients based on healthy reference data. CPM was tested by comparing pressure pain thresholds (PPTs) at TMJ and thenar (control) before, during and after the application of painful and nonpainful cold stimuli. Data were analyzed using analyses of variance.

Results

Somatosensory abnormalities were commonly detected in both patient groups. Assessment of somatosensory function at the TMJ revealed that arthralgia patients were less sensitive to warmth, cold and tactile stimuli than OA patients (P < 0.048). OA patients showed pressure hyperalgesia compared with arthralgia patients (P = 0.025). There was a significant CPM effect at both test sites during painful cold application in all groups (P < 0.001). There was no significant difference in the relative CPM effect between groups except for clinically diagnosed arthralgia patients showing reduced CPM effect compared with controls (P = 0.047).

Conclusions

Pain profiles including somatosensory function differed between TMJ arthralgia and OA patients although CPM effects were similar in patients and controls. Thus, different TMJ pain conditions may share common pain mechanisms but the present study for the first time also indicated that differential pain mechanisms could be involved.

Electronic supplementary material

The online version of this article (doi:10.1186/s10194-016-0653-6) contains supplementary material, which is available to authorized users.

Somatosensory abnormalities in Chinese patients with painful temporomandibular disorders

Background

The somatosensory phenotype of Chinese temporomandibular disorders (TMD) patients is not sufficiently studied with the use of contemporary techniques and guidelines.

Methods

A standardized quantitative sensory testing (QST) battery consisting of 13 parameters with a stringent statistical protocol developed by the German Research Network on Neuropathic Pain was performed over the most painful and corresponding contralateral sites as well as the right hand of 40 Chinese patients with TMD and pain classified according to the Diagnostic Criteria for TMD (DC/TMD). The same QST protocol was performed bilaterally over the infraorbital, mental, and hand regions of 70 age- and gender-stratified healthy Chinese controls. Z-scores and loss/gain scores were computed for each TMD patient.

Results

For patients, 82.5 % had somatosensory abnormalities in the painful facial region, while 60.0 % had abnormalities confined to the right hand. The most frequent abnormalities were somatosensory gain to pinprick (35.0 %) and pressure (35.0 %) stimuli, somatosensory loss to pinprick (25.0 %), cold (22.5 %), and heat (15.0 %) nociceptive stimuli. The most frequent loss/gain score was L0G2 (no somatosensory loss combined with a gain of mechanical somatosensory function) for both the facial (40.0 %) and hand (27.5 %) regions. Involving side-to-side differences in the evaluation increased the diagnostic sensitivity by 2.5–25.0 % across different parameters.

Conclusions

Somatosensory abnormalities were commonly detected in Chinese TMD pain patients both within and outside the primary painful region, strongly indicating disturbances in the central processing of somatosensory stimuli. The individual variations in somatosensory abnormalities indicate a possible need for development of individualized TMD pain management.

Electronic supplementary material

The online version of this article (doi:10.1186/s10194-016-0632-y) contains supplementary material, which is available to authorized users.