Pressure pain thresholds fluctuate with, but do not usefully predict, the clinical course of painful temporomandibular disorder

A survey study for the dental students' satisfaction with the "needling therapies for temporomandibular disorders" lectures

Background/purpose

Dry needling therapy and acupuncture can effectively relieve myofascial pain in temporomandibular disorders (TMDs). This study evaluated dental students' satisfaction with the "needling therapies for TMDs" lectures given in 2022 and 2023.

Materials and methods

The "needling therapies for TMDs" lectures included mainly a dry needling therapy lecture and an acupuncture lecture which were given to the fifth-year dental students in both 2022 and 2023. An additional needling therapy demonstration lecture was given in 2023 only. Immediately after the lectures, the students were asked to complete an online-based questionnaire with four survey questions regarding their satisfaction with (1) the dry needling therapy, (2) the acupuncture, (3) the overall, and (4) the needling therapy demonstration lectures using 5-point Likert scale ratings.

Results

Fifty-three (80 %) of 66 and 60 (81 %) of 74 students answered the questions in 2022 and 2023, respectively. The satisfaction rates improved from 70 % in 2022 to 83 % in 2023 for the dry needling therapy lecture, from 64 % in 2022 to 85 % in 2023 for the acupuncture lecture, and from 70 % in 2022 to 88 % in 2023 for the overall lecture. The satisfaction rate was 88 % in 2023 for the needling therapy demonstration lecture.

Conclusion

The results of this study suggest that inclusion of the needling therapy demonstration lecture in 2023 can results in a marked increase in the satisfaction rates for the lectures. The relatively-lower satisfaction rate for the acupuncture lecture in 2022 may be due to the difficulty in understanding the mechanisms underlying the acupuncture therapy.

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.

Age and Gender, but Not Pain are Associated with Pressure Pain Thresholds in Patients with Temporomandibular Disorders: A Cross-Sectional Study

Purpose

This study aims to explore the association of pressure pain thresholds (PPTs) with age, gender, and pain in patients with temporomandibular disorders (TMD).

Patients and Methods

A total of 301 TMD patients (248 female and 53 male) were recruited and classified into the high and low age groups according to their median age of 26 years. Patients' demographics, pain-related variables, TMD-related variables, and PPTs of both left and right temporomandibular joints (TMJs), masseter, and temporalis were collected.

Results

Pain duration and visual analog scale of pain (VAS) showed no significant correlations with PPTs (P>0.05). Multiple linear regression analysis revealed a significant positive association of PPTs of all six sites with males (β=0.41-0.72 kg·cm-2, 95% CI (0.19-0.38, 0.74-0.99), P<0.001), as well as with the high age group [β=0.28-0.36 kg·cm-2, 95% CI (0.07-0.20, 0.47-0.53), P<0.020]. Furthermore, PPTs of the left TMJ showed a significant negative association with left pain-related TMD (PT) [β=-0.21 kg·cm-2, 95% CI (-0.38, -0.04), P=0.026], but PPTs of the remaining sites did not show a significant association with PT (P>0.05). Stratified analysis showed that PPTs in females were associated with the high age group [β=0.25-0.37 kg·cm-2, 95% CI (0.04-0.20, 0.45-0.56), P<0.020] and that PPT of the left TMJ was associated with left PT [β=-0.21 kg·cm-2, 95% CI (-0.39, -0.03), P=0.043]. The remaining PPTs did not show a significant association with PT (P>0.05). In males, PPTs did not show significant correlations with age, PT and VAS (P>0.05).

Conclusion

PPTs in the orofacial region are associated with gender and age in TMD patients. Pain duration and intensity show no significant correlations with PPTs in TMD patients. Researchers and dentists should take age and gender into account when using PPTs as auxiliary diagnostic indicators for PT.

Is the risk of chronic pain after total temporomandibular joint replacement independent of its indications? A prospective cohort study

Chronic pain is a possible long-term complication after alloplastic temporomandibular joint reconstruction (TMJR). This study was developed to evaluate various subjective and objective measurements to determine the presence and degree of TMJ pain in patients treated with TMJR regardless of the indication for the operation. A prospective, single-centre study was performed. Data on 36 patients (56 TMJR) were collected preoperatively and at follow up two to three years postoperatively. The primary outcome variable was subjective TMJ pain (none/mild, moderate/severe) at follow up. The predictor variables were objective pressure pain thresholds (PPTs) at the ipsilateral joint(s) and muscle(s), functional parameters (incisal range of motion, maximum voluntary clenching), subjective oral health-related quality of life (OHRQoL), and demographic and surgical variables. The number of patients with moderate/severe pain decreased from 17 preoperatively to 10 at follow up. Self-reported TMJ pain was significantly reduced in the entire group (p = 0.001). Patients with moderate/severe pain at follow up were more restricted in their OHRQoL but did not differ in PPT and functional parameters from the no/mild pain group. Moderate/severe TMJ pain at follow up was associated with unilateral TMJR and more preoperative pain. This study provides preliminary evidence that despite good pain reduction in most patients, persistent pain after TMJR is common and, in rare cases, may even worsen regardless of the original diagnosis. At follow up there was a close relation between OHRQoL and TMJ pain. TMJ pain after TMJR cannot be confirmed by objective measurement methods (PPTs and functional parameters).

Pathogenesis and Differential Diagnosis of Temporomandibular Joint Disorders

Temporomandibular disorders (TMDs) are an umbrella term including disorders of the temporomandibular joint and muscles of the masticatory system. They are the most common nonodontogenic cause of pain in the orofacial region. A clear understanding of various conditions, underlying mechanisms, clinical presentation, and examination skills is required to effectively diagnose and manage these patients.

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.

Biological sex influences psychological aspects of the biopsychosocial model related to chronic pain intensity and interference among South Korean patients with chronic secondary musculoskeletal pain in rheumatic diseases

Introduction

Pain is a prominent contributor to negative personal and social outcomes, including increased disability and mortality, in many rheumatic diseases. In the Biopsychosocial model of chronic pain, psychological and social factors share roles with the biology of the injury in determining each patient's pain and suffering. The current study explored factors associated with clinical pain intensity and interference among patients with chronic secondary musculoskeletal pain in rheumatic diseases.

Methods

In total, 220 patients experiencing chronic secondary musculoskeletal pain participated. Biological factors (age, biological sex, pain condition, pain duration, pain sensitivity, and comorbidity), socio-economic factors, psychological factors (pain catastrophizing and depressive symptoms), and pain intensity and interference were measured. Descriptive, multivariable linear regression and partial correlation analyses were conducted. Subgroup analysis by sex was conducted to examine differences in how different factors affect the pain experience.

Results

The mean age of the participants was 52.3 years (SD = 12.07) and ranged from 22 to 78. Average pain intensity was 3.01 (0-10 scale) and average total pain interference score was 21.07 (0-70 scale). Partial correlation found positive correlations between pain intensity and interference with depression (intensity: R = 0.224; p = 0.0011; interference: R = 0.351; p < 0.001) and pain catastrophizing (intensity: R = 0.520; p < 0.001; interference: R = 0.464; p < 0.001). In males, pain condition (β = -0.249, p = 0.032) and pain catastrophizing (R = 0.480, p < 0.001) were associated with pain intensity. In males, the simple correlation between pain intensity and depression (R = 0.519; p < 0.001) was driven by pain catastrophizing. In females, pain catastrophizing (R = 0.536, p < 0.001) and depressive symptoms (R = 0.228, p = 0.0077) were independently associated with pain intensity. Age (β = -0.251, p = 0.042) and pain catastrophizing (R = 0.609, p < 0.001) were associated with pain interference in males, while depressive symptoms (R = 0.439, p < 0.001) and pain catastrophizing (R = 0.403, p < 0.001) were associated with pain interference in females. Again, in males, the simple correlation between pain interference and depression (R = 0.455; p < 0.001) was driven by pain catastrophizing.

Discussion

In this study, females were more directly affected by depressive symptoms than males, regarding pain intensity and interference. Pain catastrophizing was a significant factor influencing chronic pain for both males and females. Based on these findings, a sex-specific approach to the Biopsychosocial model should be considered in understanding and managing pain among Asians with chronic secondary musculoskeletal pain.

Chronic temporomandibular disorders are associated with higher propensity to develop central sensitization: a case-control study

ABSTRACT

Temporomandibular disorders (TMD) include a group of musculoskeletal disorders that may involve increased responsiveness of nociceptive neurons in the central nervous system (ie, central sensitization). To test this hypothesis further, this study examined whether, as compared with healthy subjects, patients with chronic TMD have a greater propensity to develop secondary mechanical hyperalgesia-a phenomenon that can be confidently attributed to central sensitization. In this case-control study, we assessed the area of secondary mechanical hyperalgesia induced experimentally by delivering high-frequency electrical stimulation (HFS) to the volar forearm skin in 20 participants with chronic TMD and 20 matched healthy controls. High-frequency electrical stimulation consisted in 12 trains of constant-current electrical pulses (5 mA) delivered at 42 Hz. The area of secondary mechanical hyperalgesia was evaluated 30 minutes after applying HFS. The area of secondary mechanical hyperalgesia induced by HFS was on average 76% larger in the chronic TMD group (M = 67.7 cm 2 , SD = 28.2) than in the healthy control group (M = 38.4 cm 2 , SD = 14.9; P = 0.0003). Regarding secondary outcomes, there was no group difference in the intensity of secondary mechanical hyperalgesia, but allodynia to cotton after HFS was more frequent in the chronic TMD group. To the best of our knowledge, this is the first study to show that individuals with chronic TMD have an increased propensity to develop secondary hyperalgesia in a site innervated extratrigeminally. Our results contribute to a better understanding of the pathophysiology of chronic TMD.

The contribution of pain and disability on the transition from acute to chronic pain-related TMD: A 3-month prospective cohort study

Although most cases of pain-related temporomandibular disorders (TMD) are mild and self-limiting, about 10% of TMD patients develop severe disorders associated with chronic pain and disability. It has been suggested that pain intensity contributes to the transition from acute to chronic pain-related TMD. Therefore, the aims of this current prospective cohort study were to assess if pain intensity, pain always being present, pain or stiffness on awakening, jaw activities, and interference, were associated with the transition from acute to chronic pain-related TMD at 3 months of follow-up. One hundred and nine participants, recruited from four clinics in Montreal and Ottawa, received examinations and completed the required instruments at baseline and at the 3rd month of follow-up. In a multivariable analysis including sex, age, characteristic pain index (CPI) (OR = 1.03, 95%CI = 1.01–1.06, P = 0.005), moderate to severe average pain intensity (OR = 3.51, 95%CI = 1.24–9.93, P = 0.02), disability points score (OR = 1.29, 95%CI = 1.06–1.57, P = 0.01), interferences (ORs = 1.30–1.32, P = 0.003–0.005), screening score (OR = 1.37, 95%CI = 1.08–1.76, P = 0.01), and pain always present (OR = 2.55, 95%CI = 1.08–6.00, P = 0.03) assessed at first-visit were related to the transition outcome at the 3rd month of follow-up. Further, we found that if 4 patients with acute pain-related TMD on average were exposed to these risk factors at baseline, 1 would have the transition from acute to chronic pain at 3 months of follow-up. Results indicate that these factors are associated with the transition from acute to chronic pain-related TMD, and therefore should be considered as important factors when evaluating and developing treatment plans for patients with pain-related TMD.

Alterations in kinematics of temporomandibular joint associated with chronic neck pain

BACKGROUND

Temporomandibular disorder (TMD) is an umbrella term for pain and dysfunction of the temporomandibular joint (TMJ) and its associated structures. Patients with TMD show changes in TMJ kinematics and masticatory muscle activation. TMD is commonly comorbid with non-specific chronic neck pain (NCNP), which may be one of the risk factors for TMD.

OBJECTIVES

This study aimed to investigate whether patients with NCNP have altered TMJ kinematics and masticatory muscle activity.

METHODS

This was a cross-sectional exploratory study including 19 healthy participants and 20 patients with NCNP but without TMD symptoms. TMJ kinematics was measured during mouth opening and closing, jaw protrusion and jaw lateral deviation. Surface electromyography was used to record the muscle activity of the anterior temporalis, masseter, sternocleidomastoid and upper trapezius while clenching. Furthermore, cervical posture, cervical range of motion (ROM) and pressure-pain threshold of the neck and masticatory muscles were measured.

RESULTS

Compared with the healthy group, the NCNP group showed significantly reduced upper cervical rotation ROM (p = .041) and increased condylar path length (p = .02), condylar translation (opening p = .034, closing p = .011) and mechanical pain sensitivity of the upper trapezius (p = .018). Increased condylar translation was significantly correlated with reduced upper cervical mobility and poor cervical posture (r = -0.322 to -0.397; p = .012-.046).

CONCLUSION

Increased condylar translation and path length in patients with NCNP may indicate poor control of TMJ articular movement, which may result from neck pain or may be a compensation for limited neck mobility. Evaluation of excessive TMJ translation may be considered in patients with NCNP.

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.

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.

The impact of gender of the examiner on orofacial pain perception and pain reporting among healthy volunteers

Objectives

Pain on palpation of jaw muscles is a commonly used diagnostic criterion when examining patients with orofacial pain. It is not known, however, if pain reports are affected by the gender of the examiner. Our aim was to investigate if pressure pain threshold (PPT), pressure pain tolerance (PTol), and pain intensity assessed over the masseter muscles in healthy individuals are affected by the gender of the examiner.

Materials and methods

Healthy, pain-free individuals were recruited on a voluntary basis. PPT and PTol were assessed using pressure algometry. At the PTol level, participants also rated pain intensity on a 0–10 numeric rating scale. Assessments of PPT and PTol were conducted with six repeated measurements performed twice, separately by one female and one male examiner, on each participant.

Results

In total, 84 participants (43 women; median age 24, IQR 6) were included. With a female examiner, women reported higher pain intensity than men (Mann Whitney U, p = 0.005). In the multivariable analysis, significantly higher PTol was predicted by male examiner. Also, a higher ratio between PTol and reported pain intensity was predicted by male examiner.

Conclusions

The gender of the examiner influences pain reporting and perception in an experimental setting. This effect on pain perception related to gender of the examiner is probably related to normative gender behaviors rather than to biological alterations within the examined individual.

Clinical relevance

In clinical and experimental settings, gender of the examiner may affect not only pain perception but also pain reporting, with potential implications for diagnostics in patients with pain.

Medial Prefrontal High-Definition Transcranial Direct Current Stimulation to Improve Pain Modulation in Chronic Low Back Pain: A Pilot Randomized Double-blinded Placebo-Controlled Crossover Trial

Chronic low back pain (CLBP) is highly disabling, but often without identifiable source. Focus has been on impaired anti-nociceptive mechanisms contributing to pain maintenance, though methods of targeting this impairment remain limited. This randomised-controlled cross-over pilot trial used active versus sham medial prefrontal cortex (mPFC) high-definition transcranial direct current stimulation (HD-tDCS) for 3-consecutive days to improve descending pain inhibitory function. Twelve CLBP patients were included with an average visual analogue scale (VAS) pain intensity of 3.0 ± 1.5 and pain duration of 5.3 ± 2.6 years. Pressure pain thresholds (PPTs), conditioned pain modulation (CPM), and temporal summation of pain (TSP) assessed by cuff algometry, as well as pain symptomatology (intensity, unpleasantness, quality, disability) and related psychological features (pain catastrophizing, anxiety, affect), were assessed on Day1 before 3 consecutive days of HD-tDCS sessions (each 20 minutes), at 24-hours (Day 4) and 2-weeks (Day 21) following final HD-tDCS. Blinding was successful. No significant differences in psychophysical (PPT, CPM, TSP), symptomatology or psychological outcomes were observed between active and sham HD-tDCS on Day4 and Day21. CPM-effects at Day 1 negatively correlated with change in CPM-effect at Day4 following active HD-tDCS (P = .002). Lack of efficacy was attributed to several factors, not least that patients did not display impaired CPM at baseline. TRIAL REGISTRATION: : ClinicalTrials.gov (NCT03864822). PERSPECTIVE: Medial prefrontal HD-tDCS did not alter pain, psychological nor psychophysical outcomes, though correlational analysis suggested response may depend on baseline pain inhibitory efficacy, with best potential effects in patients with severe impairments in descending pain inhibitory mechanisms. Future work should focus on appropriate patient selection and optimising stimulation targeting.

Association of temporomandibular disorders with pain sensitivity: A cohort study

BACKGROUND

Pain related to temporomandibular disorders (TMD) can be linked with multiple site pain (MSP), and may associate with increased pain sensitivity, more frequently among women than men. The aim of the study was to examine the associations of pressure pain threshold (PPT) and tolerance (PPTo) with TMD and associated MSP in the Northern Finland Birth Cohort 1966 (NFBC1966) study.

METHODS

Altogether 1961 NFBC1966 subjects attended clinical medical and dental examination at the Institute of Dentistry, University of Oulu in 2012-2013. Clinical examinations were carried out using a modified Diagnostic Criteria for TMD protocol (DC/TMD). MSP was defined based on questions regarding body pain sites. Additionally, PPT and PPTo were assessed using algometer measurements. Mann-Whitney U-test and Tobit regression models were used to analyse associations between TMD sub-diagnoses, MSP, PPT and PPTo, stratified by sex. Further models were adjusted with anxiety and depressive symptoms, which were assessed using Hopkins Symptom Checklist-25 (HSCL-25) and two-way interaction terms.

RESULTS

Among females, lower PPT and PPTo were associated with myalgia and arthralgia. Among males, lower PPT and PPTo were associated with MSP-linked TMD. Tobit regression analysis showed significantly lower PPT and PPTo values in the myalgia and arthralgia subgroups among female TMD subjects. Among females, disc displacement with reduction had an inverse association with PPT and PPTo. Among males, lower PPTo was associated with degenerative joint disease and MSP-linked TMD.

CONCLUSIONS

The pain regulatory mechanisms behind TMD act differently between the genders as local TMD among females and MSP-linked TMD among males were associated with pain sensitivity.

SIGNIFICANCE

The study shows that there are differences in the associations of painful TMD with pressure pain tolerance, pressure pain sensitivity and MSP between male and female subjects.

Temporomandibular disorders in an adult population in northern Norway: A cross-sectional study

Objectives

The aim of the study was to assess the prevalence of symptoms indicative of temporomandibular disorders (TMD) in an adult population in Troms County in Northern Norway, as well as the associations between TMD and socio‐demographic factors, dental status, self‐reported general, and oral health as well as oral health related quality of life (OHQoL).

Methods

Data were collected from a structured questionnaire and a clinical examination of a random sample of almost 2000 adults, 20–79‐year‐old, in Troms County in Northern Norway.

Results

Women had a higher prevalence of all self‐reported and clinical signs of pain and dysfunction in the temporomandibular complex compared to men. For both genders, sounds from the temporomandibular joint (TMJ) upon clinical examination was the most common symptom, followed by pain to palpation of jaw muscles. Headache was the most common of the self‐reported symptoms and sounds from the TMJ the second most common. Young women had a higher prevalence of self‐reported headache and jaw‐ and face pain compared to middle‐aged and elderly women. TMD‐related symptoms of pain were significantly associated with poor self‐reported general health and correlated with OHQoL as assessed by the oral health impact profile 14 questionnaire.

Conclusion

Being women and having moderate to poor self‐reported general health were associated with clinical signs and self‐reported symptoms of pain in the jaw, face and head region. Self‐reported symptoms of TMD correlated more strongly with OHQoL than clinical signs.

Dysmenorrhea subtypes exhibit differential quantitative sensory assessment profiles

Women who develop bladder pain syndrome (BPS), irritable bowel syndrome, or dyspareunia frequently have an antecedent history of dysmenorrhea. Despite the high prevalence of menstrual pain, its role in chronic pelvic pain emergence remains understudied. We systematically characterized bladder, body, and vaginal mechanical sensitivity with quantitative sensory testing in women with dysmenorrhea (DYS, n = 147), healthy controls (HCs) (n = 37), and women with BPS (n = 25). Previously, we have shown that a noninvasive, bladder-filling task identified a subset of women with both dysmenorrhea and silent bladder pain hypersensitivity, and we repeated this to subtype dysmenorrhea sufferers in this study (DYSB; n = 49). DYS, DYSB, and BPS participants had lower vaginal mechanical thresholds and reported more pain to a cold stimulus during a conditioned pain modulation task and greater pelvic examination after-pain than HCs (P's < 0.05). DYSB participants also had reduced body mechanical thresholds and less conditioned pain modulation compared to HCs and DYS participants (P's < 0.05). Comparing quantitative sensory testing results among the DYS and HC groups only, provoked bladder pain was the only significant predictor of self-reported menstrual pain (r = 0.26), bladder pain (r = 0.57), dyspareunia (r = 0.39), and bowel pain (r = 0.45). Our findings of widespread sensory sensitivity in women with dysmenorrhea and provoked bladder pain, much like that observed in chronic pain, suggest a need to study the trajectory of altered mechanisms of pain processing in preclinical silent visceral pain phenotypes to understand which features convey inexorable vs modifiable risk.

Chronic Pain Diagnosis Using Machine Learning, Questionnaires, and QST: A Sensitivity Experiment

In the last decade, machine learning has been widely used in different fields, especially because of its capacity to work with complex data. With the support of machine learning techniques, different studies have been using data-driven approaches to better understand some syndromes like mild cognitive impairment, Alzheimer’s disease, schizophrenia, and chronic pain. Chronic pain is a complex disease that can recurrently be misdiagnosed due to its comorbidities with other syndromes with which it shares symptoms. Within that context, several studies have been suggesting different machine learning algorithms to classify or predict chronic pain conditions. Those algorithms were fed with a diversity of data types, from self-report data based on questionnaires to the most advanced brain imaging techniques. In this study, we assessed the sensitivity of different algorithms and datasets classifying chronic pain syndromes. Together with this assessment, we highlighted important methodological steps that should be taken into account when an experiment using machine learning is conducted. The best results were obtained by ensemble-based algorithms and the dataset containing the greatest diversity of information, resulting in area under the receiver operating curve (AUC) values of around 0.85. In addition, the performance of the algorithms is strongly related to the hyper-parameters. Thus, a good strategy for hyper-parameter optimization should be used to extract the most from the algorithm. These findings support the notion that machine learning can be a powerful tool to better understand chronic pain conditions.

Hyperalgesia and Central Sensitization in Subjects With Chronic Orofacial Pain: Analysis of Pain Thresholds and EEG Biomarkers

Introduction: The presence of a temporomandibular disorder is one of the most frequent causes of orofacial pain (OFP). When pain continues beyond tissue healing time, it becomes chronic and may be caused, among other factors, by the sensitization of higher-order neurons. The aim of this study is to describe psychological characteristics of patients with chronic OFP, their peripheral pain threshold, and electroencephalography (EEG) recording, looking for possible signs of central sensitization (CS). Materials and methods: Twenty-four subjects with chronic OFP caused by temporomandibular disorder were evaluated using the Research Diagnostic Criteria for Temporomandibular Disorders Axis I and Axis II. Pain intensity, catastrophizing, and presence of CS were assessed through self-reported questionnaires. Pressure pain threshold (PPT) was recorded in facial and peripheral sites; EEG activity was recorded during open and closed eyes resting state and also during the pain threshold assessment. Pain thresholds and EEG recordings were compared with a cohort of pain-free age- and sex-matched healthy subjects. Results: Patients with chronic OFP showed a significant reduction in their pain threshold compared to healthy subjects in all sites assessed. Greater reduction in pain threshold was recorded in patients with more severe psychological symptoms. Decreased alpha and increased gamma activity was recorded in central and frontal regions of all subjects, although no significant differences were observed between groups. Discussion: A general reduction in PPT was recorded in people who suffer from chronic OFP. This result may be explained by sensitization of the central nervous system due to chronic pain conditions. Abnormal EEG activity was recorded during painful stimulation compared to the relaxed condition in both chronic OFP subjects and healthy controls.

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.

Music Modulates Awake Bruxism in Chronic Painful Temporomandibular Disorders

OBJECTIVE

In this experimental study, we aimed to determine whether guided music listening (GML) - a music intervention based on models of mood mediation and attention modulation - modulates masticatory muscle activity and awake bruxism in subjects with chronic painful muscular temporomandibular disorders (TMD myalgia, mTMD), a condition causing a significant burden to patients, their families, and healthcare systems.

BACKGROUND

Awake bruxism - a stress behavior characterized by clenching of the teeth - is a strong contributor to chronic mTMD. GML modulates psychological stress and motor responses and could thus reduce muscle activity in chronic musculoskeletal conditions, including mTMD.

METHODS

We recorded the electromyographic (EMG) activity in the right masseter of 14 women with chronic (>6 months) mTMD (median [IQR] = 39.5.3 [24.3] years) and 15 pain-free women (median [IQR] = 30.0 [3.5] years) during a GML session, including 3 music (stressful, relaxing, and participants' favorite music) and a no-music (pink noise) control blocks, each lasting 15 minutes. We measured the motor effort of the right masseter relative to the participants' maximum voluntary contraction (MVC), the muscular effort to maintain mandibular posture (EMG_posture ), and to produce spontaneous awake bruxism episodes (EMG_bruxism ), and the duration and frequency of spontaneous awake bruxism episodes. We tested between-group and within-group (between blocks) differences, as well as the effect of the interaction group by experimental block on these outcome measures.

RESULTS

In both groups, EMG_posture was significantly affected by the interaction group by experimental block (P < .001). Compared to pink noise [mean (95% CI); mTMD: 2.2 (1.6-2.8) %MVC; Controls: 1.1 (0.5-1.7) %MVC], EMG_posture increased during the stressful music block [contrast estimate (95% CI); mTMD: +0.8 (0.7-0.8) %MVC; Controls: +0.3 (0.3-0.4) %MVC; both P < .001], and decreased during the relaxing [mTMD: -0.4 (-0.5 to -0.4) %MVC; Controls: -0.3 (-0.4 to -0.3) %MVC; both P < .001] and favorite [mTMD: -0.5 (-0.6 to -0.5) %MVC; Controls: -0.5 (-0.5 to -0.4) %MVC; both P < .001] music blocks. EMG_posture was greater in mTMD individuals than controls during the favorite music [contrast estimate (95% CI): +1.1 (0.2-1.9) %MVC; P = .019] and the pink noise [+1.1 (0.2-2.0) %MVC; P = .014] blocks. EMG_bruxism was significantly affected by the interaction group by experimental block (P < .001). In mTMD participants, compared to the pink noise block [mean (95% CI); 23.8 (16.0-31.6) %MVC], EMG_bruxism increased during the stressful music block [contrast estimate (95% CI); +10.2 (8.6-11.8) %MVC], and decreased during the relaxing [-6.2 (-8.1 to -4.3) %MVC; P < .001] and favorite [-10.2 (-12.2 to -9.1) %MVC; P < .001] music blocks. These effects were not observed in the control group [mean (95% CI); pink noise: 19.3 (10.9-27.6); stressful: 21.2 (12.9-29.4) %MVC; relaxing: 21.6 (13.3-29.9) %MVC; favorite: 24.2 (15.8-32.7) %MVC; all P > .05]. EMG_bruxism was significantly greater in mTMD participants than controls during the stressful music block [contrast estimate (95% CI): +12.9 (1.6-24.2) %MVC; P = .026). GML did not affect the duration or the frequency of awake bruxism in either group (median [IQR], mTMD: 23.5 [96.7] s, range 1-1300 seconds; Controls: 5.5 [22.5], range 0-246 seconds; P = .108). The frequency of awake bruxism episodes was greater in the mTMD group compared to controls only during the pink noise block (median [IQR], mTMD: 5 [15.3] episodes, range 0-62 episodes; Controls: 1 [3] episode, range 0-27 episodes; P = .046). No significant between-group differences were found in either the overall time spent engaging in awake bruxism (median [IQR], mTMD: 23.5 [96.7] s, range 1-1300 seconds; Controls: 5.5 [22.5], range 0-246 seconds; P = .108), or during each block (all P > .05).

CONCLUSIONS

In subjects with chronic mTMD, relaxing music and the individual's favorite music decreased the muscular effort during spontaneous awake bruxism episodes by 26% and 44% (relative changes), respectively. In contrast, stressful music increases it by about 43%. Because of its positive effects on awake bruxism, GML with selected music could be a promising and non-invasive component of a multimodal approach for the management of chronic mTMD.

A novel cortical biomarker signature for predicting pain sensitivity: protocol for the PREDICT longitudinal analytical validation study

PREDICT will undertake analytical validation of a peak alpha frequency and corticomotor excitability biomarker, determining the sensitivity, specificity, and accuracy at predicting pain sensitivity.

Introduction:

Temporomandibular disorder is a common musculoskeletal pain condition with development of chronic symptoms in 49% of patients. Although a number of biological factors have shown an association with chronic temporomandibular disorder in cross-sectional and case control studies, there are currently no biomarkers that can predict the development of chronic symptoms. The PREDICT study aims to undertake analytical validation of a novel peak alpha frequency (PAF) and corticomotor excitability (CME) biomarker signature using a human model of the transition to sustained myofascial temporomandibular pain (masseter intramuscular injection of nerve growth factor [NGF]). This article describes, a priori, the methods and analysis plan.

Methods:

This study uses a multisite longitudinal, experimental study to follow individuals for a period of 30 days as they progressively develop and experience complete resolution of NGF-induced muscle pain. One hundred fifty healthy participants will be recruited. Participants will complete twice daily electronic pain diaries from day 0 to day 30 and undergo assessment of pressure pain thresholds, and recording of PAF and CME on days 0, 2, and 5. Intramuscular injection of NGF will be given into the right masseter muscle on days 0 and 2. The primary outcome is pain sensitivity.

Perspective:

PREDICT is the first study to undertake analytical validation of a PAF and CME biomarker signature. The study will determine the sensitivity, specificity, and accuracy of the biomarker signature to predict an individual's sensitivity to pain.

Registration details:

ClinicalTrials.gov: NCT04241562 (prospective).

The Usefulness of the Pressure Algometer in the Diagnosis and Treatment of Orofacial Pain Patients: A Systematic Review

Objectives

The pressure pain threshold (PPT) may be an efficient approach to screen and evaluate orofacial pain. However, the results of previous PPT studies have varied greatly. The aim of this paper was to determine whether the PPT is an efficient approach for screening and evaluating orofacial pain.

Methods

The search yielded 123 articles. After removal of duplicates and screening of abstracts, 32 articles were selected for further evaluation. The Cochrane Collaboration tool for assessing the risk of bias was used for the evaluation of the studies.

Results

The studies covered a total of 4403 adult patients, aged 16-62, and 30 children. The studies investigated the reliability and validity of the PPT (measured by a pressure algometer) in TMD patients. The PPT was investigated in relation to headache, menstrual cycle, oral contraception, occlusal interference, and occlusal appliances. Generally, the risk of bias was low to unclear. Some structural limitations were inherent in the studies, such as small samples and short duration of the testing involved. Also, the analyzed studies lacked consistency in study design and patient management. Pressure increase values differed from 20 kPa/s to 50 kPa/s and from 0.5 kg/cm²/s to 2 kg/cm²/s. Descriptions of the PPT examination points also varied, from very precise and repeatable to a simple listing of anatomical points. The number of measurements varied from 1 to 5 at each visit. The intervals ranged from 5 seconds to 15 minutes. However, some studies confirmed that the pressure algometer is an effective tool for determining the source of orofacial pain.

Conclusions

Based on the analyzed articles, the authors argue that the PPT is not an efficient approach for screening and evaluating orofacial pain. What is more, it should not be used as the only diagnostics tool for patients with orofacial pain. Importantly, however, additional factors should be considered in the future for the evaluation of the PPT, including body symmetry and posture, hormone levels and the menstrual phase in women, and the use of medications and its influence on the PPT. Further clinical trials should also be performed on the PPT, examining head and neck pain patients, with more precise study design and larger samples.

Quantitative assessment of nonpelvic pressure pain sensitivity in urologic chronic pelvic pain syndrome: a MAPP Research Network study

Experimental pain sensitivity was assessed in individuals with urologic chronic pelvic pain syndrome (UCPPS) as part of the Multidisciplinary Approach to the Study of Chronic Pelvic Pain (MAPP) Research Network. A series of computer-controlled pressure stimuli were delivered to the thumbnail bed, an asymptomatic site distant from the area of UCPPS pain that is considered to be indicative of overall body pain threshold. Stimuli were rated according to a standardized magnitude estimation protocol. Pain sensitivity in participants with UCPPS was compared with healthy controls and a mixed pain group composed of individuals with other chronic overlapping pain conditions, including fibromyalgia, chronic fatigue, and irritable bowel syndromes. Data from 6 participating MAPP testing sites were pooled for analysis. Participants with UCPPS (n = 153) exhibited an intermediate pain sensitivity phenotype: they were less sensitive relative to the mixed pain group (n = 35) but significantly more sensitive than healthy controls (n = 100). Increased pain sensitivity in patients with UCPPS was associated with both higher levels of clinical pain severity and more painful body areas outside the pelvic region. Exploratory analyses in participants with UCPPS revealed that pain sensitivity increased during periods of urologic symptom flare and that less pressure pain sensitivity at baseline was associated with a greater likelihood of subsequent genitourinary pain improvement 1 year later. The finding that individuals with UCPPS demonstrate nonpelvic pain hypersensitivity that is related to clinical symptoms suggests that central nervous system mechanisms of pain amplification contribute to UCPPS.

[Screening for temporomandibular disorders : A sensible approach?]

BACKGROUND

Temporomandibular disorders (TMDs) are typically characterized by pain in the masticatory muscles and temporomandibular joints (TMJs) and by limitation of mandibular mobility. In June 2019, the German Society of Craniomandibular Function and Disorders presented a screening tool to identify individuals with TMDs. The assessment tool consists of patient history (three questions related to jaw pain, one question related to impaired mandibular mobility) and a clinical examination (palpation of masticatory muscles and TMJs; evaluation of maximum jaw opening; assessment of the presence of occlusal disturbances; documentation of TMJ noises).

OBJECTIVES

The present article focusses on two questions: (1) Which of the nine parts of the tool are appropriate, and which are not? (2) In general, can screening for TMDs be recommended?

CONCLUSION

While the anamnestic questions, as well as the assessment of maximum mandibular opening, reflect the clinically relevant symptoms and signs of TMD patients, the remaining four clinical measures do not. Furthermore, TMD screening for painful TMDs appears unnecessary because patients suffering from orofacial pain and/or restricted mandibular mobility are likely to consult a therapist by themselves. Therefore, the use of this screening tool may lead to overdiagnosis, possibly resulting in nonindicated diagnostic and therapeutic measures.

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.

Clinical predictors of persistent temporomandibular disorder in people with first-onset temporomandibular disorder: A prospective case-control study

BACKGROUND

When patients first develop a painful temporomandibular disorder (TMD) and seek care, 1 priority for clinicians is to assess prognosis. The authors aimed to develop a predictive model by using biopsychosocial measures from the Diagnostic Criteria for Temporomandibular Disorders (DC-TMD) to predict risk of developing TMD symptom persistence.

METHODS

At baseline, trained examiners identified 260 participants with first-onset TMD classified by using DC-TMD-compliant protocols. After follow-up at least 6 months later, 72 (49%) had examiner-classified TMD (persistent cases), and 75 (51%) no longer had examiner-classified TMD (transient cases). For multivariable logistic regression analysis, the authors used blocks of variables selected using minimum redundancy maximum relevance to construct a model to predict the odds of TMD persistence.

RESULTS

At onset, persistent cases had multiple worse TMD clinical measures and, among Axis II measures, only greater baseline pain intensity (odds ratio [OR], 1.5; 95% confidence interval [CI], 1.04 to 2.2; P = .030) and more physical symptoms (OR, 1.8; 95% CI, 1.2 to 2.9; P = .004) than did transient cases. A multivariable model using TMD clinical measures showed greater discriminative capacity (area under the receiver operating characteristic curve, 0.74; 95% CI, 0.73 to 0.75) than did a model involving psychosocial measures (area under the receiver operating characteristic curve, 0.63; 95% CI, 0.62 to 0.64).

CONCLUSIONS

Clinical measures that clinicians can assess readily when TMD first develops are useful in predicting the risk of developing persistent TMD. Psychosocial measures are important predictors of onset but do not add meaningfully to the predictive capacity of clinical measures.

PRACTICAL IMPLICATIONS

When TMD first develops, clinicians usefully can identify patients at higher risk of developing persistence by using clinical measures that they logically also could use in treatment planning and for monitoring outcomes of intervention.

Quantitative sensory testing and predicting outcomes for musculoskeletal pain, disability, and negative affect: a systematic review and meta-analysis

Hypersensitivity due to central pain mechanisms can influence recovery and lead to worse clinical outcomes, but the ability of quantitative sensory testing (QST), an index of sensitisation, to predict outcomes in chronic musculoskeletal disorders remains unclear. We systematically reviewed the evidence for ability of QST to predict pain, disability, and negative affect using searches of CENTRAL, MEDLINE, EMBASE, AMED, CINAHL, and PubMed databases up to April 2018. Title screening, data extraction, and methodological quality assessments were performed independently by 2 reviewers. Associations were reported between baseline QST and outcomes using adjusted (β) and unadjusted (r) correlations. Of the 37 eligible studies (n = 3860 participants), 32 were prospective cohort studies and 5 randomised controlled trials. Pain was an outcome in 30 studies, disability in 11, and negative affect in 3. Meta-analysis revealed that baseline QST predicted musculoskeletal pain (mean r = 0.31, 95% confidence interval [CI]: 0.23-0.38, n = 1057 participants) and disability (mean r = 0.30, 95% CI: 0.19-0.40, n = 290 participants). Baseline modalities quantifying central mechanisms such as temporal summation and conditioned pain modulation were associated with follow-up pain (temporal summation: mean r = 0.37, 95% CI: 0.17-0.54; conditioned pain modulation: mean r = 0.36, 95% CI: 0.20-0.50), whereas baseline mechanical threshold modalities were predictive of follow-up disability (mean r = 0.25, 95% CI: 0.03-0.45). Quantitative sensory testing indices of pain hypersensitivity might help develop targeted interventions aiming to improve outcomes across a range of musculoskeletal conditions.

The silent epidemic of chronic pain in older adults

Chronic pain is highly prevalent among older adults where it is associated with significant suffering, disability, social isolation, and greater costs and burden to health care systems. Pharmaceutical treatment of chronic pain in older adults is usually only partially effective and is often limited by side effects including urinary retention, constipation, sedation, cognitive impairment, and increased risk of falls. Since older adults are underrepresented in clinical trials testing treatments for chronic pain, the potential impacts of polypharmacy and frailty on reported outcomes and side effect profiles are largely unknown. Thus, for current treatments, providers and patients must balance anticipated benefits of pain reduction with the known and unknown risks of treatment. Chronic pain is also a risk factor for premature death as well as accelerated cognitive decline, suggesting potential shared mechanisms between persistent pain (or its treatment) and dementia. Cognitive decline and dementia may also impact pain perception and the ability to report pain, complicating treatment decisions. Associations between persistent pain and the risks of premature death and accelerated cognitive decline make estimates for chronic pain in these populations particularly challenging. Future research is needed to improve estimates for chronic pain in older adults, to elucidate underlying mechanisms of pain with aging, and to develop and advance safer, more effective treatment options for chronic pain in older adults.

Long-term changes in biopsychosocial characteristics related to temporomandibular disorder: findings from the OPPERA study

Painful temporomandibular disorders (TMDs) are both consequence and cause of change in multiple clinical, psychosocial, and biological factors. Although longitudinal studies have identified antecedent biopsychosocial factors that increase risk of the TMD onset and persistence, little is known about long-term change in those factors after TMD develops or remits. During a 7.6-year median follow-up period, we measured change in psychosocial characteristics, pain sensitivity, cardiovascular indicators of autonomic function, and clinical jaw function among 189 participants whose baseline chronic TMD status either persisted or remitted and 505 initially TMD-free participants, 83 of whom developed TMD. Among initially TMD-free participants who developed TMD, symptoms and pain sensitivity increased, whereas psychological function worsened. By contrast, participants with chronic TMD at baseline tended to show improved TMD symptoms, improved jaw function, reduced somatic symptoms, and increased positive affect. In general, clinical and psychosocial variables more frequently changed in parallel with TMD status compared with pain sensitivity and autonomic measures. These findings demonstrate a complex pattern of considerable changes in biopsychosocial function associated with changes in TMD status. In particular, several biopsychosocial parameters improved among participants with chronic TMD despite pain persisting for years, suggesting considerable potential for ongoing coping and adaptation in response to persistent pain.

Pressure Pain Threshold and Anxiety in Adolescent Females With and Without Juvenile Fibromyalgia: A Pilot Study

OBJECTIVES

Reduced pain thresholds have been documented in adult fibromyalgia, but there are no quantitative studies of altered pain sensitivity in adolescents with juvenile fibromyalgia (JFM). The current study examined differences in pressure pain sensitivity between adolescent females with JFM and healthy controls. The relationship between levels of anxiety and pain were also examined.

METHODS

A total of 34 JFM (15.4±1.4 y old) and 31 controls (14.5±1.3 y old) completed self-report measures of pain and anxiety. Pressure pain threshold was assessed (palm and forehead sites) with a hand-held algometer. Participants indicated the first sensation of pain and then rated the intensity of pain on a Numerical Rating Scale.

RESULTS

Adolescents with JFM exhibited greater sensitivity to pressure pain compared with controls. While the difference between JFM and controls was only observed at the forehead, the intensity of pain produced by the pressure algometry at both sites was significantly higher in the JFM participants compared with controls. Correlations between clinical pain and anxiety were significant for the JFM group only. No relationships were observed between anxiety and pressure pain for either group.

DISCUSSION

This study is a first step toward investigating mechanisms of altered pain processing in adolescents with JFM. Adolescents with JFM were found be more sensitive to pressure pain than their healthy peers, which suggests a propensity for sensitization of peripheral and/or central nociceptive information often reported in adult fibromyalgia, and which does not appear to be affected by anxiety.

Acute Low Back Pain: Differential Somatosensory Function and Gene Expression Compared With Healthy No-Pain Controls

OBJECTIVES

Low back pain (LBP) is the second most frequently diagnosed pain condition in the United States, and although a majority of individuals have resolution of pain during the acute period, an estimated 40% of individuals will experience persistent pain. Given the heterogenous nature of LBP, this study sought to describe and compare somatosensory and molecular (gene expression) profiles between individuals with acute LBP and healthy no-pain controls.

METHODS

Using a previously established protocol, we comprehensively assessed somatosensory parameters among 31 no-pain control participants and 31 participants with acute LBP. Samples of whole blood were drawn to examine mRNA expression of candidate genes involved in the transduction, maintenance, and modulation of pain.

RESULTS

The acute LBP group exhibited increased pain sensitivity to cold stimuli, mechanical stimuli, including mechanical temporal summation at both the painful back area and remote location suggesting a mechanism of enhanced central nervous system excitability. In addition, deep tissue-specific peripheral sensitization was suggested due to significant differences in pressure pain threshold of the painful back area, but not the remote body site. Several genes that were differentially expressed were significantly associated with somatosensory alterations identified in the acute LBP group.

DISCUSSION

Acute LBP participants showed selective pain sensitivity enhancement and differential gene expression profiles compared with pain-free controls. Further research to characterize pain-associated somatosensory changes in the context of altered mRNA expression levels may provide insight on the molecular underpinnings of maladaptive chronic pain.

Temporal change in headache and its contribution to the risk of developing first-onset temporomandibular disorder in the Orofacial Pain: Prospective Evaluation and Risk Assessment (OPPERA) study

While cross-sectional studies have demonstrated an association between headache and temporomandibular disorder (TMD), whether headache can predict the onset of TMD is unknown. The aims of this study were to evaluate the contribution of headache to the risk of developing TMD and describe patterns of change in headache types over time. An initially TMD-free cohort of 2410 persons with low frequency of headache completed quarterly questionnaires assessing TMD and headache symptoms over a median 3.0-year follow-up period. First-onset TMD was confirmed by clinical examination in 199 participants. Baseline reports of migraine (hazard ratio [HR] = 1.67, 95% confidence interval [CI]: 1.06-2.62) or mixed headache types (HR = 4.11, 95% CI: 1.47-11.46), or headache frequency (HR = 2.13, 95% CI: 1.31-3.48) predicted increased risk of developing TMD. In addition, headache dynamics across the follow-up period before the TMD onset were evaluated in a nested case-control study where 248 incident TMD cases were matched to 191 TMD-free controls. Both headache prevalence and frequency increased across the observation period among those who developed TMD but not among controls. Patients with TMD were more likely to experience worsening in the headache type compared with that by controls, eg, prevalence of definite migraine among TMD cases increased 10-fold. Among all headache types experienced by patients with TMD before the TMD onset, migraine had the highest odds of progression relative to remission (odds ratio = 2.8, 95% CI: 1.6-4.8), whereas for controls this ratio was significant only for the tension-type headache (odds ratio = 2.1, 95% CI: 1.2-3.9). The important clinical implication of these findings is that adequate treatment of migraine may reduce the risk for developing TMD.

Overlapping Chronic Pain Conditions: Implications for Diagnosis and Classification

There is increasing recognition that many if not most common chronic pain conditions are heterogeneous with a high degree of overlap or coprevalence of other common pain conditions along with influences from biopsychosocial factors. At present, very little attention is given to the high degree of overlap of many common pain conditions when recruiting for clinical trials. As such, many if not most patients enrolled into clinical studies are not representative of most chronic pain patients. The failure to account for the heterogeneous and overlapping nature of most common pain conditions may result in treatment responses of small effect size when these treatments are administered to patients with chronic overlapping pain conditions (COPCs) represented in the general population. In this brief review we describe the concept of COPCs and the putative mechanisms underlying COPCs. Finally, we present a series of recommendations that will advance our understanding of COPCs.

PERSPECTIVE

This brief review describes the concept of COPCs. A mechanism-based heuristic model is presented and current knowledge and evidence for COPCs are presented. Finally, a set of recommendations is provided to advance our understanding of COPCs.

Adaptations in Evoked Pain Sensitivity and Conditioned Pain Modulation after Development of Chronic Neck Pain

Numerous studies demonstrate elevated pain sensitivity and impaired conditioned pain modulation (CPM) in patients with chronic musculoskeletal pain compared to healthy individuals; however, the time course of changes in pain sensitivity and CPM after the development of a chronic pain condition is unclear. Secondary analysis of data from a prospective investigation examined changes in evoked pain sensitivity and CPM before and after development of chronic neck pain (CNP). 171 healthy office workers participated in a baseline assessment, followed by monthly online questionnaires to identify those who developed CNP over the subsequent year. These individuals (N = 17) and a cohort of participants (N = 10) who remained pain-free during the follow-up period returned for a 12-month follow-up assessment of mechanical and thermal pain sensitivity and CPM. Pain sensitivity measures did not differ between groups at baseline; however, cold pain threshold decreased in the CNP group at follow-up (p < 0.05). CPM was lower at baseline in the CNP group compared to those who reported no neck pain (p < 0.02) and remained unchanged one year later. These findings indicate that CPM is reduced in healthy individuals prior to the development of chronic neck pain and the subsequent reduction of thresholds for cold but not pressure pain.

Identification of clusters of individuals relevant to temporomandibular disorders and other chronic pain conditions: the OPPERA study

The classification of most chronic pain disorders gives emphasis to anatomical location of the pain to distinguish one disorder from the other (eg, back pain vs temporomandibular disorder [TMD]) or to define subtypes (eg, TMD myalgia vs arthralgia). However, anatomical criteria overlook etiology, potentially hampering treatment decisions. This study identified clusters of individuals using a comprehensive array of biopsychosocial measures. Data were collected from a case-control study of 1031 chronic TMD cases and 3247 TMD-free controls. Three subgroups were identified using supervised cluster analysis (referred to as the adaptive, pain-sensitive, and global symptoms clusters). Compared with the adaptive cluster, participants in the pain-sensitive cluster showed heightened sensitivity to experimental pain, and participants in the global symptoms cluster showed both greater pain sensitivity and greater psychological distress. Cluster membership was strongly associated with chronic TMD: 91.5% of TMD cases belonged to the pain-sensitive and global symptoms clusters, whereas 41.2% of controls belonged to the adaptive cluster. Temporomandibular disorder cases in the pain-sensitive and global symptoms clusters also showed greater pain intensity, jaw functional limitation, and more comorbid pain conditions. Similar results were obtained when the same methodology was applied to a smaller case-control study consisting of 199 chronic TMD cases and 201 TMD-free controls. During a median 3-year follow-up period of TMD-free individuals, participants in the global symptoms cluster had greater risk of developing first-onset TMD (hazard ratio = 2.8) compared with participants in the other 2 clusters. Cross-cohort predictive modeling was used to demonstrate the reliability of the clusters.

Neuroimaging of Central Sensitivity Syndromes: Key Insights from the Scientific Literature

Central sensitivity syndromes are characterized by distressing symptoms, such as pain and fatigue, in the absence of clinically obvious pathology. The scientific underpinnings of these disorders are not currently known. Modern neuroimaging techniques promise new insights into mechanisms mediating these postulated syndromes. We review the results of neuroimaging applied to five central sensitivity syndromes: fibromyalgia, chronic fatigue syndrome, irritable bowel syndrome, temporomandibular joint disorder, and vulvodynia syndrome. Neuroimaging studies of basal metabolism, anatomic constitution, molecular constituents, evoked neural activity, and treatment effect are compared across all of these syndromes. Evoked sensory paradigms reveal sensory augmentation to both painful and nonpainful stimulation. This is a transformative observation for these syndromes, which were historically considered to be completely of hysterical or feigned in origin. However, whether sensory augmentation represents the cause of these syndromes, a predisposing factor, an endophenotype, or an epiphenomenon cannot be discerned from the current literature. Further, the result from cross-sectional neuroimaging studies of basal activity, anatomy, and molecular constituency are extremely heterogeneous within and between the syndromes. A defining neuroimaging "signature" cannot be discerned for any of the particular syndromes or for an over-arching central sensitization mechanism common to all of the syndromes. Several issues confound initial attempts to meaningfully measure treatment effects in these syndromes. At this time, the existence of "central sensitivity syndromes" is based more soundly on clinical and epidemiological evidence. A coherent picture of a "central sensitization" mechanism that bridges across all of these syndromes does not emerge from the existing scientific evidence.

Pain Mechanisms and Centralized Pain in Temporomandibular Disorders

Until recently, most clinicians and scientists believed that the experience of pain is perceptually proportional to the amount of incoming peripheral nociceptive drive due to injury or inflammation in the area perceived to be painful. However, many cases of chronic pain have defied this logic, leaving clinicians perplexed as to how patients are experiencing pain with no obvious signs of injury in the periphery. Conversely, there are patients who have a peripheral injury and/or inflammation but little or no pain. What makes some individuals experience intense pain with minimal peripheral nociceptive stimulation and others experience minimal pain with serious injury? It is increasingly well accepted in the scientific community that pain can be generated and maintained or, through other mechanisms, suppressed by changes in the central nervous system, creating a complete mismatch between peripheral nociceptive drive and perceived pain. In fact, there is no known chronic pain condition where the observed extent of peripheral damage reproducibly engenders the same level of pain across individuals. Temporomandibular disorders (TMDs) are no exception. This review focuses on the idea that TMD patients range on a continuum-from those whose pain is generated peripherally to those whose pain is centralized (i.e., generated, exacerbated, and/or maintained by central nervous system mechanisms). This article uses other centralized chronic pain conditions as a guide, and it suggests that the mechanistic variability in TMD pain etiology has prevented us from adequately treating many individuals who are diagnosed with the condition. As the field moves forward, it will be imperative to understand each person's pain from its own mechanistic standpoint, which will enable clinicians to deliver personalized medicine to TMD patients and eventually provide relief in even the most recalcitrant cases.

Painful Temporomandibular Disorder: Decade of Discovery from OPPERA Studies

In 2006, the OPPERA project (Orofacial Pain: Prospective Evaluation and Risk Assessment) set out to identify risk factors for development of painful temporomandibular disorder (TMD). A decade later, this review summarizes its key findings. At 4 US study sites, OPPERA recruited and examined 3,258 community-based TMD-free adults assessing genetic and phenotypic measures of biological, psychosocial, clinical, and health status characteristics. During follow-up, 4% of participants per annum developed clinically verified TMD, although that was a "symptom iceberg" when compared with the 19% annual rate of facial pain symptoms. The most influential predictors of clinical TMD were simple checklists of comorbid health conditions and nonpainful orofacial symptoms. Self-reports of jaw parafunction were markedly stronger predictors than corresponding examiner assessments. The strongest psychosocial predictor was frequency of somatic symptoms, although not somatic reactivity. Pressure pain thresholds measured at cranial sites only weakly predicted incident TMD yet were strongly associated with chronic TMD, cross-sectionally, in OPPERA's separate case-control study. The puzzle was resolved in OPPERA's nested case-control study where repeated measures of pressure pain thresholds revealed fluctuation that coincided with TMD's onset, persistence, and recovery but did not predict its incidence. The nested case-control study likewise furnished novel evidence that deteriorating sleep quality predicted TMD incidence. Three hundred genes were investigated, implicating 6 single-nucleotide polymorphisms (SNPs) as risk factors for chronic TMD, while another 6 SNPs were associated with intermediate phenotypes for TMD. One study identified a serotonergic pathway in which multiple SNPs influenced risk of chronic TMD. Two other studies investigating gene-environment interactions found that effects of stress on pain were modified by variation in the gene encoding catechol O-methyltransferase. Lessons learned from OPPERA have verified some implicated risk factors for TMD and refuted others, redirecting our thinking. Now it is time to apply those lessons to studies investigating treatment and prevention of TMD.

Directed Acyclic Graphs for Oral Disease Research

Directed acyclic graphs (DAGs) are nonparametric graphical tools used to depict causal relations in the epidemiologic assessment of exposure-outcome associations. Although their use in dental research was first advocated in 2002, DAGs have yet to be widely adopted in this field. DAGs help identify threats to causal inference such as confounders, bias due to subject selection, and inappropriate handling of missing data. DAGs can also inform the data analysis strategy based on relations among variables depicted on it. This article uses the example of a study of temporomandibular disorders (TMDs), investigating causal effects of facial injury on subsequent risk of TMD. We illustrate how DAGs can be used to identify 1) potential confounders, 2) mediators and the consequences of attempt to estimate direct causal effects, 3) colliders and the consequences of conditioning on colliders, and 4) variables that are simultaneously mediators and confounders and the consequences of adjustment for such variables. For example, one DAG shows that statistical adjustment for the pressure pain threshold would necessarily bias the causal relation between facial injury and TMD. Finally, we discuss the usefulness of DAGs during study design, subject selection, and choosing variables to be measured in a study.

The Emotional Brain as a Predictor and Amplifier of Chronic Pain

Human neuroimaging studies and complementary animal experiments now identify the gross elements of the brain involved in the chronification of pain. We briefly review these advances in relation to somatic and orofacial persistent pain conditions. First, we emphasize the importance of reverse translational research for understanding chronic pain-that is, the power of deriving hypotheses directly from human brain imaging of clinical conditions that can be invasively and mechanistically studied in animal models. We then review recent findings demonstrating the importance of the emotional brain (i.e., the corticolimbic system) in the modulation of acute pain and in the prediction and amplification of chronic pain, contrasting this evidence with recent findings regarding the role of central sensitization in pain chronification, especially for orofacial pain. We next elaborate on the corticolimbic circuitry and underlying mechanisms that determine the transition to chronic pain. Given this knowledge, we advance a new mechanistic definition of chronic pain and discuss the clinical implications of this new definition as well as novel therapeutic potentials suggested by these advances.

Subjective Sleep Quality Deteriorates Before Development of Painful Temporomandibular Disorder

There is good evidence that poor sleep quality increases risk of painful temporomandibular disorder (TMD). However, little is known about the course of sleep quality in the months preceding TMD onset, and whether the relationship is mediated by heightened sensitivity to pain. The Pittsburgh Sleep Quality Index was administered at enrollment into the Orofacial Pain: Prospective Evaluation and Risk Assessment (OPPERA) prospective cohort study. Thereafter the Sleep Quality Numeric Rating Scale was administered every 3 months to 2,453 participants. Sensitivity to experimental pressure pain and pinprick pain stimuli was measured at baseline and repeated during follow-up of incident TMD cases (n = 220) and matched TMD-free controls (n = 193). Subjective sleep quality deteriorated progressively, but only in those who subsequently developed TMD. A Cox proportional hazards model showed that risk of TMD was greater among participants whose sleep quality worsened during follow-up (adjusted hazard ratio = 1.73, 95% confidence limits = 1.29, 2.32). This association was independent of baseline measures of sleep quality, psychological stress, somatic awareness, comorbid conditions, nonpain facial symptoms, and demographic characteristics. Poor baseline sleep quality was not significantly associated with baseline pain sensitivity or with subsequent change in pain sensitivity. Furthermore the relationship between sleep quality and TMD incidence was not mediated via baseline pain sensitivity or change in pain sensitivity.

PERSPECTIVE

Subjective sleep quality deteriorates progressively before the onset of painful TMD, but sensitivity to experimental pain does not mediate this relationship. Furthermore, the relationship is independent of potential confounders such as psychological stress, somatic awareness, comorbid conditions, nonpain facial symptoms, and various demographic factors.

Comparison of Low Back Pain Recovery and Persistence: A Descriptive Study of Characteristics at Pain Onset

BACKGROUND

Persistent low back pain is a significant problem worldwide. Early identification and treatment of individuals at high risk for persistent low back pain have been suggested as strategies to decrease the rate of disability associated with this condition.

PURPOSE

To examine and compare demographic, pain-related, psychological, and somatosensory characteristics in a cohort of participants with acute low back pain who later went on to experience persistent low back pain or whose pain resolved within the first 6 weeks after initial onset.

METHODS

A descriptive study was conducted among men and women 18-50 years of age who had an acute episode of low back pain. Study questionnaires were administered to collect demographic information and measures of pain, coping, reactivity, mood, work history and satisfaction, and disability. A standardized protocol of quantitative sensory testing was performed on each participant at the painful area of their low back and at a remote site on their arm.

RESULTS

The sample consisted of 48 participants, of whom 19 went on to develop persistent low back pain and 29 resolved. Compared to the resolved group, the persistent low back pain group was significantly older and had a lower level of educational attainment, a higher body mass index, and higher mean "least" pain score on the Brief Pain Inventory-Short Form. Significantly higher thermal detection thresholds at the painful and remote sites as well as signs of central sensitivity differentiated the persistent pain group from the resolved group during the acute stage of low back pain.

Deep pain sensitivity is correlated with oral-health-related quality of life but not with prosthetic factors in complete denture wearers

Low pressure Pain Threshold (PPT) is considered a risk factor for Temporomandibular Disorders (TMD) and is influenced by psychological variables. Objectives To correlate deep pain sensitivity of masticatory muscles with prosthetic factors and Oral-Health-Related Quality of Life (OHRQoL) in completely edentulous subjects. Material and Methods A total of 29 complete denture wearers were recruited. The variables were: a) Pressure Pain Threshold (PPT) of the masseter and temporalis; b) retention, stability, and tooth wear of dentures; c) Vertical Dimension of Occlusion (VDO); d) Oral Health Impact Profile (OHIP) adapted to orofacial pain. The Kolmogorov-Smirnov test, the Pearson Product-Moment correlation coefficient, the Spearman Rank correlation coefficient, the Point-Biserial correlation coefficient, and the Bonferroni correction (α=1%) were applied to the data. Results The mean age (standard deviation) of the participants was of 70.1 years (9.5) and 82% of them were females. There were no significant correlations with prosthetic factors, but significant negative correlations were found between the OHIP and the PPT of the anterior temporalis (r=-0.50, 95% CI-0.73 to 0.17, p=0.005). Discussion The deep pain sensitivity of masticatory muscles in complete dentures wearers is associated with OHRQoL, but not with prosthetic factors.