Wnt signalling in oral and maxillofacial diseases.

Wnts include more than 19 types of secreted glycoproteins that are involved in a wide range of pathological processes in oral and maxillofacial diseases. The transmission of Wnt signalling from the extracellular matrix into the nucleus includes canonical pathways and noncanonical pathways, which play an important role in tooth development, alveolar bone regeneration, and related diseases. In recent years, with the in-depth study of Wnt signalling in oral and maxillofacial-related diseases, many new conclusions and perspectives have been reached, and there are also some controversies. This article aims to summarise the roles of Wnt signalling in various oral diseases, including periodontitis, dental pulp disease, jaw disease, cleft palate, and abnormal tooth development, to provide researchers with a better and more comprehensive understanding of Wnts in oral and maxillofacial diseases.

MMP-7 and MMP-9 are overexpressed in the synovial tissue from severe temporomandibular joint dysfunction.

Matrix metalloproteinases (MMPs) are tissue-enzymes that play a key role during the remodeling process, such as in inflammatory diseases. MMP-7 and MMP-9 have been shown to be implicated in extracellular matrix homeostasis and in joint disc remodeling. The objective of this study was to determine the relation of MMP-7 and MMP-9 expression with severe temporomandibular joint dysfunction, in particular with anterior disk displacement without reduction (ADDwoR), using an immunohistochemical approach. Therefore, twenty human temporomandibular synovia in the test group and ten in the control group were collected. The results showed there was a statistically significant difference (P<0.001) for morphometric and densitometric analysis of both detected MMPs in control and test groups. In conclusion, MMP-7 and MMP-9 were overexpressed in the synovial tissue of patients with ADDwoR.

Estradiol upregulates voltage-gated sodium channel 1.7 in trigeminal ganglion contributing to hyperalgesia of inflamed TMJ.

BACKGROUND: Temporomandibular disorders (TMDs) have the highest prevalence in women of reproductive age. The role of estrogen in TMDs and especially in TMDs related pain is not fully elucidated. Voltage-gated sodium channel 1.7 (Nav1.7) plays a prominent role in pain perception and Nav1.7 in trigeminal ganglion (TG) is involved in the hyperalgesia of inflamed Temporomandibular joint (TMJ). Whether estrogen could upregulate trigeminal ganglionic Nav1.7 expression to enhance hyperalgesia of inflamed TMJ remains to be explored. METHODS: Estrous cycle and plasma levels of 17ß-estradiol in female rats were evaluated with vaginal smear and enzyme linked immunosorbent assay, respectively. Female rats were ovariectomized and treated with 17ß-estradiol at 0 µg, 20 µg and 80 µg, respectively, for 10 days. TMJ inflammation was induced using complete Freund's adjuvant. Head withdrawal thresholds and food intake were measured to evaluate the TMJ nociceptive responses. The expression of Nav1.7 in TG was examined using real-time PCR and western blot. The activity of Nav1.7 promoter was examined using luciferase reporter assay. The locations of estrogen receptors (ERα and ERß), the G protein coupled estrogen receptor (GPR30), and Nav1.7 in TG were examined using immunohistofluorescence. RESULTS: Upregulation of Nav1.7 in TG and decrease in head withdrawal threshold were observed with the highest plasma 17ß-estradiol in the proestrus of female rats. Ovariectomized rats treated with 80 µg 17ß-estradiol showed upregulation of Nav1.7 in TG and decrease in head withdrawal threshold as compared with that of the control or ovariectomized rats treated with 0 µg or 20 µg. Moreover, 17ß-estradiol dose-dependently potentiated TMJ inflammation-induced upregulation of Nav1.7 in TG and also enhanced TMJ inflammation-induced decrease of head withdrawal threshold in ovariectomized rats. In addition, the estrogen receptor antagonist, ICI 182,780, partially blocked the 17ß-estradiol effect on Nav1.7 expression and head withdrawal threshold in ovariectomized rats. ERα and ERß, but not GPR30, were mostly co-localized with Nav1.7 in neurons in TG. In the nerve growth factor-induced and ERα-transfected PC12 cells, 17ß-estradiol dose-dependently enhanced Nav1.7 promoter activity, whereas mutations of the estrogen response element at -1269/-1282 and -1214/-1227 in the promoter completely abolished its effect on the promoter activity. CONCLUSION: Estradiol could upregulate trigeminal ganglionic Nav1.7 expression to contribute to hyperalgesia of inflamed TMJ.

CGRP plasma level changes in patients with temporomandibular disorders treated with occlusal splints - a randomised clinical trial.

INTRODUCTION: Occlusal splint therapy is a well-known method for the treatment of TMD. Muscle stretching and pain relief are effects of occlusal appliance. The aim of this study was to evaluate the plasma level of CGRP in patients with myofascial pain (RDC/TMD Ia) and myofascial pain with limited opening (RDC/TMD Ib) before and after muscle stretching with occlusal splint therapy. MATERIAL AND METHODS: A randomised trial was performed including 35 subjects (males = 10, females = 25) in the experimental group and 30 subjects (males = 9, females = 21) in the control group. Blood samples were taken from the external jugular vein before and after 30 days of occlusal splint therapy. Plasma levels of CGRP were measured with a Radio Immunoassay Kit (Phoenix Pharmaceuticals Inc.) and Cobra Series Auto-Gamma Counting System. RESULTS: The results of the study demonstrated that CGRP concentrations were significantly higher after occlusal splint than before splint therapy: CGRP2 = 17.02 pg/mL (SD = 5.85), CGRP1 = 13.78 pg/mL (SD = 5.12), in the experimental group (p < 0.05). In the control group, there were no statistically significant changes in CGRP levels: CGRP1 = 14.5 pg/mL (SD = 4.87) to CGRP2 = 13.5 pg/mL (SD = 4.63). In the experimental group, there was a statistically significant reduction in pain intensity, VAS1 = 5 (SD = 2.5) to VAS2 = 1 (SD = 1.04) after splint therapy (p < 0.05). In the control group, there were no statistically significant changes in pain intensity: VAS1 = 5 (SD = 2.3) to VAS2 = 4 (SD = 2.6), (p < 0.05). CONCLUSIONS: CGRP plays an important role in muscle blood flow, which is altered by changes in muscle length. Further investigation is needed to clarify the mechanism of muscle blood flow and the muscle healing process in patients with TMD.

Experimental tooth clenching. A model for studying mechanisms of muscle pain.

The overall goal of this thesis was to broaden knowledge of pain mechanisms in myofascial temporomandibular disorders (M-TMD). The specific aims were to: Develop a quality assessment tool for experimental bruxism studies (study I). Investigate proprioceptive allodynia after experimental tooth clenching exercises (study II). Evaluate the release of serotonin (5-HT), glutamate, pyruvate, and lactate in healthy subjects (study III) and in patients with M-TMD (study IV), after experimental tooth clenching exercises. In (I), tool development comprised 5 steps: (i) preliminary decisions, (ii) item generation, (iii) face-validity assessment, (iv) reliability and discriminative validity testing, and (v) instrument refinement. After preliminary decisions and a literature review, a list of 52 items to be considered for inclusion in the tool was generated. Eleven experts were invited to participate on the Delphi panel, of which 10 agreed. After four Delphi rounds, 8 items remained and were included in the Quality Assessment Tool for Experimental Bruxism Studies (Qu-ATEBS). Inter-observer reliability was acceptable (k = 0.77), and discriminative validity high (phi coefficient 0.79; P < 0.01). During refinement, 1 item was removed; the final tool comprised 7 items. In (II), 16 healthy females participated in three 60-min sessions, each with 24- and 48-h follow-ups. Participants were randomly assigned to a repetitive experimental tooth clenching task with a clenching level of 10%, 20%, or 40% of maximal voluntary clenching force (MVCF). Pain intensity, fatigue, perceived intensity of vibration (PIV), perceived discomfort (PD), and pressure pain threshold (PPT) were measured throughout. A significant increase in pain intensity and fatigue but not in PD was observed over time. A significant increase in PIV was only observed at 40 min, and PPT decreased significantly over time at 50 and 60 min compared to baseline. In (III), 30 healthy subjects (16 females, and 14 males) participated in two sessions at a minimum interval of 1 wk. Microdialysis was done to collect 5-HT, glutamate, pyruvate, and lactate and to measure masseter muscle blood flow. Two hours after the start of microdialysis, participants were randomized to a 20-min repetitive experimental tooth clenching task (50% of MVCF) or a control session (no clenching). Pain intensity was measured throughout the experiment. Substance levels and blood flow were unaltered at all time points between sessions, and between genders in each session. Pain intensity was significantly higher after clenching in the clenching session compared to the same time point in the control session. In (IV), 15 patients with M-TMD and 15 healthy controls participated in one session and the methodology described above was used. M-TMD patients had significantly higher levels of 5-HT and significantly lower blood flows than healthy controls. No significant differences for any substance at any time point were observed between groups. Time and group had significant main effects on pain intensity. Qu-ATEBS, the 7-item evidence-based quality assessment tool, is reliable, exhibits face-validity, and has excellent discriminative validity. Tooth clenching was associated with pain, fatigue, and short-lasting mechanical hyperalgesia, but not with proprioceptive allodynia. It seems that tooth clenching is not directly related to delayed onset muscle soreness. In healthy subjects and in patients with M-TMD, levels of 5-HT, glutamate, pyruvate, and lactate were unaltered after tooth clenching. But 5-HT levels were significantly higher and blood flows significantly lower in M-TMD patients than in healthy controls at all time points. These two factors may facilitate the release, and enhance the effects, of other algesic substances that may cause pain.

Interaction of IL-1ß and P2X(3) receptor in pathologic masseter muscle pain.

The exact mechanism underlying chronic masseter muscle pain, a conspicuous symptom in temporomandibular disorder, remains unclear. We investigated whether expression of P2X3 receptor (P2X3R) is involved in mechanical hyperalgesia after contraction of masseter muscle (CMM). As compared with sham rats, the head-withdrawal threshold (HWT) to mechanical pressure stimulation of masseter muscle (MM) (but not after similar stimulation of facial skin) was significantly lower, and IL-1ß level was significantly higher, in CMM rats on day 7 after CMM. The mean percentage of FG-labeled P2X3R-positive neurons was significantly increased in TG following successive IL-1ß injections into the MM for 7 days. Successive administration of an IL-1ß receptor-antagonist into the MM attenuated the increase of P2X3-IR cells in the TG. ATP release from MM after 300-g pressure stimulation of MM was also significantly enhanced after CMM. Administration into MM of the selective P2X3,2/3 receptor antagonist A-317491 attenuated the decrement of HWT in CMM rats. A significant increase in HWT was also observed at 30 min after A-317491 (60 µg) injection in IL-1ß-injected rats. These findings suggest that P2X3R expression associated with enhanced IL-1ß expression and ATP release in MM has a possible important role in MM mechanical hyperalgesia after excessive muscular contraction.

Analysis of the cytokine profiles of the synovial fluid in a normal temporomandibular joint: preliminary study.

The purpose of this study was to compare the cytokine profiles of the synovial fluid from the temporomandibular joint (TMJ) spaces of normal individuals and temporomandibular disorder (TMD) patients. Thirty-four patients with planned orthognathic surgery did not present abnormalities of the TMJ on magnetic resonance images and radiographs and did not show the symptoms identified by the Research Diagnostic Criteria for TMD (RDC-TMD); as a result, they were assigned to the control group. Twenty-two patients who sought treatment for TMD during the same period were assigned to the TMD group. Synovial fluid was collected from superior TMJ spaces, and cytokine expression was analysed by an enzyme-linked immunosorbent assay (ELISA). Significant differences were tested using Fisher's exact test (p<0.05). Granulocyte Macrophage Colony stimulating Factor (GM-CSF), interferon (INF), interleukin (IL)-1ß, IL-2, IL-6, IL-8, IL-10 and tumour necrosis factor (TNF)-α were detected in the TMD group, whereas no cytokines were detected in the control group. The most prevalent cytokines in the TMD group were IL-1ß, IL-6 and GM-CSF. IL-4 and IL-5 were not detected in either the TMD group or in the control group. None of the cytokines that were detected in patients with TMD were found in the articular spaces of normal individuals.

Posterior insular molecular changes in myofascial pain.

Temporomandibular disorders (TMD) include craniocervical pain conditions with unclear etiologies. Central changes are suspected; however, few neuroimaging studies of TMD exist. Single-voxel proton magnetic resonance spectroscopy ((1)H-MRS) was used before and after pressure-pain testing to assess glutamate (Glu), glutamine (Gln), N-acetylaspartate (NAA), and choline (Cho) levels in the right and left posterior insulae of 11 individuals with myofascial TMD and 11 matched control individuals. Glu levels were significantly lower in all individuals after pain testing. Among those with TMD, left-insular Gln levels were related to reported pain, left posterior insular NAA and Cho levels were significantly higher at baseline than in control individuals, and NAA levels were significantly correlated with pain-symptom duration, suggesting adaptive changes. The results suggest that significant central cellular and molecular changes can occur in individuals with TMD.

Human temporomandibular joint and myofascial pain biochemical profiles: a case-control study.

Neurobiological mechanisms of human musculoskeletal pain are poorly understood. This case-control study tested the hypothesis that biomarkers within temporomandibular muscle and joint disorders (TMJD) subjects' masseter muscles or temporomandibular joint (TMJ) synovial fluid correlate with plasma biomarker concentrations. Fifty subjects were recruited and categorized into TMJD cases (n=23) and pain-free controls (n=27) at the University of Minnesota School of Dentistry. Prior to specimen collection, pain intensity and pressure pain threshold masseter muscles and the TMJs were assessed. We collected venous blood; biopsied masseter muscle; and sampled TMJ synovial fluid on the subjects' side of maximum pain intensity. We assayed these tissues for the presence of nerve growth factor (NGF), bradykinin (BK), leukotreine B(4) (LTB(4) ) and prostaglandin E(2) (PGE(2) ), F(2) -isoprostane (F(2) I) and substance P (SP). The data was analyzed using Spearman Correlation Coefficients. We found that only plasma concentrations of bradykinin statistically correlated with synovial fluid concentrations (ρ=-0·48, P=0·005), but no association was found between pain intensities. The data suggests that biomarkers used to assess TMJD need to be acquired in a site-specific manner. We also discovered that F(2) I concentrations were associated with muscle pain intensity and muscle pressure pain threshold (PTT) (ß=0·4, 95%CI: 0·03-0·8) and joint PPT (ß=0·4, 95%CI: 0·07-0·8) suggesting that muscle oxidative stress is involved in myofascial pain and that F(2) -I may be a biomarker for myofascial pain.

Interstitial glutamate concentration is elevated in the masseter muscle of myofascial temporomandibular disorder patients.

AIM: To determine if myofascial temporomandibular disorder (TMD) pain patients have elevated interstitial concentrations of glutamate in the masseter muscle. METHODS: Thirteen patients (3 men, 10 women) diagnosed with myofascial TMD pain and 10 (2 men, 8 women) age-matched healthy controls participated in a single microdialysis session. Microdialysis was performed in the patients in the most painful point of the masseter muscle, while in the healthy subjects a standardized point in the muscle was chosen. Two microdialysis samples were collected over 40-minute epochs. A blood sample was also taken for analysis of plasma glutamate concentration. Numeric rating scale (NRS) scores of pain intensity and unpleasantness, McGill Pain Questionnaire data, pain drawing areas, pressure pain thresholds, pressure pain tolerances, maximum voluntary bite force, and maximum voluntary mouth opening were collected as secondary measurements. RESULTS: The median concentration of glutamate in the masseter muscle of the myofascial TMD pain patients (7.5 ± 2.6 ΜM) was significantly higher (P < .023, Mann-Whitney test) than the concentration in healthy controls (0.5 ± 0.4 ΜM). There were, however, no significant correlations between glutamate concentrations in the masseter muscle and NRS pain scores. Plasma concentrations of glutamate were similar in patients and healthy controls. CONCLUSIONS: The present study demonstrates a marked increase in interstitial glutamate concentration in the masseter muscle of myofascial TMD pain patients. These novel findings suggest that peripheral glutamate could be involved in the pathophysiology of myofascial TMD pain.

Salivary cortisol and IgA levels in patients with myofascial pain treated with occlusal appliances in the short term.

In many studies, the endocrinological response of individuals to different kinds of stresses has been tested. There seems to be widespread agreement that stress, depression, disability and dysfunctional illness behaviors are critical aspects of patients suffering from symptoms like pain, arising out of temporomandibular disorders (TMD). We aimed to explore treatment-induced changes in salivary cortisol, IgA and flow rate values in TMD patients suffering from myofascial pain. Temporomandibular disorders patients (n = 39) were randomized into two groups and treated with two different occlusal appliances. Perceived stress regarding family, work, economy, relationships, general health and stress in general was evaluated at baseline according to a verbal scale. Paraffin-stimulated saliva samples were collected before treatment and during follow-up at 6 and 10 weeks. Flow rate was measured immediately after the saliva collection while salivary cortisol and IgA were determined from samples stored at -70 degrees C. No clear association between reported stress and cortisol or IgA values could be observed at baseline. At 10 weeks follow-up, 92% of the patients felt 'better, much better, symptom-free' and no difference was found between the two appliance groups. Cortisol, IgA and flow rate values showed no systematic between appliance groups' differences. All salivary parameters showed interindividual differences but stayed intra-individually on a similar level throughout the study and no statistically significant changes could be observed when comparing before and after treatment levels. To conclude, there were no treatment-induced changes in saliva parameters despite successful appliance therapy in myofascial pain patients.

Expression of ADAMTS-5 in deformed human temporomandibular joint discs.

OBJECTIVE: To study the expression of a disintegrin and metalloproteinase with thrombospondin motifs 5 (ADAMTS-5) in tissue samples of deformed human temporomandibular joint (TMJ) discs and cells obtained from the discs. MATERIALS AND METHODS: Eleven adult human TMJ discs (nine diseased discs and two normal discs) were used in this study. The nine diseased discs were obtained from nine patients with internal derangement (ID) and osteoarthritis (OA) in the TMJ. These patients all had anteriorly displaced discs and deformed mandibular condyles, making conservative therapy impossible. The tissues were immunohistochemically stained using ADAMTS-5 antibodies. In addition, an articular disc cell line from one case was established by collagenase treatment. The subcultured cells under both normal and hypoxic conditions (O2: 2%) were incubated for 3, 6, 12 and 24 h after addition of interleukin-1beta (IL-1beta) (1 ng/mL). Subsequently, the expression of ADAMTS-5 was examined using reverse transcription-polymerase chain reaction (RT-PCR). RESULTS: The control group showed negative reactions on immunohistochemical staining. The discs extracted from cases with ID and OA presented positive reactions for ADAMTS-5. The expression of ADAMTS-5 mRNA increased under both normoxia and hypoxia with the addition of IL-1beta, and the peak was observed after 3 h. CONCLUSION: These results suggest that ADAMTS-5 is related to deformation and destruction of human TMJ discs affected by ID and OA.

MRS assessment of glutamate clearance in a novel masticatory muscle pain model.

The injection of 1.0 M glutamate into the masseter (jaw-closer) muscle results in a short period of muscle pain (5-10 min) and a prolonged period of mechanical sensitization (> 30 min). It is unclear, however, whether there is a temporal relationship between intramuscular glutamate concentration and either muscle pain or mechanical sensitization. In the present study, (1)H MRS and electrophysiological recording of masticatory muscle nerve fibers were performed in order to monitor glutamate clearance and nerve fiber activity, respectively, after injection of glutamate into rat masticatory muscles. Glutamate signal amplitude was found to decay rapidly (half-life t 1/2 = 108 +/- 42 s), and became indistinguishable from the baseline 10 min after the injection. Glutamate-evoked nerve fiber activity was also found to decay rapidly (t 1/2 = 76 +/- 28 s). These results suggest that glutamate clearance correlates well with the time course of glutamate-evoked muscle pain fiber discharge.

Effect on prostaglandin E2 and leukotriene B4 levels by local administration of glucocorticoid in human masseter muscle myalgia.

Our aim was to determine whether masseter muscle (M) and plasma (P) levels of prostaglandin E2 (PGE2) or leukotriene B4 (LTB4) are influenced by local glucocorticoid administration and whether such changes would be associated with corresponding changes in local pain or hyperalgesia. Eighteen patients with fibromyalgia and 15 with local masseter myalgia were examined immediately before and 2 weeks after intramuscular administration of glucocorticoid with regard to masseter muscle resting pain and tenderness to palpation, pressure pain threshold, maximum voluntary mouth opening (MVM), and pain on maximum voluntary mouth opening. The primary criteria for inclusion were presence of pain for a period of at least 3 months and tenderness to digital palpation in the masseter muscle region. At both visits microdialysis samples were obtained from the masseter muscle, and venous blood was collected for analysis of PGE2 and LTB4. Dialysate levels of M-PGE2 did not change significantly after glucocorticoid administration, but reduction of masseter resting pain and increase of MVM were associated with decrease of M-PGE2 in the patients with fibromyalgia. Dialysate levels of M-LTB4 increased in both groups. In the patients with local myalgia the plasma level of LTB4 also increased, and this increase was associated with a decrease of pain and masseter tenderness. In conclusion, this study shows that reduction of masseter level of PGE2 after intramuscular glucocorticoid administration is associated with a decrease of resting pain in patients with fibromyalgia. In addition, the masseter muscle level of LTB4 increases in patients with fibromyalgia and local myalgia.

Interleukin-1 beta, interleukin-6, and tissue inhibitor of metalloproteinase-1 in the synovial fluid of the temporomandibular joint with respect to cartilage destruction.

OBJECTIVE: The distribution and biological roles of interleukin (IL)-1 beta, IL-6, and tissue inhibitor of metalloproteinase-1 (TIMP-1) in the synovial fluid of patients with non-inflammatory chronic temporomandibular joint (TMJ) disorders were evaluated in relation to pain upon joint movements and X-ray and magnetic resonance imaging (MRI) findings. MATERIALS AND METHODS: TMJ aspirates were obtained from 48 patients (48 joints) with chronic TMJ disorders and from 18 controls (18 joints). The IL-1 beta and IL-6 levels in the aspirates were determined by using an enzyme-linked immunosorbent assay and the TIMP-1 level was measured by an enzyme immunoassay. Following examinations for pain upon joint movements and X-ray and MRI observations, the IL-1 beta, IL-6, and TIMP-1 levels and frequencies of their detection were compared. RESULTS: The IL-1 beta level and frequency of detection showed no correlation with pain upon joint movements or with the X-ray and MRI findings. In the frequency of detection of IL-6, there were significant differences between control (no detection) and all chronic TMJ disorder groups that were classified by imaging diagnosis (P < 0.001). A correlation was also noted between the presence of IL-6 and pain upon joint movements. The IL-6 level was correlated with the TIMP-1 level and with pain upon joint movements. TIMP-1 level was correlated with pain upon joint movements. The TIMP-1 was present in higher level from patients with chronic TMJ disorders who exhibited osseous changes on the X-ray images. CONCLUSION: The results indicated that the IL-6 and TIMP-1 levels in the TMJ aspirates of patients with chronic TMJ disorders have been raised. The former was not detected in the TMJ aspirates of the control. These findings suggest that IL-6 and TIMP-1 might play a role in the etiology of chronic TMJ disorders, but further studies are needed to validate this.

Angiogenesis in the human temporomandibular joint studied by immunohistochemistry for CD34 antigen.

The CD34 antigen is a sensitive marker of vascular endothelium and angiogenesis. Thus, we examined the expression of CD34 in 20 human temporomandibular joint (TMJ) samples with internal derangement and in 10 control specimens by an immunohistological technique using paraffin-embedded tissue and specific anti-human CD34 monoclonal antibody. In the control specimens, CD34 was observed sporadically within the TMJ discs. On the other hand, in the internal derangement specimens, CD34 was found frequently in the walls of blood capillaries within the TMJ discs. In the synovial membrane, CD34 was detected frequently in the walls of many blood capillaries in both the controls and the internal derangement specimens. Indeed, CD34 expression in internal derangement specimens was more intense than in control specimens. In the posterior loose connective tissue of the bilaminar zone, and in the anterior loose connective tissue between the upper and lower lamellae of the anterior capsular wall, CD34 was detected in abundance in the walls of blood capillaries both of the controls and the internal derangement specimens. Generally, CD34 was found rarely in the walls of large blood vessels. The presence of CD34 is suggested to be correlated with the process of angiogenesis induced by internal derangement of the TMJ.

The level of serotonin in the superficial masseter muscle in relation to local pain and allodynia.

The aim of this study was to investigate if serotonin is present in the human masseter muscle and if so, whether it is involved in the modulation of local muscle pain or allodynia. Thirty-five patients with pain and tenderness of the masseter muscle as well as ten healthy individuals were included in the study. Of the patients, 18 suffered from fibromyalgia and 17 had localized myalgia, e.g. myofascial pain in the temporomandibular system. The participants were examined clinically with special consideration to the masseter muscle and the pressure pain threshold as well as tolerance levels of this muscle were assessed. Intramuscular microdialysis was performed in order to sample serotonin and a venous blood sample was collected for analysis of the serum level of serotonin. Serotonin was present in the masseter muscle and the level was significantly higher in the initial sample than in the sample collected during steady state. The level of serotonin in the masseter muscle in relation to the level of serotonin in the blood serum was calculated. This fraction of serotonin was higher in the patients with fibromyalgia than in healthy individuals and high level of serotonin was associated with pain as well as allodynia of the masseter muscle. In conclusion, the results of this study show that serotonin is present in the human masseter muscle both immediately following puncture and in a subsequent steady state and that it is associated with pain and allodynia. The origin of the serotonin seems partly to be the blood, but our results indicate that peripheral release also occurs.

Possible involvement of histamine in muscular fatigue in temporomandibular disorders: animal and human studies.

As an approach to clarifying the molecular basis of pain and fatigue in muscles involved in temporomandibular disorders, we examined the activity of histidine decarboxylase (HDC), the enzyme which forms histamine, in the masseter muscles of mice. In the resting muscle, HDC activity was very low. Direct electrical stimulation of the muscle markedly elevated HDC activity. HDC activity rose within 3 hrs of the electrical stimulation, peaked at 6 to 8 hrs, and then gradually declined. Intraperitoneal injection of a small amount of interleukin-1 (IL-1) (from 1 to 10 microg/kg) produced a similar elevation of HDC activity in the masseter muscle. We also examined the effect of an antihistamine, chlorphenylamine (CP), on temporomandibular disorders in humans and compared it with that of an anti-inflammatory analgesic, flurbiprofen (FB). Two groups received one or the other of the drugs daily for 7 days, and they were asked about their signs and symptoms before and after the treatment. A positive evaluation of their treatment was made by 74% of the CP group, but by only 48% of the FB group. Although the effects of CP on the limitation of mouth-opening and on joint noise were negligible, about 50% of the CP group answered positively concerning the drug's effect on spontaneous pain or pain induced by chewing or mouth-opening. The positive evaluation for CP (50%) in relieving associated symptoms (headache or shoulder stiffness) was significantly greater than for FB (13%). FB showed effectiveness similar to but sometimes weaker than that of CP on several symptoms. On the basis of these and previous results and the known actions of histamine, we propose that the histamine newly formed following the induction of HDC activity, which is itself mediated by IL-1, may be involved in inducing pain and, possibly, stiffness in muscles in temporomandibular disorders.

Effect of local glucocorticoid injection on masseter muscle level of serotonin in patients with chronic myalgia.

The aim of this study was to compare the effects on the level of serotonin (5-HT) in the masseter muscle by intramuscular glucocorticoid (GC) administration in patients with fibromyalgia (FM) and localized myalgia (LM), as well as to determine associated changes in pain, tenderness, and microcirculation. The study comprised 22 patients with pain and tenderness in the masseter muscle region. Ten patients (all women) had FNI, and 12 (1 man and 11 women) had LM involving the temporomandibular system. The patients were examined clinically and by microdialysis at 2 visits 2-3 weeks apart and received local glucocorticoid treatment at the first visit. The ratio (S1/S2) between the initial level of 5-HT (S1) and steady state level (S2) was used as a relative measure of the intramuscular release of 5-HT. This ratio decreased significantly after treatment in the FM group. In the FM group there was also a negative correlation regarding changes between visits of 5-HT and changes of intramuscular temperature. In the LM group there was a negative correlation regarding changes between visits of 5-HT and changes of pressure pain threshold and pressure pain tolerance level. This study indicates that there is a reduction of the ratio between initial 5-HT and steady state level in the painful masseter muscle after intramuscular GC administration to FM patients, a reduction not present in the LM patients. In addition, 5-HT seems to be involved in the modulation of local muscle microcirculation in FM patients and in hyperalgesia in LM patients.

The role of oxygen free radicals in idiopathic facial pain.

Patients with chronic facial pain including those with facial arthromyalgia (TMJ dysfunction syndrome) were investigated for evidence of abnormal systemic and intra-articular free radical activity. Chronic facial pain patients showed significantly raised serum 2,3-dihydroxybenzoic acid after an oral dose of 1.2 g of aspirin which indicates increased systemic free radical activity. This was reflected in the TMJ aspirates of the facial arthromyalgia patients which contained thiobarbituric acid-reactive substance (TBA-RS) which is also a product of free radical activity. The synovial aspirates also contained high levels of the hyperalgesic eicosanoid 15-HETE. However, there was no difference between the painful and symptom-free joints, which suggested that in part the clinical features are probably determined by asymmetrical masticatory function or as yet unknown algesic factors such as local cytokine production.