Andreas Dawson

Comparison of pain thresholds and pain tolerance levels between Middle Easterners and Swedes and between genders

OBJECTIVE This study evaluates the presence of culture and gender differences in pain thresholds and pain tolerance levels between Middle Easterners and Swedes. METHODS Sixty-four healthy individuals, 32 Middle Easterners (16 men and 16 women, mean age: 24.6 +/- 3.4 years) and 32 Swedes (16 men and 16 women, mean age: 24 +/- 3.5 years) participated in the study. Three experimental pain tests were conducted in each participant. Pain thresholds and pain tolerance levels were measured using an algometer (mechanical stimulus), the PainMatcher((R)) (electric stimulus) and cold pressor test (thermal stimulus). RESULTS While no significant differences in pain thresholds were observed between Middle Easterners and Swedes in algometer and cold pressor tests, differences in pain tolerance levels were significant (P < 0.01 for both tests). All between-culture differences in pain perception, pain threshold and pain tolerance level were non-significant when measured with the PainMatcher. Significant between-gender differences were observed only in pain threshold with the PainMatcher (P < 0.05) and in pain tolerance level with the algometer (P < 0.01) and the PainMatcher (P <0.001). CONCLUSION This study found significant differences in two out of three pain tolerance level tests - but not pain threshold tests - between the Middle Eastern and Swedish cultures and between genders. These differences were more pronounced between Middle Eastern and Swedish men than between Middle Eastern and Swedish women. Gender differences were more pronounced within the Swedish than the Middle Eastern culture. These findings indicate that culture and gender influence pain experience.

Dopamine in plasma - a biomarker for myofascial TMD pain?

BackgroundDopaminergic pathways could be involved in the pathophysiology of myofascial temporomandibular disorders (M-TMD). This study investigated plasma levels of dopamine and serotonin (5-HT) in patients with M-TMD and in healthy subjects.MethodsFifteen patients with M-TMD and 15 age- and sex-matched healthy subjects participated. The patients had received an M-TMD diagnosis according to the Research Diagnostic Criteria for TMD. Perceived mental stress, pain intensity (0–100-mm visual analogue scale), and pressure pain thresholds (PPT, kPa) over the masseter muscles were assessed; a venous blood sample was taken.ResultsDopamine in plasma differed significantly between patients with M-TMD (4.98 ± 2.55 nM) and healthy controls (2.73 ± 1.24 nM; P < 0.01). No significant difference in plasma 5-HT was observed between the groups (P = 0.75). Patients reported significantly higher pain intensities (P < 0.001) and had lower PPTs (P < 0.01) compared with the healthy controls. Importantly, dopamine in plasma correlated significantly with present pain intensity (r = 0.53, n = 14, P < 0.05) and perceived mental stress (r = 0.34, n = 28, P < 0.05).ConclusionsThe results suggest that peripheral dopamine might be involved in modulating peripheral pain. This finding, in addition to reports in other studies, suggests that dopaminergic pathways could be implicated in the pathophysiology of M-TMD but also in other chronic pain conditions. More research is warranted to elucidate the role of peripheral dopamine in the pathophysiology of chronic pain.

Pain and intramuscular release of algesic substances in the masseter muscle after experimental tooth-clenching exercises in healthy subjects

AIMS To investigate whether experimental tooth clenching leads to a release of algesic substances in the masseter muscle. METHODS Thirty healthy subjects (16 females, 14 males) participated. During two sessions, separated by at least 1 week, intramuscular microdialysis was performed to collect masseter muscle 5-hydroxytryptamine (5-HT) and glutamate as well as the metabolic markers pyruvate and lactate. Two hours after the start of microdialysis, participants were randomized to a 20-min repetitive experimental tooth-clenching task (50% of maximal voluntary contraction) or a control session (no clenching). Pain and fatigue were measured throughout. The Friedman and Wilcoxon tests were used for statistical analyses. RESULTS No alterations were observed in the concentrations of 5-HT, glutamate, pyruvate, and lactate over time in the clenching or control session, or between sessions at various time points. Pain (P < .01) and fatigue (P < .01) increased significantly over time in the clenching session and were significantly higher after clenching than in the control session (P < .01). CONCLUSION Low levels of pain and fatigue developed with this experimental tooth-clenching model, but they were not associated with an altered release of 5-HT, glutamate, lactate, or pyruvate. More research is required to elucidate the peripheral release of algesic substances in response to tooth clenching.

Effects of experimental tooth clenching on pain and intramuscular release of 5-HT and glutamate in patients with myofascial TMD

Objectives:It has been suggested that tooth clenching may be associated with local metabolic changes, and is a risk factor for myofascial temporomandibular disorders (M-TMD). This study investigated the effects of experimental tooth clenching on the levels of 5-HT, glutamate, pyruvate, and lactate, as well as on blood flow and pain intensity, in the masseter muscles of M-TMD patients. Methods:Fifteen patients with M-TMD and 15 pain-free controls participated. Intramuscular microdialysis was performed to collect 5-HT, glutamate, pyruvate, and lactate and to assess blood flow. Two hours after the insertion of a microdialysis catheter, participants performed a 20-minute repetitive tooth clenching task (50% of maximal voluntary contraction). Pain intensity was measured throughout. Results:A significant effect of group (P<0.01), but not of time, was observed on 5-HT levels and blood flow. No significant effects of time or group occurred on glutamate, pyruvate, or lactate levels. Time and group had significant main effects on pain intensity (P<0.05 and <0.001). No significant correlations were identified between: (1) 5-HT, glutamate, and pain intensity; or between (2) pyruvate, lactate, and blood flow. Discussion:This experimental tooth clenching model increased jaw muscle pain levels in M-TMD patients and evoked low levels of jaw muscle pain in controls. M-TMD patients had significantly higher levels of 5-HT than controls and significantly lower blood flow. These 2 factors may facilitate the release of other algesic substances that may cause pain.

Development of a quality-assessment tool for experimental bruxism studies: reliability and validity.

AIMS To combine empirical evidence and expert opinion in a formal consensus method in order to develop a quality-assessment tool for experimental bruxism studies in systematic reviews. METHODS Tool development comprised five steps: (1) preliminary decisions, (2) item generation, (3) face-validity assessment, (4) reliability and discriminitive validity assessment, and (5) instrument refinement. The kappa value and phi-coefficient were calculated to assess inter-observer reliability and discriminative ability, respectively. RESULTS Following preliminary decisions and a literature review, a list of 52 items to be considered for inclusion in the tool was compiled. Eleven experts were invited to join a Delphi panel and 10 accepted. Four Delphi rounds reduced the preliminary tool-Quality-Assessment Tool for Experimental Bruxism Studies (Qu-ATEBS)- to 8 items: study aim, study sample, control condition or group, study design, experimental bruxism task, statistics, interpretation of results, and conflict of interest statement. Consensus among the Delphi panelists yielded good face validity. Inter-observer reliability was acceptable (k = 0.77). Discriminative validity was excellent (phi coefficient 1.0; P < .01). During refinement, 1 item (no. 8) was removed. CONCLUSION Qu-ATEBS, the seven-item evidence-based quality assessment tool developed here for use in systematic reviews of experimental bruxism studies, exhibits face validity, excellent discriminative validity, and acceptable inter-observer reliability. Development of quality assessment tools for many other topics in the orofacial pain literature is needed and may follow the described procedure.

Effect of experimental tooth clenching on the release of β-endorphin

AIMS To investigate the association between experimental tooth clenching and the release of β-endorphin in patients with myofascial temporomandibular disorders (M-TMD) and healthy subjects. METHODS Fifteen M-TMD patients and 15 healthy subjects were included and assigned an experimental tooth-clenching task. Venous blood was collected and pain intensity was noted on a visual analog scale. The masseter pressure pain threshold (PPT) was assessed 2 hours before the clenching task and immediately after. A mixed-model analysis of variance was used for statistical analyses. RESULTS Significant main effects for time and group were observed for pain intensity and PPT, with significantly lower mean values of pain intensity (P < .001) and PPT (P < .01) after the clenching task compared with baseline. M-TMD patients had significantly higher pain intensity (P < .001) and significantly lower PPT (P < .05) than healthy subjects. No significant time or group effects were observed for the level of β-endorphin. Neither pain intensity nor PPT correlated significantly with β-endorphin levels. CONCLUSION This experimental tooth-clenching task was not associated with significant alterations in β-endorphin levels over time, but with mechanical hyperalgesia and low to moderate levels of pain in healthy subjects and M-TMD patients, respectively. More research is required to understand the role of the β-endorphinergic system in the etiology of M-TMD.

Effects of Low‐Intensity Contractions of Different Craniofacial Muscles in Healthy Participants – An Experimental Cross‐Over Study

Repetitive jaw‐muscle activity characterized by clenching or grinding of the teeth and/or by bracing or thrusting of the mandible, ie, bruxism, is traditionally linked to pain and unpleasantness in the active muscles. The aim of this study was to investigate the effects of standardized craniofacial muscle contractions on self‐reported symptoms.

EHMTI-0301. Effect of experimental tooth clenching on the release of beta-endorphin

Several etiologic factors have been suggested for tooth grinding and clenching, but the exact mechanism is not known. One biologic explanation might be that tooth clenching activates the reward system as observed in other types of muscle exercises