Peter Svensson

Background: Orofacial myofascial pain shows variable muscle sensitivity, referred pain, and complex spatiotemporal pressure processing profiles. Methods: This participant‐, examiner‐ and data analyst‐blinded case–control study compared masticatory muscle sensitivity and entropy patterns between 28 chronic myofascial TMD pain patients and 28 age‐ and sex‐matched controls, introducing a comprehensive approach for ‘topoalgesia’ assessment. Mechanical pain sensitivity (MPS) was assessed at nine sites on the masseter and temporalis muscles bilaterally using a palpometer with 0.5, 1.0 and 2.0 kgf for 2 s. Participants rated MPS on a 0–50–100 numeric rating scale after each palpation and reported referred sensations. Entropy and center of gravity (COG) were analysed. Results: Chronic myofascial TMD pain patients reported significantly greater MPS scores than controls across all force levels and muscles ( p < 0.05). Both groups showed increased MPS with higher applied forces. TMD patients exhibited significantly greater entropy in the masseter muscle at 0.5 and 1.0 kgf, and in the temporalis muscle at 2.0 kgf ( p < 0.001). TMD patients also reported more referred sensations than controls across all force levels ( p < 0.001). COG analysis showed myofascial TMD patients presented more centrally located COG within the masseter muscle than controls particularly at lower forces. Conclusions: Results suggest that chronic myofascial TMD patients present greater muscle sensitivity, differing entropy profiles across muscles and force levels, and distinct spatiotemporal patterns compared to controls, associated with more frequent referred sensations. These findings contribute to understanding chronic muscle pain manifestations, and topoalgesia may help better track disease progression or remission over time. Significance Statement: Quantification of spatial variation in pressure sensitivity (topoalgesia) showed that chronic myofascial TMD patients diverge from healthy controls at 0.5 kg and 2.0 kg palpation forces, but not at 1.0 kg, identifying force‐specific parameters that could sharpen diagnostic sensitivity for orofacial pain.

The gender of examiner/experimenter can influence patients' pain experiences because of social and interpersonal dynamics. However, the magnitude and direction of this influence is unclear. This systematic review and meta-analysis investigated whether the gender of the examiner affects pain perception and reporting. After registration in PROSPERO (CRD42023473445), electronic searches were conducted in PubMed, Web of Science, PsycINFO, and CINAHL to identify clinical and experimental studies published up to March 18, 2025 that evaluated the impact of examiner gender on pain-related outcomes, eg, pain threshold, tolerance, and intensity. Two independent reviewers conducted abstract screening, full-text assessment, quality appraisal with the Newcastle–Ottawa Scale, and data extraction. Examiner gender was operationalized in the studies as a female/male classification corresponding to biological sex. A random-effect meta-analysis was conducted to estimate pooled effects for each pain variable. Of 3919 identified records, 27 studies (19 experimental and 8 clinical) that included 2494 participants met the inclusion criteria. Meta-analytic results showed that pain tolerance was significantly higher when assessed by male examiners (Hedges g = −0.25, 95% CI [−0.45, 0.05], I ² = 9%). A small but significant effect was found for higher pressure pain thresholds with female examiners (Hedges g = 0.20, 95% CI [0.04, 0.36], I ² = 0%), whereas no significant effects were observed for cold or heat pain thresholds. Pain intensity did not differ between female and male examiners. In conclusion, the results present meta-analytic evidence that examiner gender can influence how pain is perceived and reported. Incorporating such examiner–participant dynamics into experimental designs and clinical assessments is important for advancing pain research.

Sleep bruxism (SB) is a motor activity characterized by repetitive masticatory muscle contractions during sleep, commonly associated with tooth damage and jaw pain or headache. Pharmacological management strategies targeting its central nervous system‐related mechanisms remain limited. This study aimed to evaluate whether a low dose of a central muscle relaxant, cyclobenzaprine, reduces SB‐related muscle activity, maximum voluntary bite force and self‐reported bruxism awareness. A randomized, double‐blind, placebo‐controlled, crossover clinical trial was conducted. Twenty participants underwent baseline SB motor activity recordings followed by two intervention phases consisting of 5 mg of cyclobenzaprine or placebo for three consecutive nights. Masticatory muscle activity during sleep was quantified using portable surface electromyography. Maximum voluntary bite force was measured using a bite force‐recording device. Self‐reported outcomes related to SB and secondary effects (e.g., dry mouth) were collected each morning. Comparison of cyclobenzaprine to placebo and baseline nights failed to show a difference in mean frequency of masticatory muscle activity during sleep and maximum voluntary bite force. No self‐reported differences were observed for SB awareness. Few secondary effects were identified between cyclobenzaprine use and placebo; a significant increase in perception of tolerable dry mouth upon awakening ( p = 0.034) and a marginally statistically significant reduction in the perceived leg movements during sleep ( p = 0.046). In conclusion, low‐dose cyclobenzaprine was not effective in modifying SB–related muscle activity or masticatory muscle force, suggesting limited clinical utility for SB. Future studies using higher doses of cyclobenzaprine are warranted before ruling out its clinical utility, within a safety profile.

Objectives: Burning mouth syndrome (BMS) is defined as a chronic intraoral burning sensation occurring in the absence of identifiable local or systemic causes. Several classification systems have proposed diagnostic criteria for BMS, including the International Classification of Headache Disorders (ICHD-3), the International Classification of Diseases (ICD-11), the International Classification of Orofacial Pain (ICOP-1), and the World Congress of Oral Medicine (WCOM). However, none of these have been validated. This study aims to evaluate the diagnostic performance of ICHD-3, ICD-11, ICOP-1, and WCOM criteria for BMS and to suggest optimized diagnostic criteria. Methods: We assessed 76 consecutive patients referred for burning oral pain. Of these, 34 (28 women) were diagnosed with BMS according to the reference standard, and 42 (37 women) had other oral mucosal pain conditions. Two control groups were also recruited: 31 TMD patients (28 women) and 30 pain-free participants (26 women). Assessment involved self-report questionnaires and comprehensive clinical examinations. All patients with burning oral pain underwent additional laboratory tests. Consensus-based diagnosis constituted the reference standard, and a blinded examiner applied each set of different diagnostic criteria as the index tests. We calculated sensitivity, specificity, positive (PPV) and negative predictive values (NPV), and positive and negative likelihood ratios (LR + and LR-), and the area under the ROC curve for each index tests. Because some ICHD-3 criteria were ambiguously defined, we created operational definitions and tested three versions of the criteria. Results: No significant group differences were found in age, sex, or smoking status. None of the criteria exhibited both high sensitivity and specificity. WCOM showed the highest sensitivity (91.2%), NPV (99.2%), LR- (0.14), and AUC (0.717). In contrast, ICHD-3 definition 3 showed the highest specificity (93.2%), PPV (8.2%), and LR + (5.2), but the lowest sensitivity (35.3%). Based on these findings, we developed an optimized version of the ICOP criteria. The new criteria showed the highest sensitivity (94.1%), NPV (99.9), LR- (0.07), and AUC (0.874), while maintaining acceptable specificity (79.6%), PPV (7.4%), and LR + (4.4). Conclusion: Substantial variation exists in the diagnostic performance of current BMS criteria, with each set showing either high sensitivity or specificity. This study provides the first data-driven proposal for modified diagnostic criteria for BMS, offering a foundation for improving future versions of ICHD and ICOP.

Objectives: Aim of this high-density surface electromyography (EMG) study was to evaluate the effect of experimentally-induced pain in the masseter on the performance of a constant vertical bite-force. Material and methods: Twenty healthy participants performed two ramp-and-hold contractions at baseline and after an injection of either hypertonic saline (HS) or, as control, isotonic saline (IS) based on random assignment. The measurement was repeated after 15 min. with IS or HS, respectively. The target level of vertical bite-force was 15% of maximum voluntary contraction registered using an intra-oral device. Results: The average root-mean-square (RMS) values showed significantly lower ( p p <0.001). Conclusions: Experimental pain induced a general reduction of RMS EMG amplitude of the ipsilateral masseter and a small but significant shift away from the site of injection. Clinical relevance: The masticatory motor system seems to possess a unique adaptability to produce a constant force despite the presence of experimentally induced pain. This could represent a feature of the high resilience and adaptability of the stomatognathic system in acute painful conditions.

The association between tooth wear and sleep bruxism is unclear. This study investigates jaw muscle activity and clinical findings in patients with sleep bruxism and severe tooth wear and matched controls. Participants underwent electromyographic (EMG) recording calibrated for dynamic bite force during sleep and analysed as EMG event duration, events per hour, work volume and accumulated dynamic bite force. In addition, static maximal voluntary bite force, saliva tests, health questionnaires and clinical examination were obtained from all participants. No significant differences were found between groups regarding EMG work volume, accumulated dynamic bite force, or static maximal voluntary bite force. However, the cases had a more EMG events per hour than controls, though controls had longer events than the cases. Groups health data were similar, but the cases had a lower unstimulated saliva secretion. The finding suggest that severe tooth wear and sleep bruxism do not seem to be uniquely related to EMG work volume, accumulated dynamic bite force or static maximal voluntary bite force. However, an increased EMG activity and a marginally decreased unstimulated saliva flow was found and could play a role for severe tooth wear.

Background: Regular aerobic physical activity is increasingly being recommended for chronic pain management. The underlying mechanisms are, however, not fully understood and data concerning endogenous pain modulation (EPM) and physical activity are ambiguous. This study aimed to investigate the impact of regular aerobic physical activity on EPM mechanisms in pain‐free adults. Methods: This controlled study included 50 healthy participants: 22 in the aerobic group (≥ 3 h of aerobic‐type training per week) and 28 in the control group (no regular engagement in aerobic physical activity). Aerobic training was self‐reported. We evaluated EPM—comprising conditioned pain modulation (CPM), temporal summation of pain (TSP), and referred sensations (RS) elicited by standardised muscle palpation—across both trigeminal and spinal test sites. Cardiovascular parameters were also assessed. A composite index of normalised pain measures quantified global pain sensitivity. Results: Both groups showed a low incidence of RS. TS was significantly lower in the aerobic group, suggesting reduced facilitatory pain mechanisms. However, no differences were found in CPM between groups. The aerobic group had a lower global pain sensitivity index compared to controls. There were no differences in EPM between trigeminal or spinal test site. Conclusions: The findings highlight that aerobic physical activity positively influences facilitatory pain mechanisms but not inhibitory aspects. This research underscores the potential of facilitatory mechanisms (RS and TS) as biomarkers for monitoring the effectiveness of aerobic training in pain modulation. Further longitudinal studies are recommended to explore the relationships between aerobic physical activity and EPM mechanisms in greater depth. Significance: This study demonstrates that regular aerobic exercise has a positive impact on endogenous pain modulation by reducing temporal summation, a key facilitatory pain mechanism, in healthy individuals. This contribution advances our understanding of non‐pharmacological pain management and may lead to personalised exercise‐based strategies for pain relief.