Masticatory Myofascial Pain Syndrome: Implications for Endodontists

β2-adrenergic receptor activation decreases the mechanical sensitivity of rat masticatory muscle afferent fibres

BACKGROUND

Activation of β2 adrenergic receptors reduces cutaneous mechanical pain thresholds in rats. While β2 adrenergic receptor activation may contribute to mechanisms that underlie temporomandibular joint pain, its effect on masticatory muscle pain sensitivity is uncertain.

OBJECTIVES

The current study sought to determine the extent to which β adrenergic receptors are expressed by masticatory muscle afferent fibres, and to assess the effect of local activation of these receptors on the mechanical sensitivity of masticatory muscle afferent fibres in rats.

METHODS

Trigeminal ganglion neurons that innervate the rat (n = 12) masseter muscle and lower lip were identified by tissue injection of fluorescent dyes and were then stained with antibodies against β1 or β2 adrenergic receptors. Extracellular recordings from 60 trigeminal ganglion neurons that innervate the masticatory muscle were undertaken in a second group of anaesthetised rats of both sexes (n = 37) to assess afferent mechanical activation thresholds. Thresholds were assessed before and after injection of the β adrenergic receptor agonists into masticatory muscle.

RESULTS

β1 and β2 adrenergic receptor expression was greater in labial skin than in masticatory muscle ganglion neurons (p < .05, one-way ANOVA, Holm-Sidak test). There was a higher expression of β2 adrenergic receptors in masticatory muscle ganglion neurons in males than in females. The mixed β agonist isoproterenol increased afferent mechanical activation threshold in male but not female rats (p < .05, Mann-Whitney test). In male rats, salbutamol, a β2 selective agonist, also increased afferent mechanical activation threshold but hydralazine, a vasodilator, did not (p < .05, Mann-Whitney test).

CONCLUSION

Activation of β2 adrenergic receptors decreases the mechanical sensitivity of masticatory muscle afferent fibres in a sex-related manner.

Creation of myofascial pain syndrome-like muscle by artificial electrical stimulation and stretching treatment

BACKGROUND

Myofascial pain syndrome（MPS）is a common chronic pain disorder characterized by muscle hardness, low extensibility, restriction of range of motion (ROM)　and pain with trigger point (TP). Eccentric contraction has been used in past animal studies of MPS. However, clinical experience suggests that concentric contraction is also involved in MPS formation.

NEW METHODS

In this study, we adopted artificial electrical stimulation to create artificial concentric contraction (ACC) in rat gastrocnemius muscle. After ACC, muscle hardness, torsion and range of motion (ROM) were compared between before ACC, after ACC, and stretching group. To clarify the association with pain, the expression of pERK in DRG were analyzed.

COMPARISON TO EXISTING METHODS

Previous animal studies have created MPS models by inducing eccentric contractions in muscles. In this study, full tetanus contraction of the gastrocnemius muscle was achieved via tibial nerve stimulation. This method substituted muscle contraction due to abnormal excitation.

RESULTS

We found that artificial abnormal contraction (ACC) induced muscle hardness and ROM restriction. The pERK expression in DRG was increased by ACC. Analysis of muscle tissue sections revealed a meandeling structure in muscle fibers. The stretching treatment improved these indicators. These results were similar to feature of the MPS muscles.

CONCLUSIONS

The ACC caused by artificial electrical stimulation leads to the characteristic of MPS in rat gastrocnemius muscle. This ACC model can be one of the useful options for MPS analysis.

Global hotspots and trends in Myofascial Pain Syndrome research from 1956 to 2022: A bibliometric analysis

Myofascial Pain Syndrome (MPS) is a prevalent disease, and the related literature research has been increasing in recent years. However, there is a lack of scientific and comprehensive bibliometric analyses in the MPS research field. This study aimed to summarize and visualize the literature distribution laws, research hotspots and development trends in MPS based on bibliometric methods. Relevant literature on MPS research from 1956 to 2022 was retrieved from the Web of Science Core Collection database. Quantitative and visual analyses of the collected literature were performed using Microsoft Office 2021, Bibliometrics, VOSviewer, and CiteSpace. A total of 1099 papers were included, and the number of papers in this research field is generally upward. The USA has the most publications (270), and Univ Sao Paulo is the institution with the most publications (31). Hong CZ and Calvo-Lobo C have the same number of publications and are the authors with the most publications (20), and Simons DG is the author with the most co-citations (1078). Journal of Musculoskeletal Pain is the journal with the most publications (61), and Pain is the journal with the most co-cited papers (2598) and the highest impact factor (7.926). Lidocaine injection versus dry needling to myofascial trigger point. The importance of the local twitch response is the reference with the highest number of co-citations (136). The top 5 keywords in this period are myofascial pain syndrome (571), trigger points (218), pain (97), myofascial pain (92), and myofascial trigger point (80). The keywords of recent bursts are dry needling (2016-2022), efficacy (2020-2022), validity (2020-2022), temporomandibular joint disorder (2020-2022), and orofacial pain (2020-2022). This study summarizes and visualizes the evolution, research hotspots, and future trends of the global MPS domain from 1956 to 2022. It is helpful for scholars to understand the general situation of MPS research quickly and provide a reference for clinical decision-making and future research directions.

Kinesio Taping as a Therapeutic Tool for Masticatory Myofascial Pain Syndrome-An Insight View

Myofascial pain syndrome (MPS) is thought to stem from masticatory muscle hypersensitivity. Masticatory myofascial pain syndrome (MMPS) is characterized by multiple trigger points (MTrPs), also known as hyperirritable points, in taut bands of affected muscles, regional muscle pain, or referred pain to nearby maxillofacial areas like teeth, masticatory muscles or the temporomandibular joint (TMJ). Muscle stiffness, reduced range of motion, muscle weakening without atrophy, and autonomic symptoms may accompany regional discomfort. Multiple treatments have been utilized to reduce trigger points and mandibular function restrictions. As a result of these incapacitating symptoms, MMPS can significantly impair many elements of quality of life. The application of Kinesio tape (KT) is a non-invasive method of treating dormant myofascial trigger points. Utilizing the body's innate capacity for self-repair, this technique entails taping specific regions of the skin. KT alleviates discomfort, decreases swelling and inflammation, enhances or suppresses motor function in the muscles, stimulates proprioception, promotes lymphatic drainage, stimulates blood flow, and expedites tissue recovery. However, studies conducted to assess its effects have frequently yielded contradictory results. To the best of our knowledge, just a few research has looked into the therapeutic effects of KT on MMPS. The purpose of this review is to determine the efficacy of KT as a therapeutic tool for regular treatment or as an adjunct to existing therapy for MMPS based on the evidence presented in this review. To establish KT as a reliable independent treatment option, additional research is necessary to confirm the efficacy of KT techniques and applications, specifically randomized clinical trials.

Assessment of Concordance between Chairside Ultrasonography and Digital Palpation in Detecting Myofascial Trigger Points in Masticatory Myofascial Pain Syndrome

INTRODUCTION

Masticatory myofascial pain is a musculoligamentous syndrome that can mimic odontogenic pain. Pain referral to odontogenic structures can be traced to hyperirritated myofascial trigger points (MTrPs). This pragmatic study evaluated the concordance between ultrasonography and palpation in detecting MTrPs in the masseter and temporalis muscles.

METHODS

Fifty-seven patients suspected to have temporomandibular disorder were included. MTrPs were palpated manually by expert clinicians. Ultrasonography was then performed by a blind sonographer. The quantity of MTrPs and the involved muscle sections, the pain occurrence, and the location of the MTrPs within the muscle sections were compared using the mean difference (MD) and concordance statistics (Cohen κ and the interclass correlation coefficient [ICC]) as applicable.

RESULTS

Ultrasonography located MTrPs as 2.1 ± 1.3 mm² hypoechoic nodules at a depth of 7 ± 3.3 mm. Ultrasonography moderately agreed with palpation on the quantity of MTrPs per patient (MD = 1; 95% confidence interval [CI], 0.06-1.9; ICC = 0.56; 95% CI, 0.32-0.72). Palpation detected marginally more involved muscle sections per patient (MD = 0.7; 95% CI, 0.06-1.34.05; ICC = 0.64; 95% CI, 0.44-0.77) with more pain occurrence per patient (MD = 1.4; 95% CI, 0.56-2.28; ICC = 0.13; 95% CI, -0.26 to 0.41). There was a discordance in the location of the MTrPs within the muscle sections per patient (κ = -0.46; 95% CI, -0.77 to -0.14).

CONCLUSIONS

Ultrasonography and palpation concurred moderately to substantially on the quantity of MTrPs and the involved muscle sections but disagreed on the location of the MTrPs within the muscle sections. Ultrasonography has the potential as a chairside diagnostic aid to help clinicians determine an accurate diagnosis, enhance patient experience during examination, and avoid unnecessary treatments that can mitigate the risk of iatrogenic damage.

Diagnostic Applications of Ultrasonography in Myofascial Trigger Points: A Scoping Review and Critical Appraisal of Literature

Objective:

Myofascial trigger points (MTrPs) are pathognomonic of myofascial pain syndrome. The detection ability of MTrPs via ultrasonography is underreported and the characteristics of MTrPs are not sufficiently standardized. The objective was to summarize the characteristics and diagnostic abilities of ultrasonography for MTrP investigations.

Materials and Methods:

A multi-database, and bibliography hand-search was implemented. Studies of ≥10 patients, published after 1980, appraising ultrasonography as a diagnostic aid for myofascial pain syndrome were included. The Quality Assessment of Diagnostic Accuracy Studies 2 (QUADAS-2) tool was used to evaluate the diagnostic accuracy of the included studies.

Results:

Six cross-sectional studies met the inclusion criteria. The back and trapezius muscles were the most studied locations. The diagnostic studies were of low-medium risk of bias. The studies reported a large range of diagnostic metrics (accuracy 58%–100%, sensitivity 33%–91%, specificity 75%–100%, positive predictive value 91%–100%, negative predictive value 47%–97%, positive likelihood ratio 3.6, and negative likelihood ratio 0.12–0.67).

Conclusion:

This review found low-medium risk of bias evidence in support of ultrasonography for MTrP investigations. The clinical studies identified in the scoping review used gray-scale ultrasound equipment systems with a 5 to 14 MHz transducer to diagnose MTrPs and the local twitch response, and MTrPs were visualized mostly as hypoechoic nodules.