Botulinum toxin type A applications for masticatory myofascial pain and trigeminal neuralgia: what is the evidence regarding adverse effects?

Temporomandibular Joint Disorders in Elderly Patients

The management of temporomandibular disorders (TMDs) in elderly patients can present a significant challenge for dentists due to its multifactorial etiology, aging-related changes that contribute to TMD, and the fragile psychological state of these patients. Despite the growing prevalence of TMD in the elderly population, the scientific literature provides limited information about effective management strategies for this group. Therefore, it is crucial for researchers and clinicians to focus on improving our understanding of TMD in the elderly population and to develop more effective treatment approaches. This article provides an overview of the prevalence, etiology, pathophysiology, and management of TMD in elderly patients, with a particular emphasis on the challenges associated with this population. By increasing our knowledge of TMD in the elderly, we can improve the quality of care provided to this vulnerable patient group.

Current Perspectives on the Adjunctive Use of Botulinum Toxin A in Endodontic Practice for Nonodontogenic Pain Management: A Web-Based Survey

INTRODUCTION

Despite the increasing use of botulinum toxin A (BoNT-A) in dentistry, there is limited research on its use in endodontics, a specialty that often receives referrals for dental pain that can coexist with nonodontogenic pain. The purpose of this study was to assess whether endodontists believe BoNT-A can be useful in an endodontic practice as an adjunctive treatment for nonodontogenic conditions overlapping with dental pain.

METHODS

A 23-question survey was emailed to 3,979 members of the American Association of Endodontists. Descriptive statistics, bivariate analysis, and logistic regression were performed with significance at α = 0.05.

RESULTS

Among the 211 respondents confirmed to be endodontists in the United States, 1 in 11 (9.14%) currently administer BoNT-A treatment. The top nonodontogenic conditions indicated for BoNT-A were myofascial orofacial pain (49.22%) and temporomandibular joint disorders (41.97%). Half of the endodontists (50.26%) believe that BoNT-A could be useful for nonodontogenic conditions overlapping with dental pain. Regression analysis identified variables significantly associated with this belief: BoNT-A can improve patient satisfaction (P < .05), BoNT-A training should be offered in residency (P < .05), BoNT-A would increase profitability (P < .05), and BoNT-A will be incorporated more in the future (P < .05).

CONCLUSION

Endodontists have split opinions on administering BoNT-A for nonodontogenic conditions overlapping with dental pain. Including BoNT-A training in residency may be key to encouraging multidisciplinary pain management in endodontics.

Occlusal splint or botulinum toxin-a for jaw muscle pain treatment in probable sleep bruxism: A randomized controlled trial

OBJECTIVES

To conduct an equivalency randomized controlled trial comparing occlusal splint (OS) and botulinum toxin-A (BTX-A) on jaw muscle pain in probable sleep bruxism.

METHODS

Sixty patients (≥18 years, probable sleep bruxism, and jaw muscle pain) were randomly allocated into groups. The primary outcome was the reduction of jaw muscle pain, assessed using the Graded Chronic Pain Scale (GCPS, v2.0). Secondary outcomes included: parameters of jaw opening and mandibular mobility; distribution of muscle pain; Jaw Functional Limitation Scale-20 (JFLS-20), Oral Behaviors Checklist (OBC); and Oral Health Impact Profile-14 (OHIP-14). Only the evaluator was blinded. Multilevel mixed-effects regression models were used.

RESULTS

Fifty-nine patients (30 received OS and 29 BTX-A) were analyzed at baseline, 3 and 6 months follow-up. One patient dropped out after receiving the intervention. No differences between the interventions were observed concerning the GCPS (p = 0.627), although a significant reduction was observed at 3 (OR=13.26, 95%CI[6.61-26.59]) and 6 months (OR=12.36, 95%CI[4.93-30.98]), regardless of the treatment. BTX-A showed a lower score reduction on JFLS-20 than OS (OR=0.29, 95%CI[0.11-0.82]). BTX-A presented inferior results for the parameters: opening without pain(p = 0.045), unassisted maximum opening(p = 0.024), assisted maximum opening(p = 0.041), and protrusion(p = 0.016). An improvement in OHIP-14 scores was observed at 3 (IRR=1.08, CI95%[1.02-1.14]) and 6 months (IRR=1.10, CI95%[1.04-1.16]), regardless of the intervention. BTX-A participants(n = 23;79,3%) reported mild discomfort during chewing.

CONCLUSION

OS and BTX-A can effectively decrease the GCPS scores, improve OHRQoL, and enhance functional outcomes in sleep bruxist patients with jaw muscle pain. OS demonstrated slight advantages in specific parameters.

CLINICAL SIGNIFICANCE

Both occlusal splints and botulinum toxin-A effectively reduce jaw muscle pain in bruxist patients, improving quality of life and mandibular function. Clinically, occlusal splints may offer additional benefits in specific functional parameters. (NCT03456154).

Evaluation of craniocervical posture after myofascial pain treatment in adults with bruxism: A randomized clinical trial

BACKGROUND

Despite numerous clinical studies on bruxism management, critical evaluation parameters, including the impact of bruxism pain on quality of life and secondary issues like changes in craniocervical posture, are often disregarded.

RESEARCH QUESTION

Evaluate the effect of two treatments on the craniocervical posture of adult patients with myofascial pain.

METHODS

This parallel randomized clinical trial included 60 patients with myofascial pain due to probable bruxism that fulfilled the study requirements. A computer-generated random sequence was used to allocate treatments: botulinum toxin-A or occlusal appliance. Follow-up time was 3 and 6 months. Kyphosis angle (α) and head posture measurement by cervical radiograph were assessed using two-way repeated measures ANOVA (alpha = 0.05).

RESULTS

Sixty patients were randomized (mean age 30 ± 7.6) and 6 were excluded from the analysis (did not attend follow-up). No statistically significant difference was observed for the head posture measure (p = 0.98) and kyphosis angle (p = 0.74). Mild pain was reported by one patient after botulinum toxin-A application.

SIGNIFICANCE

Results indicate that craniofacial posture does not seem to be influenced by the treatment of pain in bruxers. If a better posture is desired, this should probably be targeted with other therapies.

TRIAL REGISTRATION

Clinical Trials NCT03456154.

Botulinum Toxin-A for the Treatment of Myogenous Temporomandibular Disorders: An Umbrella Review of Systematic Reviews

OBJECTIVE

Temporomandibular disorders (TMDs) encompass several conditions that cause pain and impair function of the masticatory muscles (M-TMDs) and temporomandibular joints. There is a large interest among clinicians and researchers in the use of botulinum toxin-A (BoNT-A) as a treatment for M-TMD. However, due to the lack of consistent evidence regarding the efficacy as well as adverse events of BoNT-A, clinical decision making is challenging. Therefore, this umbrella review aimed to systematically assess systematic reviews (SRs) evaluating BoNT-A treatment effects on pain intensity, mandibular movements, and adverse events in patients with M-TMDs.

METHOD

An electronic search was undertaken in the databases MEDLINE, EMBASE, CINAHL, Cochrane Central Registry of Controlled Trials (CENTRAL), Web of Science, Epistemonikos, ClinicalTrials.gov, and ICTRP to identify SRs investigating BoNT-A effects on M-TMDs, published from the inception of each database until 6 December 2023. The quality of evidence was rated according to the critical appraisal checklist developed by the umbrella review methodology working group. Only high-quality SRs were included.

RESULTS

In total, 18 SRs were included. BoNT-A was shown to be more effective than placebo to reduce pain intensity, but not compared to standard treatments. Additionally, BoNT-A was not superior to placebo or standard treatments regarding improvement of mandibular movements. BoNT-A was considered to have a higher risk for adverse events on muscle and bony tissue compared with other treatments.

CONCLUSION

The synthesis in this umbrella review provides the highest level of evidence present. Taken together, there are indications of effectiveness of BoNT-A for treatment of M-TMDs, supported by moderate evidence. However, considering the risk of causing serious adverse events, treatment with BoNT-A is recommended to be the last treatment alternative.

Histomorphometric Changes of the Masseter Muscle of Rats After a Single Injection of Botulinum Toxin Type A

BACKGROUND

It has been reported that botulinum toxin type A (BoNT-A) produces structural changes in masticatory muscles. However, not all histomorphometric parameters affected by BoNT-A parameters have been assessed. This study investigated the histomorphometric changes in the masseter muscle of rats after a single injection of BoNT-A.

METHODS

Forty-four adult animals were randomly divided into control group (n = 22) and BoNT-A group (n = 22). Controls received a single dose of 0.14 mL/kg of saline in masseter muscles, and the BoNT-A group received a 7 U/Kg of BoNT-A. The groups received the same volume of injected substances. Animals were sacrificed on 7th (n = 5), 14th (n = 5), 21st (n = 5), 28th (n = 4) and 90th (n = 3) days post-treatment. Histological masseter tissue slides were obtained from hematoxylin-eosin treatment and analyzed in optical microscopy regarding muscle cross-sectional area, amount of connective tissue and quantity and diameter of myocytes. For statistical analysis, generalized linear models were used to compare the data (ANOVA). In all test, the significance level of 5% was set.

RESULTS

BoNT-A values of cross-sectional area of the masseter muscle were significantly lower than controls (p < 0.01) throughout the study. Regarding myocytes quantity, BoNT-A subgroups presented higher values than controls (p < 0.0001) since the 14th day until the end of the study; however, the diameter of myocytes was smaller in all BoNT-A subgroups (p < 0.0001) in all assessment points. The amount of connective tissue was higher in BoNT-A subgroups (p < 0.0001) throughout the study.

CONCLUSION

A single injection of BoNT-A altered the structure of masseter muscle of rats, regarding its histomorphometric parameters.

NO LEVEL ASSIGNED

This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Botulinum toxin-A effects on pain, somatosensory and psychosocial features of patients with refractory masticatory myofascial pain: a randomized double-blind clinical trial

The antinociceptive effect of BoNT-A have been well documented in animal studies; however, results of few but well-designed randomized placebo-controlled clinical trials about BoNT-A efficacy in masticatory myofascial pain (MFP) are inconsistent. Therefore, the present randomized, double-blind, placebo-controlled clinical trial evaluated the efficacy of BoNT-A in patients with refractory MFP. Twenty-eight patients with pain reduction of less than 30% despite conservative treatment and with an average pain intensity of > 50 mm on the visual analogue scale (VAS) participated. Patients were randomly assigned to receive a total of 80 U of BoNT-A or saline solution (SS) injected into the masseter and anterior temporalis muscles. Pain intensity (VAS), quantitative sensory testing (QST), conditioned pain modulation (CPM), and psychosocial status were examined. Follow-up was performed at 1 and 6 months. For repeated-measure comparisons between evaluation times, Friedman test with Bonferroni correction was used for pain and somatosensory variables and the Wilcoxon test for the psychosocial variables. The Mann-Whitney test was used for all comparisons between groups. The BoNT-A group had a significant decrease in pain intensity at follow-ups compared with the SS group (p < 0.001). QST assessment revealed higher pressure pain threshold values in the masseter muscle for BoNT-A group compared to SS (p < 0.03) at all follow-ups. No differences were found for mechanical pain threshold and wind-up ratio values (p > 0.05) in the entire study. The BoNT-A group presented the most efficient CPM effect (p < 0.03) only at the 1 month follow-up in the masseter muscle. There was a significant time effect for BoNT-A in all psychosocial variables (p < 0.05) and a drug effect in the Central Sensitization Inventory (p < 0.01), Pittsburgh Sleep Quality Index (p < 0.004), and Healthy Survey 36 (p < 0.05) at 6 months follow-up. The study demonstrates that a single injection-session of BoNT-A has positive effects on the hall pain spectrum of patients with refractory masticatory myofascial pain.

Adverse effect of botulinum toxin-A injections on mandibular bone: A systematic review and meta-analysis

INTRODUCTION

Botulinum toxin-A (BTX) is a potent neurotoxin that is emerging in the scope of dental practice for its ability to temporarily paralyse musculature and reduce hyperfunction. This may be desirable in diseases/disorders associated with hyperactive muscles such as the muscles of mastication, most implicated in painful temporomandibular disorders (TMDs). The use of BTX extends beyond its indications with off-label use in TMD's and other conditions, while potential adverse effects remain understudied. BTX is well-established hindlimb paralysis model in animals leading to significant bone loss with underlying mechanisms remaining unclear. The objective of this study is to systematically review the literature for articles investigating changes in mandibular bone following BTX injections and meta-analyse available data on reported bone outcomes.

METHODS

Comprehensive search of Medline, Embase and Web of Science retrieved 934 articles. Following the screening process, 36 articles in animals and humans were included for quantitative synthesis. Articles in human individuals (6) and three different animal species (14) presented mandibular bone outcomes that were included in the meta-analysis.

RESULTS

The masseter and temporalis muscles were frequently injected across all species. In humans, we observe a decrease of about 6% in cortical thickness of mandibular regions following BTX injection with no evident changes in either volume or density of bone structures. In animals, bone loss in the condylar region is significantly high in both cortical and trabecular compartments.

DISCUSSION

Our analysis supports the concept of BTX-induced bone-loss model in animal mandibles. Further, bone loss might be confined to the cortical compartments in humans. Most studies did not address the reality of repeated injections and excessive dosing, which occur due to the reversible action of BTX. More rigorous trials are needed to draw a full picture of potential long-term adverse effects on bone.

Long-Term Effects of a Single Application of Botulinum Toxin Type A in Temporomandibular Myofascial Pain Patients: A Controlled Clinical Trial

This study assessed the long-term effects of botulinum toxin type A (BoNT-A) in subjective pain, pain sensibility, and muscle thickness in persistent myofascial temporomandibular-disorder pain (MFP-TMD) patients. Fourteen female subjects with persistent MFP received BoNT-A treatment with different doses (10U-25U for temporalis muscle and 30U-75U for masseter muscle). The treatment was injected bilaterally in the masseter and anterior temporalis muscles in a single session. Clinical measurements included: self-perceived pain (VAS), pain sensibility (PPT), and muscles thickness (ultrasonography). Follow-up occurred 1, 3, 6, and 72 months after treatment for VAS and PPT and 1, 3, and 72 months for ultrasonography. For statistical analysis, the Friedman test with the Bonferroni test for multiple comparisons as a post hoc test was used for non-parametric repeated measures comparisons among the evaluation times. A 5% probability level was considered significant in all tests. VAS values presented a significant decrease throughout the study (p < 0.05). Regarding PPT values, a significant increase was found when comparing baseline data with post-treatment follow-ups (p < 0.05), and even though a significant decrease was found in muscle thickness when baseline values were compared with the 1- and 3-months assessments, no differences were found when compared with the 72 months follow-up (p > 0.05). A single injection of BoNT-A presents long-term effects in reducing pain in persistent MFP-TMD patients, and a reversibility of adverse effects on masticatory-muscle thickness.

Effect of Botulinum Toxin Injection on EMG Activity and Bite Force in Masticatory Muscle Disorder: A Randomized Clinical Trial

Botulinum toxin type A (BoNT-A) is increasingly used in treating masticatory muscle pain disorder; however, safe doses and reinjection intervals still need to be established. The purpose of this randomized clinical trial was to evaluate the degree and duration of the impairment of masticatory muscle performance. Fifty-seven subjects were randomly divided into two groups: one of which received BoNT-A first (n = 28) while the other received saline first (n = 29), with the cross-over being in week 16, and a total follow-up period of 32 weeks. A total dose of 50 U of BoNT-A was injected in the masseter and temporal muscles bilaterally. Electromyographic (EMG) activity and bite forces were assessed. A significant reduction in EMG activity was observed up to week 18 (p ≤ 001), with total recovery at week 33. A significant reduction in maximum bite force was observed up to week 11 (p ≤ 005), with total recovery at week 25. In conclusion, when treating masticatory muscle pain disorder with 50 U of BoNT-A, a reinjection interval of 33 weeks can be considered safe since the recovery of muscle function occurs by that time.

Efficacy of Botulinum Toxin Type-A I in the Improvement of Mandibular Motion and Muscle Sensibility in Myofascial Pain TMD Subjects: A Randomized Controlled Trial

This study assessed the effects of botulinum toxin type A (BoNT-A) in mandibular range of motion and muscle tenderness to palpation in persistent myofascial pain (MFP) patients (ReBEC RBR-2d4vvv). Eighty consecutive female subjects with persistent MFP, were randomly divided into four groups (n = 20): three BoNT-A groups with different doses and a saline solution group (placebo control group). Treatments were injected bilaterally in the masseter and anterior temporalis muscle in a single session. Clinical measurements of mandibular movements included: pain-free opening, maximum unassisted and assisted opening, and right and left lateral excursions. Palpation tests were performed bilaterally in the masseter and temporalis muscle. Follow-up occurred 28 and 180 days after treatment. For the statistical analysis the Mann–Whitney U-test with Bonferroni correction was used for groups comparisons. Regardless of dose, all parameters of mandibular range of motion significantly improved after 180 days in all BoNT-A groups, compared with the control group. Palpation pain over the masseter and temporalis muscles were significantly reduced in all BoNT-A groups regardless of dose, compared with the control group, after 28 and 180 days of treatment. Independent of doses, BoNT-A improved mandibular range of motion and muscle tenderness to palpation in persistent MFP patients.

Botulinum toxin A in dentistry and orofacial surgery: an evidence-based review - part 1: therapeutic applications

Objective An evidence-based review on the safety and efficacy of botulinum toxin type-A (BoNTA) in orofacial conditions, focusing on the therapeutic applications and role of BoNTA as an adjuvant treatment.Data source and selection Data was collected using PubMed (Medline), Cochrane Library of Systematic Reviews and Cochrane Central Register of Controlled Trials electronic databases. Having satisfied the search parameters, 32 studies for therapeutic applications and 26 for BoNTA as an adjunctive treatment were included. The quality of relevant studies was assessed using the Best Evidence Topics (BETs) Critical Appraisal Tool.Data extraction The highest level of evidence (LOE) behind BoNTA safety and efficacy was for wound healing and scar management in the orofacial surgery context, where BoNTA was presented as an adjunctive modality. Level-I evidence was controversial for temporomandibular disorders and bruxism. However, it showed promising results for painful temporomandibular disorders of myogenic origin refractory to conservative therapies, and to decrease muscle contraction intensity in sleeping bruxism. There was only one level-II study for persistent recurrent aphthous stomatitis. Data showed limited level-III evidence for orofacial pain conditions (temporomandibular joint recurrent dislocation and pain, burning mouth syndrome or atypical odontalgia), oral cancer complications, or as an adjuvant to maxillofacial and orthognathic surgeries. Benefits of BoNTA in prosthodontics had weak level-IV evidence. No evidence was found among the periodontology field.Conclusion There is growing evidence to support the safety and efficacy of BoNTA in the investigated orofacial pathological conditions, with high levels of satisfaction from the patient and clinician perspective. However, there are some inconsistencies and limited high-quality evidence available. Well-designed controlled clinical trials are necessary to evaluate long-term safety, efficacy and cost-effectiveness before BoNTA is widely adopted with irrefutable evidence-based clinical guidelines.

Effectiveness of nonsurgical treatments for trigeminal neuralgia: an overview protocol

ABSTRACT Purpose: to present an overview protocol for systematic reviews to synthesize and describe available evidence on the effectiveness of nonsurgical treatments for trigeminal neuralgia. Methods: the protocol follows the method proposed by PRISMA-P guidelines for protocol reports. The search will be made in MEDLINE, EMBASE, LILACS, Cochrane, Web of Science, Scopus, SpeechBITE, PeDRO, and the grey literature (Google Scholar and ProQuest Dissertations and Theses), with no restriction on language or time of publication. A search strategy developed for MEDLINE will be adapted for each database. Two independent reviewers will screen the articles by title and abstract. Then, they will read the full texts of included articles, following the eligibility criteria. In case of disagreements, a third reviewer will come to a consensus. The data will be extracted with a standardized form. Information on the risk of bias and GRADE assessment will be recorded. AMSTAR-2 will assess the overall result reliability of the systematic reviews. Results will be presented in a flowchart, tables, and a narrative description. Final Considerations: once carried out, this protocol will describe the current body of research on the topic and identify existing gaps on the basis of evidence.

A efetividade dos tratamentos não cirúrgicos na neuralgia do trigêmeo: um protocolo de overview

RESUMO Objetivo: apresentar um protocolo de Overview das revisões sistemáticas (RSs) para sintetizar e descrever evidências disponíveis sobre a efetividade dos tratamentos não cirúrgicos na neuralgia do trigêmeo. Métodos: o protocolo seguirá o método proposto pelas diretrizes do PRISMA-P para relato de protocolos. A busca será realizada nas bases de dados eletrônicas: MEDLINE, EMBASE, Lilacs, COCHRANE, Web of Science, Scopus, SpeechBITE, PeDRO, além de consulta à literatura cinzenta (Google Scholar e ProQuest Dissertations and Theses), sem restrições de idioma ou período de publicação. Uma estratégia de busca foi desenvolvida para MEDLINE e será adaptada para cada base de dados. O rastreio dos artigos pelo título e resumo será realizado por dois revisores independentes. Em seguida, farão leitura dos textos completos dos artigos incluídos, conforme os critérios de elegibilidade. Em discordância, um terceiro revisor fará o consenso. Os dados serão extraídos por meio de um formulário padronizado. Serão registradas informações de risco de viés e avaliação do GRADE. A ferramenta AMSTAR II avaliará a confiança geral dos resultados das RSs. Os resultados serão apresentados em um fluxograma, tabelas e descrição narrativa. Considerações Finais: a execução deste protocolo descreverá o corpo atual de pesquisa sobre o tema e identificará lacunas existentes na base de evidências.

Masticatory Myofascial Pain Syndrome: Implications for Endodontists

INTRODUCTION

Masticatory myofascial pain syndrome can present similarly to other dental conditions in odontogenetic structures. Endodontists should be familiar with the symptomology and pathophysiology of masticatory myofascial pain syndrome to avoid misdiagnosis, incorrect treatment, and medicolegal repercussions. The aim of this review was to provide a foundational summary for endodontists to identify and correctly manage masticatory myofascial pain syndrome.

METHODS

A narrative review of the literature was performed through a MEDLINE search and a hand search of the major myofascial pain textbooks.

RESULTS

Masticatory myofascial pain syndrome is a musculoligamentous syndrome that can present similarly to odontogenic pain or refer pain to the eyebrows, ears, temporomandibular joints, maxillary sinus, tongue, and hard palate. Currently, the most comprehensive pathophysiology theory describing masticatory myofascial pain syndrome is the expanded integrated hypothesis. The most widely accepted diagnostic guidelines for masticatory myofascial pain syndrome are the Diagnostic Criteria for Temporomandibular Disorders; however, their diagnostic capability is limited. There is no hierarchy of treatment methods because each patient requires a tailored and multidisciplinary management aimed at regaining the muscle's range of motion, deactivating the myofascial trigger points, and maintaining pain relief.

CONCLUSIONS

The pain patterns for masticatory myofascial pain syndrome are well-known; however, there is a lack of consensus on the most proper method of trigger point diagnosis or pain quantification. The diagnostic strategies for masticatory myofascial pain syndrome vary, and the diagnostic aids are not well developed.

Botulinum toxin type A and acupuncture for masticatory myofascial pain: a randomized clinical trial

BoNT-A has been widely used for TMD therapy. However, the potential benefits compared to dry needling techniques are not clear.

Modulatory effect of botulinum toxin type A on the microglial P2X7/CatS/FKN activated-pathway in antigen-induced arthritis of the temporomandibular joint of rats

Analgesic mechanism of Botulinum toxin type A (BoNT/A) involves retrograde axonal transport to central nervous system, where it may interact with sensory neurons. Though, some authors suggested that BoNT/A antinociceptive action may also be associated with the inhibition intracellular factors and neuromodulators expressed by immune cells, especially by microglia. Antigen-induced arthritis in the temporomandibular joint (TMJ) of rats is signal by P2X7 receptor/Cathepsin S (CatS)/Fractalkine (FKN) microglia-activated pathway. Thus, we aimed to evaluate the possible modulatory effect of an intra-TMJ injection of BoNT/A on the P2X7/CatS/FKN microglia-activated pathway in the trigeminal subnucleus caudalis of rats with antigen-induced arthritis of the TMJ. A model of antigen-induced arthritis was used on Wistar rats (n = 40) by systemic injections of an emulsion containing complete Freund's adjuvant and methylated bovine serum albumin (mBSA) diluted in PBS. The arthritic condition was stablished by an intra-TMJ injection of mBSA (10 μg/TMJ/week) for 3 weeks. Then, animals were treated with an intra-TMJ injection of BoNT/A (onabotulinumtoxinA, Allergan®; 7U/kg) or vehicle saline. Animals were euthanized 24 h, 7 or 14 days after BoNT/A treatment and their trigeminal nucleus caudalis was harvested to evaluate the protein level of microglial purinergic P2X7 receptor and CX3 chemokine receptor 1 (CX3CR1) by Western blot, and to measure the protein level of microglial modulators CatS, FKN, and the pro-inflammatory cytokines tumor necrosis alfa (TNF-α) and interleukin 1β (IL-1β) by enzyme-linked immunosorbent assay (ELISA). The antigen-induced arthritis in the TMJ significantly increased the protein levels of P2X7, CatS, FKN, TNF-α and IL-1β in the trigeminal subnucleus caudalis (P < 0.05). The intra-TMJ injection of BoNT/A reduced the protein levels of P2X7 in all time points tested. Additionally, BoNT/A significantly reduced the protein levels of CatS, FKN, and TNF-α 14 days after treatment. However, IL-1β was significantly reduced just 24 h after the BoNT/A intra-TMJ treatment. Based on our results, we can suggest that the intra-TMJ injection of BoNT/A may promote a central effect by reducing the P2X7/CatS/FKN microglia-activated pathway in the trigeminal subnucleus caudalis.

Efficacy and Safety of Botulinum Toxin Type A on Persistent Myofascial Pain: A Randomized Clinical Trial

This study assessed the safety and efficacy of three different doses of BoNT-A for persistent myofascial pain (MFP). One hundred female subjects were randomly assigned into five groups (n = 20): oral appliance (OA), saline solution (SS) and three BoNT-A groups with different doses. Pain intensity and pressure pain threshold were evaluated up to 24 weeks after treatment. Adverse effects related to muscle contraction, masticatory performance, muscle thickness and mandibular bone volume were also assessed. Changes over time were compared within and between groups. The “nparLD” package and Wilcoxon signed-rank test were used to analyze the data. BoNT-A reduced pain intensity (p < 0.0001) and increased pressure pain threshold (p < 0.0001) for up to 24 weeks compared to the placebo. No differences were found between BoNT-A and OA at the last follow-up. A transient decline in masticatory performance (p < 0.05) and muscle contraction (p < 0.0001), and a decrease in muscle thickness (p < 0.05) and coronoid and condylar process bone volume (p < 0.05) were found as dose-related adverse effects of BoNT-A. Regardless of the dose, BoNT-A was as effective as OA on MFP. Notwithstanding, due to BoNT-A dose-related adverse effects, we suggest the use of low doses of BoNT-A in MFP patients that do not benefit from conservative treatments.