IntramuscularInjectionsandDryNeedlingwithinMasticatoryMusclesinManagementofMyofascialPain.SystematicReviewofClinicalTrials

Myofascial pain is a significant cause of disability that may affect up to 85% of the population and represents a common symptom of temporomandibular disorders (TMDs). The management of this condition varies widely, with growing interest in recent years in needling therapies within masticatory muscles due to their perceived simplicity and effectiveness in pain reduction. However, the field has been characterized by inconsistency in treatment methods, making objective comparison of clinical trials difficult. The International Classification of Orofacial Pain (ICOP) and Diagnostic Criteria for Temporomandibular Disorders (DC/TMD) provide frameworks for diagnosis, but treatment approaches remain heterogeneous.

This systematic review was conducted to address the urgent need to systematize knowledge about needling techniques in masticatory muscles and to compare current approaches implemented in clinical trials.

The authors conducted a systematic review following PICOS and PRISMA protocols, registering their protocol in PROSPERO (ID 272124). They searched PubMed and BASE databases on April 18, 2021, using comprehensive search strategies combining terms related to masticatory muscles, needling techniques, pain, and treatment. The search yielded 367 articles, of which 28 were included for detailed analysis after screening and full-text assessment. Two authors independently screened titles and abstracts (Cohen's Kappa κ = 0.98), with three authors conducting full-text evaluation.

Eligibility criteria required adult patients with myofascial orofacial pain, therapeutic punctures into masticatory muscles (excluding acupuncture and nerve blocks), and clinical studies with evidence levels 1-3 published in English after 2011. The authors extracted data on study characteristics, needling methods, navigation systems, needle penetration spots, injected substances and doses, and number of treatment sessions. Importantly, this review focused on describing and comparing techniques rather than assessing the effectiveness or scientific quality of individual studies.

The 28 included articles described 32 distinct trials when accounting for studies comparing multiple methods or substances. The masseter muscle was the most frequently targeted (65% of interventions, 711 total cases), followed by temporalis (27%, 294 cases), lateral pterygoid (8%, 90 cases), and medial pterygoid (less than 1%, 5 cases). Botulinum toxin was the most studied substance, particularly for masseter and temporal muscles. For masseter injections, 17 studies used botulinum toxin, 7 used local anesthetics, 4 used deep dry needling, 2 used platelet-rich plasma, 1 used superficial dry needling, and 1 used collagen.

All temporal muscle studies except one used botulinum toxin; the exception used lidocaine. Pterygoid muscle needling was scarcely studied with non-standardized techniques.

Manual palpation was the dominant navigation method (72.5% of trials), with EMG used in 11.8%, EPI® electrotherapy equipment in 3.9%, MRI in 2.0%, and the method unspecified in 9.8%. The number of injection sites varied considerably: for masseter, 2-5 sites were common; for temporalis, 2-3 sites. Botulinum toxin dosing ranged from 20-150 IU for masseter and 10-100 IU for temporalis, with 30-50 IU and 20-25 IU as dominant values respectively. Local anesthetic dosing was typically 0.2-0.5 mL per puncture.

Over 85% of included articles were published in 2016 or later, indicating rapidly growing interest in the field. All analyzed papers claimed effectiveness of needling therapies in decreasing pain, increasing maximum mouth opening, and/or improving pain threshold.

This systematic review reveals that needling therapies within masticatory muscles are increasingly popular and generally considered effective, but the field suffers from significant methodological heterogeneity that limits objective comparison across studies. For clinicians, the predominance of manual palpation as a navigation method suggests this remains the standard approach, though EMG and imaging-based guidance may be particularly valuable for deeper muscles like the lateral and medial pterygoid where access is more challenging. The concentration of research on botulinum toxin for masseter and temporal muscles means these have the most established evidence base, while newer substances like platelet-rich plasma and collagen show promise but require further investigation. The review highlights important gaps: very limited research on medial pterygoid needling, insufficient high-quality trials comparing non-botulinum toxin substances, and lack of standardized protocols.

The authors note that needling of masticatory muscles can serve as a successful supporting and alternative therapy for myofascial pain, but emphasize the need for more consistent, standardized approaches in future clinical trials to enable meaningful comparison of outcomes. Clinicians should be aware that while botulinum toxin is well-studied, concerns about potential adverse effects with repeated high-dose use (including possible bone density changes) warrant monitoring, and that lower doses may avoid these risks while still providing benefit.