Modifica di Transcutaneous Electric Nerve Stimulation


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| autore = Gianni Frisardi
| autore2 = 
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}}
Abstract: This chapter delves into the contentious topic of Transcutaneous Electrical Nerve Stimulation (TENS), a method that continues to spark debate within the International Scientific Community. Despite being invalidated by the Research Diagnostic Criteria (RDC) for diagnosing Temporomandibular Disorders (TMD), TENS remains widely discussed and practiced. The RDC ruled that both the freeway space and myocentric trajectory, key elements in TENS-based diagnostics and prosthetic rehabilitation, have a low predictive value (PPV: 0.17). However, this chapter aims to dissect the technical and methodological aspects of the TENS method to understand its potential and limitations.

Temporomandibular disorders affect the temporomandibular joint (TMJ), a biarticulate joint responsible for complex movements during mastication. Various studies suggest that around 25% of the global population shows signs or symptoms of TMD, with a higher prevalence in women. Numerous therapeutic approaches, including pharmacological interventions and physical therapy such as low-level laser therapy (LLLT) and TENS, are being explored to manage TMD symptoms. TENS has gained recognition for its non-invasive, drug-free approach to pain management, applying low-frequency electrical currents through surface electrodes. It works by stimulating sensory nerves and modulating pain signals, potentially improving muscle relaxation and reducing discomfort in TMD patients.

While TENS shows promise in some clinical studies, its comparative efficacy against traditional analgesics and other treatment modalities for TMD remains understudied. This chapter also reviews relevant studies that have evaluated the duration of TENS therapy, its effects on jaw muscle relaxation, and its influence on mandibular movement and pain reduction. By examining these findings, the chapter seeks to clarify the role of TENS in clinical practice and highlight areas requiring further investigation.

==Introduction==

In this chapter, we consider another highly debated topic: Transcutaneous Electrical Nerve Stimulation (TENS), on which there is still no unanimous opinion within the International Scientific Community. This premise is confirmed by the fact that, although the Research Diagnostic Criteria (RDC) have categorically invalidated the clinical procedure in diagnosing patients with Temporomandibular Disorders, the procedure is still considered valid. It continues to be discussed, articles are published, and it is still practiced. This inconsistency is demonstrated by scientific papers in the literature with intermediate and ambiguous conclusions, which generate only questions without providing valid answers.

The RDC has clinically deemed the TENS procedure invalid based on the freeway space and myocentric trajectory, both as diagnostic elements for Temporomandibular Disorders (TMD) and as part of masticatory prosthetic rehabilitation treatment. As can be seen from the specific section of Table 1 presented in the chapter [[Research Diagnostic Criteria (RDC)]], it is clear that both freeway space and TENS trajectory were excluded due to a low predictive value (PPV: 0.17). While this might be true, it is essential to delve into the technical and methodological details to understand the rationale behind this decision. For this reason, we will briefly but thoroughly describe the TENS method to better understand its weaknesses and strengths.

{| class="wikitable"
| colspan="5" |'''Table 1:''' TMD diagnostic methodologies analyzed and excluded by the DRC due to lack of scientific validation
|-
|'''Diagnostic Tests'''
|'''Cutoff'''
|'''Sensitivity'''
|'''Specificity'''
|'''PPV'''
|-
| colspan="5" |'''Electrical stimulation methods''' 
|-
|Free rest space before stimulation ''(Cooper and Rabuzzi 1984)''<ref name=":1">BC Cooper, D D Rabuzzi. Myofacial pain dysfunction syndrome: a clinical study of asymptomatic subjects. Laryngoscope. 1984 Jan;94(1):68-75. doi: 10.1002/lary.5540940116.</ref>
|0.75-2.0 mm
|0.42
|0.62
|0.17
|-
|Free rest space after electrical stimulation ''(Cooper and Rabuzzi 1984)''<ref name=":1" />
|0.75-2.0 mm
|0.76
|0.19
|0.11
|-
|Closure trajectory before and after electrical stimulation ''(Cooper and Rabuzzi 1984)''<ref name=":1" />
|Undefined
|0.75 
|0.27
| 0.12
|-
| colspan="5" |<small>Cutoff: Parameters and significance limits used to separate healthy from sick subjects for each reported test.</small><small>Sensitivity: The ability of the specified test to identify truly sick subjects in a mixed sample of healthy and sick subjects.</small><small>Specificity: The ability of the specified test to identify healthy subjects in a mixed sample of healthy and sick subjects.</small><small>Positive Predictive Value (PPV): The ratio of the specified test’s ability to identify truly sick patients to the total sick population in a mixed sample of healthy and sick subjects.</small>
|}

=== TENS and Temporomandibular Disorders===
The temporomandibular joint (TMJ) is a hinge joint with biarticular properties, enabling the complex movements required for chewing<ref>Okoje VN, Aladelusi TO, Abimbola TA. Managing temporomandibular joint dislocation in ibadan: a review of 11 cases. Ann Ib Postgrad Med 2017;15:96-10.</ref>. Temporomandibular disorder (TMD) occurs when the TMJ and associated anatomical structures are affected<ref>Maini K, Dua A. Temporomandibular Syndrome. Treasure Island, FL: StatPearls Publishing; 2024.</ref><ref>Murphy MK, MacBarb RF, Wong ME, Athanasiou KA. Temporomandibular disorders: a review of etiology, clinical management, and tissue engineering strategies. Int J Oral Maxillofac Implants 2013;28:e393-414. doi: 10.11607/jomi.te20.</ref>. Approximately 25% of individuals worldwide show signs or symptoms of TMD<ref>Warren MP, Fried JL. Temporomandibular disorders and hormones in women. Cells Tissues Organs 2001;169:187-92. doi: 10.1159/000047881.</ref>. TMD occurs 1.5 to 2.5 times more frequently in women than in men<ref>Warren MP, Fried JL. Temporomandibular disorders and hormones in women. Cells Tissues Organs 2001;169:187-92. doi: 10.1159/000047881.</ref>.

Various therapeutic approaches are being studied for managing TMD, aiming to relieve pain and improve jaw function<ref>Gil-Martínez A, Paris-Alemany A, López-de-Uralde-Villanueva I, La Touche R. Management of pain in patients with temporomandibular disorder (TMD): challenges and solutions. J Pain Res 2018;11:571-87. doi: 10.2147/JPR.S127950.</ref>. Although surgical and non-surgical methods are available for treating TMD, conservative treatment is the initial and primary option<ref>Abouelhuda AM, Khalifa AK, Kim YK, Hegazy SA. Non-invasive different modalities of treatment for temporomandibular disorders: review of literature. J Korean Assoc Oral Maxillofac Surg 2018;44:43-51. doi: 10.5125/jkaoms.2018.44.2.43.</ref>. Pharmacological therapies include the use of nonsteroidal anti-inflammatory drugs (NSAIDs), antidepressants, and muscle relaxants. Another treatment component consists of occlusal and physical therapy techniques, such as low-level laser therapy (LLLT) and Transcutaneous Electrical Nerve Stimulation of the trigeminal nerve (TENS)<ref>Rezazadeh F, Hajian K, Shahidi S, Piroozi S. Comparison of the Effects of Transcutaneous Electrical Nerve Stimulation and Low-Level Laser Therapy on Drug-Resistant Temporomandibular Disorders. J Dent (Shiraz) 2017;18:187-92.</ref>.[[File:Myomonitor.jpg|thumb|400x400px|'''Figura 1:''' Disposizione degli elettrodi registranti sul muscolo Temporale e massetere. L'elettrodo stimolante in regione della Articolazione Temporomandibolare.]]TENS (Figure 1) has gained recognition as a non-invasive and drug-free technique for pain management in TMD. It involves applying 

low-frequency electrical currents to the skin through surface electrodes<ref>Shanavas M, Chatra L, Shenai P, Rao PK, Jagathish V, Kumar SP, et al. Transcutaneous electrical nerve stimulation therapy: An adjuvant pain controlling modality in TMD patients - A clinical study. Dent Res J (Isfahan) 2014;11:676-9.</ref><ref>Martimbianco ALC, Porfírio GJ, Pacheco RL, Torloni MR, Riera R. Transcutaneous electrical nerve stimulation (TENS) for chronic neck pain. Cochrane Database Syst Rev 2019;12:CD011927. doi: 10.1002/14651858.CD011927.pub2.</ref>. These currents stimulate sensory nerves and modulate pain signals transmitted to the central nervous system (CNS), altering pain perception. TENS is used in TMD patients to target muscles and nerves surrounding the TMJ, promoting muscle relaxation, reducing muscle spasms, and relieving discomfort.<ref>Hsieh YL, Yang CC, Yang NP. Ultra-Low Frequency Transcutaneous Electrical Nerve Stimulation on Pain Modulation in a Rat Model with Myogenous Temporomandibular Dysfunction. Int J Mol Sci 2021;22:9906. doi: 10.3390/ijms22189906.</ref><ref>Gil-Martínez A, Paris-Alemany A, López-de-Uralde-Villanueva I, La Touche R. Management of pain in patients with temporomandibular disorder (TMD): challenges and solutions. J Pain Res 2018;11:571-87. doi: 10.2147/JPR.S127950.</ref>

By comparing the advantages and disadvantages of different approaches, clinicians can select the most appropriate treatment option for each patient<ref>Beutler LE, Someah K, Kimpara S, Miller K. Selecting the most appropriate treatment for each patient. Int J Clin Health Psychol 2016;16:99-10. doi: 10.1016/j.ijchp.2015.08.001.</ref>.

Studies have evaluated the efficacy, safety, and feasibility of TENS in reducing pain and improving masticatory function in TMD patients<ref>Chellappa D, Thirupathy M. Comparative efficacy of low-Level laser and TENS in the symptomatic relief of temporomandibular joint disorders: A randomized clinical trial. Indian J Dent Res 2020;31:42-7. doi: 10.4103/ijdr.IJDR_735_18.</ref>.
Despite the growing recognition of TENS as a non-invasive approach for managing TMD, there is still a lack of a comprehensive comparative analysis of its effectiveness against commonly used analgesics for TMD treatment<ref>Wu M, Cai J, Yu Y, Hu S, Wang Y, Wu M. Therapeutic Agents for the Treatment of Temporomandibular Joint Disorders: Progress and Perspective. Front Pharmacol 2021;11:596099. doi: 10.3389/fphar.2020.596099.</ref>. Therefore, we found it interesting to extract conclusions from specific articles and correlate them with our own interpretations, which will generate topics for further discussion. Let’s see which ones:

*Rémi Esclassan<ref>Rémi Esclassan 1, Anaïs Rumerio 2, Paul Monsarrat 1 2, Jean Claude Combadazou 1 2, Jean Champion 1 2, Florent Destruhaut 1 2, Christophe Ghrenassia 1 2. Optimal duration of ultra low frequency-transcutaneous electrical nerve stimulation (ULF-TENS) therapy for muscular relaxation in neuromuscular occlusion: A preliminary clinical study. Cranio. 2017 May;35(3):175-179. doi: 10.1080/08869634.2016.1171479. Epub 2016 Apr 8.</ref> (2017), whose primary goal was to determine the duration of ultra-low frequency TENS (ULF-TENS) application necessary to achieve sufficient relaxation of the masticatory muscles. Overall, the results suggest that an optimal ULF-TENS application should last 40 minutes to achieve sufficient muscle relaxation in both patients with masticatory system disorders and healthy subjects—a duration that aligns with everyday clinical practice.

<blockquote>
The question that arises is when and why a healthy subject’s muscle would be in a non-relaxed state, requiring TENS to achieve relaxation.
</blockquote>

* Rafaella Mariana Fontes de Bragança<ref>Rafaella Mariana Fontes de Bragança 1, Carolina Almeida Rodrigues 1, Melissa Oliveira Melchior 1, Laís Valencise Magri 1, Marcelo Oliveira Mazzetto 1. Ultra-low frequency transcutaneous electric nerve stimulation does not affect the centric relation registration. Cranio. 2018 Jan;36(1):19-28. doi: 10.1080/08869634.2016.1278107. Epub 2017 Jan 27.</ref> (2018), whose objective was to evaluate the influence of ULF-TENS on mandibular condyle displacement and the repeatability of centric relation (CR) registration. ULF-TENS did not affect total condylar displacement, regardless of the CR registration technique used. The 'bimanual' technique showed improvement in repeatability after ULF-TENS use.

<blockquote>
The question raised by reading this article is why TENS would improve the repeatability of the bimanual centric relation technique—perhaps the continuity of afferent stimuli to mesencephalic nuclei leads to a sort of loss in the stereognostic effect of the mandible? If so, we should understand the neurophysiological function of TENS both peripherally and centrally, which is no easy task.
</blockquote>

*Yuanxiu Zhang<ref>Yuanxiu Zhang 1 2 3 4, Jinglu Zhang 1 3, Lin Wang 1 2 3, Kelun Wang 3 5, Peter Svensson 4 6 7. Effect of transcutaneous electrical nerve stimulation on jaw movement-evoked pain in patients with TMJ disc displacement without reduction and healthy controls. Acta Odontol Scand. 2020 May;78(4):309-320. doi: 10.1080/00016357.2019.1707868. Epub 2019 Dec 26.</ref> (2020), whose goal was to assess the effect of TENS on pain and movement patterns after repeated mandibular movements in patients with temporomandibular joints (TMJ) pain and disc displacement without reduction (DDwoR) and to compare them with healthy volunteers. The results indicated that movement-evoked pain was spontaneously reduced by TENS in patients with painful TMJ and DDwoR. Interestingly, TENS reduced movement-evoked pain and improved mandibular motor function during repeated movements. These findings could have implications for TENS treatment in patients with painful TMJ and DDwoR.

<blockquote>
This assertion, moreover, was made by Peter Svensson (co-author of the article), an active collaborator in the RDC Consortium<ref>Eric Schiffman, Richard Ohrbach, Edmond Truelove, John Look, Gary Anderson, Jean-Paul Goulet, Thomas List, Peter Svensson, Yoly Gonzalez, Frank Lobbezoo, Ambra Michelotti, Sharon L Brooks, Werner Ceusters, Mark Drangsholt, Dominik Ettlin, Charly Gaul, Louis J Goldberg, Jennifer A Haythornthwaite, Lars Hollender, Rigmor Jensen, Mike T John, Antoon De Laat, Reny de Leeuw, William Maixner, Marylee van der Meulen, Greg M Murray, Donald R Nixdorf, Sandro Palla, Arne Petersson, Paul Pionchon, Barry Smith, Corine M Visscher, Joanna Zakrzewska, Samuel F Dworkin; International RDC/TMD Consortium Network, International Association for Dental Research; Orofacial Pain Special Interest Group, International Association for the Study of Pain. Diagnostic Criteria for Temporomandibular Disorders (DC/TMD) for Clinical and Research Applications: recommendations of the International RDC/TMD Consortium Network and Orofacial Pain Special Interest Group†. J.Oral Facial Pain Headache. 2014 Winter; 28(1):6-27. doi: 10.11607/jop.1151.</ref> and a strong supporter of excluding TENS as a clinical procedure, in 2014, prior to the release of the referenced article. Again, the uncertainty focuses on the mechanism of action—whether it's a form of 'Gate Control' or purely a phenomenon related to trigeminal neuromotor mechanisms?
</blockquote>

*Syeda Mahnoor Fatima<ref>Syeda Mahnoor Fatima, Tooba Zahoor, Ramsha Nawaz, Ahmed Tanveer, Syeda Soveba Zaidi. Role of transcutaneous electrical nerve stimulation in temporomandibular joint disorders. J Pak Med Assoc. 2024 Sep;74(9):1645-1648. doi: 10.47391/JPMA.10874.</ref> (2024) presented alarming epidemiological data, showing that 60% of the general population suffer from at least one TMD symptom, and 48% of TMD patients exhibited clinical symptoms, including muscle tension and difficulty opening the mouth<ref>Ryan J, Akhter R, Hassan N, Hilton G, Wickham J, Ibarag S. Epidemiology of Temporomandibular Disorder in the General Population: a systematic review. Adv Dent & Oral Health 2019;10:555787. doi: 10.19080/ADOH.2019.10.555787.</ref>. One subgroup treated with microcurrent nerve stimulation (MENS) showed significant improvement in VAS scores<ref>Saranya B, Ahmed J, Shenoy N, Ongole R, Sujir N, Natarajan S. Comparison of Transcutaneous Electric Nerve Stimulation (TENS) and Microcurrent Nerve Stimulation (MENS) in the Management of Masticatory Muscle Pain: A Comparative Study. Pain Res Manag 2019;2019:8291624. doi: 10.1155/2019/8291624.</ref>.

<blockquote>
The startling statistic of 60% of the population experiencing TMJ Disorders with muscle stiffness or reduced mouth opening prompts only two questions: Of the world’s 8 billion people, are at least 4.8 billion suffering from TMD? Perhaps we are losing control of the data, or there is a fundamental error in clinical assessment. Are we sure we have the knowledge and valid tools to interpret the TMD condition in patients? Based on the previously discussed chapters in the 'Normal Science' section, it doesn’t seem so. Nevertheless, we will delve deeper into the topic to determine if there is an epistemological anomaly.
</blockquote>

Even more shocking is a very recent article by Taseef Hasan Farook<ref>Taseef Hasan Farook, Tashreque Mohammed Haq, Lameesa Ramees, James Dudley. Predictive modelling of freeway space utilising clinical history, normalised muscle activity, dental occlusion, and mandibular movement analysis. SCI Rep.</ref>, published in 2024 in Scientific Reports, part of the prestigious Nature Publishing Group, which concludes with the following assertions.

The "freeway space" is the distance between the dental arches at rest<ref>Pleasure, M. A. Correct vertical dimension and freeway space. J Am Dental Assoc 43, 160–163 (1951).</ref>. It is a critical parameter in dental prosthetics, influencing occlusion and vertical dimension<ref>Pleasure, M. A. Correct vertical dimension and freeway space. J Am Dental Assoc 43, 160–163 (1951).</ref>. Adequate freeway space ensures prosthetic stability and prevents temporomandibular disorders (TMD) and muscle fatigue<ref>Farook, T. H., Rashid, F., Alam, M. K. & Dudley, J. Variables influencing the device-dependent approaches in digitally analysing jaw movement—a systematic review. Clin. Oral. Investig. 27(2), 489–504 (2022).</ref>. TENS (Transcutaneous Electrical Nerve Stimulation) is used to relax the muscles and assess the correct vertical dimension in relation to the freeway space<ref>Snyder, B., TENS and the treatment of TMJ dysfunction. J Prosthet Dent 45, 335–338 (1981).</ref><ref>Farook, T. H. & Dudley, J. Automation and deep (machine) learning in temporomandibular joint disorder radiomics. A Systematic review. J. Oral. Rehabil. 50(6), 501–521 (2023).</ref>.

[[File:Question 2.jpg|left|150x150px]]
{{q2|So, if TENS is not performed, could the vertical dimension even in healthy individuals be incorrect? |... in our opinion, all these intellectually interesting and scientifically stimulating discussions lead to a common denominator: 'Muscle tone,' a topic we will address in the next two chapters, correlating it with the 'Freeway space.'}}


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