Electrical Stimulation of the Mandibular Nerve for Pain and Function Management in Temporomandibular Disorders

Overview

Temporomandibular disorders (TMD) encompass dysfunction and pain of the masticatory muscles and temporomandibular joint (TMJ). Pain in the TMJ, restricted jaw movement, and joint sounds are common conditions in this disorder. This can impact patients' ability to perform daily activities such as eating, speaking, laughing, or yawning, significantly affecting their quality of life. The TMJ and masticatory muscles are innervated by the auriculotemporal branch and the mandibular nerve (V3), a branch of the trigeminal nerve. An estimated 60% to 70% of the population shows signs of TMD, of which up to 12% report intense symptoms requiring treatment. Percutaneous electrical nerve stimulation (PENS) could be a clinically relevant therapy in TMD patients applied through minimally invasive physiotherapy. To our knowledge, there are no trials evaluating the non-surgical clinical efficacy of PENS on the mandibular nerve. The project's objective is to assess the effectiveness of PENS on the mandibular nerve in this type of condition.

Pain is the most common and limiting feature of Temporomandibular Disorders (TMD), affecting approximately 75% of the population at some point in life. These disorders involve dysfunction and pain in the masticatory muscles and temporomandibular joint, impacting patients' quality of life. An estimated 60-70% of the population shows signs of TMD, with up to 12% requiring treatment. The peak incidence occurs between 20 and 40 years, predominantly affecting women (8:1 compared to men). Temporomandibular Disorder often coexists with other medical conditions, such as headaches. The most common diagnoses are myofascial pain, followed by disc displacement with reduction and arthralgia. Prevalence ranges from 3% to 15%, with new case rates between 2% and 4%. Prognosis for myofascial TMD varies, with studies indicating persistence, remission, and relapse. The economic cost associated with TMD is significant, with studies revealing considerable expenses on treatments. The multifactorial pathophysiology of myofascial pain is influenced by bruxism, stress, psychological conditions, and fibromyalgia. Risk factors include genetics, psychological stress, and parafunctional habits. Clinical manifestations include pain, decreased jaw mobility, and additional symptoms in the head and neck. Diagnosis involves physical examination, palpation of muscles and joints, and imaging tests such as magnetic resonance imaging. Specific diagnostic criteria have been proposed. Conservative treatment, including physiotherapy, manual therapy, exercises, splints, and pharmacological modalities, is the primary option. However, there are limitations in the effectiveness of some approaches. Physiotherapy is considered effective by 72% of respondents in the United Kingdom. The musculoskeletal system related to the temporomandibular joint (TMJ) consists of masticatory, facial expression, and neck muscles, playing specific roles in jaw movement. Elevator muscles (masseter, temporal, and medial pterygoid) close the mouth, depressors (digastric and lateral pterygoid) open it, protractors (temporal and lateral pterygoid) move it forward, and retractors (masseter and medial pterygoid) move it backward. Facial expression and neck muscles contribute to additional functions. Motor innervation of the TMJ comes from the trigeminal nerve, specifically its mandibular branch (V3), which also innervates masticatory muscles. This nerve divides into branches such as the ophthalmic, maxillary, and mandibular, providing sensitivity to different areas of the face, mouth, and jaw. Blood supply to the TMJ occurs through the superficial temporal artery and the mandibular artery, supplying blood to the skin, muscles, and surrounding joint structures. Regarding the biomechanics and functionality of the TMJ, its complexity and crucial role in jaw movements such as chewing, speaking, and yawning are emphasized. Manual therapy, specifically cervico-mandibular therapy, has shown significant improvements in disability related to temporomandibular disorders (TMD). The combination of manual therapy for the orofacial region and the cervical spine has proven to be more effective than home exercises or cervical treatment alone. Therapeutic exercise in the TMJ has demonstrated moderate short-term effects and variable long-term effects in reducing pain and improving range of motion in patients with TMJ dysfunction. Passive and active stretches, as well as postural exercises, are useful for increasing range of motion and reducing pain. Percutaneous electrical nerve stimulation (PENS) emerges as a relevant option for managing pain in TMD patients. PENS, applied through ultrasound-guided needles, can influence orofacial pain and jaw movement, offering analgesic benefits through peripheral and central mechanisms. PENS is considered a minimally invasive intervention and has been successfully used in chronic pain treatment. In summary, a detailed understanding of the anatomy, function, innervation, and vascularization of the TMJ, combined with therapeutic approaches such as manual therapy, exercise, and PENS, is essential for comprehending and effectively addressing temporomandibular disorders.