Myofascial pain syndrome (MPS) is common syndrome in patients with musculoskeletal pain problems. It's a pain condition originating from muscle and surrounding fascia. Patient usually complains from localized pain in a certain area or referred pain of various patterns. On physical examinations, trigger points (TrPs) may reveal on the involved muscles. (Tantanatip, Chang,2018). TrPs are usually palpable and hyperirritable nodule found within a taut band of muscle. By Stimulating these points, two characteristic phenomena are produced: sudden contractions of the taut band and referred pain, which is known as the local twitch response (LTR). Active MTrPs usually produce pain spontaneously, and sometimes referred pain, while Latent MTrPs produce referred pain in response to the applied pressure, but not spontaneously (Simons, D.G, 2004).

Multiple factors can contribute to MPS. The risk factors are; Traumatic events, ergonomic factors (e.g., overuse activities, abnormal posture, Structural factors (e.g., spondylosis, scoliosis, osteoarthritis), systemic factors (e.g., hypothyroidism, vitamin D deficiency, iron deficiency). (Saxena,et al,2015), however Intramuscular injections are considered the first-line treatment for myofascial TrPs(Yilmaz, et al 2021). Injections could be wet as local anesthetic agents, steroid, platelet rich plasma, saline or botulinum toxin, or it could be dry by dry needling without solutions MPS is a result of inappropriate activity of acetylcholine (ACh) at the neuromuscular junction, producing a sustained contraction of the sarcomere. The ACh-related effects are relevant to the taut band development, which leads to increasing the local energy demand or energy crisis (Simons, D.G, 2004). The pain in the local muscle occurs secondary to the substances released from the damaged muscle, and from the extracellular fluid around the TrP, such as protons (H+) on acid-sensing ion channels which occurs in ischemia and in exercise. In these metabolic conditions, sensitizing amines may be released stimulating the nociceptors and giving rise to pain. Therefore, MTrPs are better defined by two phenomena: altered ACh activity and nociceptive stimulation (Sluka, Kalra, Moore,2001). The fact of myofascial muscles are a part of the stomatognathic system, any imbalance in this system could have a disturbing impact on its function such as mastication, posture and non-physiological occlusion, affecting the patient's quality of life (Fiorillo, 2020).

Botulinum toxin type A is a neurotoxin used to reduce excessive muscle contraction. Its produced by gram-positive, anaerobic, spore-forming bacilli known as Clostridium botulinum which is widely distributed in aquatic and soil environments. (Tiwari,Nagalli 2024). Botulinum toxin inhibits neurotransmission at the neuromuscular junction. Several transport proteins participate in the process by which ACh is released; these proteins aggregate to form the SNARE complex (Soluble NSF (N-Ethylmaleimide-Sensitive Factor) Attachment Protein Receptor, responsible for fusion of the vesicles of ACh with the membrane and the subsequent release of the neurotransmitter. The heavy chain of the toxin has a high affinity for the membrane receptors and, once bound, BTA undergoes endocytosis. The light chain is released within the cell, where it acts as a zinc-dependent endoprotease. After cleavage of one of the proteins of the SNARE complex by BTA, the complex does not form and ACh is not released. (Aikawa,et al , 2006) Magnesium sulfate (MgSO4) is commonly used as analgesics for treatment of musculoskeletal problems, snice having muscle relaxant and vasodilator properties. (Ibrahim, Raoof, Mosaad,2021). These properties can likely be attributed to its ability to block presynaptic acetylcholine discharge from neuromuscular and sympathetic junctions (Dahle, et al ,1995). Therefore, MgSo4 injections are an effective treatment modality for myofascial TrPs of the masseter muscle. It helps in reducing the pain and improving the maximum mouth opening, in addition to the quality of patient's life. (Refahee, Mahrous, Shabaan,2022)

Intervention After the MTP is located and the overlying skin had been disinfected with alcohol, the taut muscle band is pinched between the thumb and index finger, and the needle is inserted 1-2 cm away from the targeted MTP at an angle of 30º to the skin. A negative aspiration should be performed to prevent any intravascular injections (Taşkesen, Cezairli, 2023). Group 1: 2ml MgSo4 (Magnesium sulfate sterile ampoule 10 ml, 100 mg/ml = 0.41 mMol/ml. Egyptian Int. Pharmaceutical Industries Co., Egypt). Group 2: 2ml of BTX and Group 3: 2 ml of saline