Myofascial pain syndrome is a neuromuscular problem characterized by muscle spasms, pain, and the presence of myofascial TrPs that present as muscle band contractions [17, 22,23,24]. TrPs most commonly affect the masseter muscles in the orofacial region, and are one of the major triggers of nonodontogenic pain [25, 26].
Because myofascial muscles are a part of the stomatognathic system, imbalance in any part of this system could have a detrimental impact on its function such as chewing, posture and non-physiological occlusion.that affect the patient's quality of life .
Injection of myofascial TrPs with different materials such as saline, local anesthesia, botulinum toxin, and platelet rich plasma injections can help reduce pain and has been seen to be widely tolerated [22, 28, 29]. However, many patients exhibit recurrence of myofascial pain after a short period of injections, highlighting the unmet clinical need for a new treatment measure with a longer lasting effect.
The aim of the current study was to evaluate the clinical efficacy of MgSo4 injections in the treatment of masseter muscles with TrPs when compared to saline injections. MgSo4 has been recommended for the treatment of myofascial TrPs due to its muscle relaxant and vasodilator properties that can have a pain-relieving effect. Few studies till date have examined the effects of MgSo4 on various musculoskeletal inflammatory disorders [9,10,11,12].
This study included 180 patients, and 84.4% of both study groups were female. This findings, in agreement with previous epidemiological evidence on tempero-mandibular disorders, can be attributed to hormonal and bio-behavioral factors, a higher demand for treatment among females, and their increased tendency toward psychological disorders [30, 31].
The mean age of patients in the MgSo4 group was 35.91 ± 12.61 years whereas that in the saline group was 30.53 ± 8.51 years, and this was in agreement with previous evidence that found that myofascial TrPs typically occurred in patients aged between 27 and 50 years .
The current study used the VAS scale to estimate pain intensity at each study interval, and significantly lower values were observed in patients receiving MgSo4 injections at all follow-up intervals when compared to patients receiving saline injections (P < 0.05). This could likely be attributed to the increased vasodilation provided by the former in several vascular beds, resulting in greater blood flow to the trigger point and removal of irritating substances that cause pain. Additionally, it also eliminates muscle tension and excessive tenderness by competing with calcium at the motor end plate and reducing acetyl choline discharge [33, 34]. This, in turn, leads to reduction of pain intensity at the site of injection, and these findings are in harmony with those of Ibrahim et al. , who also reported observing a palliative effect following iontophoresis with MgSO4 in healthy adult volunteers. Furthermore, Sane et al. , studied the effect of local injection of ropivacaine and bupivacaine injection with magnesium sulfate on postoperative pain in vertebral laminectomy surgery and concluded that local anesthesia combined with magnesium sulfate provided greater postoperative analgesia and considerably reduced postoperative opioid use.
On the other hand, Ahmed et al. , tested the efficacy of ultrasound-guided erector spinae plane block with and without the addition of magnesium sulphate on pain control in patients with postherpetic neuralgia and found that the addition of magnesium sulphate made no difference when compared to the use of bupivacaine alone.
The MMO was significantly higher in the MgSO4 group up to 3 months of follow-up (p < 0.001), although this statistical significance ceased to exist after 6 months (p = 0.121). Increased tension in the muscular band, inhibition of motor activity, muscle shortening, and occurrence of spasms often results in hypomobility, and the improvement in MMO observed in this study could be attributed to the muscle relaxation effect of MgSO4 which lowers acetylcholine release at the myoneural junction, blocking peripheral neuromuscular transmissions and inhibiting skeletal muscle contractions .
This is harmonized with the finding of Fathy et al. , who compared the efficacy of transforaminal MgSO4 injection against Ozone on pain intensity and functional disability in patients with lumbar disc prolapse and concluded that MgSO4 offered better analgesia, noticeably reduced analgesic ingestion and improved the functional disability.
Quality of life is an important parameter when evaluating the outcomes of various treatment measures for chronic pain. OHIP-14 is a specific tool used to assess oral function and measure oral health related quality of life. In the current study, all treatment groups exhibited improvement in the OHIP-14 score at the follow-up assessments, with the MgSo4 injection group exhibiting significantly better outcomes compared to the saline injection group (P < 0.001). This could be attributed to a reduction in pain intensity and improvement of function in the former [19, 38,39,40,41].
Compromised quality of life has been often reported for patients suffering from chronic pain which recovered with different treatment that improves the pain level . This is in line with Azi et al. , who evaluate the analgesic effect of trigger point acupuncture combined with cyclobenzaprine chlorhydrate and sodium dipyrone. Azi et al. concluded that pain relief and improvement in quality of life at 4 weeks in both groups. Moreover, Brodsky et al. , evaluated change in health-related quality of life at the group and individual levels in a consecutive series of patients with chronic myofascial neck pain and concluded that considerable improvement over time was found for all scores post-treatment of myofascial neck pain.
The present study had several limitations. First, it did not compare the effects of MgSo4 injections to any other materials such as local anesthesia, botulinum toxin, or platelet rich plasma. Second, objective methods of assessment such as EMG could not be used due to limited resources.