The patients will be randomly assigned to one of the two groups according to the treatment method: group I (masseter group) and group II (masseter &sternocleidomastoid group) where each patient will be injected 0.5ml in each trigger point (TrPs) of magnesium sulphate according to the treatment group by the same operator. The treatment method for TrPs will be the primary predictor variable. Patients will be examined at the following intervals: during diagnosis, 1-month, 3-months, and 6-months post-injection. The participated patients will be assessed using pain score measured on a 10-point visual analogue scale (VAS), the 0 indicating no pain and 10 indicating the worst pain ever

Inclusion Criteria:

• definite diagnosis of myofascial pain
• presence of one or more unilateral or bilateral trigger points in the masseter muscle and sternocleidomastoid muscle;
• no history of any invasive procedures of the related masseter muscle.

Exclusion Criteria:

• any painful conditions (other than myofascial trigger points) affecting the orofacial region
• any systemic diseases that could masticatory function (e.g., rheumatoid arthritis and epilepsy);
• pregnancy and lactation