This is a prospective, single- center, randomized (1:1) clinical trial comparing the effectiveness of magnesium sulphate injections in treatment of myofascial trigger points in the masseter muscle versus the saline injection.

The proposal presents the magnesium sulphate (MgSO4) as a possible injection treatment for TrPs. The MgSO4 prevents the release of pre-synaptic acetylcholine from neuromuscular and sympathetic junctions that could explain the ability of the MgSO4 to relax the muscle and reduce pain Specific aim: evaluate the effectiveness of magnesium sulphate injections in treatment of myofascial trigger points in the masseter muscle versus the saline injection.

Hypothesis: the injection of masseter muscle trigger points with magnesium sulphate is more effective than saline injection in pain relief.

Inclusion Criteria:

• Definite diagnosis of myofascial pain with a referral, based on the DC/TMD criteria
• the presence of one or more trigger points in the unilateral or bilateral masseter muscle
• no history of any invasive procedures in the related masseter muscle.

Exclusion Criteria:

• Factors that can cause pain in the orofacial region other than MTPs (decayed tooth, TMJ internal disorder).
• Any systemic disease that possibly affects the masticatory system such as rheumatoid arthritis and epilepsy
• pregnancy and lactation.