Botulinum toxin (BOTOX®) injections into the masseter muscle are an effective treatment for nocturnal bruxism, with several trials using various dosages of botulinum toxin for this purpose. The aim was to evaluate the effectiveness of injecting 10MU of botulinum toxin A (BTXA) into the masseter muscle to reduce nocturnal bruxism, the sample will randomly divided into 2 groups.

In the injection group, Patients will inject with 10 MU of botulinum toxin type A (BOTOX® - Allergan Inc. - Dublin - Ireland) per side at two sites into the masseter muscle bilaterally.

In this Placebo group, patients will prick twice at the inferior prominent part of the masseter muscle observed using the stinger pen used in the blood glucose meter.

The evaluation will make by Electromyography (EMG) analysis, Visual Analogue Scale (VAS) values.

Nocturnal bruxism (NB) is a disorder of maxillomandibular activity characterized by nonfunctional grinding and clenching of teeth while sleeping.

NB can cause teeth attrition, dental prostheses/implant failure, tooth sensitivity, pain in the teeth, jaw, masticatory muscle, and temporomandibular joint (TMJ), neck pains and headache, periodontal disease, oral or facial pain, and perhaps tooth loss. The diagnosis of nocturnal bruxism is based on complaints of tooth grinding or clenching, as well as one or more of the following signs: nonfunctional teeth attrition, sounds consistent with bruxism, and jaw muscle discomfort. Teeth wear and TMJ dysfunction can both be caused by bruxism. In some circumstances, delaying therapy might lead to luxation and degenerative arthritis of the temporomandibular joint.

For the treatment of bruxism, many treatment approaches such as occlusal splints and pharmacologic medications such as psychobehavioral therapy or L-dopa, and psychobehavioral therapy have been examined but is not enough evidence to define a standard of reference approach for SB treatment.

Botulinum toxin (Botox®) is an exotoxin generated by the bacteria Clostridium botulinum that causes muscle inactivity by blocking acetylcholine release from cholinergic nerve terminals into the neuromuscular junction. In the last two decades, several studies have been conducted to investigate the efficacy of botulinum toxin type A (BTXA) in reducing nocturnal bruxism, and the results have been promising. These studies have used different doses of botulinum toxin ranging from 20 mouse units (MU) and 25 MU to 30 MU in the masseter. Most of these studies did not take into account the relationship between the amount of botulinum toxin dose and alteration of the masseter muscle's size and the shape of the lower third of the face, where injection of more than 20 MU into the masseter muscle affects its size and is an effective treatment for masseter muscle hypertrophy for at least 9 months. To avoid the unwanted side effects of doses greater than 20 MU, the trial aimed to evaluate the effectiveness of injecting 10 MU of the Botulinum toxin into the masseter muscle in reducing the nocturnal bruxism.

The idea of the research will explain to all patients, and the information sheets will distribute to them, then their consent will obtain.

Inclusion Criteria:

1. Moderate to severe pain in the masseter muscles during clinical examination.
2. Age range between 18 and 40 years.
3. Tooth-grinding sounds corroborated by family members or caregivers.
4. Attrition in occlusal surface of posterior teeth.

Exclusion Criteria:

1. Loss two posterior teeth or more (except for third molars).
2. Fixed or movable prosthodontics for more than four dental units.
3. Advanced malocclusion (Class II occlusion Model II - deep bite - open bite).
4. Temporomandibular disorders.
5. Pain in the orofacial region.
6. Insomnia.
7. Known botulinum toxin allergy.
8. Pregnancy.
9. Neuromuscular disease.
10. Bleeding disorders.
11. Antibiotic therapy, pulmonary disease that produced coughing during sleep.
12. Infectious skin lesion at the site of the injection.