The intra-articular injection is considered the first line of minimally invasive treatment of joint disease as it has an analgesic, antimicrobial effect and an immune system stimulating action as it is one of the most powerful detoxication agents.

Aim of the study: This study aims to evaluate the therapeutic effect of intra-articular injection of two different concentrations of ozone gas in the treatment of internal derangement of TMJ.

A total of 20 patients suffering from internal derangement of TMJ will be included in the study. These patients will be randomly assigned to one of two groups. Group A will receive 2 ml ozone-oxygen gas mixture that will be injected intra-articularly with concentration 6 microns/ml (study group). Group B will receive 2ml intra articular ozone-oxygen gas injection with concentration 12 microns/ml (control group). Both groups will receive three sessions of intraarticular injection, one session per week. The first session will be arthrocentesis by ozonated water as a lavage then intraarticular injection with ozone-oxygen gas mixture. Then, the other two sessions will be intraarticular gas injection only. Assessment will be done by measuring the maximum mouth opening and by using Helkimo's index to measure the improvement of symptoms .The follow up period will be 1 month , 3 months and 6 months after the sessions.

Inclusion Criteria:

1. Adult patients above 18 years old.
2. Patients suffering from sounds during condylar movements (clicking or popping).
3. Patients suffering from limited mouth opening and impaired joint movements.
4. Patients who did not respond to conservative treatment as a first line of treatment.

Exclusion Criteria:

1. Patients with history of condylar fracture.
2. Patients with degenerative joint disease.
3. Coagulopathy blood disorders.
4. Presence of infection at the site of injection.