Temporomandibular disorders (TMDs) are the major cause of non-dental pain in orofacial area. Laser therapy can be considered as one of the most recent treatment approaches in the field of physiotherapy. The special features of laser light such as coherence, monochromaticity, and collimation can result in the ability of laser light to modify cellular metabolism, increase tissue repair and reduce edema and inflammation. Several studies demonstrated successful results regarding the use of low level lasers in releasing pain of musculoskeletal conditions, but there are also contradictory reports in this field, and the clinical effectiveness of this treatment modality has been debated in some review articles. A few studies evaluated the efficacy of low level laser therapy in the treatment of temporomandibular disorders and the associated myofacial pain. There are remarkable variations in the methodology of these researches and some reported insufficient data regarding the physical properties of the laser used. The aim of this study is to evaluate the effectiveness of low level laser therapy in improving the sign and symptoms of patients suffering from myofacial pain syndrome.

This study will be implemented on 20 patients referring to Department of Prosthetic Dentistry of Mashhad Dental School. The patients are selected according to the RDC/TMD criteria to include those having temporomandibular disorders with muscular origin. The patients will be randomly assigned to two groups: Group 1 (treatment group) will receive low level laser therapy. The laser light will be applied with 890 nm diode laser (Mustang 2000+, Russia) with frequency of 1500 Hz, and dose of 2 J/cm2 per point in the painful muscles.

In Group 2 (placebo) the low power laser will be applied with a minimal dose that is very lower than the threshold necessary for therapeutic effects. Laser therapy for both the treatment and placebo groups will be applied on all painful muscles three times a week for four weeks. Patients will be evaluated at the start of the treatment, after the 6th and 12th sessions of laser therapy and also one month after the end of the treatment. At each evaluation, the maximum mouth opening with or without pain and masticatory muscle tenderness will be measured. Pain will be measured through the Visual Analogue Scale (VAS). The range of lateral and protrusive mandibular movements, and the difficulty in chewing food will also be evaluated.

Inclusion Criteria:

• The patients are selected according to the RDC/TMD criteria to include those having temporomandibular disorders with muscular origin.

Exclusion Criteria:

1. Patients with disk displacement (with or without reduction)
2. patients with temporomandibular joint arthralgia or osteoarthritis
3. patients with systemic disease affecting temporomandibular joint
4. patients receiving analgesic or antidepressant drugs