The literature describes the cause of a temporomandibular disorder (TMD) as a multifactorial event. It can be influenced by anatomical, neuromuscular, traumatic or psychosocial factors. Disturbances often occur in the condyle-disc complex of the temporomandibular joint. The relationship between the articular disc and the condyle head is pathologically altered. The Diagnostic Criteria for Temporomandibular disorders (DC / TMD) describe the displacement of the disc in 4 different forms: disc displacement with reduction; disc displacement with reduction and intermittent locking; disc displacement without reduction with limited opening and disc displacement without reduction without limited opening. TMDs are a common clinical picture that appears in particular in people between the age of 20 and 40 years. About 33% of the total population show signs and symptoms of TMD.

Studies prove that the displacement of the disc with reduction is the most common disorder among temporomandibular joint disorders. According to the DC / TMD, this clinical picture shows intracapsular and biomechanical alterations. If the mouth is closed, the articular disc is often located in front of the mandibular condyle; if the mouth is opened, the disc moves back to its original position on the condyle. Anterior disc displacement appears to be the most common, although a medial or lateral displacement is also possible. During the disc repositioning clicking, popping or snapping noises are usually recorded. Temporomandibular joint disorders such as disc displacement, can also cause pain. Overstretching of the posterior ligament and a compression of the bilaminar zone mandibular movements can be pain-related. Therefore, clicking, popping or snapping noises in the area of the temporomandibular joint (TMJ) correlate with pain in the surrounding tissue. Those complaints intensify when opening the mouth or chewing food.

The treatment of TMD should be oriented on evidence-based procedures that are easy to implement in practice and have a long-term positive effect on the patient's symptoms. Conservative methods including combinations of behavior change, physiotherapy, splint-therapy and medication are most popular. The physiotherapeutic treatment should pursue different strategies, including manual therapy methods (e.g. mobilization and stretching of the temporomandibular joint and / or the neck area) and the demonstration of exercises in everyday life (e.g. self-mobilization and stretching of the masticatory muscles and / or cervical spine) and in addition educating the patient (e.g. about the perception of parafunctions or relaxation techniques). Conservative attempts for patients with TMD should be the first choice. However, there is still no clear data situation and the data pool of randomized clinical studies on this topic needs to be improved. So far studies demonstrate a positive effect of the tested therapy forms. But the individual studies differ greatly in terms of the patient pool, diagnosis, treatment modalities and the result. Furthermore, a precisely described procedure is missing in some papers. Therefore, an exact reproducibility for practitioners is not executable. More research is needed into the benefits of various non-invasive treatments for TMD.

The primary goal of this study is to decrease the ambiguity in this scientific field. In the past various manual and physiotherapeutic exercise methods have already been tested.

This study is also intended to examine the effectiveness of muscle training for the treatment of patients with anterior disc displacement with reduction. The exercises are primarily supposed to train the lateral pterygoid muscle. The treatment with an equilibration appliance in the lower jaw serves as a comparison group.