The study group will be selected from patients who previously presented with various temporomandibular disorder (TMD) complaints to the Temporomandibular Disorders Clinic of the Department of Complete and Removable Dentures at the Faculty of Dentistry, Istanbul University. During routine examinations, TMD-DC (Diagnostic Criteria for Temporomandibular Disorders) forms are completed to aid in achieving an accurate diagnosis. Subsequently, patients suspected of having TMD of masticatory muscle origin but without a definitive diagnosis are routinely referred for ultrasonographic (USG) imaging. Patients meeting these criteria will be included in the study. Participants will be divided into two groups. The first group will consist of patients who have already undergone USG imaging during their routine examination, have been definitively diagnosed with masticatory muscle disorders based on clinical and radiographic findings, and have initiated routine occlusal splint therapy in the clinic. The 12-week treatment process of these patients will not be altered in any way. At the final follow-up session after the 12-week routine treatment protocol, the TMD-DC form completed at baseline will be re-administered, and the two forms will be compared to evaluate changes in symptoms and pain levels. Another USG imaging will also be performed at this session. The second group, serving as the control group, will include patients who have previously undergone USG imaging during routine examination and have received a definitive diagnosis of masticatory muscle disorders based on clinical and radiographic evaluations, but have not yet begun treatment. Patients whose turn for treatment begins during the study period will be excluded from this group. At the end of the 12-week period, the TMD-DC form will be re-administered, and a second USG imaging will be performed. This process will not interfere with the patients' position in the treatment queue, and treatment will commence as scheduled. In the second USG session, changes in the thickness and elasticity of the masseter, temporalis, trapezius, sternocleidomastoid, and splenius capitis muscles will be assessed by comparing the two imaging records.