ANATOMICAL & CLINICAL STUDY OF THE MASTICATORY MUSCLES THAT ATTACH TO THE TEMPOROMANDIBULAR JOINT DISC AND THEIR ROLE IN PATIENTS WITH BRUXISM
Mohamed Atif Said Ahmed* and Walid Ghanem**
Department of Anatomy*, Faculty of Medicine, Zagazig University, Department of Oral and Maxillofacial Surgery**, Faculty of Dentistry, Suez Canal University, Egypt.
The temporomandibular joint )TMJ) is classified as a hinge-sliding joint. It has a unique structure and function compared to other joints. The articular disc is the most important anatomical structure of the TMJ. The disc completely divides the TMJ into two distinct compartments. The masticatory muscles are not simply a group of clearly independent muscles. The aim of the study was to define the general morphology of the TMJ disc, mandibular condyle and the attachment of masticatory muscles to the disc. We aimed also to investigate the relation of the maxillary artery and superficial temporal artery to the TMJ disc. Clinically we aimed to evaluate the relationship between disc displacement and dysfunction of the masticatory muscles in patients with bruxism. Materials and methods: Detailed dissection was performed on 32 head halves of 16 cadavers. Retrospective study using CT of 15 patients and MRI of 10 patients of the temporomandibular joint region were analysed. The study involved also 12 bruxism patients. Each patient was subjected to CT and MRI. Results: The disc is divided into an anterior band of 2.2 mm ± 0.3 mm in thickness, a posterior band 2.8 mm ± 0.5 mm thick, and a thinner intermediate zone of 1mm ± 0.2 mm thickness. Mandibular condyle is an ovoid condylar process. It is 18.0 mm ± 4.5 mm side to side and 9.0 mm ± 2.0 mm from front to back. The mean width of the glenoid fossa was 19.0 mm ± 4.0 mm. The upper head of the lateral pterygoid muscle was seen to insert into the anteromedial two thirds of the temporomandibular joint disc. Temporalis muscle is one unit muscle has different bundles. The midmedial bundle inserted into the disc of the temporomandibular joint just anterior to the area into which muscle fibres of the upper head of the lateral pterygoid were inserted. In 8 specimens, the midmedial bundle was tightly adjoined to the lateral surface of the upper head of the lateral pterygoid. The discotemporal bundle was attached on the anterior and anteromedial one third of the disc adjacent to the insertion of the upper head of the lateral pterygoid. In 7 specimens, the zygomatico-mandibularis was attached to the anterior surface of the disc. The fibers of the posterosuperior part of the masseter muscle were attached on the anterolateral one third of the disc. The deepest layer of the masseter muscle covers the lateral surface of zygomaticomandibularis. The average vertical distance between the maxillary artery and the most superior point of the articular disc was determined as 3.67±0.58 mm. The superficial temporal artery was 2.5 ± 0.45 mm behind the articular disc and its mean diameter was determined as 4.37 ±0.45 mm. Twelve bruxism patients with unilateral functional sides were studied. MRI examinations revealed the status of each muscle of masticatory muscles in affected and non-affected sides. Facial asymmetry and effusion on the contralateral sides were detected in all patients through MRI. Flattening, erosion and osteophyte formation of the condyles of the affected sides were also detected. It was concluded that the TMJ disc is a very important structure and the clinician must have the ability to formulate the diagnosis based on understanding of the morphological aspects of the disc and the surrounding muscles. The results may be helpful for understanding the anatomy and biomechanics of the temporomandibular joint, especially relative to the development of disc displacement.