Every time you eat, speak, swallow, or yawn, you utilize your temporomandibular joints, muscles of mastication, and associated structures.
I’m starting a series of posts on temporomandibular disorders (TMDs). Today’s focus is on temporomandibular joint (TMJ) anatomy. Let’s begin by fleshing out the difference between TMJ and TMD.
What do these two acronyms mean, and are they synonymous with each other?
I'm glad you asked!
Temporomandibular Joint (TMJ)
TMJ, short for temporomandibular joint, is the anatomical structure formed by the condyle of the mandibular bone (jawbone) that fits into the glenoid fossa of the temporal bone (which is part of the skull). The articular disc sits between the condyle and temporal bone, preventing both bones from rubbing against each other.
Temporomandibular Disorders (TMDs)
While TMD, short for temporomandibular disorders, is an umbrella term for a broad group of conditions affecting the TMJ and its associated structures, including muscles, ligaments, and nerves. There are many different disorders under the broader terminology of TMD. Therefore, TMD is not a specific diagnosis.
In summary, TMJ is the structure, while the disorder is TMD.
Everyone has two TMJs on both sides of the skull, but fortunately, most people do not have a TMD.
Temporomandibular Joint (TMJ) Anatomy
A healthy TMJ allows for both rotational and translational movement during mouth opening.
The condyle, the most superior aspect of the mandible, articulates at the base of the cranium (skull) with the glenoid (mandibular) fossa, an ovoid depression on the inferior surface of the temporal bone.
The Articular Disc
The articular disc, made up of fibrocartilage, separates these two bones and divides the joint into two compartments filled with synovial fluid:
The inferior joint space: bound inferiorly by the condyle and superiorly by the inferior surface of the articular disc.
The superior joint space: bound inferiorly by the superior surface of the articular disc and superiorly by the temporal bone’s glenoid or mandibular fossa.
The articular disc has a thinner central portion known as the intermediate zone. In a normal joint, the condylar head fits into this intermediate zone.
Anteriorly, the disc is attached to the superior lateral pterygoid muscle and the capsular ligament, which surrounds and encompasses the joint. Posteriorly, it is attached to the richly vascularized and highly innervated retrodiscal tissue. Medially and laterally, collateral ligaments attach the disc to the condyle.
Ligaments
In addition to the capsular and collateral ligaments mentioned above, other ligaments also function to protect the TMJ by helping to passively support and restrain joint movement.
Temporomandibular ligament: the thickened lateral portion of the joint capsule. It influences the rotational opening movement of the mandible and prevents posterior dislocation of the joint. (1)
Stylomandibular ligament: runs from the styloid process to the angle of the mandible and limits excessive mandibular protrusive movements
Sphenomandibular ligament: extends from the spine of the sphenoid bone to the lingula on the medial aspect of the ramus of the mandible
Innervation and Vascular Supply of the TMJs
The TMJ is innervated by the auriculotemporal, masseteric, and deep temporal nerves, which are branches of the mandibular division of the trigeminal nerve.
The superficial temporal artery, which arises from the external carotid artery, provides the primary vascular supply. Additional vasculature is provided by the deep auricular artery, ascending pharyngeal, and anterior tympanic arteries.
Muscles of Mastication
Multiple muscles, collectively known as muscles of mastication, attach to the mandible and work together to facilitate movements of the TMJ.
Movement of the TMJ is necessary for jaw functions such as talking, chewing, swallowing, and yawning. The muscles of mastication are also involved in oral parafunctional habits (overuse behaviors) such as teeth grinding (bruxism), clenching, bracing, and tapping, in which individuals subconsciously overwork and overuse their TMJs and muscles.
The major muscles of mastication and their functions are listed below.
​ | ​Muscle | Function (1) |
1 | Temporalis | Elevates mandible (Closes mouth) Retraction |
2 | Masseter | Elevates mandible (Closes mouth) |
3 | Medial Pterygoid | ​Elevates mandible (Closes mouth) |
4 | Inferior Lateral Pterygoid | Protrusion Lateral movements of the mandible Depresses mandible |
5 | Superior Lateral Pterygoid | Stabilization of the condyle and disc during function |
​ | ​ | ​ |
Although these are the predominant muscles of mastication, other muscles of the head and neck, such as the digastric, suprahyoid, and infrahyoid muscles, provide additional support during mastication.
Join me next time as I discuss the epidemiology of TMDs.
Until next time….
Dr. Idahosa
Reference:
© 2023. Temporomandibular Joint: Anatomy and Function. Dr. Chizobam Idahosa.
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