The Anatomy of the Temporomandibular Joint
The temporomandibular joint is a modified-hinge type of synovial joint made up of the condylar process of the mandible and the mandibular fossa of the temporal bone. The surfaces of the joint are lined with fibrocartilage, which is unusual for a synovial joint — most are lined with hyaline cartilage. The joint has an articular disc in the middle of the joint cavity. The temporomandibular joint allows you to open and close your mouth and allows for elevation, depression, protrusion, retrusion, and lateral movements of the jaw.
The muscles that move the temporomandibular joint are called the muscles of mastication. They include the following:
Temporalis: This muscle originates on the temporal fossa of the temporal bone. It’s innervated by the mandibular nerve (CN V3), and it elevates and retracts the mandible.
Masseter: This muscle originates on the inferior and medial part of the maxillary process of the zygomatic bone and the zygomatic arch. It inserts onto the angle of the jaw and the lateral part of the ramus of the mandible. It’s innervated by the mandibular nerve and elevates the mandible.
Lateral pterygoid: This muscle has two heads that originate in two places: The superior head originates on the greater wing of the sphenoid, and the inferior head originates on the lateral pterygoid plate of the sphenoid bone. The superior head inserts on the joint capsule and the articular disc. The inferior head inserts on the condyloid process of the mandible. The lateral pterygoid muscles protract (move forward) the mandible when both the left and right contract together. When one lateral pterygoid contracts, it swings the jaw to the contralateral side. It is innervated by the mandibular nerve.
Medial pterygoid: This muscle also has two heads. One head originates on the lateral pterygoid plate and the pyramidal process of the palatine bone, and the other head originates on the tuberosity of the maxilla. Both heads insert onto the medial part of the ramus of the mandible. It’s innervated by the mandibular nerve, and it works with the masseter to elevate the mandible.
The fibrous layer of the joint capsule has a thickened portion, called the lateral ligament, that strengthens the joint laterally. The stylomandibular ligament runs from the styloid process of the temporal bone to the angle of the mandible. The sphenomandibular ligament runs from the sphenoid bone to the lingula of the mandible.