The temporomandibular joint (TMJ) is the main connection between the skull and the lower jaw. It comprises the participating area of the squamous portion of the temporal bone, the articular disc within the joint capsule, the head of mandible and the surrounding ligaments.
Compartments of the temporomandibular joint
The joint is separated into a superior and an inferior compartment by the articular disc.
- The superior compartment is bordered superiorly by the mandibular fossa of the temporal bone and inferiorly by the articular disc itself. It contains 1.2 mL of synovial fluid and is responsible for the translational movement of the joint.
- The inferior compartment has the articular disc as a superior border and the condyle of the mandible as an inferior border. It is slightly smaller with an average synovial fluid volume of 0.9 mL and allows rotational movements.
Capsule and ligaments
The joint capsule originates from the border of the mandibular fossa, encloses the articular tubercle of temporal bone and inserts at the neck of mandible above the pterygoid fovea. It is so loose that the mandible can naturally dislocate anteriorly without damaging any fibers of the capsule.
The TMJ is supported by the following ligaments:
- The medial and lateral collateral ligaments (also known as the discal ligaments) help connect the medial and lateral sides of the articular disc to the same side of the condyle.
- The temporomandibular ligament is located on the lateral aspect of the capsule and its function includes preventing the lateral or posterior displacement of the condyle.
- The stylomandibular ligament arises from the styloid process and attaches to the mandibular angle. It is responsible for allowing the mandible to protrude.
- The sphenomandibular ligament stretches between the spine of the sphenoid bone and the lingula of the mandible. It contributes to the limitation of extensive protrusive movements and jaw opening.
The TMJ is supplied by three arteries. The main supply comes from the deep auricular artery (from the maxillary artery) and the superficial temporal artery (a terminal branch of the external carotid artery). In addition the joint is provided by the anterior tympanic artery (also a branch of the maxillary artery). The venous blood drains through the superficial temporal vein and the maxillary vein.
The mandibular nerve (third branch of the trigeminal nerve) provides the main nerve supply of the TMJ. Additional innervation comes from the masseteric nerve and deep temporal nerves. Parasympathetic fibers of the otic ganglion stimulate the synovial production. Sympathetic neurons from the superior cervical ganglion reach the joint along the vessels and play a role in pain reception and the monitoring of the blood volume.