The temporomandibular joint or cranio-mandibular complex, is a bicondylar synovial joint that is established between the temporal bone (one of the bones of the skull) and the lower maxilla (of the mandible). They are actually two joints, one right and one left, one on each side of the head, working together synchronously.
A joint is an anatomical structure that joins two bones or a bone and cartilage. The function of the joints, in addition to constituting the union between different bones, is to provide the anatomical structure that allows generating movements between rigid structures. However, some joints, such as those in the skull, are not mobile.
Temporomandibular joint (Source: Jose Larena via Wikimedia Commons)
A synovial joint is one that has an articular capsule within which are the articular structures covered with cartilage and bathed in synovial fluid, which is a liquid rich in hyaluronic acid that nourishes the cartilage and reduces friction between the joint surfaces.
A bicondyle joint is one in which both bones that make up the joint have a condyle each. Within the classification of the joints are part of the condilarthrosis.
A condyle is a rounded protrusion located at one end of a bone and is part of the articular structure of the bone.
The temporomandibular joint is, then, a joint in which the condyles of the temporal bone, covered with cartilage and immersed in synovial fluid, join with the condyles of the mandibular bone, which are also covered by cartilage. This joint is surrounded by a joint capsule and stabilized by a set of ligaments.
characteristics
The temporomandibular joint is the joint that establishes the connection between the temporal bone and the jaw. It is located on both sides of the head and in front of the ears. They are two joints that work synchronously and represent the only mobile joints between the bones of the skull.
It is formed by the condyles of the lower jaw and the condyles and the glenoid cavity of the temporal bone. Between them is a fibrous pad or meniscus of connective tissue called the articular disc. The synovial cavities of this joint are located above and below the articular disc, forming spaces like "sacs".
Temporomandibular joint schematic (Source: Henry Vandyke Carter via Wikimedia Commons)
The synovial cavities are filled with the synovial fluid that is produced by the synovial membrane. This membrane covers the entire internal portion of the joint capsule, except for the cartilage surface. This cartilage is fibrocartilaginous in nature.
The term synovial derives from the Greek syn (with) and the Latin ovum (egg), that is, "with the appearance of an egg" and, in fact, this liquid looks like egg white. It is a plasma ultrafiltrate with few proteins and cells and has the same electrolyte composition as plasma.
Longitudinal section of the temporomandibular joint (Source: Dr. Johannes Sobotta via Wikimedia Commons)
Synovial fluid contains hyaluronic acid, which is responsible for the slimy consistency that gives it an egg white appearance. Its function is to nourish and lubricate the articular cartilage, reducing friction between the articular surfaces during movement.
The joint capsule is lax and has three ligaments that stabilize this joint. These ligaments are the temporomaxillary ligament, the sphenomaxillary ligament, and the stylomaxillary ligament.
Movements
The temporomandibular joint allows 3 types of movements: 1) those for opening and closing the mouth, that is, raising and lowering the lower jaw, 2) those for protrusion and retrusion of the mandible, that is, forward and forward projection movements. back, 3) lateral movements of the lower jaw to the right and left.
This joint is used for speaking, yawning, chewing, swallowing, and for some facial expressions.
The movements of this joint are produced by a series of muscles that, when contracted, generate the joint movements described above. Collectively, these muscles are called the masticatory muscles.
These muscles are the masseters, the internal or medial and external or lateral pterygoids, and the temporal muscles. Masseters elevate the lower jaw. The temporalis muscle elevates the lower jaw and displaces the maxillary condyle back. The external or lateral pterygoid moves the lower jaw forward and laterally, while the internal one elevates the lower jaw.
Pathologies
The pathologies that affect the temporomandibular joint can be very diverse. They can have an infectious, traumatic, neoplastic (tumor) or autoimmune origin and can affect the bone or cartilage structure of the joint, the muscles or the ligaments involved in said joint.
There is data that suggests that at least 40% of the world population has presented or presents some problem in the temporomandibular joint. Among the most frequent pathologies is the syndrome of temporomandibular dysfunction.
This syndrome is considered a non-inflammatory joint disorder with impaired function of any of the joint structures with an abnormal displacement, usually anterior, of the joint disc.
The main manifestations of this syndrome are pain, limitation of joint movement which causes difficulty in opening the mouth and a joint noise called joint click. When this pathology progresses chronically, there is usually an asymptomatic period that follows the acute phase, and then reappears as osteoarthrosis (degenerative joint cartilage).
In many cases, the syndrome only presents as an acute condition that does not necessarily progress. It is seen in both men and women, but is more common in women (3 to 1 ratio). The highest incidence occurs between 40 and 50 years, and the lowest is for those under 20 years.
Other pathologies of the temporomandibular joint are muscle disorders or myopathies and joint disorders or arthropathies. Among the former, the most frequent are bruxism and myofascial syndrome, and among the latter are dislocations, disc displacements and blockages, among others.
Bruxism among the latter pathologies is one of the most frequent after temporomandibular dysfunction syndrome. It consists of clenching or grinding the teeth outside of the physiological movements of chewing or swallowing.
It occurs frequently at night, causing morning pain, tooth wear and muscle pain, tension and stiffness when chewing. Although it can have many causes, one of the most important is stress.
References
- Bell, Welden E. Understanding Temporomandibular Biomechanics: An Explanation. Journal of Craniomandibular Practice, 1983, vol. 1, no 2, p. 27-33.
- Kasper, Dennis L., et al. Harrison's principles of internal medicine. 2001.
- Putz, Reinhard; PABST, Reinhard. Sobotta-Atlas of Human Anatomy: Head, Neck, Upper Limb, Thorax, Abdomen, Pelvis, Lower Limb; Two-volume set. 2006.
- Sharma, Shalender, et al. Etiological factors of temporomandibular joint disorders. National journal of maxillofacial surgery, 2011, vol. 2, no 2, p. 116.
- Spalteholz, Werner. Atlas of human anatomy. Butterworth-Heinemann, 2013.
- Tuz, Hakan H.; ONDER, Ercument M.; KISNISCI, Reha S. Prevalence of otologic complaints in patients with temporomandibular disorder. American Journal of Orthodontics and Dentofacial Orthopedics, 2003, vol. 123, no 6, p. 620-623.