Temporomandibular joint

The temporomandibular joint (articulatio temporomandibularis) or TMJ is an articulation between the mandible and the temporal bone. The TMJ is a paired, modified, combined, bicondylar joint which is capable of a range of motions under the control and restraint of a number of muscles and ligaments.

It is formed by the:

  • Articular surfaces of the mandibular fossa (the anterior part of mandibular fossa) which are concave.
  • Articular tubercle which is convex.
  • Head of the mandible.

Articular disc

The articulating surfaces are complemented by a fibrous articular disc (discus articularis) located between them. The central part of the disc is thinner and is known as the intermidiate zone. It separates the disc into the anterior and posterior band. The articular disc divides the joint into the superior and inferior joint compartment. It is attached to the condyle by ligaments that permit rotation on the condyle during jaw movements. It also cushions the joint and the weight load is must bear. The bands of the disc are attached to the medial and lateral poles of the condyle.

Ligaments

The TMJ is supported by the ligaments which surround the articular capsule as follows:

  • Lateral ligament (ligamentum laterale) which connects the zygomatic arch with the neck of the mandible.
  • Sphenomandibular ligament (ligamentum sphenomandibulare) is attached to the sphenoid spine, and the petrotympanic fissure, and to the mandibular lingula near the mandibular foramen. It assists in lateral move- ment of the mandible.
  • Stylomandibular ligament (ligamentum stylomandibulare) which is attached to the styloid process, and to the posterior margin of the angle and the ramus of the mandible. It passes along the medial side of articular capsule but does not join with them. The maxillary vessels separate the ligament from the neck of mandible. The lateral pterygoid muscle and the auriculotemporal nerve are located superiorly and lateraly to sphenomandibular ligament.
  • Medial ligament (ligamentum mediale) passes from petrotympanic fissure to the neck of mandible.
  • Bilaminar zone forms the ligamentous structures posteriorly to the articular disc. It is composed of a stratum of the connective tissue which forms the upper and lower parts that are separated by the highly vascularizated region. It also allows condyle to move anteriorly.

Clinical comments

Styloid or Eagle syndrome was described in 1937 by Watt Eagle. It is the ossification of the stylohyoid ligament or excessive elongation of the styloid process. The syndrome is associated with restricted movements of TMJ, pain during movements of the cervical part of the vertebral column and/or facial pain.

The following movements of the TMJ are possible:

  • Elevation
  • Depression
  • Protrusion
  • Retraction
  • Angulation, lateral movements
  • Circumduction – combination of all movements

Mastication is an initial part of the process in which food is prepared for digestion. It occurs in the oral cavity. It is a combination of movements like protrusion, retraction and lateral and medial rotation. The elevation is generated by the temporalis, masseter and medial pterygoid muscle. It is a very strong movement. The lateral pterygoid is connected with the depression, protrusion and angulation. The forward movements, such as protrusion, is generated by the medial and lateral pterygoid. The backward movements, such as retraction are connected with the temporalis and partly with the masseter, digastric and geniohyoid muscles. In angulation, the lateral and medial pterygoid play  a significant role.

Clinical comments

The Anterior Disc Displacement (ADD) gives changes in the smooth movements of the joint as a consequence of an anatomic disturbance in the relationship of the disc-condyle complex. In ADD the articular disc is positioned anteromedially to the condyle in the closed position. During opening the condyle slides over the posterior band of the disc. Clinically it is usually accompanied by a clicking sound during opening the mouth.

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