The temporomandibular joint (TMJ) is a bilateral synovial condyloid joint between the head (condyle) of the mandible and the mandibular fossa and articular tubercle of the temporal bone. It is an atypical synovial joint because:
Its articular surfaces are covered by fibrocartilage rather than hyaline cartilage.
An intra-articular fibrocartilaginous disc divides the joint into upper and lower cavities, producing two functionally distinct compartments.
The TMJ is subjected to frequent and varied activity. In addition to powerful chewing forces, it is active in speaking and swallowing, where movements are smaller and finely controlled. The joint therefore combines high loading capacity with precision of movement and is in near-constant use throughout daily life.
Articular Disc and Joint Compartments
The articular disc is a biconcave fibrocartilaginous structure that:
Lies between the mandibular condyle and the temporal bone.
Divides the joint into:
Upper compartment – between the disc and the temporal bone.
Primarily permits gliding (translation) movements of the condyle-disc complex over the articular eminence
Lower compartment – between the disc and the mandibular condyle.
Responsible for hinge (rotation) movements of the condyle beneath the disc.
The disc is:
Firmly attached to the neck of the mandible and to the joint capsule.
Loosely attached posteriorly to a region of vascular, innervated tissue (retrodiscal tissue), which allows limited movement of the disc.
Movements of the TMJ
The mandible can be:
Depressed (mouth opening)
Elevated (mouth closing)
Protruded (brought forwards)
Retracted (pulled backwards)
Moved side to side (lateral excursion, as in grinding)
Movement at the TMJ has two components, which occur in different compartments but function together:
Gliding (translation) – in the upper compartment
The mandibular condyle and disc move together anteriorly and posteriorly over the articular surface of the temporal bone.
This component is most important in protrusion, retraction and wide opening of the mouth.
Hinge (rotation) – in the lower compartment
The condyle of the mandible rotates against the inferior surface of the disc.
This component is prominent in the early phase of mouth opening and closing.