The jaw is the foundation of an individual’s face. The temporomandibular joint is the joint of the jaw and is often referred to as TMJ. It is a bilateral synovial articulation between the mandible and temporal bone.
- The name of the joint is derived from the two bones which form the joint: the upper temporal bone which is part of the cranium (skull), and the lower jawbone or mandible. The TMJ definition may mean that it acts as a sliding hinge, connecting the jawbone to the skull.
The Anatomy Of TMJ
The temporomandibular joint capsule and its possible association with other structures near the joint are not fully explained. A three-dimensional analysis based on sagittal, frontal, and horizontal serial sections through the human TMJ region was started. Capsular elements which directly connect the temporal bone with the mandible were seen only on the lateral side of the joint.
In the posterior, anterior, and medial regions of the joint, the upper and lower laminae of the articular disc are attached independently either to the temporal bone of the mandibular condyle. The shaping of the articular cavities and the texture of the joint capsule allows activities of the articular disc primarily in the anteromedial direction.
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On the entire medial side of the joint, the articular disc and its capsular attachments are in close relation with the fascia of the lateral pterygoid muscle whereby a small portion of the upper head of this muscle inserts directly into the anteromedial part of the articular disc. As a result, both the upper and the lower heads of the lateral pterygoid muscle are likely to influence the position of the articular disc directly during TMJ movements.
The articular disc is connected to the fascia of the masseter muscle, and part of the lateral ligament inserts into the temporalis fascia. Since these attachments are relatively weak, neither the temporalis nor the masseter muscles are considered to act directly on the articular disc; instead, through afferents from muscle spindles, they may take part in signaling the position of the TMJ components.
Function
TMJ definition is identified as a “ginglymi arthrodial” joint since it is both a ginglymus (hinging joint) and an arthrodial (sliding) joint. The mandibular fossa is a concave depression in the squamous portion of the temporal bone. These two bones are separated by an articular disc, which divides the TMJ definition into two distinct sections.
The lower section allows for the rotation of the condylar head around an instantaneous axis of rotation. When the mouth opens, two distinct motions occur at the joint. The first motion is rotation around a horizontal axis through the condylar heads.
The second motion is a translation. The condyle and meniscus move together interiorly beneath the articular eminence. In the closed mouth position, the thick posterior band of the meniscus lies immediately above the condyle.
As the condyle translates forward, the thinner intermediate zone of the meniscus becomes the articulating surface between the condyle and the articular eminence. When the mouth is fully open, the condyle may lie beneath the anterior band of the meniscus.