Temporomandibular Joint

Before we can talk about the Temporomandibular joint disorder, its symptoms and treatments we have to explain a few basic things about the temporomandibular joint or TMJ.

What is the temporomandibular joint?

The temporomandibular joint is the joint that connects the lower jaw (mandibular jaw) with the skull and you can feel it in front of the ear during mouth movements. There are 2 TMJs on each side of the face that work in unison to permit movement for one bone (mandible).


TMJ Anatomy

On the contrary of what it seems the lower jaw is the jaw that moves during activity like chewing, talking, breathing . This movement can be done thanks to the Temporomandibular Joint.

TMJ is the most used joint in our body. It is composed by the round upper end of the lower jaw called condyle; the socket called articular fossa or glenoid fossa and the articular disk. The articular disc is found in between these articular surfaces, made of cartilage that absorbs the stress as a pillow and allows the function of the joint when the mouth opens and closes. The articular disc divides the TMJ in two compartments: the lower compartment composed by the condyle and the lower surface of the disc with rotation function and the upper compartment composed by the temporal bone and the upper surface of the disk with translation function.
Other important components of the temporomandibular joint are: the ligaments that reinforce the joint during the function and the capsule that is a membrane composed by fibrous tissue that surrounds the temporomandibular joint.

During the opening of the mouth the lower jaw (mandible) does two types of movement thanks to the particular structure of the TMJ. The first movement is a pure rotation. The jaw moves in a hinge axis and the mouth opens only for 4 mm. The second movement is a translation. The condyle slides forward until it has to pass the articular eminence and the mouth opens more than 4 mm.
There are four types of movement of the mandible: protrusion, or forward excursion; retrusion, the reversal of protrusion and the two lateral excursions (left and right).

The main causes of movement for the lower jaw are the muscles. They are also the main causes for TMJ pain but we are going to talk in another article about this. There are different types of muscles:

  • the muscles that lower the mandible: suprahyoid muscles
  • the muscles that pull up the mandible: temporalis, masseter and medial pterygoid
  • the muscles for protrusion: lateral pterygoid, masseter
  • the muscles for retrusion: temporalis, digastric and suprahyoid muscles.

As you can see a muscle might help in more than one kind of movement.

Since the temporomandibular joint is such a complex anatomical structure, if one of its components doesn’t work or is inflamed causes problems in the joint and these means problems in different functions like chewing, opening and closing the mouth, staying right etc. It could cause also pain that sometimes is difficult to diagnose. For more information follow us in the future articles.

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