Overview

Temporomandibular Joint

The temporomandibular joint is often simply refered to as the TMJ. Its name dervies from two bones that articulate, namely the mandible and the temporal bone. We can locate the TMJ by simply putting a finger in front of the ear and open and close the mandible, when the mandible is depressed the condylar head and be felt moving forwards.

           Rotating skull, highlighted in red is the mandible               Rotating skill image, in red is the temporal bone

Left: Skull image highlighting the mandible.

Right: Showing the location of the temporal bone on the skull.

 

Skull images courtesy of https://commons.wikimedia.org/wiki/File:Rotation_mandible_bone.gif and https://commons.wikimedia.org/wiki/File:Rotation_temporal_bone.gif. Images are in the public domain and thus free of any copyright restrictions.
 

 

Articulations

The condylar head of the mandible articulates with the mandibular (glenoid) fossa, the articular fossa is covered by fibrocartilage which is a unique feature that also forms an articular disc which seperates the two bones that is involved in absorbing shock from chewing, talking and yawning. The articular disc creates two cavities in which non-cartilaginous surfaces are line with synovial membrane an thus creating a synovial joint, one of a few in the human body.

 

             temporomandibular joint

 

TMJ image courtesy of https://commons.wikimedia.org/wiki/File:Gray309.png. Image is in the public domain and thus free of any copyright restrictions.

 

The image above shows how the condylar head fits into the mandibular fossa fossa of the temporal bone forming the "ball and socket" joint, with the added ability to slide making the joint one of the most complex in the body.

 

Movement

The mandible is moved by the four main muscles of mastication which are the:

  • Masseter
  • Temporalis
  • Medial Pterygoid
  • Later Pterygoid

All of which are innvervated by the mandibular division, V3, of the trigeminal nerve.

Through these muscles and three ligaments (the temporomandibular ligament, stylomandibular ligament and the sphenomandibular ligament) holding the mandible in place, four types of movements can be performed by the TMJ:

  • Elevation
  • Depression
  • Protraction
  • Retraction

The powerful masseter muscles is involved in closing of the mouth when contracted and assisted by the the medial ptyergoids and the temporalis, which also retracts the mandible. Whilst the lateral pterygoid opens the mouth by moving the condylar head down into the articular eminence of the temporal bone along with the articular disc.

The following video shows a computer animation of a real mandible in action achieved by dynamic MRI imaging and 3D modelling. The various movements previously described can be seen by this computer model:

The following video is of a dissection of the TMJ with the articular disc still intact. When the mandible is protruded the articular disc can be seen sliding fowards down the articular eminence: