Morphological and functional features of the human temporomandibular joint

The temporomandibular joint is a complex bilateral synovial articulation composed by the two temporal bones and the mandible. The skeletal surfaces are covered by a layer of fibrous connective tissue, are highly incongruent, and are separated by a fibrous disc, that reduces joint incongruence, increases joint stability, and allows movements of the lower jaw with six degrees of freedom. The joint develops from a phylogenetically older articulation typical of non-mammalian vertebrates, and its development is strictly related to that of the middle ear. The characteristics of this joint are unique, and its features are among those used to define the class Mammalia and separate mammals from other vertebrates. In particular, the human joint possesses several differences from that of the other mammals, and animal models cannot be easily used to investigate its dynamic and kinematic characteristics.