Temporomandibular joint
The temporomandibular joint (Latin: articulatio temporomandibularis ) is the flexible connection between the lower jaw and the rest of the skull . In vertebrates , more precisely from the jaws (Gnathostomata) and with the exception of mammals , the jaw joint establishes the connection between the articular and quadratic bones ( primary jaw joint ). In mammals, however, these bones are transformed into ossicles and form the joint between the hammer and anvil . The temporomandibular joint in mammals is therefore a secondary temporomandibular joint and is formed by the articular cartilage of the lower jaw and the scaly part of the temporal bone .
Temporomandibular joint of mammals
The joint-forming bone parts of the temporomandibular joint in mammals are the mandibular fossa of the temporal bone and the head of the lower jaw (caput mandibulae) . The lower jaw fossa is bounded in front by the articular tuberosity and behind by the retroarticular process . The joint head sits on the roller protrusion ( processus condylaris) of the lower jaw branch (Ramus mandibulae) .
The joint cavity of the temporomandibular joint is divided by a movable cartilage disc , the disc , into an upper joint space (towards the actual joint socket at the base of the skull) and a lower joint space (towards the joint head of the lower jaw). In the upper half there is mainly a sliding movement, whereas in the lower half there is a rotary movement.
Functional aspects in humans
Ideally, both jaw heads should sit centrally in the joint pit in the final bite, with the cartilage discs between the jaw head and joint pits. The joints should be symmetrical to each other, the masticatory muscles on both sides should have the same tension and length, and the rows of teeth in the posterior region should have even multipoint contacts on the right and left. With every act of swallowing, all these parameters are unconsciously checked by the brain. If asymmetries occur (e.g. after placing a filling that is too high), an involuntary compensation mechanism is set in motion. Either the early contact is wiped away by increased rubbing of the teeth - which can often be seen in bare areas on freshly placed fillings - or the patient shifts the lower jaw until he again feels multiple contacts on both sides of the teeth. However, the symmetry and the even tension of the muscles on both sides are lost, which can lead to a vicious circle (→ bruxism and craniomandibular dysfunction ).
The dental specialty of Gnathology deals with the analysis of misalignments of the temporomandibular joint and the restoration of the ideal position . The axiography is used to determine the individual hinge axis .
Temporomandibular joint of birds
The jaw joint of birds consists of up to three joints, the articulationes mandibulares :
- The articulatio mandibulosphenoidalis is the connection between the processus mandibularis medialis of the lower jaw and the os parasphenoidale .
- The articulatio quadratomandibularis is functionally the most important joint and connects the os articular of the lower jaw with the os quadratum . In ducks , a meniscus is embedded in the joint .
- The ectethmomandibular articulation is only formed in honey-eaters and represents the connection between the upper edge of the lower jaw and the ectethmoid bone .
literature
- Franz-Viktor Salomon (Ed.): Textbook of poultry anatomy . Fischer Jena / Stuttgart, 1993. ISBN 3-334-60403-9
- Franz-Viktor Salomon: musculoskeletal system . In: Salomon et al. (Ed.): Anatomy for veterinary medicine . Enke Stuttgart, 2004, pp. 22-234. ISBN 3-8304-1007-7
Individual evidence
- ↑ Federative Committee on Anatomical Terminology (FCAT) (1998). Terminologia Anatomica . Stuttgart: Thieme