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Temporomandibular Disorders. Robin J. M. Gray
Читать онлайн.Название Temporomandibular Disorders
Год выпуска 0
isbn 9781119618751
Автор произведения Robin J. M. Gray
Жанр Медицина
Издательство John Wiley & Sons Limited
In the simplest terms, the temporomandibular joint is the articulation between the upper and lower jaws. The teeth form the contacts between the upper and lower jaws, and the muscles are the motors that move the mandible. This system is unique in that the TMJs are paired; any stimulus that affects one joint or any other single part of the articulatory system can have a ‘knock‐on effect’ in the rest of the system.
It is important to have an understanding of anatomy not only to be able to differentiate between what is physiological and what is pathological but also to understand the objectives of some treatment options.
Figure 2.1 The temporomandibular joint
(M. Ziad Al‐Ani, Robin J.M. Gray.)
Histology
There are four distinct layers or zones described in the articular surface of the condyle and mandibular fossa. These layers are the articular zone, proliferative zone, cartilagenous zone, and calcified zone (Figure 2.2):
1 The articular zone is dense fibrous connective tissue and forms the outer functional surface of the condyle head. As a result of this fibrous connective tissue layer, it is suggested that it is less susceptible to the effect of ageing and breakdown over time. In addition, despite a poor blood supply, it has a better ability to repair, good adaptation to sliding movement, and the ability to act as a shock absorber when compared with hyaline cartilage.
2 The proliferative zone is mainly cellular and is the area in which undifferentiated germinative mesenchyme cells are found. This layer is responsible for the proliferation of the articular cartilage and the proliferative zone is capable of regenerative activity and differentiation throughout life.
3 The cartilagenous zone contains collagen fibres arranged in a criss‐cross pattern of bundles. This offers considerable resistance against compressive and lateral forces but becomes thinner with age.
4 The calcified zone is the deepest zone and is made up of chondrocytes, chondroblasts, and osteoblasts. This is an active site for remodelling activity as bone growth proceeds.
Figure 2.2 The four distinct zones described in the articular surface of the condyle and mandibular fossa
(M. Ziad Al‐Ani, Robin J.M. Gray.)
The joint capsule
The joint capsule (Figure 2.3) envelops the articular disc and is attached superiorly to the rim of the glenoid fossa and articular eminence and inferiorly to the neck of the condyle. Posteriorly it is attached to the bilaminar zone and anteriorly becomes continuous with the pterygoid muscle attachment. Although it is thin both anteriorly and posteriorly, it is strengthened laterally by the lateral temporomandibular ligament which is not a discrete ligament but a thickened part of the capsule.
Figure 2.3 The joint capsule
(M. Ziad Al‐Ani, Robin J.M. Gray.)
Synovial membrane
The glistening inner surface of the capsule comprises the synovial membrane. At birth, this membrane covers all internal joint surfaces but is lost from articular surfaces as function commences. The flexibility of the inner surface of the capsule is increased by finger‐like projections (villi) of the synovial membrane which disperse the synovial fluid.
The function of the synovial membrane is considered to be
regulatory because it controls electrolyte balance and nutrients
secretory via the interstitial cells
phagocytic.
Synovial fluid is a clear, pale‐yellow, viscous solution secreted by the synovial tissues and consists mainly of an ultrafiltrate of plasma enriched with a proteoglycan‐containing hyaluronic acid synthesised by synovial cells. The high viscosity of this fluid is a result of the presence of sodium hyaluronate which provides lubrication. The synovial fluid also allows removal of degradation products from the joint space, lubrication of the joint surfaces, and nutrition of the vascular parts of the joint.
Ligaments
The temporomandibular ligament
The temporomandibular ligament is a strong band of fibrous tissue originating as a thickening of the lateral aspect of the joint capsule. It starts at the root of the zygoma and passes obliquely towards the posterior margin of the neck of the condyle, blending into the joint capsule. In the rest position, this ligament is relaxed, but it is thought that, during retrusive and protrusive movements of the condyle, it limits movement in an anteroposterior direction.
The stylomandibular ligament
This is considered as an accessory ligament. It is a specialised band of cervical fibrous tissue extending from the styloid process to the medial border of the mandible at its angle (Figure 2.4). The function of this ligament is not clear but it is thought to limit anteroposterior movements of the mandible.
Figure 2.4 The position of stylomandibular ligament.
(M. Ziad Al‐Ani, Robin J.M. Gray.)
The sphenomandibular ligament
This