Download Type of joint

Temporomandibular joint
Commonly known as TMJ, is the
articulation of the mandible with the opposing surface of
the temporal bone and because of the arched shape of
mandible tow articulating units are necessary and so the
term “bilateral diarthrosis” is used.
The function of TMJ is the movement of mandible in
various planes and direction so the activities involved in
ingestion, mastication and speech can be executed.
Type of joint
TMJ is a synovial joint, this joint permits significant
movement and forms between glenoid fossa, articular
eminence (parts of temporal bone) and condyle process
(part of mandibular bone) which are united and
surrounded by a capsule that creats a joint cavity. This
cavityis lined by synovial membrane and filled by
synovial fluid and separated by articular disk into upper
and lower synovial cavity.
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Development of TMJ
At 3 months of gestation the first evidence of TMJ
begins to form by appearance of tow distinct regions of
mesenchymal condensation temporal and condylar
blastema between developing ramus of mandible and
developing squamus tympanic bone.
Ossification begins first in temporal blastema while
condylar blastema is still condensed mesenchyme, a
cleft appears immediately above it that becomes the
inferior joint cavity. The condylar blastema
differentiates into (condylar cartilage), and second cleft
appears in relation to temporal ossification that becomes
the upper joint cavity, with the appearance of this cleft,
the primitive articular disk is formed .
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The condyle
The condyle is mainly cancellous bone so its central
mass is comprised of plates, tubules and mostly
trabeculae seperated by marrow.The articulating surface
is composed of dense fibrous connective tissue or
fibrocartilage, beneath it found very thin layer of
hyaline cartilage .
Articular fossa and eminence
Articular fossa is composed of compact bone that is
continuous with that of the articular eminence.
Athin fibrous connective tissue layer covers the fossa
and eminence uniformly, except on the posterior aspect
of eminence tissue forms much thicker band this is
believed to be a product of increased stress because in
this area the condyle and articular disk slide across the
eminence. The cellular componets of the fibrous bundles
are few, consisting mainly of fibroblasts, chondrocytes
and mesenchymal cells.
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Articular disk
Articular disk is composed of fibrocartilage, as
maturation progresses the fibrocartilage is replaced
by dense fibrous connective tissue. The cells of the
disk are mostly fibroblasts. The principal fibers is collagen;
elastic fibers occur only in small amounts .
Synovial membrane and synovial fluid
Synovial membrane lines
synovial cavity consists
of intimal layer of
synoviocytes that
overlie subintimal layer
which is highly
vascular, loose, areolar
connective tissue . The
deeper connective
tissue is densely fibrous
with fibrocytes that
maintain collagen bundles.
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Synoviocytes produce synovial fluid. It is a viscous,
transparent, yellowish liquid consisting of a proteinmucopolysaccharide complex. This fluid provides
nutrition to disk and articular surfaces .
The capsule and ligaments
The capsule consists of a vascular dense collagenous
membrane that seals the joint space and provides passive
stability. The lateral aspect of capsule is thickened to form
the temporomandibular ligament, this ligament with
stylomandibular ligament and sphenomandibular ligament
are associated with synovial joint to strengthen the
articulation and check excess movement .
blood and nerve supply
The vascular supply of TMJ is via the superficial
temporal and maxillary branches of the external carotid
artery. Venous drainage by retromandibular vein. Nerve
supply is contributed by branches of auriclotemporal
and masseteric nerves of the mandibular division of the
trigeminal nerve. Vasomotor and sensory endings are
present in the connective tissue of synovial membrane .
Movement of the mandible
Three movements characterize TMJ articulation: hinge
and slide (opening and closing) ; retrusive and
protrusive (liding back and forth); and lateral (sideward)
movements. These mivement are result of the action of
the jaw and cervical muscles .
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This figure shows the muscles that associated in
movement of mandible :
The defects of TMJ
1.Myofascial pain dysfunction (MPD) syndrome, this is
related masticatory muscle spasm.
2.Osteoarthritis, this is related to trauma or excessive
stress on articular system .
3.TMJ may also affected by congenital and
developmental anomalies, traumatic injuries and various
forms of benign and malignant neoplasia.
TMJ disorders and MPD syndrome, both can cause
difficulty in opening the mouth and in eating; and both
can lead to clicking or popping sounds in the joint .
Oral histology the temporomandibular joint .
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