TMJ Disorders and Orofacial.pdf - E-Lib FK UWKS

12 Anatomy of the Masticatory System
Embryology of the Temporomandibular Joint and the Muscles of Mastication
During the development of the temporomandibular joint
the articular fossa is the first structure to become recognizable.
This occurs during weeks 7-8 (Burdi 1992). It first
appears as a concentration of mesenchymal cells over an
area of tissue that later differentiates into disk and capsule.
Between the tenth and eleventh weeks the fossa begins to
ossify. Development of the cortical layer and the bony trabeculae
is more rapid in the fossa than in the condyle. The
fossa develops first as a protrusion on the original site of the
zygomatic arch and grows in a medial-anterior direction
(Lieck 1997). At the same time the articular eminence
Joint development
18 Tenth week
A histological section in the frontal
plane showing the condylar process
(1) and Meckel's cartilage (2) at the
tenth week of embryonic development.
The condylar process is rounded
over and surrounded by a layer of
especially dense mesenchyme (arrows).
It lies lateral to Meckel's cartilage.
The fast-growing dorsocranial
portion of the accumulation of
cartilage cells creates the distinctive
shape of the condyle.
19 Eleventh week
Above: A human temporomandibular
joint in the frontal plane at the
eleventh week of development.
This represents the same area
shown in Figure 19 only 10 days further
along. The condylar process is
beginning to ossify (arrows). At this
time the swallowing reflex is also
developing and is accompanied by
the formation of secondary cartilage
in the temporomandibular
joint (Lakars 1995).
Contributed by R. Wurgaft Dreiman
Below: Sagittal section of a temporomandibular
joint at the same
stage of development. Above the
condyle (1) is a distinct concentration
of mesenchymal cells (arrows).
At its inferior region the mesenchymal
thickening is already beginning
to detach from the condyle as the
lower joint space forms. During this
time the first collagen fibers of the
disk become visible and increase
greatly in number until the twelfth
week.
Contributed by R.J. Radlanski
begins to develop. The condyle, at first cartilaginous, develops
between the tenth and eleventh weeks from an accumulation
of mesenchymal cells lateral to Meckel's cartilage
(Burdi 1992). Enchondral ossification progresses apically,
creating a bony fusion with the body of the mandible. After
the fifteenth week the chondrocytes have differentiated
enough so that the cartilage already exhibits the typical
postnatal organization of structure (Perry et al. 1985), and
from the twentieth prenatal week onward only the superficial
portion of the process consists of cartilage.