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

14 Anatomy of the Masticatory System
Development of the Upper and Lower Joint Spaces
The upper and lower joint spaces arise through the formation
of multiple small splits in the dense mesenchyme from
which the condyle, disk, and fossa arose previously.
The lower joint space appears first at about the tenth week
(50-65 mm CRL), but later the upper joint space overtakes
it in its development (Burdi 1992). At first the space is
extensively compartmentalized, and it is only later that the
individual cavities merge (Bontschev 1996). The lower joint
space lies close to the embryonic condyle.
Joint development
23 Twenty-sixth week
Completely formed human temporomandibular
joint with physiolgical
lower and upper joint spaces.
Trabecula-like structures can be
identified in both joint spaces
where the disk has not yet separated
completely from the temporal
and condylar portions. At present it
has not been conclusively determined
whether or not this type of
incomplete separation could be
one cause of disk adhesions.
24 Development of the joint
spaces
Above: Three-dimensional reconstruction
from a series of histological
sections of the developing joint
space (yellow) of a right temporomandibular
joint. In the center of
the picture is the condyle (1); to the
right of it lies the coronoid process
(2). To the left behind the condyle is
Meckel's cartilage (3). The upper
joint space arises approximately 2
weeks after the lower.
Below: Three-dimensional reconstruction
of the lower joint space
(green) of the same joint. Initially
the mesenchyme in the condylar
region (1) is still uniformly structured,
but in weeks 10-12 it begins
to tear in several places mesial and
distal to the condyle. The resulting
clefts run together to form the
lower joint space. A region of concentrated
mesenchyme remains
between the two joint spaces, from
which the fibrocartilaginous articular
disk is later formed.
Contributed byR.]. Radianski
(Figs. 23-25)
The upper joint space appears after about the twelfth week
(60-70 mm CRL) and spreads posteriorly and medially over
Meckel's cartilage with its contour corresponding to that of
the future fossa. After week 13 the lower joint space is
already well formed as the upper joint space continues to
take shape. From its beginning, the upper joint space has
fewer individual islands of space and grows more rapidly
than the lower joint space. After week 14 both joint spaces
are completely formed. During weeks 16-22 the lumens of
the chambers become adapted to the contours of the sur-