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

16 Anatomy of the Masticatory System
Glenoid Fossa and Articular Protuberance
The temporal portion of the joint can be divided into four
functional parts from posterior to anterior: postglenoidal
process, glenoid fossa, articular protuberance, and apex of
the eminence. The inclination of the protuberance to the
occlusal plane varies with age and function (Kazanjian
1940), but is 90% determined at the age of 10 years (Nickel
et al. 1988). Three fissures can be found at the transition to
the tympanic plate of the temporal bone: the squamotympanic,
petrotympanic, and petrosquamous fissures (Fig. 28).
In patients with disk displacement, these fissures are fre-
27 Inclination of the articular
protuberance to the occlusal
plane
This graph (adapted from that of
Nickel et al. 1988) indicates the inclination
of the posterior slope of
the eminence (articular protuberance)
in relation to the occlusal
plane. Accordingly, at the age of 3
years the eminence has reached
50% of its final shape (Nickel et al.
1997). Between the tenth and
twentieth year there is a difference
of only 5°. The study material originates
from the osteological collection
of Hamman-Todd and Johns
Hopkins, Cleveland Museum of
Natural History.
28 Joint region of the temporal
bone
Inferior view of the temporal
portion of a defleshed temporomandibular
joint. Near the upper
border of the picture is the articular
eminence (1) and at the far left is
the external auditory meatus (2). In
the posterior portion of the fossa
the squamotympanic fissure (3) is
found laterally, and the petrosquamous
(4) and petrotympanic (5) fissures
are found medially. Both the
superior stratum of the bilaminar
zone and the posterior portion of
the joint capsule, and sometimes
also the fascia of the parotid gland
can insert into these fissures.
29 Ossification of the fissures
and disk displacement
Inferior view of a temporal bone
with partially ossified fissures. The
lateral half of the squamotympanic
fissure is completely ossified (arrows).
The superior stratum of the
bilaminar zone can now insert only
into the periosteum in this region.
It has been shown that these fissures
are ossified in more than 95%
of patients with disk displacement,
whereas in joints without disk displacement
normal fissure formation
prevails (Bumann et al. 1991).
quently ossified (Bumann et al. 1991). Under physiological
conditions the only parts of the temporal portion of the
joint that are covered with secondary cartilage are the protuberance
and the eminence (Fig. 31). Secondary cartilage is
formed only when there is functional loading. Before the
fourth postnatal year stimulation of the cells of the perioseum
leads to the formation of secondary cartilage (Hall
1979, Thorogood 1979, Nickel et al. 1997). With no persisting
functional load the chondrocytes of the condyle would
differentiate into osteoblasts (Kantomaa and Hall 1991).