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

The superior stratum is attached posteriorly to the bony
auditory meatus, the cartilaginous part of the auditory meatus,
and the fascia of the parotid gland (Scapino 1983). Four
insertion variations can be distinguished (Bumann et al.
1999).
The inferior stratum inserts on the posterior side of the
condyle below the fibrocartilaginous articulating surface
and is responsible for stabilizing the disk on the condyle.
Anterior disk displacement is possible only when the predominantly
collagenous inferior stratum becomes overstretched.
The superior stratum, on the other hand, is
responsible for retracting the articular disk, especially dur-
Function
Stabilization of the disk in the sagittal plane
Proprioception Cell nutrition
Progressive adaptation Fibrosis
Regressive adaptation
Inflammation Overextension with
inflammation Perforation
BilaminarZone 25
ing the initial phase of closure, but is of lesser importance in
the occurrence of anterior disk displacement (Eriksson et al.
1992). These facts are very important to consider in the
diagnosis and treatment of disk displacements. Continuous
posterior or posterosuperior loading of the bilaminar zone
eventually leads to fibrosis and sometimes to the formation
of a pseudodisk (Hall et al. 1984, Isberg et al. 1986, Kurita et
al. 1989, Westesson and Paesani 1993, Bjornland and
Refsum 1994).
54 Histology of the trilaminar
zone
The superior stratum (1), genu vasculosum
(2), and inferior stratum
(3) can be clearly distinguished
from one another. Sensory and
sympathetic nerve fibers provide
pain perception and regulation of
blood-vessel tonus. Here the neuropeptides
A and Y effect vasoconstriction
(Lundberg et al. 1990,
Grundemar and Hakanson 1993)
while vasodilation is brought about
by the vasoactive intestinal peptide,
the peptide histidineisoleucine
amide and acetylcholine
(Widdicombe1991).
55 Progressive adaptation
(fibrosis)
Chronic overloading brings about
fibrosis (arrows) and reduction of
the number of blood vessels. Such
fibrosis can be seen in 64-90% of
patients, depending on the position
of the disk. Posterior and posterosuperior
condylar displacement
without adaptation of the
bilaminar zone is a common cause
of joint pains. Therefore, previous
adaptation of the bilaminar zone
can be considered a favorable factor
for treatment.
56 Function and structural
adaptation of the bilaminar zone
In addition to supplying nutrients
and proprioception, the inferior
stratum is of special importance in
stabilizing the disk in the sagittal
plane. Increased functional loading
can lead to its fibrosing. Our own
studies indicate that in spite of mechanical
loading, fibrosis does not
occur in 10-36% of joints. Chronic
nonphysiological overloading usually
results in perforation, overextenion.
or inflammation.