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

(p. 148) are unsuitable for determining a therapeutic condylar
position (Pullinger and Hollender 1985). Therefore the
current definitions of centric relation are geared more
toward the functional conditions (van Blarcom 1994, Dawson
1995, Lotzmann 1999). It has been demonstrated experimentally
that the surfaces of the temporomandibular joint
are subjected to loads of 5-20 N (Hylanderl979, Brehnan et
al. 1981, Christensen et al. 1986). In a patient's habitual
occlusion this force is partially intercepted by the occluding
premolars and molars. Tooth loss can lead to higher joint
loading and regressive adaptation (van den Hemel 1983,
Christensen et al. 1986, Seligman and Pullinger 1991). How-
Positional Relationships of the Bony Structures 21
ever, if the joint's capacity for adaptation is sufficiently
great, degenerative changes may be avoided (Helkimo 1976,
Kirveskari and Alanen 1985, Roberts et al. 1987). The direction
of functional loading is anterosuperior against the
articular protuberance (Dauber 1987). Clear evidence for
this is the presence of the load-induced secondary cartilage
on the joint surfaces in this region.
Positioning of the condyles on the protuberances is accomplished
exclusively through the antagonistic activity of the
neuromuscular system and from a functional standpoint
requires no border position.
42 Relationships in the frontal
plane
Schematic depiction of the joint
space relationships in the frontal
plane. A number of studies have reported
that the dimensions found
in the lateral, central, and medial
parts may vary greatly (Christiansen
et al. 1987, Vargas 1997).
Although the lateral portion is affected
more frequently by degenerative
changes, the width of the joint
space is usually least at its center
(blue line).
43 Contours on the temporal
surface of the joint
Schematic drawing (modified from
Hassoetal. 1989) of the contours in
the lateral (green), central (blue),
and medial (red) regions of the
joint. The entire protrusive functional
path is represented as a convex
bulge that can vary markedly as
the result of regressive or progressive
adaptation. Therefore, the
loads borne by the lateral and
medial portions of the joint during
function are also influenced by the
morphology of the articular protuberance
(Oberg et al. 1971, Hylander
1979, Hinton 1981).
44 Relationships in the medial
part of the joint
Schematic drawing (modified from
Christiansen et al. 1987) of the positional
relationships in the medial
portion of a left temporomandibular
joint. This finding also emphasizes
the fundamental principles of
physiological joint movements. As
with all other joints, the temporomandibular
joint has a passive
"play" space in all directions and is
thus not confined to any border position.
Average values: 1 = 3.4 mm; 2 =
4.4 mm