T.M.J. muscles of mastication

1. The Temporomandibular
joint
T.M.J
Dr. Haydar Muneer Salih

2. The temporomandibular joint (TMJ)
is a modified hinge type of synovial
joints, permitting gliding (translation)
and a small degree of (rotation) in
addition to flexion (elevation) and
extension (depression) movements
typical for hinge joints.

4. ◦ It is composed of the temporal bone
and the mandible, as well as a
specialized dense fibrous structure,
the articular disk, several ligaments,
and numerous associated muscles.

6. Articulation occurs between the
articular tubercle and the anterior
portion of the mandibular fossa of the
temporal bone above and the head
(condyloid process) of the mandible
below. The articular surfaces are
covered with fibrocartilage.

8. Bony Structures
The articular portion of the temporal bone
is composed of the articular or mandibular
fossa, a concave structure extending from
the posterior slope of the articular
eminence to the postglenoid process,
which is a ridge between the fossa and
the external acoustic meatus. The surface
of the articular fossa is thin and may be
translucent on a dry skull. This is not a
major stress-bearing area.

11. The articular eminence
◦It is a transverse bony prominence that
is continuous across the articular surface
mediolaterally. The articular eminence is
usually thick and serves as a major
functional component of the TMJ. The
articular eminence is distinguished from
the articular tubercle, a nonarticulating
process on the lateral aspect of the
zygomatic root of the temporal bone,
which serves as a point of attachment of
collateral ligaments.

13. Cartilage and Synovium
◦Lining the inner aspect of all
synovial joints, including the TMJ,
are two types of tissue: articular
cartilage and synovium. The space
bound by these two structures is
termed the synovial cavity, which is
filled with synovial fluid.

14. The articular surfaces of both the
temporal bone and the condyle are
covered with dense articular
fibrocartilage, a fibrous connective
tissue. This fibrocartilage covering has
the capacity to regenerate and to
remodel under functional stresses.

17. The synovial membrane
◦Is a thin, smooth, richly innervated
vascular tissue without an epithelium
Synovial cells, somewhat
undifferentiated in appearance, serve
both a phagocytic and a secretory
function and are thought to be the site
of production of hyaluronic acid, a
glycosaminoglycan found in synovial
fluid.

18. Synovial fluid
Is considered an ultrafiltrate of plasma.
It contains a high concentration of
hyaluronic acid, which is thought to be
responsible for the fluid’s high viscosity
The proteins found in synovial fluid are
identical to plasma proteins Functions
of the synovial fluid include lubrication
of the joint, phagocytosis of particulate
debris, and nourishment of the articular
cartilage

19. Ligaments
◦The lateral temporomandibular
ligament strengthens the lateral aspect
of the capsule, and its fibers run
downward and backward from the
tubercle on the root of the zygoma to
the lateral surface of the neck of the
mandible. This ligament limits the
movement of the mandible in a
posterior direction and thus protects
the external auditory meatus

21. ◦The sphenomandibular ligament lies
on the medial side of the joint . It is a thin
band that is attached above to the spine of
the sphenoid bone and below to the
lingula of the mandibular foramen.
◦The stylomandibular ligament lies
behind and medial to the joint and some
distance from it. It is merely a band of
thickened deep cervical fascia that
extends from the apex of the styloid
process to the angle of the mandible.

23. Capsule
The capsule surrounds the joint and is
attached above to the articular tubercle
and the margins of the mandibular
fossa and below to the neck of the
mandible.

25. The articular disc
It is composed of oval plate of dense
fibrous connective tissue and is
nonvascularized and noninnervated, an
adaptation that allows it to resist pressure.
It is divides the joint into upper and lower
cavities. It is attached circumferentially to
the capsule.. The upper surface of the
disc is concavoconvex to fit the shape of
the articular tubercle and the mandibular
fossa; the lower surface is concave to fit
the head of the mandible

27. Blood supply
Superficial temporal, deep auricular
and anterior tympanic arteries.
Venous drainage
Superficial temporal and maxillary
veins.
Nerve Supply
Auriculotemporal, posterior deep
temporal and masseteric branches of
the mandibular nerve.

29. MUSCLES OF MASTICATION
TMJ movements are produced chiefly by
the muscles of mastication. These four
muscles (temporal, masseter, and
medial and lateral pterygoid muscles)
develop from the mesoderm of the
embryonic first pharyngeal arch;
consequently, they are all innervated by
the nerve of that arch, the (motor root of
the trigeminal ) mandibular nerve (CN
V3). All muscles of mastication originate
on the skull and insert on the mandible

30. The temporalis muscle
is a large fan-shaped muscle taking its
origin from the temporal fossa and lateral
aspect of the skull, Its fibers pass between
the zygomatic arch and the skull and insert
on the mandible at the coronoid process
and anterior border of the ascending ramus
down to the occlusal surface of the
mandible, posterior to the third molar tooth.

33. The temporalis muscle
◦The function of the temporalis muscle
is to elevate the mandible for closure. It
is not a power muscle. In addition
contraction of the middle and posterior
portions of the temporalis muscle can
contribute to retrusive movement of the
mandible. to a small degree unilateral
contraction of the temporalis assists in
deviation of the mandible to the
ipsilateral side

35. The masseter muscle
a short rectangular muscle taking its origin
from the zygomatic arch and inserting on
the lateral surface of the mandible, it is the
most powerful elevator of the mandible and
functions to create pressure on the teeth,
particularly the molars, in chewing motions.
The masseter muscle is composed of two
portions, superficial and deep, which are
incompletely divided, both the superficial
and deep portions of the masseter muscle
are powerful elevators of the mandible

37. The masseter muscle
but they function independently and
reciprocally in other movements. The
deep layer of the masseter is always
inactive during protrusive movements
and always active during forced
retrusion, whereas the superficial
portion is active during protrusion and
inactive during retrusion.

39. The medial pterygoid muscle
is rectangular in shape and takes its
origin from the pterygoid fossa and the
medial surface of the lateral plate of the
pterygoid process, with some fibers
arising from the tuberosity of the
maxilla and the palatine bone. Its fibers
pass inferiorly and insert on the medial
surface of the mandible, inferiorly and
posteriorly to the lingual

42. The medial pterygoid muscle
The main function of the medial
pterygoid is elevation of the mandible,
but it also functions somewhat in
unilateral protrusion in a synergism
with the lateral pterygoid to promote
rotation to the opposite side

44. The lateral pterygoid muscle
◦It has two portions that can be considered
two functionally distinct muscles.
◦The larger inferior head originates from
the lateral surface of the lateral pterygoid
plate. Its fibers pass superiorly and
outward to fuse with the fibers of the
superior head at the neck of the
mandibular condyle, inserting into the
pterygoid fovea.

45. The lateral pterygoid muscle
◦The superior head originates from the
infratemporal surface of the greater
sphenoid wing, and its fibers pass
inferiorly, posteriorly, and outward to
insert in the superior aspect of the
pterygoid fovea, the articular capsule,
and the articular disk at its medial
aspect, as well as to the medial pole of
the condyle

48. The lateral pterygoid muscle
◦The primary function of the inferior
head is protrusive and contralateral
movement. The function of the superior
head of the lateral pterygoid muscle is
predominantly involved with closing
movements of the jaw and with
retrusion and ipsilateral movement

50. TMJ Dislocation

53. TMJ Ankylosis

54. TMJ Ankylosis