Download The Temporomandibular joints, muscles, and teeth, and their

Primary teeth should be in normal alignment
And occlusion shortly after age of 2, with all
the roots fully formed by the time the child is
3 years old.
After a teeth have fully erupted and have
assumed their respective positions in the
arches, the rapid development of the jaws
is sufficient to create a slight space between
some of them.
Separation of anterior teeth because
of the
process that is caused by the growth
of the
jaws and the approach of the
permanent
teeth from the lingual side.
TEMPOROMANDIBULAR
ARTICULATION
- An example of diathrosis and its
movements are a combination of
gliding movements and a loose hinge
movement.
- The osseous portions of the joints are the
anterior portions of the mandibular fossa
and articular eminence of the temporal
bone and the condyloid process of the
mandible.
-Articular disc: interposed between the
condyle and temporal bone.
* acts as a cushion; for support
* dense collagenous connective tissue
MANDIBULAR FOSSA
- Oval or oblong depression in the
temporal bone just anterior to the
auditory candl.
- Bounded anterior by the eminentia
articularis externally by the middle root of
the zygoma and the auditory process
and posteriorly by the zygopanic plate
of the petrous portion of the bone.
CONDYLOID PROCESS
- Convex on all bearing surfaces, althoug
somewhat flattened posteriorly, and its
knoblike form is wider lateromedially
than anteroposteriorly.
- The condyle is perpendicular to the
ascending ramus of the mandible.
JOINT CAPSULE
- TMJ is enclosed in a capsule that is
attached at the border of the
articulating surfaces of the mandibular
fossa and eminence of the temporal
bone and to the neck of the mandible.
- Anterolateral side of the capsule may be
thickened to form a band
→ temporomandibular ligament
-
It appears to originate on the zygomatic
arch and to pass backward to attach on
the lateral and/ or distal surface of the
neck of the mandible.
MANDIBULAR LIGAMENT
- Accessory ligament are considered part
of the masticatory apparatus, including
yellow stylomandibular and
sphenomandibular articulation, although
they may stabilize the articular system
during jaw movements.
- Sphenomandibular ligament: from the
angular spine of the sphenoid bone and
from the petrotympanic fissures and
ends broadly at the lingual of the
mandible.
Otomandibular ligaments: connect the
middle ear and temporomandibular
joint.
- Articular disc: interarticular dick consists
of fibrous tissue shaped to
accommodate the shape of the
condyle and concavity of the
mandibular fossa.
- Thicker anteriorly and posteriorly and a
central zone.
- Superior ad inferior heads of the lateral
pterygoid fovea of the mandible w/ a
part of the superior head inserting into
the disk and capsule.
-
MANDIBULAR POSITIONS
- Tooth determined position
- Centric relation: defined as maximum
intercuspation of the teeth
- Centric relation: jaw to jaw relation
determined by the condyles position of
the mandible in w/c the condyles are in
their upperment midmost position in the
mandibular fossae and related anteriorly
to the distal slope of the articular
eminence.

- Rest position: postural position of the
mandible determined largely by
neuramuscular activity and to a lesser
degree by the viscoelastic properties of
the muscles.

Mastication functions, as well as speaking and
swallowing, involve reflex contraction and
relaxation of the muscles of mastication whose
activity is initiated voluntarily.

The masticatory muscles concerned with
mandibular movements include the lateral
pterygoid, digastric, masseter, medial pterygoid,
and temporalis muscle and also the mylohyoid
and the geniohyoid muscles.



Origin:
› Inferior head: outer
surface of lateral
pterygoid plate
› Upper or superior head:
greater sphenoid wing
Insertion: anterior surface of
the neck of the condyle.
Note! There is an insertion of
some fibers to the capsule
of the joint and to the
anterior surface of the
articular disc.

Inervation: nerve V

Action:
› The Lateral Pterygoid is anatomically suited for
protraction, depression and contra lateral
abduction and may also be active during other
movements for joint stabilization.
Superior Head
1.
2.
Active during various jawclosing movements only as
chewing, clenching of teeth
and during swallowing.
Positions or stabilize the
condylar head and discs
against the articular
eminence during mandibular
closing
Inferior Head
1.
2.
Active during jaw-opening
movements and protrusion
only
Assists the translation of the
condyle downward, anteriorly,
and contra laterally during
jaw opening.



Origin: from
zygomatic arch to
ramus and body of
the mandible.
Insertion: from the
region of the second
molar on the lateral
surface of the
mandible to the
posterior lateral
surface or the ramus.
The superficial part of
the masseter muscle
is separated distinctly
only from the deeper
layer of the muscle at
the posterior upper
part of the muscle.

Partial coverings:
› Platysma Muscle
 Activated during firm
clenching in some
individuals and
sometimes active in
facial expressions
(because it has some
insertion in the orbicular
muscle)
› Risorius Muscle
 Is affected by emotions
and is active in facial
expressions.

The masseter muscle is covered
partly and to a variable degree
with the parotid gland tissue.

Action:
› Active during forceful jaw
closing and may assist in
protrusion of the mandible.

The center of lower third of the
masseter muscle is about 2 to 3
cm from the anterior border
sternocleidomastoid muscle,
which contracts during
clenching in some individuals.

Innervation: fifth nerve
(masseter nerve)

Zygomaticomandibular Muscle
› Origin: Inner surface of the
zygomatic arch
› Insertion: Coronoid process
› It may be an antagonist to
the posterior temporalis
and a synergist for the
lateral pterygoid muscle.


Origin: Medial
surface of the
lateral pterygoid
plate and from
the palatine bone
Insertion: medial
surface of the
angle of the
mandible and on
the ramus up to
the mandibular
foramen.

Action:
› Elevation and lateral positioning of the
mandible
› Active during protrusion

Innervation: a branch of the mandibular
division of the fifth nerve.




Fan shaped muscle that
passes the zygomatic
arch
Origin: temporal fossa
Insertion: anterior border
and mesial surface of
the coronoid process of
the mandible and along
the anterior border of
the ascending ramus of
the mandible.
The anterior fibers
extends along the
anterior ramus almost to
the third molar.



Innervation: temporal branches of the
mandibular division of the fifth nerve.
The muscle has 3 component parts and
appears to behave as if it consisted of 3 distinct
parts.
Action:
› Principal positioner of the mandible during
elevation.
Anterior Part
Posterior Part
1.
2.
Active in retruding the
mandible
Act as an antagonist to the
masseter in retruding jaw
1.
2.
Active in clenching
Act as a synergist with the
masseter in clenching
There is a tendon between the anterior and
posterior digastric muscle that is attached by a
hooplike strip of fascia to the hyoid bone
 The attachment of the anterior digastric muscle is
at or near the lower border of the mandible and
near the midline
 The anterior digastric muscle is covered by
platysma muscle, and beneath lie the mylohyoid
and geniohyoid muscles.
 All of these muscles are considered to be active
during various jaw opening.
 Innervation:

› Anterior digastric muscle: A mylohyoid branch of the
mandibular division of the fifth nerve
› posterior digastric muscle: The digastric branch of the
fascia nerve