4. Classification of Joints
Fibrous joints: the 2 bones are connected by fibrous
Primary: Bones are connected by hyaline cartilage or
fibrocartilage, occurring between ossification centers.
This cartilage may ossify with age. Examples in humans
are the "growth plates" in long bones. These joints
allow for only a little movement, such as in the spine or
5. Secondary: Fibrocartilaginous joints, usually
occurring in the midline.
Examples in human anatomy would be the
intervertebral discs and the pubic symphysis.
Synovial joints: Consist of 2 bones covered by
hyaline cartilage united and surrounded by a
6. Why is the TMJ unique
It functions bilaterally in harmony
The articular disc is movable during joint
The articular surfaces are covered by
fibrocartilage and not hyaline cartilage
The fibrocartilage is considered as the growth
center for the mandible
7. Parts Of The Joint
8. 1- Articular Eminence
A raised area located on
the articulated surface of
the temporal bone.
9. 2- Articular Fossa
The part of the temporal
bone which mates to the
upper surface of the disk
is the glenoid (or
10. 3- Condyle
The part of the
mandible which mates
the disc. The condylar
head is about 20 mm
wide mediolaterally and
10 mm thick
11. 4- Capsule
The capsule is a fibrous membrane that
surrounds the joint and incorporates the
It attaches to the articular eminence, the articular
disc and the neck of the mandibular condyle.
12. 5- Ligaments
There are three ligaments associated with the
TMJ: one major and two minor ligaments.
The major ligament:
The Temporomandibular Ligament, is actually
the thickened lateral portion of the capsule,
and it has two parts: an outer oblique portion
and an inner horizontal portion.
The two minor ligaments:
The stylomandibular ligament separates the
infratemporal region (anterior) from the
parotid region (posterior), and runs from the
styloid process to the angle of the mandible.
The sphenomandibular ligament runs from the spine of
the sphenoid bone to the lingula of mandible.
These ligaments are important in that they define the
border movements or the farthest extents of
movements of the mandible. Movements of the
mandible made past the extents functionally allowed by
the muscular attachments will result in painful stimuli,
and thus, movements past these more limited borders
are rarely achieved in normal function.
16. 6- Synovial Fluid
The synovial fluid is a derivative of plasma and
contains low-molecular weight molecules,
including glucose, urea, uric acid and proteins.
The level of these molecules varies depending
on the degree of inflammation in the joint. Total
protein in normal synovial fluid is approximately
1.5 to 1.8 g/dl. In the inflamed state, this level
17. 7- Articular Disc
The articular disc is a fibrous extension of the
capsule in between the two bones of the joint.
The disc functions as articular surfaces against
both the temporal bone and the condyles and
divides the joint into two sections. It is
biconcave in structure and attaches to the
condyle medially and laterally.
18. 7- Articular Disc
The anterior portion of the disc splits in the
vertical dimension, coincident with the insertion
of the superior head of the lateral pterygoid. The
posterior portion also splits in the vertical
dimension, and the area between the split
continues posteriorly and is referred to as the
19. 7- Articular Disc
Unlike the disc itself, this piece of connective
tissue is vascular and innervated, and in some
cases of anterior disc displacement, the pain felt
during movement of the mandible is due to the
condyle compressing this area against the
articular surface of the temporal bone.
20. Innervation and vascularization
Sensory innervation of the temporomandibular joint is
derived from the auriculotemporal and masseteric
branches of V3 .
Its arterial blood supply is provided by branches of the
external carotid artery, predominately the superficial
temporal branch. Other branches of the external
carotid artery namely: the deep auricular artery, anterior
tympanic artery, ascending pharyngeal artery, and
maxillary artery- may also contribute to the arterial
blood supply of the joint.
In order to work properly, there is neither
innervation nor vascularization within the
central portion of the articular disc. Had there
been any nerve fibers or blood vessels, people
would bleed whenever they moved their jaws;
however, movement itself would be too painful.
22. Biomechanics of the joint during function
During jaw movements, only the mandible
23. Biomechanics of the joint during function
The two movements that occur at this joint are
anterior gliding and a hinge-like rotation.
When the mandible is depressed during opening
of the mouth, the head of the mandible and
articular disc move anteriorly on the articular
surface until the head lies inferior to the articular
24. Biomechanics of the joint during function
As this anterior gliding occurs, the head of the
mandible rotates on the inferior surface of the
This permits simple chewing or grinding
movements over a small range.
25. Jaw Movements: Muscle Action
The mandible is moved primary by the four
muscles of mastication: the masseter, medial
pterygoid, lateral pterygoid and the temporalis.
These four muscles, all innervated by V3, work
in different groups to move the mandible in
26. Jaw Movements: Muscle Action
Contraction of the lateral pterygoid acts to pull
the disc and condyle forward within the glenoid
fossa and down the articular eminence; thus,
action of this muscle serves to open the mouth.
The other three muscles close the mouth; the
masseter and the medial pterygoid by pulling up
the angle of the mandible and the temporalis by
pulling up on the coronoid process.
27. Jaw Movements: Muscle Action
Depression (Open mouth)
Elevation (Close mouth)
Protrusion (Protrude chin)
Masseter (superficial fibres)
Retrusion (Retrude chin)
Masseter (deep fibres)
Side-to-side movements (grinding and
Temporalis on same side
Pterygoid muscles of opposite side
28. Depression & Elevation
29. Depression & Elevation
30. Lateral Movement
31. Lateral Movement
32. Lateral Movement (Medial View)
33. Protrusion & Retraction
34. Protrusion & Retraction
35. Jaw Movements
The Role Of The Disc
On mouth closure, the inferior belly of the
lateral pterygoid muscle relaxes and the condyle
is pulled back to the fossa by the action of the
masseter, medial pterygoid and temporalis
muscles; however, the disc is firmly attached to
the condyle and it pivots to its anterior position
by means of the reciprocally innervated superior
belly of the lateral pterygoid muscle.
36. Jaw Movements
The Role Of The Disc
On mouth opening, contraction of the inferior
belly of the lateral pterygoid muscle pulls the
condyle downward and forward along the
posterior aspect of the articular eminence; at this
junction, the superior head of the lateral
pterygoid muscle is relaxed, and this allows the
disc to pivot posteriorly. The condyle, together
with the tightly connected disc, slides down the
slope of the eminence.