Bài giảng nha khoa Temporomandibular joint

§TEMPOROMANDIBULAR JOINT

People’s Teacher
Prof. Hoàng Tử Hùng, DDS, PhD
E:
W: hoangtuhung.com


Learning objectives:
At the end of this presentation students should be able to:
1- describe the skeletal components and articular surfaces of the
temporomandibular joint
2- describe the articular disc and related structures
3- describe the joint capsule and synovial membranes
4- describe the mechanics of the assembly of condylar-disc movement

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INTRODUCTION
The temporomandibular joint (TMJ(s)) is one of
the most complex joint(s) in the body.
TMJ provides for both hinging and sliding movements
 classified as a ginglymo-arthrodial joint

Five components of TMJ:
1. Articular surfaces:
•
•

Mandibular condyle

Cranial articular surface

2. Articular disc
3. Joint capsule
4. Synovial membranes
5. Ligaments

The mandible functionally operates as
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a third-order
lever


1. ARTICULAR SURFACES
Mandibular condyle
Dimensions:
- mediolateral: 15 - 20 mm
- anteroposterior: 8 - 10 mm
Two poles:
lateral pole and medial pole
The medial pole is more prominent than the lateral
anterosuperior aspect is working surface of the condyle
A line drawn through the two poles will extend medially and
posteriorly toward the anterior border of foramen magnum
where it meets the corresponding line from the other side at
an angle ≈ 145 - 160º
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The cranial articular surface (temporal surface)

The temporal articular surface is situated on the inferior
part of the squamous portion of temporal bone,
just anterior to the tympanic bone and
posterior to the root of the zygomatic process
Consists of:
- An anterior eminence: the glenoid (articular) eminence
- A posterior depression: the mandibular, or glenoid, or
articular fossa
The articular surfaces (condyle and temporal) are covered
by nonvascularized noninnervated dense fibrous
connective tissue (not by hyaline cartilage as in the case of
other load-bearing joints).
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TB


2. ARTICULAR DISC
A biconcave oval structure interposes between
condyle and articular fossa
It is a firm but flexible structure and composed of
dense fibrous avascular connective tissue,

In the sagittal plane, it can be divided into three regions:
The posterior part ( ̴ band) is thicker than anterior part
( ̴ band) [≈ 3 vs 2 mm], the central part is thinnest
(intermediate zone) ≈ 1 mm. Vessels and nerve have
only in peripheral area

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2. ARTICULAR DISC (cont’d 1)
Retrodiscal tissue or Bilaminar zone
The posterior border of the disc is attached by retrodiscal tissue
Consists of: - The body of retrodiscal tissue, and
- Two laminae of connective tissue
Body of retrodiscal tissue
Composed of loose connective tissue rich in vascular and nerve
supply (“neurovascular tissue”)*
Shunting system:
A network of blood vessels with elastic walls allow blood to rush in
to fill the space between the disk and posterior wall of articular
capsule when the condyle moves forward
When the condyle moves back, the blood shunted out the vessels
(the system “vascular knee”)
*The anterior tympanic artery supplies thewww.hoangtuhung.com
retrodiscal tissue


2. ARTICULAR DISC (cont’d 2)
Superior retrodiscal lamina
A lamina of connective tissue which contains highly elastic
fibers covers the superior retrodiscal tissue and attaches the
disc posteriorly to the tympanic plate
Superior retrodiscal lamina helps to prevent the retrodiscal
tissue from being trapped between the disc and the
eminence as the disc slides back on mandibular closure

Inferior retrodiscal lamina

An inelastic band of collagen from the posteroinferior
border of the disc attaches to the back of condyle
(posterior ligament or inferior retrodiscal lamina).
It acts to stabilize the disc on top of condyle and prevents
the disc from rotating too far forward and from being
displaced anteriorly
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2. ARTICULAR DISC (cont’d 3)
Collateral (discal) ligaments
In the frontal plane, medial part is thicker than lateral part
The collateral (discal) ligaments extend medially and
laterally, bend downward and attach to the condyle below
corresponding condyle poles.
Discal ligaments are true ligament, composed of
collagenous connective tissue (inelastic). They permit the
disc to be rotated antero-posteriorly on the condyle and
form the condyle-disc complex or condyle-disc assembly

Articular upper and lower compartments
The disc is continuous with the articular capsule anteriorly
and distally.
The discal ligaments and articular ligament divide articular
space into two compartments: upper ̴ and lower ̴
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Borders of compartments:
upper: the articular fossa and
the superior surface of the disc

Lower: the inferior surface of
the disc and the condyle


3. ARTICULAR CAPSULE
The joint capsule surrounds the articular surfaces and
defines the anatomical and functional boundary
Wide at the temporal surface and tapering toward
the condyle neck
Articular capsule consists of three layers:
1. the capsule: an acellular with thick bands of collagen forms
the outer boundary of the joint
2. the subsynovial tissue: a connective tissue rich in vascular and nerve supply
3. the synovial membrane: (presented separately)
Afferent nerve fibers for proprioception and nociception are branches of the
auriculotemporal, masseteric, and posterior deep temporal nerves
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3. ARTICULAR CAPSULE (cont’d 1)
On the temporal surface of TMJ, joint capsule
runs along:
‒ Anteriorly: eminence crest
‒ Laterally: outside of the root of zygomatic
process, lateral edge of the eminence and
articular fossa
‒ Posteriorly: squamotympanic fissure
‒ Medially: sphenosquamosal suture
‒ Anteromedially: not discrete tructure*

*since the superior head of the lateral pterygoid
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muscle attach to the fused capsule and disc


3. ARTICULAR CAPSULE (cont’d 2)
Anteriorly, the capsule is attached to the disc and to
the superior head of lateral pterygoid muscle by
tendinous fibers
Posteriorly, some fibers of the capsule blend with the
bilamina zone,
Elastic bundles also extend from squamotympanic
fissure ( ̴ Glasser) to the posterior of the condyle neck

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4. SYNOVIAL MEMBRANES
TMJ possesses two synovial membranes for each compartment
Synovial membrane is the inner most layer of articular capsule
Composed of a thin layer specialized vascularized connective tissue lines the inner surfaces
of the joint capsule
The synovial membrane form folds over
the retrodiscal tissue when the condyle
and disc are retruded.
Small projections (synovial villi) may also
extend into the superior and inferior joint
compartments anteriorly
The two synovial spaces only intercommunicate
when the disc is pathologically perforated

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4. SYNOVIAL MEMBRANES (cont’d 1)
Synovial membranes produce synovial fluid, a proteoglycan-hyaluronic acid complex
The volume of the TMJ compartments and synovial fluid are not defined, the joint
spaces are normally collapsed but can be inflated by injecting fluid
The synovial fluid act:
1. as a medium for nutritional and metabolic interchange of the articular surfaces which
are nonvascular
2. as a lubricant between articular surfaces during function
3. the synovial tissue may possess immunologic capacity. Macrophages are also present
in articular spaces, they probably eliminate cellular debris and toxic products
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5. LIGAMENTS
Collateral and posterior discal ligaments (above)
Capsular and Temporomandibular ligaments
The TMJ capsule is a ligamentous capsule.
The capsule is reinforced laterally by the TM ligament.
TM ligament is a strong, tight fibers that consists of an
outer oblique portion and an inner horizontal portion.
Ligaments are innervated by both proprioceptors
and nociceptors
Ligaments play an important role in protecting structures. They are collagenous
connective tissue and have a particular length; they do not stretch.
If extensive forces applied to a ligament, whether suddenly or over a prolonged period of
time, the ligament can be elongated www.hoangtuhung.com

5. LIGAMENTS (cont’d 1)

capsule

The outer portion extends from the base of
process of the temporal bone downward and
oblique to the neck of the condyle

Outer oblique
portion

The inner portion extends from the outer
surface of the articular eminence posteriorly
and horizontally to the lateral pole of the
condyle and posterior part of the disc

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Inner horizontal
portion

Zygomatic process
(temporal bone)


5. LIGAMENTS (cont’d 2)
Accessory ligaments
Sphenomandibular ligament: from the sphenoid bone

extends downward to the mandibular lingula
Stylomandibular ligament: from styloid process
extends downward and forward to the angle of the
mandible. It limits excessive protrusive movements
Pterygomandibular ligament: from hamulus to the
retromolar area of mandible
These are not true articular ligaments
- they have no direct relationship with the joint
- they may help to limit the mandibular movements
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MECHANICS OF CONDYLAR MOVEMENT
Nature of condyle-disc assembly in mandibular movements
The structure of two synovial compartments facilitates
rotational and translational movements of the condyle disc
assemblies
The disc can slide forwards and backwards over the condyle
and generally moves together with the condyle.
During movements the plastic nature of the disc allow
continuous adaptation between the opposing convex
articulating surfaces
The loose retrodiscal tissue is seated posteriorly to the
disc, filled the temporal fossa and moved forwards and
backwards toghether with the disc www.hoangtuhung.com


MECHANICS OF CONDYLAR MOVEMENT (cont’d, 1)
Condyle-disc assembly in centric relation

In centric relation, the disc is positioned on top of the condyle
at the most forward position that posterior ligament allows.
“The condyles articulate in the anterior-superior position
against the posterior slopes of the articular eminences” (GPT*
2017)

*The Glossary of Prosthodontic Terms
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MECHANICS OF CONDYLAR MOVEMENT (cont’d. 2)

Opening:
As the inferior belly of lateral pterygoid muscle (LPm.)
starts to pull the condyle forward, the superior belly of
LPm releases contraction to allow the elastic fibers to
start pulling the disc more to the top of the condyle

Maximum opening:
When the condyle reaches the eminence crest, the disc
should be directly on top of the condyle
The elastic fibers have rotated the disc back
The superior belly of LPm is in realease
Posterior
ligament becomes more lax as the disc moves back
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