Bài giảng nha khoa Temporomandibular joint

Trang 2 Learning objectives: At the end of this presentation students should be able to:1- describe the skeletal components and articular surfaces of the temporomandibular joint2- descri

§TEMPOROMANDIBULAR JOINT

People’s Teacher Prof Hoàng Tử Hùng, DDS, PhDE: tuhung.hoang@gmail.com

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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The temporomandibular joint (TMJ(s)) is one of

the most complex joint(s) in the body

The mandible functionally operates as

TMJ provides for both hinging and sliding movements

 classified as a ginglymo-arthrodial joint

Five components of TMJ:

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an angle ≈ 145 - 160º

Two poles:

lateral pole and medial pole

The medial pole is more prominent than the lateral

anterosuperior aspect is working surface of the condyle

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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

TB

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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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

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”)

Body of retrodiscal tissue

*The anterior tympanic artery supplies the retrodiscal tissue www.hoangtuhung.com

2 ARTICULAR DISC (cont’d 2)

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

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

Superior retrodiscal lamina

Inferior retrodiscal lamina

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2 ARTICULAR DISC (cont’d 3)

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 ̴

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

Collateral (discal) ligaments

Articular upper and lower compartments Borders of compartments:

upper: the articular fossa and the superior surface of the disc Lower: the inferior surface of the disc and the condyle

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3 ARTICULAR CAPSULE

Wide at the temporal surface and tapering toward

the condyle neck

The joint capsule surrounds the articular surfaces and

defines the anatomical and functional boundary

Afferent nerve fibers for proprioception and nociception are branches of the auriculotemporal, masseteric, and posterior deep temporal nerves

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)

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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

muscle attach to the fused capsule and disc

3 ARTICULAR CAPSULE (cont’d 1)

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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

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

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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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Synovial membranes produce synovial fluid, a proteoglycan-hyaluronic acid complex

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

4 SYNOVIAL MEMBRANES (cont’d 1)

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

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5 LIGAMENTS

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

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

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Collateral and posterior discal ligaments (above)

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

5 LIGAMENTS (cont’d 1)

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

capsule

Inner horizontal portion

Zygomatic process (temporal bone)

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5 LIGAMENTS (cont’d 2)

Accessory ligaments

These are not true articular ligaments

- they have no direct relationship with the joint

- they may help to limit the mandibular movements

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

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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)

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

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

Opening:

Maximum opening:

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MECHANICS OF CONDYLAR MOVEMENT (cont’d, 3)

The disc is pulled as far forward as posterior ligament allowThe superior belly of LPm holds its contraction to maintain

the disc in its correct alignmentThe disc is stopped in perfect alignment with the direction of

loading through the condyle The inferior belly of LPm stays passive

As the jaw closes, the condyle starts to move back, The disc is pulled back,

The superior belly of LPm starts its contraction, the inferiorbelly of LPm releases,

The condyle is pulled backward by elevator muscles:

[temporal (posterior part) muscle]

Closing:

Closed:

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