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Temporomandibular Joint

(TMJ)

Temporomandibular Joint

(TMJ)

Alex ForrestAssoci ate Profess or of For ensic Od ontol ogyForensic Science Research & Innovation Centre, Griffith University

Consultant Forensic Odontologist,Queensland Health Forensic and Scientific Services,39 Kessels Rd, Coopers Plains, Queensland, Australia 4108

Oral Biology

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You should be able to describe the structure of the TMJ and

its movements in preparation for understanding the roles of

the muscles of mastication in moving the mandible.

Learning ObjectiveLearning Objective

StructureStructure

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The Temporomandibular Joint is the site of articulation

between the mandible and the cranium.

It is a bilateral synovial joint, and serves to open and close

the jaws, and to approximate the teeth of each jaw during

mastication.

StructureStructure

It consists of parts of the

mandible and temporal

bones which are covered

by cartilage, and

surrounded by several

ligaments including a

joint capsule.

Between the two bones is

a fibrous articular disk,breaking the joint into two

separate synovial-lined

compartments.

http://www.tmj.com/b1_patient.html

Structure

Several pairs of muscles

attached to the mandible

produce movements

required to suckle, ingest

and masticate food,

swallow and yawn, andproduce speech.

They are called the

muscles of mastication

and the accessory

muscles of mastication.

http://e-ortho.tripod.com/orofacialPain.htm

The mandible possesses two articular surfaces, the

condyles, which are located on the upper end of each of

the bilateral condylar processes.

Alex Forrest 2008

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Each condyle articulates with a meniscus (articular disk)

which lies between it and the temporal bone.

http://chiropracticresearch.org/NEWS_chiropractic_and_tmj.htm

The condyles, which

are characteristically

"football-shaped, are

directed at an oblique

angle, so that if the

planes of the long

axes were continuedthey would meet at

the front of the

foramen magnum.

Modified from: Scott, JH & Dixon, AD. Anatomy for Students

of Dentistry. Edinburgh, Churchill Livingstone, 3rd Edition

1972. p. 150.

The Temporal BoneThe Temporal Bone

The site of articulation on the temporal bone is on the inferior

surface of the zygomatic process. It is called the glenoid fossa

or the mandibular fossa.

Grays Anatomy,

35th Ed, Longman,London 1973, p.

293.

Alex Forrest 2008

While on the dried skull the mandibular condyle appears to

articulate within the glenoid fossa between the bony articular

tubercle and the post-glenoid process, in real life it probably

articulates about the tubercle.

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TheAr ticu lar Disk (meniscus) is a compact, dense fibrous

connective tissue plate.

It is roughly oval in shape and lies between the mandibular

condyle and the articular eminence of the temporal bone.

http://cpmcnet.columbia.edu/dept/dental/Dental_Educational_Software/TMJ/LatTMJ2.gif

Its inferior surface is concave to fit the convex surface of

the condyle. Superiorly, its surface is concavo-convex.

The disk is thickest at its periphery and thinnest in the

stress-bearing part of the joint.

Modified from: Posselt, U, Physiology of Occlusion and Rehabilitation, Blackwell

Scientific, Oxford, 2nd Edition 1973.

The coverings of the

articular surfaces of the

condyle and articular

eminence are composed of

dense fibrous connective

tissue.The heaviest stress-

bearing areas of the disk

are also fibrocartilage, and

indeed the whole disk may

become fibrocartilaginous

in later life.

http://e-ortho.tripod.com/orofacialPain.htm

These fibrocartilaginous

structures are all

essentially avascular, butthey are bathed in

synovial fluid which

provides nourishment as

well as lubrication.

http://e-ortho.tripod.com/orofacialPain.htm

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LigamentsLigaments

Anatomy textbooks describe several ligaments around the

TMJ.

They do not always clearly differentiate between the

ligaments of the joint (which are true ligaments), and the

accessory ligaments, some of which are not true

ligaments, but are simply thickenings in sheets of fascia.

LigamentsLigaments

From Grays Anatomy, 35th Ed, Longman, London 1973, p. 408

The ligaments of the joint comprise thejo in t capsule, and the

medial and lateral ligaments.

The capsule is reinforced along its medial and lateral margins

by bundles of collagenous fibres.

From Grays Anatomy, 35th Ed, Longman, London 1973, p. 408

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The medial part is a slight thickening of the capsular ligament

and the lateral part, which is more strongly reinforced, is known

as the lateral ligament ortemporomandibular ligament.

From Grays Anatomy, 35th Ed, Longman, London 1973, p. 408

Accessory LigamentsAccessory Ligaments

The accessory ligaments are basically thickenings in sheets of

fascia. They are not ligaments in the true sense, and they

definitely are not strong enough to fulfil the "suspensory" role

sometimes assigned to them in textbooks.

Instead, they have stretch receptors which feed into reflex

control loops and thus prevent excessive opening and

protrusion of the mandible.

Accessory LigamentsAccessory Ligaments

The sphenomandibular

ligament is a derivative of

Meckel's cartilage, and

runs between the spine of

the sphenoid bone and the

lingula of the mandible.

It is clinically importantbecause if local

anaesthetic solution is

deposited anterior to it

during an inferior dental

block injection, it will

prevent the diffusion of the

solution posteriorly and

result in a failed block.From Grays Anatomy, 35th Ed, Longman, London 1973,

p. 408

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The stylomandibular

ligament is a

thickening of the deep

cervical fascia, and

extends from the

styloid process of the

temporal bone to theposterior border of the

angle of the mandible.

From Grays Anatomy, 35th Ed, Longman, London 1973, p. 408

InnervationInnervation

The joint capsule is sensitive, and is heavily endowed

with sensory endings from the mandibular division of the

trigeminal nerve, primarily through its auriculotemporal

branch.

Additional fibres to the joint are derived from the

masseteric branch of the mandibular nerve.

Blood SupplyBlood Supply

Blood supply is via the maxillary artery and by branches ofthe superficial temporal artery.

Venous drainage is via the pterygoid plexus, and lymphatic

drainage is via the buccal and submandibular lymph nodes.

Movements of the TMJMovements of the TMJ

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During its movements, the mandible swings on its elevator

muscles, and on the other tissues which suspend it from

the cranium.

The mandible may be depressed, elevated, protruded,

retruded, moved laterally, and returned to its resting

position. It may be rotated around an axis passing

roughly through both condyles.

Chewing i s a combination of all of these movements.

MovementsMovements

Jaw Opening is a combination of protrusion, depression,

and rotation about the intercondylar axis.

Jaw Closing is a combination of retrusion, elevation and

rotation.

Protrusion cannot occur without depression to

disocclude the teeth.

MovementsMovements

When the mandible is swung to one side, the contralateral

condyle is pulled forwards, downwards and medially.

The ipsilateral condyle remains in its fossa, undergoing only

slight movement, being slightly depressed, swung slightly

laterally, and rotated around a vertical axis.

This is sometimes known as "Bennett Movement".

MovementsMovements

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Ligaments & FunctionLigaments & Function

Ligaments act to limit t he range of a movement in a joint .

The limiting function of TMJ ligaments should not be regarded

as purely mechanical.

Ligaments contain receptors that are sensitive to tension

generated within the ligament.

Afferents from these nerve endings probably instigate the

appropriate reflex control on opposing muscle groups.

Ligaments and FunctionLigaments and Function

The Lateral

Ligament of T.M.J.

limits the movement

of the condyle to an

arc, the radius of

which is determined

by the ligament.It may also play a

part in limiting the

movement of the

mandible when it is

swung towards the

contralateral side.

From Grays Anatomy, 35th Ed, Longman, London 1973, p. 408

The Medial

Ligament of T.M.J.

is more vertically

aligned than thelateral ligament. It

probably limits

depression of the

mandible.

From Grays Anatomy, 35th Ed, Longman, London 1973, p. 408

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The

Sphenomandibular

Ligament limits

depression of the

mandible and

prevents dislocation

of the joint. The

Pterygoid Fascia is

continuous with the

sphenomandibularligament, and should

therefore serve a

similar function.

From Grays Anatomy, 35th Ed, Longman, London 1973, p. 408

The Stylomandibular

Ligament is suitably

aligned to limit the

movement of the

mandible towards the

ipsilateral side.

During such movement,

the angle of themandible swings away

from the midline.

From Grays Anatomy, 35th Ed, Longman, London 1973, p. 408

The meniscus may also be

regarded as a ligament.

Its strong attachment to the

anterior margin of the

articular eminence (on theone hand), and to the

posterior surface and both

poles of the condyle (on the

other hand) enable it to

restrain the amount of

retrusion of the mandible.

http://e-ortho.tripod.com/orofacialPain.htm

The mandible may be forcibly retruded up to 1.5 mm.posterior to its normal maximum intercuspal position, and

the amount of retrusion possible represents the amount of

"slack" in the meniscus and lateral ligaments.

Ligaments and FunctionLigaments and Function

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You should be able to describe the structure of the TMJ and

its movements in preparation for understanding the roles of

the muscles of mastication in moving the mandible.

Learning ObjectiveLearning Objective

The End