TEMPOROMANDIBULAR JOINT &

MUSCLES OF MASTICATION

CONTENTS

• Introduction

• Temporomandibular Joint

– Evolution

– Embroyology

– Anatomy

– Histology

• Muscles Of Mastication

• Biomechanics

• Temperomandibular Disorders

• Conclusion

• References

JOINT

• Joint is a junction between two or more bones & is

responsible for movement, growth or transmission of

forces.

• Classification

Based on function

Synarthosis Diarthosis

Synarthrosis

Fibrous

Suture

Syndesmosis

Gomphosis

Cartilagenous

Primary

Secondary

Diarthosis - Synovial joint

• Permits significant movement

• Features:

- 2 bones (articular surface covered by hyaline cartilage)

- capsule

- synovial fluid

• Classified based on shape of articular surfaces

TEMPOROMANDIBULAR JOINT

So called a temporomandibular joint as the involving bones are

the mandible & the os temporale.

Synonyms:

Compound system

Synovial joint

Ginglymoarthrodialjoint,

Diarthoidaljoint

Evolution

• Amphibian skull: Confinement of teeth to dentary bone.

• Articulation : between the terminal portion of the meckel’s

cartilage (articulare) & palatoquadrate bar.

• Reptile skull: Joint in the same palatoquadrate & articulare but

dentary joint is increased in size.

• Mammal like reptile fossil:

– Dentary is increased greatly & possess a coronoid process.

– Jaw articulation is still the same.

• Mammals: Dentary articulates with the temporal bone.

Embryology of TMJ

• Ontogenetically & Phylogenitically tmj is a secondary joint.

• Temperomandibular joint

• 7th week - Articulation between malleus and incus at the

dorsal end of Meckel’s cartilage - PRIMARY

JOINT .

• 8th week- Membranous Bone laid down in a plate like form

lateral to Meckels cartilage.

• 10 weeks- evidence of future joint as mesenchyme between the

condylar cartilage & developing temporal bone.

• 12 weeks:

2 mesenchymal condensations

Condylar grows dorsolaterally

Ossification of temporal blastema

Inferior joint cavity

Differentiation of condylar into cartilage & Sup.joint cavity

Formation of disc

• 13th week : Condyle and articular disk have moved up into

contact with temporal bone.

• Remnant of meckels cartilage - sphenomandibular ligament

• Full differentiation of all articular surfaces occurs by 4th fetal

month.

Differences

Neonatal tmj Adult tmj

Mandibular fossa Flat Concave

Articular

eminence

Absent Present

GENES REQUIRED FOR THE

FORMATION OF TMJ

• Key gene noted to be expressed in condylar cartilage is

INDIAN HEDGEHOG (IHH)

Secreted by prehypertrophic chondrocytes that are just

entering the differentiation pathway.

• FGF and FGF receptor (Fgfr) gene families - all stages of bone

development.

• Fgfr1 – periosteum of the condyle and fossa

• Fgfr2 – perichondrium of the condyle and fossa

• Fgfr3 - immature chondrocytes of the condyle .

Pecularities of tmj

A. Bilateral diarthosis

B. Articular surface covered by fibrocartilage

C. Last joint among diarthoidals to begin development

D. Development from 2 blastemas

Synovial joint( 7th week) TMJ

Articular surface of tmj

• Upper – articulae eminence of mandibular fossa of temporal

bone

• Lower – condylar process of mandible

mandibular fossa of temporal bone

condylar process of mandible

Components of TMJ

• Bony components:

1. Mandibular condyle

2. Glenoid fossa

3. Articular eminence

1. CONDYLE:

• Transversely elliptical in shape

• Head is covered with fibro-cartilage-articulates with anterior

part of mandibular fossa of temporal bone

PosteriorAnterior

Soft tissue componets

ARTICULAR DISC:

• Dense fibrous connective tissue

• Avascular except at the extreme periphery of the disc.

• Saggital plane:

• Anterior view:

– Thick medially corresponding to increased space between

condyle & articular fossa

Attachment of articular disc

• Between Attachments to capsular ligament is tendinous fibres

of superior lateral pterygoid

• Disc attaches to capsular ligament not only anteriorly &

posteriorly but also medially & laterally.

• Movements of tmj:

– Superior cavity: Gliding movement.

– Inferior cavity: Rotatory +Gliding movement

• Functions of articular disc

i. Separation

ii. Protection

iii. stabilization

During functional movements of

condyle

Synovial membrane

• Internal surfaces of cavity are surrounded

by specialized endothelial cells forming

synovial lining.

• The lining located at the anterior border

of retrodiscal tissue produces synovial

fluid.

Synovial fluid

• Ultra filtrate of blood plasma

• Clear or pale yellow, viscous, slightly alkaline fluid.

• Dialysate of blood that also contains mucin( hyaluronic acid)

lymphocytes, monocytes, and macrophages.

• Functions

a. Nutrition of articular cartilage

b. Lubrication of the joint cavity

c. Prevents wear & tear.

character Normal plasma Synovial fluid

Chief content water Hyaluronic acid

protein High protein content Low protein content

amount 55% of total blood

volume

2ml

Mechanism of lubrication

• Primary mechanism of lubrication

• Prevents friction in moving joint

Boundary lubrication

• Facilitates Metabolic exchange

• Eliminates small amount of friction in Compressed but not moving joint

Weeping lubrication

Ligaments

• Collagenous & act predominantly as restraints to motion of the

condyle and the disc.

Functional ligaments

Accessory ligaments

FUNCTIONAL LIGAMENTS

Temperomandibular Collateral/Discal Capsular

Temperomandibular ligament

• Broad ligament formed due to thickening of lateral part of

capsular ligament

1. Outer oblique portion:

Resists excessive dropping of condyle during mouth

opening

Oop resists the impingement submandibular &

retromandibular structures..

2. Inner horizontal portion:

Prevents further posterior movement of condyle into the

gleniod fossa

Eg: During extreme trauma to mandible, neck of condyle

fractures before the retrodiscal tissues are injured.

Collateral ligament

• Syn: Discal ligaments

• Possess vascular supply & are innervated.

Function:

• Gliding & hinging movements

Capsular ligament

• Surrounds the joint.

• Attachments:

• Functions:

1. Resists forces that tend to dislocate the articular surfaces.

2. Retains synovial fluid.

3. Provides proprioception

ACCESSORY LIGAMENTS

Sphenomandibularligament

Stylomandibularligament

Sphenomandibular ligament

• Derived from fibrous envelope of Meckel’s cartilage of first

branchial arch

• No significant movement

Stylomandibular ligament

• Formed by thickening of deep fascia

• Separates parotid gland from submandibular gland

HISTOLOGY OF TMJ

• 4 distinct zones in the articular surfaces of condyle &

mandibular fossa

i. Articular zone

ii. Proliferative zone

iii. Fibro Cartilagenous zone

iv. Calcified zone

RELATIONS OF TMJ

Blood Supply Of TMJ:

• Posteriorly - Superficial temporal A.

• Inferiorly - internal MaxillaryA.

• Anteriorly - middle meningeal A.

Others

• Deep auricular artery

• Anterior tympanic artery

Nerve supply:

• Branches of mandibular nerve

• Auriculotemporal nerve

• Deep temporal nerve

• Massetric nerve

Lymphatic drainage:

1. Anterior surface of TMJ -parotid lymph nodes.

2. Posterior & medial surface of TMJ - submandibular

lymph node

3. Lateral surface of TMJ - pre auricular and parotid lymph

nodes

Muscles of mastication

• Four muscles are present

• They are

A. Masseter

B. Temporalis

C. Medial pterygoid

D. Lateral pterygoid

MASSETER

• Nerve supply:

Palpation:

• Applied anatomy

a) The motor part of mandibular nerve is tested by asking the

patient to clench his teeth and then feeling for the contracting

masseter and temporalis muscles.

b) If one masseter is paralysed the jaw deviates to paralyzed side

on opening the mouth by action of normal lateral pterygoid of

opposite side.

TEMPORALIS

Action :-

i. Elevates mandible

ii. Lateral movements.

iii. Retraction: posterior fibres

Applied anatomy :

• Temporal tendonitis:

- sharp headaches at temple joint.

MEDIAL PTERYGOID

• Nerve supply- medial pteygoid nerve.

• Blood supply: Maxillary artery.

• Action:

i. Elevation

ii. protrusion

iii. side to side movements

• Palpation:

• Applied anatomy

Bleeding created by needle puncture in medial pterygoid

muscle produces a hematoma followed by fibrosis and

subsequent trismus.

LATERAL PTERYGOID

• Nerve supply - branch of ant div of madibular nerve

• Blood supply: Maxillary artery.

• Action- Depression, protrusion & side to side movements

• When medial and lateral pterygoids of two sides act together

they protrude the mandible so that lower incisors project in

front of upper.

• Upper head - Chewing

• lower head - Protrusion.

• Palpation –Palpate by pressing in a superior, medial, &

posterior direction.

• Sphenomandibularis-5th muscle

• Discovered by Dunn et al in the mid

1990s at University of Maryland,

Baltimore.

• Considered to be a part of temporalis.

• Origin- Infratemporal surface of greater

wing of sphenoid bone.

Insertion-Temporal crest of mandible.

• Blood supply- From maxillary artery, from vessels of medial

pterygoid.

• Nerve supply- Not yet determined

• Function: Considered as an elevator muscle of mandible

Temporalis

Temporalis,

Geniohyoid,

Digastric

Lateral

pterygoid

Lateral pterygoid

Suprahyoid

Masseter

Medial &

Lateral pterygoid

Movements of

mandible

EXAMINATION OF TMJ

• Interincisally : 53- 58 mm

• Restricted mouth opening:

– Mouth opening : < 40 mm

– Lateral & protrusive movement:< 8mm

PALPATION OF TMJ

• Pain & tenderness of TMJ is determined by digital palpation

when mandible is in both stationary & dynamic movements.

• Lateral palpation

• Posterior palpation

AUSCULTATION :

Click : single sound with short duration. If loud = popping

Crepitus: multiple gravel like sounds.

GERBER RESILIENCE TEST:

Enables to measure the resilience & thickness of the discus

articularis.

useful to plan possible corrections that is necessary through

dental occlusion.

Normal range :0.6 to 0.9mm & even up to 1.2mm

Musculoskeletal stability

Interarticularpressure

Ligaments

Stabilization of joint:

I. Musculoskeletal stability:

Orthopedically Stable joint is when the condyles are in their antero

superior position in the glenoid fossa, resulting against posterior

slopes of articular eminence with discs properly interposed.

II. Ligaments:

Stabilise the joint by limiting the movement

Ligaments elongate but are not streched

Compromising the normal jaw function

III. Interarticular pressure:

• Pressure between the articular surfaces of articular eminence

& the condyle

• Absence of inter articular pressure results in separation of

joints and dislocation

Functional appliance

Increased contractile

activity of the LPM

Intensification of repetitive activity of the retrodiscal pad

Increase in growth stimulating factors

Change in trabecularorientation

Additional growth of condylarcartilage

Additional subperiostealossification of

posterior border of mandible

Supplementary lengthening of

mandible

OPERATION OF FUNCTONAL APPLIANCES

TemporomandibularJoint Disorders

A. Derangement of condyle -disc complex

i) Disc displacements

ii) Disc dislocation with reduction

iii) Disc dislocation without reduction

B. Structural incompatibility of the articular surfaces

1. Deviation in form

a. Disc

b. Condyle

c. Fossa

2. Adhesions

a. Disc to condyle

b. Disc to fossa

3. Subluxation

4. Spontaneous dislocation

C. Inflammatory disorders

1. Synovitis/ capsulitis

2. Arthritidis

3. Osteoarthritis

4. Polyarthritidis

D. Inflammatory disorders of associated structures

a)Temporal tendonitis

b)Stylomandibular ligament inflammation

Disc displacement:

Causes:

• Break down of normal rotation of condyle due to elongation of

discal ligaments& inferior retrodiscal lamina resulted from

trauma.

• Thinning of posterior border of disc predisposes to

derangement

• Displaced condyle

positioned anteriorly by

lateral pterygoid.

• Constant application results in

thinning of posterior disc &

allows the disc to be displaced

more anteriorly.

Clinical examination

normal range of movements

Joint sounds are seen

• Disc dislocation with reduction :

Disc dislocation:

Further elongation of inf.retrodiscal lamina , discal ligament &

sufficient thinning of posterior border.

Results in slippage of joint. Disc & condyle no longer articulate

disc dislocation.

If the patient can manipulate to reposition the condyle onto

posterior border of disc , disc is termed reduced in nature

Management:

• Reduce the intracapsular pain

• Definitive treatment of disc displacement is to reestablish a

normal condyle disc relationship.

• Anterior positioning appliance by Format .

– This appliance is worn 24 hrs a day for3 to 6 months.

– Appliance repositions the condyle back into the disc

Disc displacement with out reduction:

• Further elongation leads to loss in elasticity of superior

retrodiscal lamina & recapturing is difficult.

• Anterior positioning appliance - contraindicated because it will

aggrevate the condition by forcing the disc even more forward.

• Supportive therapy/ surgical therapy is indicated.

Deviation in form:

• Supportive therapy - Patient education

• In case of muscle hyperactivity : stabilization appliance is

used.

Adhesions:

When adhesions are present breaking the fibrous attachment is

only definitive treatment

It is done by using arthroscopic surgery

Subluxation:

• Only definitive treatment by surgical alteration of joint i.e, by

eminectomy.

• Supportive therapy .

Spontaneous dislocation:

• surgical therapy is indicated

Conclusion

Temporomandibular joint & Masticatory muscles form the

vital part of orofacial system both structurally and

functionally.

It is crucial for an orthodontist to recognize the

musculoskeletal stability of the joint and be aware of problems

related to deviation from this point.

References:

• Management of Temporomandibular Disorders & Occlusion –

Jeffrey Okeson III

• Principles of Oral and Maxillofacial Surgery- Peterson's Vol 1

• Dentofacial Orthopedics with Functional Appliances – Graber,

Rakosi, Petrovic, II ed

• Text book of oral histology- Ten cate

• Human anatomy – B.D Chaurasias 5th Ed

• Grey’s anatomy – 38th edition

• Craniofacial development: Sperber

• Graber, Vanarsdal, Vig