TMJ and Muscles of Mastication

Dr Rania Gabr

Objectives• Identify the parts of the mandible.• Know the type and formation of temporomandibular

joint.• Understand the attachment of the capsule and

ligaments of the temporomandibular joint.• Explain the mechanism of movements taking place at

temporomandibular joint.• Define the stability factors of the joint.• Explain the muscles of mastication with their origin,

insertion, nerve supply and actions.• Discuss maxillary artery.

Gross Anatomy

This is a synovial joint of condylar variety.COMPONENTS:• Mandibular condyles

• Articular surfaces of Temporal bone

• Capsule

• Articular disc

• Ligaments

• ARTICULAR SURFACES- A. Upper part -

a) Articular eminence, b) ant. part of mandibular

fossa.

B. Inferior surface -

head of the mandible.

ARTICULAR DISC(MENISCUS)

• Fibro cartilaginous tissues• Disc divides the compartment

into 2:• Upper formed by Temporal bone

and articular disc (Menisco temporal)

• Lower formed by mandible and articular disc (Menisco mandibular)

CAPSULE• Fibrous membrane that

surrounds the joint• Covers the joint from all

around• Thin above the disc and thick

below it• Encloses the disc• Attaches above: to the

margins of the mandibular fossa

• Attaches below: to the neck of the mandible

• The inner aspect of capsule attaches to disc– Above disc – capsule loose– Below disc - tight

LIGAMENTS

Major Ligaments Temporomandibular

ligament Lateral ligament

Minor Ligaments Stylo mandibular ligament Spheno mandibular

ligament

Movements

• Elevation• Depression• Retraction• Protraction• Side to side

• Side to side – grinding movements– Mandible is alternately protracted and retracted with the two

sides moving in opposite directions so that one side is protracted while the other is retracted

– Actions combined with elevation and depression, rhythmically and alternately.

– Opening of the jaw (depression) ,is primarily passive or gravity assisted.

Movements

MUSCLES

• Messeter

• Temporalis

• Medial pterygoid

• Lateral pterygoid

INNERVATION• TRIGEMINAL NERVE:

Mandibular div.• SENSORY– Auriculo temporal nerve:

from the posterior division of the mandibular nerve

– Messeteric nerve: from the anterior division of the mandibular nerve

• MOTOR– Mandibular division of

trigeminal nerve

TemporalisIts a fan shaped muscleCovered by temporal fasciaOrigin: Medial wall of the

temporal fossa and temporal fascia

Insertion: Anterior margin of coronoid process and anterior border of the ramus of mandible

Nerve supply: Deep temporal branch of anterior division of mandibular nerve 14

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TEMPORAL FASCIA

Attachment:

Above: Superior temporal line

Below: It splits into 2 layers and insert into respective borders of zygomatic bone

ACTION: ANT - Elevation of the mandiblePOST – Retraction of mandible

Anterior fibres – vertical

Middle fibres - Oblique

Posterior fibres - Horizontal

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Masseter

It is quadrilateral in shape. Can be palpated in living

subjects on clenching the teeth It consists of 2 layers :

Superficial and deep. Origin: Lower margin and deep aspect of

zygomatic archInsertion: Lateral surface of ramus and

coronoid process of mandible

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Nerve supply:

Masseteric nerve from

the anterior division of

mandibular nerve.

Action:Elevates the mandibleSuperficial fibres: Protracts the mandible

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Pterygoid muscles• There are medial and

lateral pterygoid muscles.

• They extend from the pterygoid plates and insert in the mandible.

Lateral pterygoid

Medial pterygoidBuccinator

Partotid duct

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Lateral pterygoid It is a short, thick muscle

consisting of two partsI) Upper headII) Lower head

Origin:Upper head: Infratemporal

surface of greater wing of sphenoid

Lower head: Lateral surface of the lateral pterygoid plate

Insertion: Pterygoid fovea (depression on the front of the neck of the mandible)

Some fibres of upper head may insert in the capsule of tempero-mandibular joint

Upper head

Lower head

Capsule of TMJ

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Lat. Pterygoid - Attachment

Infra temporal Sufrace of greater wing of sphenoid

Lateral surface of lateral pterygoid plate

Upper head

Lower head

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Action: opening of mouth (Depression of mandible) by pulling forward the head of mandible. Upper head – chewing, Lower head – protrusion.

Side to side movements: combined action of medial and lateral pterygoid

Nerve supply: Anterior division of mandibular nerve

Medial pterygoid• It consists of large deep head

and small superficial head. Origin: Deep head: Arises from the

medial surface of lat.pterygoid plate

Superficial head:Tuberosity of maxilla

Insertion:Medial surface of ramus and angle of mandible.

Nerve supply: Branch from the trunk of mandibular nerve

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Superficial head

Deep head

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Action: Elevation of mandible. Together with lateral pterygoid, it helps in side to side chewing movement.

Superficialfibres

Deep fibres

VASCULARISATION

• Branches of External Carotid Artery– Superficial temporal

artery– Deep auricular artery– Anterior tympanic artery– Ascending pharyngeal

artery– Maxillary artery

VASCULARISATION• The Blood supply to

TMJ is only Superficial, i.e there is no blood supply inside the capsule

• TMJ takes its nourishment from Synovial fluid

Clinical AnatomyTrismus:

Tonic spasm of both masseters is the characteristic symptom of tetanus which produces “lock jaw”

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Clinical Anatomy (contd...) Submasseteric space

infection: Infection around 3rd molar tooth may seep into the space between the attachment of masseter with mandible which leads to visible swelling and limitation of jaw movements

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Clinical Anatomy (contd...)Paralysis of lateral

pterygoid muscles causes the jaw to deviate towards the paralysed side on opening the mouth as a result of action of normal muscle.

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