dsb mastication

8/8/2019 Dsb Mastication

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TMJ & muscles of mastication

• LECTURE OUTLINE

• embryological origin

• temporomandibular joint

• muscles of mastication

• innervation

– referred pain

1st branchial arch derivatives

• mandible• muscles of mastication (& others)

• innervated by CN V3

• new principle

– NP7: The nerve that supplies the muscles

acting at a joint also supplies tissues of

that joint and the skin over the muscles

and/or the joint. (Hilton’s law)

Temporomandibular joint

mandibular

fossa

mandibular

condyle

mandibular

eminence

Marieb

TMJ structure

• histological classification - synovial – articular surfaces

• mandibular fossa & eminence (tubercle)

• mandibular condyle (head)

• lined with fibrocartilage – possible adaptation and remodelling

– articular disc

• fibrocartilagenous with variable thickness• biconcave (condyle & eminence are convex)

• attaches to condyle, capsule, retrodiscal tissueand lateral pterygoid muscle

• creates superior and inferior joint cavities

TMJ sagittal section

Hiatt: 13-1A

Movement

of articular

disk

Hiatt: 13-1B & C



TMJ structure 2• histological classification - synovial

– capsule• loose attachments above disk (to temporal

bone)

• tight attachments below disk (to mandible)

– ligaments• temporomandibular

– lateral

• sphenomandibular – medial

• stylomandibular – posterior

• all prevent separation of articular surfaces – inferior movement of mandible

TMJ function

• two joints must function together

• classification by shape• hinge (inferior cavity)

• gliding (superior cavity)

• ‘hinge with movable sockets’

– movements possible• elevation & depression

• protraction (protrusion) & retraction (retrusion)

• side-to-side (lateral deviation)

• wide opening of mouth requires protrusion inupper cavity and depression in lower cavity

– may lead to dislocation anteriorly

Depression

of the

mandible

Manual: I-3

(A) Protraction

(superior joint

cavity)

plus

Typical dislocation

(B) Depression

(inferior joint

cavity)

arc of opening

Lateral deviation of the mandible

Manual: I-4

Muscles of mastication• primary muscles

– attachments

• insertion on mandible

• origin on other bones of skull

– temporalis

– masseter

– medial and lateral pterygoids

• accessory muscles

– attachments

• one attachment on mandible

– digastric, mylohyoid, geniohyoid

Primary muscles of mastication• temporalis

– origin• temporal fossa (radiating fibres)

– insertion• coronoid process of mandible

• masseter – origin

• zygomatic arch

– insertion• angle and ramus of mandible



Temporalis & masseter

M17: Increasing the distance between the axis for

movement and the point of application of a force

producing the movement (i.e., increasing the lever

arm) increases the mechanical advantage. Hiatt: 12-4

Pterygoid muscles

Hiatt: 12-5

Primary muscles of mastication

• medial pterygoid

– origin

• medial surface of lateral pterygoid plate ++

– insertion

• medail surface of angle of mandible

• lateral pterygoid

– origin

• lateral pterygoid plate ++

– insertion

• condyle of mandible and capsule/articular disk

Actions of primary musclesopening closing protrusion retrusion lateral

deviation

temporalis

masseter

medialpterygoid

lateral

pterygoid

TMJ – transverse section

head of

mandible

coronoid

processtemporalis

masseter

lateral

pterygoid

Insight: H3

Accessory muscles

• assist with depression of mandible(opening of mouth)

– only effective if hyoid fixed

• infrahyoid muscles

Manual: I-5

hyoid bone



CNV - Trigeminal nerve

• nerve type: mixed

– General Somatic

Afferent (GSA)

fibres

• general sensation

to anterior head

– SVE fibres

• muscles of mastication

Marieb: Table 13.2

Trigeminal nerve (CN V)

• distribution of sensory fibres in CN V3

– cutaneous• lower lip, chin

– sensory to deeper structures

• facial expression muscles

• oral cavity

• mandible & lower teeth

• TMJ

Referred pain• new principle

– P17: Pain carried by a particular branch of a

particular nerve arising from pathology in one

organ or region of the body may be perceived by

the brain as coming from another organ or region

of the body supplied by another branch of the

same parent nerve.

• trigeminal nerve has a common ganglion for

all three divisions – pain may refer from maxillary sinuses or upper

teeth (innervated by CNV2) to TMJ (inn. by CNV3)

– TMJ pain may refer to teeth and jaw

dsb mastication

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