Functions of mandible

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Osteology of the mandible

Coronoid

process

condylar

process

Mentalforamen

mandibular foramen

Mylohoid

Mylohoidgroove

Subamndibular fossa

Sublingual

Digastricfossa

Genialtubercles

Pterygoid fossa

Temporal fossa

� Bounded by the superior andinferior temporal lines.

� Inferiorly, the infratemporalcrest separates it from theinfratemporal fossa.

� The floor is formed by parts of

the four bones that form thepterion.

Superior temporalline

Inferior temporal

Infratemporal crest

frontal parietal

temporalsphenoid

pterion

Temporal fossa� Roof: temporal fascia.

± Attached to the superior temporal lineand passes down to the upper borderof the zygomatic arch.

� Superficial temporal vessels andauriculotemporal nerve are superficialto the temporal fascia.

� The deep temporal vessels and nerves

are deep to the temporal muscle

Temporal fascia

Superficialtemporal vessels

Auriculo-temporalnerve

Muscles of mastication:

� Temporalis

� Masseter

� Medial pterygoid

� Lateral pterygoid

All are attached to the mandible All receive motor supply from the mandibular division of the trigeminal nerve (the only

division that carries motor fibers).

Muscles of mastication: temporalis� Fan shaped

(triangular) muscle,attached to the

temporal fossa and

temporal fascia.

� Inserted into the

coronoid process

of the mandible

� The upper and anterior fibers elevate the mandible

(close the jaws).� The posterior fibers retract the mandible, they are

the only fibers to do so.

temporalis

Deeptemporalnerves and

vessels

Temporal fascia

Coronoidprocess

Muscles of mastication: masseter� Quadrate muscle

� Between the zygomatic arch and the angle and

lateral surface of the ramus of the mandible.

� It acts to close the jaws and contributes to

protrusion.

masseter

Lateral pterygoid muscle� Has two heads:

± lateral surface of the

lateral pterygoid plate

(inferior head)

± infratemporal surface of

the greater wing of the

sphenoid (superior head).

� Inserted into the neck of themandible and the capsule and

intra-articular disk of the TMJ.

� The muscle draws the condyle

and intra-articular disc

forwards from the glenoid

fossa down the slope of

articular eminence: Active

opening of the mouth.

Superior head

Inferior head

Intra-articular disc

Medial pterygoid muscle

� Medial surface of the lateral

pterygoid plate (deep head).

� Tuberosity of the maxilla

(superficial head).

� Muscle fibers run downwards,

backwards, and laterally to beinserted into the deep surface of

the angle of the mandible

(opposite the insertion of

masseter).

Superficialhead

deep head

Medialpterygoid

� The muscle thus moves themandible upwards, forwards, and

medially (i.e. closes the mouth and

when acting on one side it moves

the mandible to the opposite side).

Temporomandibular joint (TMJ)� Type: A modified hinge type of synovial

joint� Articulation: between the condyle of the

mandible on one side and the articular

tubercle and mandibular fossa of the

temporal bone on the other side.

Mandibular fossa

Articular tubercle

Mandibular head

TMJ- intra-articular disc

� Made of fibrocartilage.� Covers both the mandibular fossa and the articular eminence in front of it (so that it is

shaped like a jockey¶s cap).

� Its circumference blends with the capsule.

� It divides the joint into a superior and inferior compartments.

� The gliding movements of protrusion and retrusion occur in the superior compartment.

� The hinge movements of depression and elevation occur in the inferior compartment.

Mandibular

Articular tubercle

Mandibular head

Articular disc

Ligaments� The lateral ligament

(temporomandibular):intrinsic, very strong.

± Prevents posterior dislocationand fracturing the tympanicplate when a severe blow fallson the chin.

� Two other ligaments (extrinsic) neither of them provides muchstrength to the joint.

± Stylomandibular ligament(thickened band of parotidfascia) runs from the styloidprocess to the angle of themandible.

± Sphenomandibular ligamentruns from the spine of the

sphenoid to the lingula of themandible.

Lateral lig.

stylomandibular lig.

sphenomandibular lig.

Tympanic plate

Movements

� Opening-closing

� Protraction-retraction

� Side to side movements

Movements� Opening-closing

the head of the mandible rotates on

the disk like the movement of a hinge

joint (lower compartment of the joint).

In addition to the simplehinge movement, the

disc carrying the head

with it glides forward

(upper compartment of

the joint).

Movements� The forward movement of the

mandibular head can be easily felt byplacing a finger in front of or in the

external acoustic meatus.

� Opening of the mouth:

± Passive: produced by gravity (a

simple hinge). The falling open

of the jaw during sleep illustrates

the effect of gravity. ± Active: produced by

submandibular muscles

(digastric, mylohyoid, and

geniohyoid) + lateral pterygoid

(being attached to the neck,

capsule and disc) producing the

foreword movement (a

compound hinge and gliding).

� Closure of the mouth is produced by

temporalis, masseter, and medial

pterygoid.

� Closure is therefore much more

powerful than opening

Mandibular head

Mandibular fossa

Mandibular head

Mandibular fossa

Mouth closed Mouth open

Lateral view of TMJ

Movements� Protraction-retraction

± Occurs in the upper compartment

of the joint

± Protraction: masseter, lateral and

medial pterygoid.

± Retraction: posterior fibers of

temporalis.� Side to side movements

± Occur in the upper compartment

± Produced by the pterygoids acting

on either side alternately.

Types of Mandibular Movement

� Rotational movement

± Horizontal axis of rotation

± Frontal (vertical) axis of rotation

± Sagittal axis of rotation

� Translational movement

Rotational Movement

� Around the horizontal axis (hinge axis)

Rotational Movement

� Around the frontal (vertical) axis

Rotational Movement

� Around the sagittal axis

Translational movement

TMJ dislocation

� When the mouth is open, the TMJ is very unstable.

� A blow on the mandible may cause anterior

dislocation bringing the condylar process in front of

the articular tubercle.Mouth open

TMJ dislocation

� Posterior dislocation isuncommon being resisted by thepostglenoid tubercle and thestrong lateral ligament.

Lateral lig.

Functions of mandible

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