muscles of mastication

7/21/2019 Muscles of Mastication

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MASTICATION,

MUSCLES & MECHANISM

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ContentsContentsIntroductionIntroduction

Development Of Muscles Of MasticationDevelopment Of Muscles Of Mastication

Primary Muscles Of MasticationPrimary Muscles Of Mastication

Function Of MusclesFunction Of Muscles

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The process by which food is crushed and groundThe process by which food is crushed and ground by teeth by teeth

The first step of digestionThe first step of digestion

Increases the surface area of food to allow moreIncreases the surface area of food to allow moreefficient breakdown by enzymesefficient breakdown by enzymes

Food after swallowing is called O!"#Food after swallowing is called O!"#



Mastication is the repetitive se$uence of %awMastication is the repetitive se$uence of %aw

opening and closing with a profile in the verticalopening and closing with a profile in the vertical

plane calledplane called CHEWING CYCLE.CHEWING CYCLE. HREE PHASES:

1. OPENING PHASEthe mouth is opened andthe mandible is depressed



2.2. CLOSING PHASECLOSING PHASE

&the mandible is raised&the mandible is raisedtowards the ma'illatowards the ma'illa

3. OCCLUSAL ORINTERCUSPAL

PHASE

&the mandible is stationaryand the teeth from bothupper and lower arches

appro'imate



INTRODUCTIONINTRODUCTION

#keletal components of body are held together#keletal components of body are held together

and moved by skeletal muscles(and moved by skeletal muscles(

The attachment of the muscle to the fi'ed part isThe attachment of the muscle to the fi'ed part is

known asknown as originorigin and attachment to the movableand attachment to the movable

part ispart is insertioninsertion((

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)ll the muscles arise from cranium and insert in the )ll the muscles arise from cranium and insert in themandible(mandible(

)ll the muscles develop from the mesoderm of Ist )ll the muscles develop from the mesoderm of Ist

pharyngeal arch(pharyngeal arch(

)ll the muscles are supplied by nerve of I pharyngeal arch )ll the muscles are supplied by nerve of I pharyngeal arch

*Mandibular nerve+(*Mandibular nerve+(

)ll the muscles act against the gravity *anti&gravity+ e'cept )ll the muscles act against the gravity *anti&gravity+ e'cept

lateral pterygoidlateral pterygoid((

GENERAL FEATURESGENERAL FEATURES



PRIMARY MUSCLES OFPRIMARY MUSCLES OF

MASTICATIONMASTICATION The muscles of mastication are of two typesThe muscles of mastication are of two types

Primary Primary

)ccessory )ccessory

P,IM),- M"#.!/#P,IM),- M"#.!/#

MasseterMasseter

TemporalisTemporalis

!ateral Pterygoid!ateral Pterygoid

Medial PterygoidMedial Pterygoid 9



Aessor! "#s$es Aessor! "#s$es

DigastricDigastric && 00stst ),.1 ),.1

MylohyoidMylohyoid && 00stst ),.1 ),.1

2eniohyoid2eniohyoid && "pper cervical somites"pper cervical somites

PlatysmaPlatysma && 33ndnd ),.1 ),.1

uccinatoruccinator && 33ndnd ),.1 ),.1

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M%sseterM%sseter

2reek word 42reek word 4masetermaseter5& a5& a

chewerchewer

This is aThis is a $uadrilateral$uadrilateral musclemuscle

which covers the lateral part which covers the lateral partof ramus of mandible(of ramus of mandible(

It consists ofIt consists of 6 layers6 layers which which

blend anteriorly( blend anteriorly(

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OriginOrigin

S#&er'ii%$ $%!er ($%rgest)S#&er'ii%$ $%!er ($%rgest)

It is the largest component that arises from the anterior two thirds of theIt is the largest component that arises from the anterior two thirds of the

lower border of the zygomatic archlower border of the zygomatic arch

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Middle LayerMiddle Layer

The middle layer takes its origin from the medial surface ofThe middle layer takes its origin from the medial surface ofthe anterior two&thirds and the lower border of posteriorthe anterior two&thirds and the lower border of posterior

one third of the archone third of the arch



Deep LayerDeep Layer

The deep layer arises from the whole length of medialThe deep layer arises from the whole length of medialsurface of the zygomatic archsurface of the zygomatic arch

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Insertion #uperficial layer#uperficial layer

)ngle )ngle of mandibleof mandible

!ower part!ower part of lateral surface ofof lateral surface of

mandibular ramus(mandibular ramus(

Middle layerMiddle layer

middle partmiddle part of mandibularof mandibularramus(ramus(

Deep layerDeep layer upper partupper part of mandibularof mandibular

ramusramus

coronoidcoronoid process(process(

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M%sseterM%sseter

7erve supply 7erve supply #upplied by#upplied by "%sseteri"%sseteri

ner*ener*e a branch of anteriora branch of anteriordivision of mandibular nervedivision of mandibular nerve

lood supply lood supply #upplied by#upplied by "%sseteri"%sseteri

%rter! %rter! branch of ma'illary branch of ma'illaryarteryartery

8enous drainage through 8enous drainage through"%sseteri *ein"%sseteri *ein

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MASSETER MASSETER

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The mainThe main function function ofof

masseter muscle ismasseter muscle is

• Elevation Elevation of the mandibleof the mandible

• lateral movementslateral movements of theof the

mandible for efficientmandible for efficient

chewing and grinding of thechewing and grinding of the

foodfood

• unilateral chewingunilateral chewing

• Retraction Retraction of the mandibleof the mandible



Te"&or%$isTe"&or%$is

It is a powerful fan shapedIt is a powerful fan shaped

chewing muscle whichchewing muscle which

fills temporal fossafills temporal fossa

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ORIGINORIGINFloor of temporal fossa*inferior temporal line+Floor of temporal fossa*inferior temporal line+

Overlying temporal fascia of the side of skullOverlying temporal fascia of the side of skull

TEMPORALIS



InsertionInsertionMargins 9 deep surface of coronoid processMargins 9 deep surface of coronoid process

)nterior order of ,amus )nterior order of ,amus



Middle fib"e$ - Obli%e



ACTION:

ANT - Elevation of the

mandiblePOST !et"a#tion of mandible

Ante"io" fib"e$ ve"ti#al

Middle fib"e$ - Obli%e

Po$te"io" fib"e$ - Ho"i'ontal

2825-01-2014



ActionActionIt can be divided into 6 distinct areas according toIt can be divided into 6 distinct areas according to

fiber direction and functionfiber direction and function TheThe Anterior fibers Anterior fibers are directed almost vertically&are directed almost vertically&elevation of mandibleelevation of mandible

TheThe middle fibersmiddle fibers run obli$uely forward as theyrun obli$uely forward as theypass downward &elevate and retrude the mandiblepass downward &elevate and retrude the mandible

TheThe posterior fibers posterior fibers are aligned almostare aligned almosthorizontally & retrusion of mandiblehorizontally & retrusion of mandible



Nerve SupplyNerve Supply

Deep temporal branches of the anteriorDeep temporal branches of the anterior

trunk of the mandibular nervetrunk of the mandibular nerve

Blood SupplyBlood Supplyy the middle 9 deep temporal arteries( They the middle 9 deep temporal arteries( The

middle temporal artery is a branch of themiddle temporal artery is a branch of the

superficial temporal artery 9 the deepsuperficial temporal artery 9 the deeptemporal arteries are branches of thetemporal arteries are branches of the

ma'illary artery ma'illary artery



L%ter%$ &ter!goi+L%ter%$ &ter!goi+

It is a short thick conical muscle with definiteIt is a short thick conical muscle with definite

upper and lower headsupper and lower heads31

LATERAL PTERYGOIDLATERAL PTERYGOID




OriginOrigin

"pper head arises from infra temporal surface and"pper head arises from infra temporal surface and

crest of greater wing of sphenoid bonecrest of greater wing of sphenoid bone

!ower head from the lateral pterygoid plate!ower head from the lateral pterygoid plate 32

L%ter%$ &ter goi+L%ter%$ &ter!goi+




InsertionInsertion Fibers run backwards and laterally and converge into theFibers run backwards and laterally and converge into the

pterygoid fovea on anterior surface of neck of mandiblepterygoid fovea on anterior surface of neck of mandible

Into anterior margin of articular disc andInto anterior margin of articular disc and

capsule of TM:capsule of TM:

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7erve supply 7erve supply

) branch from anterior ) branch from anterior

division of thedivision of the

mandibular nervemandibular nerve

lood supply lood supply

Ma'illary arteryMa'illary artery

)scending palatine )scending palatine

artery artery 34

L t $ t i+L t $ t i+




)ction )ction Depresses theDepresses the

mandible to openmandible to open

mouthmouth

!at( 9 Medial!at( 9 Medialpterygoid of bothpterygoid of both

sides contract tosides contract to

protrude the mandibleprotrude the mandible

when contract when contract

alternatively producesalternatively produces

chewing movementschewing movements

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Me+i%$ &ter!goi+Me+i%$ &ter!goi+

This is $uadrilateralThis is $uadrilateralmuscle having a smallmuscle having a small

superficial head and asuperficial head and a

large deep head whichlarge deep head which

forms the ma%or part offorms the ma%or part of

musclemuscle

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OriginOrigin #uperficial head from#uperficial head from

ma'illary tuberosityma'illary tuberosity

Deep head from medialDeep head from medial

surface of lateralsurface of lateral

pterygoid plate and partpterygoid plate and part

of palatine boneof palatine bone

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InsertionInsertion

Fibers run backwards;Fibers run backwards;downwards and laterallydownwards and laterally

into the roughened areainto the roughened area

of medial surface of theof medial surface of the

angle mandibleangle mandible

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7erve supply 7erve supply ranch of the mainranch of the maintrunk of mandibulartrunk of mandibularnervenerve

lood supply lood supply y facial arteryy facial artery lingual veinlingual vein

)ction )ction /levates and protrudes/levates and protrudes

the mandiblethe mandible

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MANDI,ULAR MO-EMENTS ANDMANDI,ULAR MO-EMENTS AND

ROLE PLAYED ,Y MUSCLESROLE PLAYED ,Y MUSCLES

/levation of mandible/levation of mandible The temporalis elevates the coronoid processThe temporalis elevates the coronoid process Masseter and medial pterygoid elevate the angle ofMasseter and medial pterygoid elevate the angle of

mandiblemandible !ateral pterygoid rela'es as muscles e'ert upward!ateral pterygoid rela'es as muscles e'ert upward

tractiontraction

Depression of mandibleDepression of mandible !ateral pterygoid e'erts a forward pull on neck of!ateral pterygoid e'erts a forward pull on neck of

mandiblemandible #up( 1ead of lateral pterygoid pulls articular disc#up( 1ead of lateral pterygoid pulls articular disc

down of articular tubercledown of articular tubercle )ccessory muscle help in drawing mandible down( )ccessory muscle help in drawing mandible down(

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Protrusion of mandibleProtrusion of mandible

!ateral pterygoid and medial pterygoid!ateral pterygoid and medial pterygoidcontractscontracts

,etrusion of mandible,etrusion of mandible Posterior fibers of Temporalis with help ofPosterior fibers of Temporalis with help of

Mylohyoid; Digastric 9 2eniohyoid draw theMylohyoid; Digastric 9 2eniohyoid draw themandible backwardsmandible backwards

!ateral shift of mandible!ateral shift of mandible contraction of lateral pterygoid on one sidecontraction of lateral pterygoid on one side

and medial pterygoid on the other side(and medial pterygoid on the other side(42



Ations Ations

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Mastication is the process wherebyMastication is the process whereby

ingested food is cut or crushed in to smallingested food is cut or crushed in to small

pieces; mi'ed with saliva and formed in topieces; mi'ed with saliva and formed in to

a bolus in preparation for swallowing(a bolus in preparation for swallowing(

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MASTICATIONMASTICATION

8arious functions have been ascribed to8arious functions have been ascribed to



8arious functions have been ascribed to 8arious functions have been ascribed to

mastication in humans( It <&mastication in humans( It <&

0( /nables the food bolus to be easily swallowed0( /nables the food bolus to be easily swallowed

3( Mi'es the food with saliva; initiating digestion3( Mi'es the food with saliva; initiating digestion

by the activity of salivary amylase by the activity of salivary amylase

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6( /nhances the digestibility of food by<6( /nhances the digestibility of food by<

a( decreasing the size of particles to increase thea( decreasing the size of particles to increase the

surface area for enzyme activity surface area for enzyme activity

b( refle'ly stimulating the secreation of digestive b( refle'ly stimulating the secreation of digestive

%uices *eg( #aliva and gastric %uice+ %uices *eg( #aliva and gastric %uice+

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=( Prevents irritation of the gastrointestinal=( Prevents irritation of the gastrointestinal

system by large food massessystem by large food masses

>( /nsures healthy growth and development of>( /nsures healthy growth and development of

the oral tissues(the oral tissues(

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FORCES OF MASTICATIONFORCES OF MASTICATION

The ma'imum biting force that can be applied to the teethThe ma'imum biting force that can be applied to the teeth

varies from individual to individiual( varies from individual to individiual(

Male are able to e'ert more masticatory force then females(Male are able to e'ert more masticatory force then females(

The masticatory force e'erted on anterior teeth is >? poundThe masticatory force e'erted on anterior teeth is >? pound

*0?&0> @gs+ and on molars is 3?? pounds around >? @gs*0?&0> @gs+ and on molars is 3?? pounds around >? @gs

appro'imately(appro'imately(

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CHEING CYCLECHEING CYCLE



Mammals generally chew on one side at a time(Mammals generally chew on one side at a time(

Two methods of chewing have been distinguished; depending uponTwo methods of chewing have been distinguished; depending upon

the initial te'ture of the foodthe initial te'ture of the food and theand the stage in its breakdown(stage in its breakdown(

AA PunctureBcrushing(PunctureBcrushing( 1ard food is first crushed and pierced between1ard food is first crushed and pierced between

the teeth without direct tooth&to&tooth contact(the teeth without direct tooth&to&tooth contact(

AA #hearing strokeB2rinding phase(#hearing strokeB2rinding phase( This method involves tooth contactsThis method involves tooth contacts

that take place only after the food has been sufficiently reduced(that take place only after the food has been sufficiently reduced(

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CHEING CYCLECHEING CYCLE

The chewing cycle involves three basic phases *or strokes+ of theThe chewing cycle involves three basic phases *or strokes+ of the



The chewing cycle involves three basic phases *or strokes+ of theThe chewing cycle involves three basic phases *or strokes+ of the

mandible in relation to the ma'illa(mandible in relation to the ma'illa(

From a position in which the %aw is open; theFrom a position in which the %aw is open; the closing strokeclosing stroke resultsresults

in the teeth being brought into initial contact with the foodC thein the teeth being brought into initial contact with the foodC the work done in this phase is really against gravity( work done in this phase is really against gravity(

This is followed by theThis is followed by the power strokepower stroke; when the food undergoes; when the food undergoes

reduction( Movement of the mandible in this phase is slower thanreduction( Movement of the mandible in this phase is slower than

in the closing stroke because of the resistance caused by the food;in the closing stroke because of the resistance caused by the food;

even though there may be vastly greater masseter and temporaliseven though there may be vastly greater masseter and temporalismuscle activity during this time(muscle activity during this time(

Finally; there is theFinally; there is the opening strokeopening stroke; when the mandible is lowered;; when the mandible is lowered;

with an initial slower stage followed by a faster stage( with an initial slower stage followed by a faster stage(

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EN-ELOPE OF MOTIONEN-ELOPE OF MOTION



The pathway followed by the mandible during chewing isThe pathway followed by the mandible during chewing is

termed the envelope of motionE( This demonstrates thetermed the envelope of motionE( This demonstrates thesymmetrical mandibular movements produced duringsymmetrical mandibular movements produced during

opening and closing of the %aw(opening and closing of the %aw(

The envelope of motion is the volume of space withinThe envelope of motion is the volume of space within which all movements of a specified point on the which all movements of a specified point on the

mandible occur( The envelope is limited by anatomicalmandible occur( The envelope is limited by anatomical

considerations such as ligaments and tooth contacts(considerations such as ligaments and tooth contacts(

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EN-ELOPE OF MOTIONEN-ELOPE OF MOTION



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lue tra%ectory

,ed tra%ectory

-ellow tra%ectory

2reen tra%ectory

The yellow tra%ectory depicts a two&phased; consciousThe yellow tra%ectory depicts a two&phased; conscious



movement from the rest position to the fully openedmovement from the rest position to the fully opened

position( The first phase is a hinge&like movement duringposition( The first phase is a hinge&like movement during

which the condyles remain retruded within the which the condyles remain retruded within the

mandibular fossae( hen the teeth become separated bymandibular fossae( hen the teeth become separated byappro'imately 3> mm; the second phase of openingappro'imately 3> mm; the second phase of opening

occurs and involves anterior movement or protrusion ofoccurs and involves anterior movement or protrusion of

the condyles down the articular eminences(the condyles down the articular eminences(

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lue tra%ectory

,ed tra%ectory

-ellow tra%ectory

2reen tra%ectory

The blue and red tra%ectories describe a biphasic path ofThe blue and red tra%ectories describe a biphasic path of



closure from the fully opened mandibular position;closure from the fully opened mandibular position;

which can be performed only with conscious effort( The which can be performed only with conscious effort( The

first phase *the blue tra%ectory+ takes the mandible up tofirst phase *the blue tra%ectory+ takes the mandible up to

a protruded closed position; while the second phase *thea protruded closed position; while the second phase *thered tra%ectory+ takes the mandible from this protrudedred tra%ectory+ takes the mandible from this protruded

contact position to a retruded contact position(contact position to a retruded contact position(

The green tra%ectory describes the free; habitual;The green tra%ectory describes the free; habitual;unconscious movement during both mandibular openingunconscious movement during both mandibular opening

and closingand closing

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Th i t th f th dibl i th fi tTh i t th f th dibl i th fi t



The points on the ramus of the mandible in the figure representThe points on the ramus of the mandible in the figure represent

the centres of rotation during opening and closure(the centres of rotation during opening and closure(

Point ) is the fulcrum associated with simple hinge movements(Point ) is the fulcrum associated with simple hinge movements(The path described between points ) and represents the shift ofThe path described between points ) and represents the shift of

the centre of rotation of the mandibleC this shift occurs because ofthe centre of rotation of the mandibleC this shift occurs because of

the transition from a pure hinge movement at the condyle tothe transition from a pure hinge movement at the condyle to

protrusion and rotation during opening *with the reverse duringprotrusion and rotation during opening *with the reverse during

closing+(closing+(

Point has been described as representing the point of rotationPoint has been described as representing the point of rotation

around the attachment of the sphenomandibular ligament at thearound the attachment of the sphenomandibular ligament at the

lingula(lingula(

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CONTROL OF MASTICATIONCONTROL OF MASTICATION



One older view; theOne older view; the cerebral hemispheres theory cerebral hemispheres theory ; held that; held that

mastication was a conscious act; a patterned set of instructionsmastication was a conscious act; a patterned set of instructions

originating in the higher centres of the central nervous systemoriginating in the higher centres of the central nervous system*in particular the motor corte'+ and descending to directly drive*in particular the motor corte'+ and descending to directly drive

the motor neurones within the brainstem *trigeminal; facial andthe motor neurones within the brainstem *trigeminal; facial and

hypoglossal motor neurones+(hypoglossal motor neurones+(

)nother older idea; )nother older idea;

the refle' chain theory the refle' chain theory

; held that mastication; held that mastication

involved a series of interacting chains of refle'es( )ccordingly;involved a series of interacting chains of refle'es( )ccordingly;

sensory input from the region of the mouth *e(g( pressure on thesensory input from the region of the mouth *e(g( pressure on the

teeth+ triggered the motor neurones in the brainstem to elicit ateeth+ triggered the motor neurones in the brainstem to elicit a

%aw opening movement( In turn; this movement produced %aw opening movement( In turn; this movement produced

another sensory input *e(g( from stretch receptors in the %awanother sensory input *e(g( from stretch receptors in the %awmuscles+; which resulted in a %aw closing refle'(muscles+; which resulted in a %aw closing refle'(

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CONTROL OF MASTICATIONCONTROL OF MASTICATION

)lthough there are several well recognized types of %aw refle'; ob%ections to )lthough there are several well recognized types of %aw refle'; ob%ections to



g g yp % ; b%g g yp % ; %

the refle' chain theory have been raised on the basis that masticationthe refle' chain theory have been raised on the basis that mastication

involves prolonged bursts of muscle activity and not the brief and abruptinvolves prolonged bursts of muscle activity and not the brief and abrupt

behaviour usually associated with refle' activation of muscle( behaviour usually associated with refle' activation of muscle(

) third theory; ) third theory; the rhythm *pattern+ generator theory the rhythm *pattern+ generator theory ; has recently been; has recently been

updated to e'plain rhythmic %aw functioning( This theory is based upon theupdated to e'plain rhythmic %aw functioning( This theory is based upon the

proposition that there are central pattern generators *.P2s+ within theproposition that there are central pattern generators *.P2s+ within the

brainstem that can be stimulated from either higher centres or sensory brainstem that can be stimulated from either higher centres or sensory

inputs in the region from the mouth; so that they are driven into rhythmicinputs in the region from the mouth; so that they are driven into rhythmicactivity( This idea could account for rhythmic activity obtained byactivity( This idea could account for rhythmic activity obtained by

stimulating either the motor corte' or; in decerebrate animals andstimulating either the motor corte' or; in decerebrate animals and

anencephalies *where the cerebral hemispheres are congenitally absent+;anencephalies *where the cerebral hemispheres are congenitally absent+;

the oral cavity(the oral cavity(

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The hypothesis is that the sensory input generated byThe hypothesis is that the sensory input generated by

closing on hard food supports the generation of rhythmicclosing on hard food supports the generation of rhythmic

%aw activity; whereas closure on a softened bolus %aw activity; whereas closure on a softened bolus

promotes tongue movement and food transport; elicitingpromotes tongue movement and food transport; eliciting

a swallow< the effect is to terminate the rhythmic %awa swallow< the effect is to terminate the rhythmic %awactivity(activity(

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muscles of mastication

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