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DEVEOPMENT OF MUSCLESDEVEOPMENT OF MUSCLES OFOF
MASTICATIONMASTICATION
 The muscular system develops from intra embryonicThe muscular system develops from intra embryonic
mesodermmesoderm
 Muscle tissues develop from embryonic cells calledMuscle tissues develop from embryonic cells called
myoblast.myoblast.
 Muscular component ofMuscular component of BranchialBranchial archarch form manyform many
striated muscles in the head and neck region.striated muscles in the head and neck region.
 Muscles of mastication are derived from first orMuscles of mastication are derived from first or
MANDIBULAR ARCH.MANDIBULAR ARCH.
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INDIAN DENTAL ACADEMY
Leader in continuing Dental Education
CONTENTSCONTENTS
 INTRODUCTIONINTRODUCTION
 DEVELOPMENT OF MUSCLES OF MASTICATIONDEVELOPMENT OF MUSCLES OF MASTICATION
 TYPES OF MUSCLESTYPES OF MUSCLES
 ANATOMY OF MUSCLESANATOMY OF MUSCLES
 GENERAL MECHANISM OF MUSCLE CONTRACTIONGENERAL MECHANISM OF MUSCLE CONTRACTION
 MUSCLES OF MASTICATIONMUSCLES OF MASTICATION
 PATHOLOGICAL CONDITIONS AFFECTING MUSCLESPATHOLOGICAL CONDITIONS AFFECTING MUSCLES
 PROSTHODONTIC CONSIDERATIONSPROSTHODONTIC CONSIDERATIONS
 CONCLUSIONCONCLUSION
 REFERENCESREFERENCES
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MuscleMuscle:: TTISSUE CHARACTERIZED BY AGGREGATION OF CELLSISSUE CHARACTERIZED BY AGGREGATION OF CELLS
WHOSE PRIMARY ROLE IS TO PRODUCE CONTRACTION,AND ALLOWINGWHOSE PRIMARY ROLE IS TO PRODUCE CONTRACTION,AND ALLOWING
MOVEMENTS OF PARTS AND ORGANS OF THE BODY.MOVEMENTS OF PARTS AND ORGANS OF THE BODY.
IT MAY ALSO BE DEFINED AS A BANDIT MAY ALSO BE DEFINED AS A BAND
OF CONTRACTILE FIBROUS TISSUE,WHICH PRODUCE MOVEMENTS IN ANOF CONTRACTILE FIBROUS TISSUE,WHICH PRODUCE MOVEMENTS IN AN
ANIMAL BODY.ANIMAL BODY.
MasticationMastication :: RHYTHMIC OPPOSITION AND SEPARATION OF JAWSRHYTHMIC OPPOSITION AND SEPARATION OF JAWS
WITH THE INVOLVEMENT OF TEETH ,LIPS CHEEKS AND TOUNGE FORWITH THE INVOLVEMENT OF TEETH ,LIPS CHEEKS AND TOUNGE FOR
CHEWING OF FOOD IN ORDER TO PREPARE IT FOR SWALLOWING ANDCHEWING OF FOOD IN ORDER TO PREPARE IT FOR SWALLOWING AND
DIGESTION.DIGESTION.
MAIN PURPOSE OF MASTICATION IS TOMAIN PURPOSE OF MASTICATION IS TO
REDUCE THE SIZE OF FOOD PARTICLES TO A SIZE THAT IS CONVINIENTREDUCE THE SIZE OF FOOD PARTICLES TO A SIZE THAT IS CONVINIENT
FOR SWALLOWING{BOLUS FORMATION} WITH THE HELP OF SALIVA.FOR SWALLOWING{BOLUS FORMATION} WITH THE HELP OF SALIVA.
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LATERAL VIEW OF A FOUR WEEK EMBRYO SHOWING
MUSCLES DERIVED FROM BRANCHIAL ARCHES
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EIGHT WEEK EMBRYO SHOWING DEVELOPMENT
OF FACIAL MUSCLES AND TRUNCK MUSCULATUREwww.indiandentalacademy.comwww.indiandentalacademy.com
SKETCH OF 20 WEEK FETUS SHOWING MUSCLES
DERIVED FROM BRANCHIAL ARCHES
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TYPES OF MUSCLESTYPES OF MUSCLES
 Muscle cells are mainly of three typesMuscle cells are mainly of three types
1.1. STRIATED MUSCLESTRIATED MUSCLE
a. SKELETAL OR VOLUNTARYa. SKELETAL OR VOLUNTARY
b. CARDIC MUSCLEb. CARDIC MUSCLE
2.2. NON-STRIATED,SMOOTH ORNON-STRIATED,SMOOTH OR
INVOLUNTARYINVOLUNTARY
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Longitudinal section of human
Skeletal muscle showing
Characterstic banding pattern.
Transverse section of skeletal muscle
Fiber containing myofibrils and muscle
Cell nuclei,endomysial sheath lie between
The muscle fiber
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LONGITUDINAL
SECTION OF CARDIAC
MUSCLEI
TRANSVERSE
SECTION OF CARDIAC
MUSCLE
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Longitudinal section of non striated or smooth muscle
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SKELETAL MUSCLESKELETAL MUSCLE
 Units of skeletal muscle are theUnits of skeletal muscle are the muscle fibersmuscle fibers,each of which,each of which
act as a single cell having hundreds of nuclie(syncytial striatedact as a single cell having hundreds of nuclie(syncytial striated
myocytes).myocytes).
 Fibers are arranged in bundles of various sizes and patternFibers are arranged in bundles of various sizes and pattern
calledcalled fasciculifasciculi..
 Connective tissue fills the spaces between muscle fibres withinConnective tissue fills the spaces between muscle fibres within
a fasciculus where it is known as thea fasciculus where it is known as the endomysciumendomyscium..
 Each fasciculus is also surrounded by a strong connectiveEach fasciculus is also surrounded by a strong connective
tissue sheath ortissue sheath or perimysciunperimysciun..
 Surrounding the whole muscle liesSurrounding the whole muscle lies epimyscium.epimyscium.
 Cell membrane of muscle fibre is known asCell membrane of muscle fibre is known as sarcolemmasarcolemma whilewhile
their cytoplasm is calledtheir cytoplasm is called sarcoplasmsarcoplasm..
 Sarcoplasm is divided into longitudinal threads orSarcoplasm is divided into longitudinal threads or myofibrilsmyofibrils
each of 1micro meter in diam.each of 1micro meter in diam.
 Each muscle fiber consists of several hundred to severalEach muscle fiber consists of several hundred to several
thousandthousand myofibrilsmyofibrils www.indiandentalacademy.comwww.indiandentalacademy.com
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THE ULTRASTRUCTURE OF SKELETALTHE ULTRASTRUCTURE OF SKELETAL
MUSCLEMUSCLE
Electron microscope show myofiril to be composed of myofilaments these are divided
Transversely by z band into serially repeating reagions termed sarcomeres about 2.5
Micro-meter long in resting state.
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ACTIN AND MYOSIN FILAMENTACTIN AND MYOSIN FILAMENT
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GENERAL MECHANISM OF MUSCLEGENERAL MECHANISM OF MUSCLE
CONTRACTIONCONTRACTION
SLIDING FILAMENT MECHANISM.SLIDING FILAMENT MECHANISM.
 Caused by interaction of cross bridges from myosin filamentCaused by interaction of cross bridges from myosin filament
with the actin filament.with the actin filament.
 Action potential causes sarcoplasmic reticulum to causesAction potential causes sarcoplasmic reticulum to causes
release of calcium ion.release of calcium ion.
 Calcium ion combines with troponin c of troponinCalcium ion combines with troponin c of troponin
tropomyosin complex causing a confirmational change. Andtropomyosin complex causing a confirmational change. And
it moves deeper between two actin strands.it moves deeper between two actin strands.
 This uncovers the active sites of actin allowing these toThis uncovers the active sites of actin allowing these to
attract the myosin head and cause contraction to proceed.attract the myosin head and cause contraction to proceed.
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Interaction Between The ‘Activated’ ActinInteraction Between The ‘Activated’ Actin
Filament And the Myosin Bridges-The ‘WalkFilament And the Myosin Bridges-The ‘Walk
Along Theory’ of contractionAlong Theory’ of contraction
 When myosin head attaches to a active site ,it causes head toWhen myosin head attaches to a active site ,it causes head to
tilt towards the arm and drag the actin filament along with it,tilt towards the arm and drag the actin filament along with it,
 This tilt of the head is calledThis tilt of the head is called Power strokePower stroke..
 After tilting head automatically breaks away from the activeAfter tilting head automatically breaks away from the active
sitesite
 Next it returns to perpendicular position and combines withNext it returns to perpendicular position and combines with
new active site farther down along the actin filament.new active site farther down along the actin filament.
 Thus the heads of myosin filament bend back back and forthThus the heads of myosin filament bend back back and forth
and walk along the actin filament.and walk along the actin filament.
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MUSCLE FUNCTIONMUSCLE FUNCTION
The motor unit can carry only one action i.e. contraction or shortening,The motor unit can carry only one action i.e. contraction or shortening,
the entire muscle, however has three potential function.the entire muscle, however has three potential function.
 A)A) ISOTONIC CONTRACTIONISOTONIC CONTRACTION
When the muscle shorten and moves a load, the contraction isWhen the muscle shorten and moves a load, the contraction is
isotonic. Hence the load remains constant and equal to the muscleisotonic. Hence the load remains constant and equal to the muscle
tension throughout the most of the period of contraction. It occurs intension throughout the most of the period of contraction. It occurs in
the masseter, when the mandible is elevated forcing the teeththe masseter, when the mandible is elevated forcing the teeth
through a bolus of food.through a bolus of food.
 B)B) ISOMETRIC CONTRACTIONISOMETRIC CONTRACTION
When a muscle does not shorter and length remains same (iso-When a muscle does not shorter and length remains same (iso-
same, metry- length), but develops tension, the contraction issame, metry- length), but develops tension, the contraction is
isometric. Such type of contraction occurs when muscle attempts toisometric. Such type of contraction occurs when muscle attempts to
move a load that is greater than the tension developed in muscles,move a load that is greater than the tension developed in muscles,
this occurs in masseter when an object is held between the teeth.this occurs in masseter when an object is held between the teeth.
eg. Pipe or pencil.eg. Pipe or pencil.
 C)C) CONTRACTION RELAXATIONCONTRACTION RELAXATION
When stimulation of the motor unit is discontinued the fibres ofWhen stimulation of the motor unit is discontinued the fibres of
motor unit relax and return to their normal length. This is seen inmotor unit relax and return to their normal length. This is seen in
masseter when the mouth opens to accept new bolus of food duringmasseter when the mouth opens to accept new bolus of food during
mastication.mastication.
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FIBER TYPESFIBER TYPES
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Muscle hypertrophy atrophy andMuscle hypertrophy atrophy and
hyperplasiahyperplasia
 HYPERTROPHYHYPERTROPHY: when total: when total mass of musclemass of muscle
enlarges.,oncrease in actin and myosin filament inenlarges.,oncrease in actin and myosin filament in
response to maximal force causing enlargement ofresponse to maximal force causing enlargement of
muscle fiber.muscle fiber.
 HYPERPLASIA:HYPERPLASIA: Under rare condition of extremeUnder rare condition of extreme
muscle force generation actual no of muscle fibermuscle force generation actual no of muscle fiber
have been observed to increase.have been observed to increase.
 ATROPHY:ATROPHY: When total mass of muscle decreases.When total mass of muscle decreases.
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MUSCLES OF MASTICATIONMUSCLES OF MASTICATION
Mastication forcesMastication forces The aev maximumThe aev maximum
sustainable biting force is 756N{170 pounds}.sustainable biting force is 756N{170 pounds}.
Molar region:Molar region: Biting force range 400-890NBiting force range 400-890N
Premolar region:Premolar region: Biting force range 222-445NBiting force range 222-445N
Cuspid regionCuspid region:: Biting force range 133-334NBiting force range 133-334N
Incisor regionIncisor region:Biting force range 89-111N:Biting force range 89-111N
{20-55 pounds}{20-55 pounds}
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PRIMARY MUSCLES OFPRIMARY MUSCLES OF
MASTICATIONMASTICATION
 MASSETERMASSETER
 TEMPORALISTEMPORALIS
 MEDIAL AND LATERAL PTERYGOIDMEDIAL AND LATERAL PTERYGOID
SECONDARY MUSCLES OF MASTICATIONSECONDARY MUSCLES OF MASTICATION
The suprahyoid group of muscles being used asThe suprahyoid group of muscles being used as
secondary or supplementary muscles they aresecondary or supplementary muscles they are
 DigastricDigastric
 MylohyoidMylohyoid
 GeniohyoidGeniohyoid
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THE MASSETERTHE MASSETER
QQuadrilateral and and consist of three layers.uadrilateral and and consist of three layers.
ATTACHEMENTSATTACHEMENTS
Superficial LayerSuperficial Layer :: Arises by thick aponeurosis.Arises by thick aponeurosis.
From zygomatic process of maxilla and anterior 2/3From zygomatic process of maxilla and anterior 2/3
of lower border of zygomatic arch,pass downwardof lower border of zygomatic arch,pass downward
and back wards at an angle of 45degree and insertedand back wards at an angle of 45degree and inserted
into lower part of lateral surface of ramus ofinto lower part of lateral surface of ramus of
mandiblemandible
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 MIDDLE LAYERMIDDLE LAYER: Arises from: Arises from
anterior 2/3 of the deep surfaceanterior 2/3 of the deep surface
and posterior 1/3 of the lowerand posterior 1/3 of the lower
border of the zygomaticborder of the zygomatic
arch,pass vertically downwardsarch,pass vertically downwards
and and inserted into middle partand and inserted into middle part
of ramus.of ramus.
 DEEP LAYER:DEEP LAYER: Arises from deepArises from deep
surface of the zygomatic arch,surface of the zygomatic arch,
pass vertically downwards andpass vertically downwards and
inserted into the upper part of theinserted into the upper part of the
ramus and into the coronoidramus and into the coronoid
process.process.
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RELATIONS OF MASSETERRELATIONS OF MASSETER
SUPERFICIASUPERFICIA
 IntegumentIntegument
 PlatysmaPlatysma
 RisoriusRisorius
 Zygomaticus majorZygomaticus major
 Parotid glandParotid gland
 Parotid ductParotid duct
 Branches of facialBranches of facial
nervenerve
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DEEP SURFACEDEEP SURFACE
Overlies the,Overlies the,
 Insertion ofInsertion of
temporalis and ramustemporalis and ramus
of the mandible.of the mandible.
 In front buccinatorIn front buccinator
and the buccal nerve.and the buccal nerve.
 Massetric nerve andMassetric nerve and
artery.artery.
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ANTERIORANTERIOR MarginMargin
projects over theprojects over the
buccinator and is crossedbuccinator and is crossed
below by the facial vein.below by the facial vein.
POSTERIORPOSTERIOR MarginMargin
is overlapped by theis overlapped by the
parotid gland.parotid gland.
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Nerve supplyNerve supply ::
 MASSETRICMASSETRIC
NERVE, a branch ofNERVE, a branch of
anterior division ofanterior division of
mandibular nerve (whichmandibular nerve (which
is the 3rd part of V cranialis the 3rd part of V cranial
nerve- trigeminal nerve).nerve- trigeminal nerve).
Blood supplyBlood supply::
 Maxillary artery,Maxillary artery,
which is a branch ofwhich is a branch of
external carotid artery.external carotid artery.
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ACTIONS OF MASSETERACTIONS OF MASSETER
Actions:Actions:
Elevates the mandible to close the mouthElevates the mandible to close the mouth
and to occlude the teeth in mastication.and to occlude the teeth in mastication.
Its activity in the resting position isIts activity in the resting position is
minimal.minimal.
 It has a small effect in side-to-sideIt has a small effect in side-to-side
movement, protraction and retraction.movement, protraction and retraction.
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THE TEMPORALISTHE TEMPORALIS
TEMPORAL FASCIAETEMPORAL FASCIAE
 Thick aponeurotic sheet that roofs over the temporalThick aponeurotic sheet that roofs over the temporal
fossa and covers the temporalis muscle.fossa and covers the temporalis muscle.
ATTACHEMENTSATTACHEMENTS
 Fan shapedFan shaped
 Arises from whole of temporal fossa.(except the partArises from whole of temporal fossa.(except the part
formed by zygomatic bone) and deep surface offormed by zygomatic bone) and deep surface of
temporal fasciatemporal fascia
 Fibers converge and descend into a tendon .Fibers converge and descend into a tendon .
 It passes through the gap between the zygomatic archIt passes through the gap between the zygomatic arch
and the side of the skulland the side of the skull
 Attached to medial surface,apex,anterior and posteriorAttached to medial surface,apex,anterior and posterior
border of coronoid process and anterior border of theborder of coronoid process and anterior border of the
ramus of the mandible as far as last molar.ramus of the mandible as far as last molar.
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RELATIONS OF TEMPORALISRELATIONS OF TEMPORALIS
SUPERFICIALSUPERFICIAL
 SkinSkin
 Auricularis anteriorAuricularis anterior
 Temporal fasciaTemporal fascia
 Superficial temporal vesselsSuperficial temporal vessels
 Auriculotemporal nerveAuriculotemporal nerve
 Temporal branch of facial nerveTemporal branch of facial nerve
 Galea aponeuroticaGalea aponeurotica
 Zygomatic archZygomatic arch
 massetermasseter
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DEEP SURFACEDEEP SURFACE
 Temporal fossaTemporal fossa
 Lateral pterygoidLateral pterygoid
 Superficial head of medialSuperficial head of medial
pterygoidpterygoid
 Small part of buccinatorSmall part of buccinator
 Maxillary arteryMaxillary artery
 Deep temporal nervesDeep temporal nerves
 Buccal vessels and nerveBuccal vessels and nerve
ANTERIOR border is seperatedANTERIOR border is seperated
from the zygomatic bone by afrom the zygomatic bone by a
mass of fat.mass of fat.
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BLOOD SUPPLYBLOOD SUPPLY
 Deep temporal part ofDeep temporal part of
maxillary arterymaxillary artery
NERVE SUPPLYNERVE SUPPLY
 Temporalis isTemporalis is
supplied by the deepsupplied by the deep
temporal branches oftemporal branches of
the anterior trunk ofthe anterior trunk of
mandibular nerve.mandibular nerve.
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ACTIONS OF TEMPORALISACTIONS OF TEMPORALIS
 Elevates the mandible,this movement requiresElevates the mandible,this movement requires
both the upward pull of anterior fibers andboth the upward pull of anterior fibers and
backward pull of the posterior fibers.backward pull of the posterior fibers.
 Posterior fibers draw the mandible backwardsPosterior fibers draw the mandible backwards
after it has been protuded.after it has been protuded.
 It is also a contrbutor to side to side grindingIt is also a contrbutor to side to side grinding
movement.movement.
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ELEVATION OF MANDIBLEELEVATION OF MANDIBLE
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POSTERIOR FIBER DRAWSPOSTERIOR FIBER DRAWS
MANDIBLE BACKWARDSMANDIBLE BACKWARDS
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SIDE TO SIDE GRINDINGSIDE TO SIDE GRINDING
MOVEMENTMOVEMENT
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LATERAL PTERYGOIDLATERAL PTERYGOID
ATTACHMENTSATTACHMENTS
It is a short thick muscle with two parts or headIt is a short thick muscle with two parts or head
 UPPERUPPER head arise from infratemporal surface andhead arise from infratemporal surface and
infratemporal crest of greater wing of sphenoid boneinfratemporal crest of greater wing of sphenoid bone
 LOWERLOWER head arise from lateral surface of lateralhead arise from lateral surface of lateral
pterygoid plate.pterygoid plate.
 Its fibers pass backwards and laterally to be inserted intoIts fibers pass backwards and laterally to be inserted into
a depression(pterygoid fovea)on the front of the neck ofa depression(pterygoid fovea)on the front of the neck of
the mandible and into the articular capsule and disc ofthe mandible and into the articular capsule and disc of
the temporomandibular articulation.the temporomandibular articulation.
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RELATIONS OF LATERALRELATIONS OF LATERAL
PTERYGOIDPTERYGOID
SUPERFICIALSUPERFICIAL
 Ramus of the mandibleRamus of the mandible
 Maxillary arteryMaxillary artery
 Tendon of temporalis and the masseter,Tendon of temporalis and the masseter,
DEEP SURFACEDEEP SURFACE
 Upper part of the madial pterygoidUpper part of the madial pterygoid
 Sphenomandibular ligamentSphenomandibular ligament
 Middle meningeal arteryMiddle meningeal artery
 Mandibular nerveMandibular nerve
UPPER BORDERUPPER BORDER
 Upper border is in relation with temporal and messetricUpper border is in relation with temporal and messetric
branches of the mandibular nervebranches of the mandibular nerve
LOWER BORDERLOWER BORDER
 In relation with lingual and inferior alveolar nerveIn relation with lingual and inferior alveolar nerve
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NERVE SUPPLYNERVE SUPPLY
 The lateralThe lateral
pterygoid is suppliedpterygoid is supplied
by a branch ofby a branch of
anterior division of theanterior division of the
mandibular nervmandibular nerv
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BLOOD SUPPLYBLOOD SUPPLY
PterygoidPterygoid
branch of 2ndbranch of 2nd
part of maxillarypart of maxillary
arteryartery
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ACTIONS OF LATERALACTIONS OF LATERAL
PTERYGOIDPTERYGOID
 Assists in opening the mouth with suprahyoidAssists in opening the mouth with suprahyoid
muscle.muscle.
 Slow elongation while closing the mouth withSlow elongation while closing the mouth with
masseter and temporalismasseter and temporalis
 Acting with medial pterygoid of same sideActing with medial pterygoid of same side
advances the condyle ,while the jaw rotatesadvances the condyle ,while the jaw rotates
through the opposite condyle(when the medialthrough the opposite condyle(when the medial
and lateral pterygoid of the two sides contractand lateral pterygoid of the two sides contract
alternatively to produce side to side movementsalternatively to produce side to side movements
of mandible eg chewing).of mandible eg chewing).
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 When the medial and lateral pterygoids of twoWhen the medial and lateral pterygoids of two
sides act together they protrude the mandible sosides act together they protrude the mandible so
that the lower incisors project in front of thethat the lower incisors project in front of the
other.other.
 Some authorities have ascribed different actionsSome authorities have ascribed different actions
to the two parts of pterygoid muscle.to the two parts of pterygoid muscle.
 The upper (superior)head being involved inThe upper (superior)head being involved in
chewingchewing
 The inferior in protrusion,electromyographicThe inferior in protrusion,electromyographic
records in rhesus monkey favors this view.records in rhesus monkey favors this view.
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The combinded efforts of the Digastrics and LateralThe combinded efforts of the Digastrics and Lateral
Pterygoids provide for natural jaw opening.Pterygoids provide for natural jaw opening.
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SIDE TO SIDE GRINDINGSIDE TO SIDE GRINDING
MOVEMENTMOVEMENT
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Medial and lateral pterygoid actMedial and lateral pterygoid act
together to protrude the mandibletogether to protrude the mandible
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MEDIAL PTERYGOIDMEDIAL PTERYGOID
ATTACHEMENTSATTACHEMENTS
 It is a thick quadrilateral muscleIt is a thick quadrilateral muscle
 Attached to medial surface of lateral pterygoid plate andAttached to medial surface of lateral pterygoid plate and
grooved surface of pyramidal process of the palatinegrooved surface of pyramidal process of the palatine
bone.bone.
 A more superficial slip from the lateral surface ofA more superficial slip from the lateral surface of
pyramidal process of the palatine bone and tuberosity ofpyramidal process of the palatine bone and tuberosity of
maxillamaxilla
 Its fibers pass downwards laterally and backwardsIts fibers pass downwards laterally and backwards
 Attached by a strong tendinous lamina ,to the postero-Attached by a strong tendinous lamina ,to the postero-
inferior part of the medial surfaces of the ramus and theinferior part of the medial surfaces of the ramus and the
angle of the mandibleangle of the mandible
 It is attached as high as mandibular foramen and as farIt is attached as high as mandibular foramen and as far
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RELATIONS OF MEDIALRELATIONS OF MEDIAL
PTERYGOIDPTERYGOID
SUPERFICIALSUPERFICIAL
 Upper part of muscle is separated from theUpper part of muscle is separated from the
lateral pterygoid muscle bylateral pterygoid muscle by
a) lateral pterygoid platea) lateral pterygoid plate
b) lingual nerveb) lingual nerve
c) inferior alveolar nervec) inferior alveolar nerve
 Inferiorly the muscle is separated from ramus ofInferiorly the muscle is separated from ramus of
mandible by same nerves,the maxillary arterymandible by same nerves,the maxillary artery
and sphenomandibular ligament.and sphenomandibular ligament.
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NERVE SUPPLYNERVE SUPPLY
 Branch of theBranch of the
main trunk of themain trunk of the
mandibular nerve.mandibular nerve.
BLOOD SUPPLYBLOOD SUPPLY
 Pterygoid branchPterygoid branch
of 2nd part ofof 2nd part of
maxillary arterymaxillary artery
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Actions of medial pterygoidActions of medial pterygoid
 Assits in elevating the mandibleAssits in elevating the mandible
 Acting with the lateral pterygoid they protrude itActing with the lateral pterygoid they protrude it
•Acting with medial pterygoid of sameActing with medial pterygoid of same
side advances the condyle ,while the jawside advances the condyle ,while the jaw
rotates through the oppositerotates through the opposite
condyle(when the medial and lateralcondyle(when the medial and lateral
pterygoid of the two sides contractpterygoid of the two sides contract
alternatively to produce side to sidealternatively to produce side to side
movements of mandible eg chewing)movements of mandible eg chewing)
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Secondary muscles taking part inSecondary muscles taking part in
the masticationthe mastication
The 4 primary muscles of mastication are inThe 4 primary muscles of mastication are in
turn supported or supplemented by fewturn supported or supplemented by few
secondary muscles known assecondary muscles known as
SUPRAHYOID GROUP of muscles theySUPRAHYOID GROUP of muscles they
areare
DIGASTRICDIGASTRIC
MYLOHYOIDMYLOHYOID
GENIOHYOIDGENIOHYOID
STYLOHYOID is other suprahyoid muscle,STYLOHYOID is other suprahyoid muscle,
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DIGASTRICDIGASTRIC
•The muscle has secondary role in mastication as
a depressor muscle adding to the action of lateral
pterygoid muscle when mouth is to be opened
agains resistance. Elevation of hyoid bone
MYLOHYOID
•The secondary role of this muscle is evidnent as a
depressor seen in action when mouth is to be
opened against resistance.
•It elevates the floor of mouth to help in deglutition.
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GENIOHYOIDGENIOHYOID
•Geniohyoid elevates the hyoid bone and draws it
forward, thus acting as a partial antagonist to
stylohyoid.
•When the hyoid bone is fixed, it depresses the
mandible
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PATHOLOGICAL CONDITIONSPATHOLOGICAL CONDITIONS
AFFECTING MUSCLESAFFECTING MUSCLES
CLASSIFICATION OF DISEASES OFCLASSIFICATION OF DISEASES OF
MUSCLEMUSCLE
II PRIMARY MYOPATHIESPRIMARY MYOPATHIES
a)Dystrophiesa)Dystrophies
b)Myotoniasb)Myotonias
c)Hypotoniasc)Hypotonias
d)Myastheniasd)Myasthenias
e)Myositise)Myositis
f)Metabolic defectsf)Metabolic defects
g)Miscellaneous(amyloplasias,contractures,degeng)Miscellaneous(amyloplasias,contractures,degenwww.indiandentalacademy.comwww.indiandentalacademy.com
II.II.SECONDARY MYOPATHIESSECONDARY MYOPATHIES
a)a)AtrophyAtrophy
1)Denervation1)Denervation
2)Disuse and fixation2)Disuse and fixation
3)Ageing and cachexia3)Ageing and cachexia
b) Hypertrophyb) Hypertrophy
1) Developmental1) Developmental
2) Functional2) Functional
c) Endocrinec) Endocrine
d) Internal environmentd) Internal environment
1)Chemical1)Chemical
2)Vascular2)Vascular
e)Infectione)Infection
1.Specific(trichinella,toxoplasma,coxsackie virus,1.Specific(trichinella,toxoplasma,coxsackie virus,tetanustetanus))
2.General(rikettsial,typhoid,pneumococcal pneumonia)2.General(rikettsial,typhoid,pneumococcal pneumonia)
3.Post infection asthenia.3.Post infection asthenia.
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DISEASES OF SKELETAL MUSCLEDISEASES OF SKELETAL MUSCLE
 Disorders that produce predominantly myofiberDisorders that produce predominantly myofiber
atrophy including neurogenic atrophy andatrophy including neurogenic atrophy and
myofiber atrophy.myofiber atrophy.
 Disorders of the neuromuscularDisorders of the neuromuscular
junction(exemplified byjunction(exemplified by myasthenia gravismyasthenia gravis))
 Selected primary myopathies includingSelected primary myopathies including
inflammatory myopathies and muscularinflammatory myopathies and muscular
dystrophies.dystrophies.
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MYASTHENIASMYASTHENIAS
a)Myasthenia gravisa)Myasthenia gravis
b)familial periodic parslysisb)familial periodic parslysis
c)aldosteronismc)aldosteronism
Latter two are very rare diseases.Latter two are very rare diseases.
MYASTHENIA GRAVISMYASTHENIA GRAVIS
 Acquired autoimmune disorder of neuromuscularAcquired autoimmune disorder of neuromuscular
transmission charecterized by muscle weaknesstransmission charecterized by muscle weakness
ETIOLOGYETIOLOGY
 Antibodies to acetylcholine receptor on skeletal muscleAntibodies to acetylcholine receptor on skeletal muscle
fiberfiber
 Assosiation with systemic lupusAssosiation with systemic lupus
erythematosis,rheumatoid artheritis,sjogren syndrome.erythematosis,rheumatoid artheritis,sjogren syndrome.
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CLINICAL FEATURESCLINICAL FEATURES
 May be present at any age, chiefly inMay be present at any age, chiefly in
adults,predilection for womenadults,predilection for women
 Rapidly developing weakness in voluntaryRapidly developing weakness in voluntary
muscles following even minor activitiesmuscles following even minor activities
 Of interest toOf interest to PROSTHODONTISTPROSTHODONTIST is the factis the fact
that muscles of mastication and facialthat muscles of mastication and facial
expression are involved by this diseaseexpression are involved by this disease
frequently before any other muscle group.frequently before any other muscle group.
Patient chief complaint may bePatient chief complaint may be
difficulty in mastication and deglution, anddifficulty in mastication and deglution, and
dropping of the jaw . Speech is often slow anddropping of the jaw . Speech is often slow and
slurred. Disturbance in taste sensation in someslurred. Disturbance in taste sensation in some
patient.patient.
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 Diplopia, ptosis,drooping of the face,lend a veryDiplopia, ptosis,drooping of the face,lend a very
sorroful appearance to the patient.sorroful appearance to the patient.
 Pt rapidly exausted,lose wt,death frequentlyPt rapidly exausted,lose wt,death frequently
occurs from respiratory failure.occurs from respiratory failure.
 Clinical course variable,some enter acuteClinical course variable,some enter acute
exacerbation of their disease and sccumb butexacerbation of their disease and sccumb but
others live for many years,on this basis twoothers live for many years,on this basis two
forms are recognized.forms are recognized.
a)Steadily progressivea)Steadily progressive
b)a remitting relapsing typeb)a remitting relapsing type
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TREATMENT AND PROGNOSISTREATMENT AND PROGNOSIS
 Drug of choice used in treatment provides suchDrug of choice used in treatment provides such
remarkable relief of symptoms in very short time.remarkable relief of symptoms in very short time.
 Physostigmine administered intramuscularlyPhysostigmine administered intramuscularly
improves the strength of the affected muscle in aimproves the strength of the affected muscle in a
matter of minutesmatter of minutes
 No cure is known even though the prognosis isNo cure is known even though the prognosis is
good in the relapsing type.good in the relapsing type.
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TETANUS(LOCK JAW)TETANUS(LOCK JAW)
 Tetanus is a disease of the nervous systemTetanus is a disease of the nervous system
characterized by intense activity of motor neuroncharacterized by intense activity of motor neuron
and resulting in severe muscle spasmand resulting in severe muscle spasm
 Caused by exotoxins of gram positive bacillusCaused by exotoxins of gram positive bacillus
Ciostridium tetani.Ciostridium tetani.
CLINICAL FEATURESCLINICAL FEATURES
 Pain and stiffness in the jaws and neckPain and stiffness in the jaws and neck
muscles ,with muscle rigidity producing trismusmuscles ,with muscle rigidity producing trismus
and dysphagiaand dysphagia
 Rigity of facial muscles producing the typicalRigity of facial muscles producing the typical
risus sardonicusrisus sardonicus
 Sometimes whole body becomes affectedSometimes whole body becomes affected
characterized by opisthotonoscharacterized by opisthotonos
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TREATMENTTREATMENT
 All patients should receive antimicrobial drugsAll patients should receive antimicrobial drugs
 Active and passive immunization.Active and passive immunization.
 Surgical wound careSurgical wound care
 Anticonvulsant if indicatedAnticonvulsant if indicated
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PROSTHODONTICPROSTHODONTIC
CONSIDERATIONSCONSIDERATIONS
MASTICATIORY CYCLEMASTICATIORY CYCLE
 The pathways of the mandible in chewing isThe pathways of the mandible in chewing is
referred to as the chewing cyclereferred to as the chewing cycle
 Masticatory cycle consists of three phasesMasticatory cycle consists of three phases
1) Opening phase(mandible is depressed)1) Opening phase(mandible is depressed)
2) Closing phase(mandible is elevated)2) Closing phase(mandible is elevated)
3) Intercuspal phase(ICP)3) Intercuspal phase(ICP)
 The chewing cycle can take many forms and theThe chewing cycle can take many forms and the
classicclassic tear droptear drop shape when viewed in frontal orshape when viewed in frontal or
saggital plane is oversimplification of realitysaggital plane is oversimplification of reality
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 In opening phase teethIn opening phase teeth
and condyle move downand condyle move down
and forwardand forward
 Early closing phase manEarly closing phase man
moves laterally to themoves laterally to the
selected chewing sideselected chewing side
 Chewing side condyleChewing side condyle
moves to upwardmoves to upward
reareward position well inreareward position well in
advance of theadvance of the
intercuspal phase(SRP)intercuspal phase(SRP)
 During rest of closingDuring rest of closing
phase to ICP chewingphase to ICP chewing
side condyle show aside condyle show a
slight forward(.33mm)slight forward(.33mm)
and medialand medial
movement(Bennett)movement(Bennett)
(.2mm)(.2mm)
 Non chewing sideNon chewing side
condyle lags somewhatcondyle lags somewhat
behind.behind.
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 There are about 15 chews in a series from theThere are about 15 chews in a series from the
time of food entry until swallowingtime of food entry until swallowing
 Aev jaw opening during chewing is between 16-Aev jaw opening during chewing is between 16-
20mm20mm
 Aev lateral displacement on chewing is betweenAev lateral displacement on chewing is between
3 and 5mm3 and 5mm
 Duration of masticatory cycle varies between .Duration of masticatory cycle varies between .
6and 1 sec6and 1 sec
 Men chew faster and have a shorter occlusalMen chew faster and have a shorter occlusal
phase than women,it also depends on the typephase than women,it also depends on the type
of foodof food
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FACTORS THAT REGULATE JAW MOTIONSFACTORS THAT REGULATE JAW MOTIONS
 NEUROMUSCULAR SYSTEMNEUROMUSCULAR SYSTEM
 GUIDING INFLUNCES OF CONTACTINGGUIDING INFLUNCES OF CONTACTING
TEETHTEETH
 MANDIBULAR MUSCULATURE WHEN TEETHMANDIBULAR MUSCULATURE WHEN TEETH
NOT IN CONTACTNOT IN CONTACT
 LIMITING OF MOVEMENT BY CONDYLELIMITING OF MOVEMENT BY CONDYLE
The condyles and teeth modify mandibularThe condyles and teeth modify mandibular
movements initiated by neuromuscular system.movements initiated by neuromuscular system.
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INFLUENCE OF OPPOSING TOOTH CONTACTINFLUENCE OF OPPOSING TOOTH CONTACT
IN COMPLETE DENTUREIN COMPLETE DENTURE
 The occlusal surface should meet evenly onThe occlusal surface should meet evenly on
both sidesboth sides
 In this manner mandible is not deflected from itsIn this manner mandible is not deflected from its
normal path of closure,nor are the denturesnormal path of closure,nor are the dentures
displaced from residual ridgesdisplaced from residual ridges
 When mandibular movements are made theWhen mandibular movements are made the
inclined planes of the teeth should pass overinclined planes of the teeth should pass over
one another snoothlyone another snoothly
 It should not disturb the influence of condylarIt should not disturb the influence of condylar
guidance posteriorly and incisal guidanceguidance posteriorly and incisal guidance
anteriorlyanteriorly
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NEUROMUSCULAR REGULATION OFNEUROMUSCULAR REGULATION OF
MANDIBULAR MOTIONMANDIBULAR MOTION
 Mastication is a programmed event residing in aMastication is a programmed event residing in a
“chewing center” located within the brain“chewing center” located within the brain
stem(reticular formation of the pons)stem(reticular formation of the pons)
 The cyclic nature of mastication is the result ofThe cyclic nature of mastication is the result of
the action of this central pattern generatorthe action of this central pattern generator
 Concious effort may either induce or terminateConcious effort may either induce or terminate
chewing ,but it is not required for thechewing ,but it is not required for the
continuation of chewingcontinuation of chewing
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REST POSITIONREST POSITION
 It is established by muscles and gravityIt is established by muscles and gravity
 There are two hypothesis abput postural restThere are two hypothesis abput postural rest
positionposition
1)Active mechanism,when muscles are in a1)Active mechanism,when muscles are in a
state of minimal contraction to maintain thestate of minimal contraction to maintain the
postureposture
2)Passive mechanism, elastic elements of2)Passive mechanism, elastic elements of
the jaw musculature and not any muscle activitythe jaw musculature and not any muscle activity
balanve the influence of gravitybalanve the influence of gravity
 Numerous studies have shown EMG activity atNumerous studies have shown EMG activity at
restrest
 A range of reduced muscle tension upto anA range of reduced muscle tension upto an
interocclusal distance of about 10mm has beeninterocclusal distance of about 10mm has been
reportedreported
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IMPORTANCE OF OCCLUSALIMPORTANCE OF OCCLUSAL
HARMONYHARMONY
 When closing muscle pull mandible without interferenceWhen closing muscle pull mandible without interference
it is stooped by bone at medial poleit is stooped by bone at medial pole
 If tooth inclines interfere lateral pterygoid is forced toIf tooth inclines interfere lateral pterygoid is forced to
position the mandible to accommodate to the teethposition the mandible to accommodate to the teeth
 There are many variations of timing and degree ofThere are many variations of timing and degree of
muscle contraction to position the mandible for maximummuscle contraction to position the mandible for maximum
intercuspation of the teeth.intercuspation of the teeth.
 Pattern of deviation is reinforced every time contact isPattern of deviation is reinforced every time contact is
mademade
 Imortant facet of propioceptive memory is that it fades ifImortant facet of propioceptive memory is that it fades if
reinforcement of pattern ceases.reinforcement of pattern ceases.
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 Elimination of interfering contacts permit anElimination of interfering contacts permit an
almost immediate return to normal musclealmost immediate return to normal muscle
functionfunction
 Willamson Showed using EMG procedures thatWillamson Showed using EMG procedures that
posterior tooth intrference caused hyperactivityposterior tooth intrference caused hyperactivity
of elevator muscleof elevator muscle
 But if the anterior guidance was allowed toBut if the anterior guidance was allowed to
disclude all posterior teeth from any contactdisclude all posterior teeth from any contact
other than CR elevator muscle stopped activeother than CR elevator muscle stopped active
contraction or reduced it.contraction or reduced it.
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TOOTH INTERFERENCESTOOTH INTERFERENCES
 The reason muscle changes jaw position in theThe reason muscle changes jaw position in the
presence of interferences is to protect thepresence of interferences is to protect the
interfereing tooth or teeth from absorbing entireinterfereing tooth or teeth from absorbing entire
occlusal forceocclusal force
 Muscles become patterned to the deviousMuscles become patterned to the devious
closure ,such memorized patterns of muscleclosure ,such memorized patterns of muscle
activity are calledactivity are called ENGRAMSENGRAMS
 Because of engrams it is easy to be fooled byBecause of engrams it is easy to be fooled by
freely hinging jaw that appears to be in correctfreely hinging jaw that appears to be in correct
CR.CR.
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OCCLUSAL PLANEOCCLUSAL PLANE
 The curvature of the posterior plane of occlusionThe curvature of the posterior plane of occlusion
are divided intoare divided into
1)An anteroposterior curve called the1)An anteroposterior curve called the
curve of speecurve of spee..
2)Mediolateral curve referred to as2)Mediolateral curve referred to as
thethe curve of wilsoncurve of wilson
Curve of SpeeCurve of Spee
 Begins at cusp tip pf lower cuspid and follow theBegins at cusp tip pf lower cuspid and follow the
buccal cusp tip of bicuspid and molars, curvebuccal cusp tip of bicuspid and molars, curve
line forms an arc through the condyle.line forms an arc through the condyle.
 It aligns each tooth for maximum resistance toIt aligns each tooth for maximum resistance to
functional loadingfunctional loading
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 To prevent increaseTo prevent increase
muscle loading of themuscle loading of the
teeth and the joints duringteeth and the joints during
protrusive movement.protrusive movement.
 If there is any toothIf there is any tooth
contact posterior tocontact posterior to
canine during excursioncanine during excursion
the elevator muscles arethe elevator muscles are
triggered intotriggered into
hypercontractionhypercontraction
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CURVE OF WILSONCURVE OF WILSON
 Mediolateral curve that contacts the buccal andMediolateral curve that contacts the buccal and
lingual cusp tips on each side of archlingual cusp tips on each side of arch
 Results from inward inclination of posterior teethResults from inward inclination of posterior teeth
 In maxillary arch reverse is there because ofIn maxillary arch reverse is there because of
outward inclination of posterior teeth.outward inclination of posterior teeth.
There are two reasons for this inclination ofThere are two reasons for this inclination of
posterior teethposterior teeth
1) one has to do with resistance to1) one has to do with resistance to
loadingloading
2)second has to do with masticatory2)second has to do with masticatory
functionfunction
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 Axial alignment of allAxial alignment of all
posterior teeth is nearlyposterior teeth is nearly
parallel with the strongparallel with the strong
inward pull of the medialinward pull of the medial
pterygoid musclepterygoid muscle
 Aligning both upper andAligning both upper and
lower posterior teeth withlower posterior teeth with
the principal direction ofthe principal direction of
muscle contractionmuscle contraction
produce the greatestproduce the greatest
resistance to masticatoryresistance to masticatory
forces, and forms curveforces, and forms curve
of wilsonof wilson
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 There is another reasonThere is another reason
for the curve offor the curve of
wilson,tounge andwilson,tounge and
buccinator must placebuccinator must place
food onto occlusalfood onto occlusal
table,there must be easytable,there must be easy
access for the food to getaccess for the food to get
to the occlusal tableto the occlusal table
 The inward inclination ofThe inward inclination of
the lower occlusal tablethe lower occlusal table
for direct access fromfor direct access from
linguallingual
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 The outward inclination ofThe outward inclination of
the upper occlusal tablethe upper occlusal table
provides access from theprovides access from the
buccal for the foodbuccal for the food
 When the curve of wilsonWhen the curve of wilson
is made too flat ease ofis made too flat ease of
masticatory function maymasticatory function may
be impaired because ofbe impaired because of
increased activityincreased activity
required to get the foodrequired to get the food
onto the occlusal tableonto the occlusal table
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BRUXISMBRUXISM
Bruxism is the clenching or grinding of the teeth when theBruxism is the clenching or grinding of the teeth when the
individual is not chewing or swallowingindividual is not chewing or swallowing
 It can occur as a brief rhythmic strong contractions of theIt can occur as a brief rhythmic strong contractions of the
jaw muscles during eccentric lateral jaw movements,or injaw muscles during eccentric lateral jaw movements,or in
maximum intercuspation,which is called clenching.maximum intercuspation,which is called clenching.
 CausesCauses
1) Assosiated with stressful events1) Assosiated with stressful events
2)Non stress related or hereditary2)Non stress related or hereditary
 Increased masseter muscle tension is directly related toIncreased masseter muscle tension is directly related to
stress situation during the day.stress situation during the day.
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 Increased stress levelsIncreased stress levels
are strongly correlatedare strongly correlated
with increased levels ofwith increased levels of
masseter muscle activitymasseter muscle activity
at nightat night
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 Bruxism can not be casually described asBruxism can not be casually described as
"hyperactivity of the lateral pterygoid". "hyperactivity of the lateral pterygoid". 
                                                            
. The definitive component of bruxism is the degree. The definitive component of bruxism is the degree
of parafunctional elevation, that is, the clenchingof parafunctional elevation, that is, the clenching
component.  An accurated definition of bruxism is: component.  An accurated definition of bruxism is: 
Jaw clenching, with or without forcibleJaw clenching, with or without forcible
excursive movements, where the intensityexcursive movements, where the intensity
of the clenching dictates the severity (orof the clenching dictates the severity (or
lack of) grindinglack of) grinding ..
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Each of the graphics below displays identical degreess ofEach of the graphics below displays identical degreess of
LP "hyperactivityLP "hyperactivity::
•Only the graphic toOnly the graphic to
the far left can bethe far left can be
considered NOTconsidered NOT
be bruxism,be bruxism,
although there ISalthough there IS
hyperactivity of thehyperactivity of the
LPsLPs
graphic at thegraphic at the
far right is thefar right is the
most extrememost extreme
form ofform of
bruxism).bruxism).
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 Bruxism may lead toBruxism may lead to
-tooth wear-tooth wear
-fracture of the teeth or restoratrion-fracture of the teeth or restoratrion
-uncosmetic muscle hypertrophy-uncosmetic muscle hypertrophy
 TreatmentTreatment
-coronoplasty-coronoplasty
-maxillary stabalization appliance-maxillary stabalization appliance
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Normal function versusNormal function versus
parafunctionparafunction
The image to the left is demonstrating
normal reciprocal functioning of the Lateral
Pterygoids and
Masseters/Med.Pteygoids/Temporalis'.
The Lateral Pterygoids advance the
condyles, thereby opening the mouth
(depressing the mandible), with the
assistance of the Digastric
The oblique orientation of the Masseters
and Medial Pterygoids create a sling. The
non-working side Medial Pterygoid contacts
simultaneously with the opposide side
working Masseter.
It is this oblique orientation of the
Med.Pterygoids and Masseters that create
the functional "shift" of the mandible, not an
unilateral contraction of a Lateral Pterygoid
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 In the event theIn the event the
Temporalis' do not ceaseTemporalis' do not cease
their active contractions,their active contractions,
scenarios of varyingscenarios of varying
degrees of parafunctiondegrees of parafunction
result, as the Lateralresult, as the Lateral
Pterygoids encounterPterygoids encounter
resistance to theirresistance to their
attempts at condylarattempts at condylar
advancement, therebyadvancement, thereby
increasing their intensityincreasing their intensity
of contraction and strainof contraction and strain
on their origins andon their origins and
insertions: the pterygoidinsertions: the pterygoid
plates of the sphenoidplates of the sphenoid
bone, and the condylarbone, and the condylar
neck and disc. neck and disc. 
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 The degree of frequency,The degree of frequency,
duration and intensity ofduration and intensity of
the contractions of athe contractions of a
Lateral Pterygoid is aLateral Pterygoid is a
function of the resistancefunction of the resistance
provided by theprovided by the
parafunction ipsilateralparafunction ipsilateral
and/or contralateraland/or contralateral
Temporalis.  ForTemporalis.  For
example, in the animationexample, in the animation
to the left, as a Lateralto the left, as a Lateral
Pterygoid attempts toPterygoid attempts to
translate its condyle, it istranslate its condyle, it is
met with resistancemet with resistance
provided by theprovided by the
contralateral Temporalis,contralateral Temporalis,
thereby causing thethereby causing the
Lateral Pterygoid to pullLateral Pterygoid to pull
its condyle in a medialits condyle in a medial
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The maximum clenching intensity occurs inThe maximum clenching intensity occurs in
the musculoskeletally stable positionthe musculoskeletally stable position
 The mandibular positionThe mandibular position
of the temporalis' mostof the temporalis' most
intense contraction is notintense contraction is not
when the teeth arewhen the teeth are
together, but when theytogether, but when they
are a particular distanceare a particular distance
apart, and separated byapart, and separated by
an object (such as aan object (such as a
splint, or food).splint, or food).
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CANINE RISE SERVE S TO DIFFUSECANINE RISE SERVE S TO DIFFUSE
PARAFUNCTIONPARAFUNCTION
 temporalis persists in thetemporalis persists in the
elevation of the mandible,elevation of the mandible,
the canine teeththe canine teeth
contralateral to thecontralateral to the
translating condyle aretranslating condyle are
often exploited to endureoften exploited to endure
the load, thereby allowingthe load, thereby allowing
the force to be directed inthe force to be directed in
an anterior (and slightlyan anterior (and slightly
medial) direction, bracedmedial) direction, braced
by the slope of theby the slope of the
eminence.  This is calledeminence.  This is called
"canine guidance","canine guidance",
allowing the posteriorallowing the posterior
teeth to separate. teeth to separate. 
www.indiandentalacademy.comwww.indiandentalacademy.com
 Although the lateralAlthough the lateral
engagement of theengagement of the
canines can help tocanines can help to
diffuse the effects ofdiffuse the effects of
parafunction, an end-to-parafunction, an end-to-
end canine contact canend canine contact can
serve to perpetuate theserve to perpetuate the
effects of parafunction. effects of parafunction. 
The animationThe animation
demonstrates andemonstrates an
excursive movement thatexcursive movement that
allows for canine-to-allows for canine-to-
canine clenching.  Caninecanine clenching.  Canine
teeth can alow for nearteeth can alow for near
maximal voluntarymaximal voluntary
temporalis clenchingtemporalis clenching
intensityintensity
www.indiandentalacademy.comwww.indiandentalacademy.com
Parafunctional chewing cycle: "Outside-inParafunctional chewing cycle: "Outside-in""
 Normal opening isNormal opening is
straight, unless astraight, unless a
chronically-chronically-
tensed/fatigued LPtensed/fatigued LP
advances its condyleadvances its condyle
"faster" that the"faster" that the
contralateral LP.contralateral LP.
 Excursive parafunctionExcursive parafunction
does notdoes not engage theengage the
canine during closing (ie,canine during closing (ie,
from the outside-in).from the outside-in).
 The above example does The above example does
not really happen. not really happen. 
Interferences areInterferences are
enganged by the LP uponenganged by the LP upon
opening (at rightopening (at right
www.indiandentalacademy.comwww.indiandentalacademy.com
Parafunctional chewing cycle: "Inside-out"Parafunctional chewing cycle: "Inside-out"
 Deviation upon opening isDeviation upon opening is
abnormal and is usuallyabnormal and is usually
thethe
result of excursiveresult of excursive
parafunctional openingparafunctional opening
against resistance. against resistance. 
Ideally, this activity wouldIdeally, this activity would
engage a canine, engage a canine, 
but can still fatigue abut can still fatigue a
lateral pterygoidlateral pterygoid
depending upon thedepending upon the
intensity of resistanceintensity of resistance
provided by the occludingprovided by the occluding
canines.  Occasionally,canines.  Occasionally,
canine tip-to-tip clenchingcanine tip-to-tip clenching
perpetuates the clinicalperpetuates the clinical
presentation of unilateralpresentation of unilateral
headache andheadache and
contralateral joint strain.contralateral joint strain.www.indiandentalacademy.comwww.indiandentalacademy.com
REFERENCESREFERENCES
 Kieth L. Moore, The developing human ,fourth editionKieth L. Moore, The developing human ,fourth edition
19921992
 Peter.L.Williams,Roger Worwik Grays Anatomy ,thirty sixPeter.L.Williams,Roger Worwik Grays Anatomy ,thirty six
edition 1980edition 1980
 B.D.Chaurasias, Human anatomy,third edition 2000B.D.Chaurasias, Human anatomy,third edition 2000
 Keith L.Moore,Clinically Oriented Anatomy fourth editionKeith L.Moore,Clinically Oriented Anatomy fourth edition
19921992
 Anne M.R Agur,Grants atlas of anatomy 10 edition 1991Anne M.R Agur,Grants atlas of anatomy 10 edition 1991
 R.M.H Mc Minn,.R.T.Hutchings ,third edition1994R.M.H Mc Minn,.R.T.Hutchings ,third edition1994
 Arthur C Guyton,John E Hall,Textbook of MedicalArthur C Guyton,John E Hall,Textbook of Medical
Physiology 10 edition 2000Physiology 10 edition 2000
 William f ganong,Review of Medical Physiology,eighteenWilliam f ganong,Review of Medical Physiology,eighteen
edition 1997edition 1997
www.indiandentalacademy.comwww.indiandentalacademy.com
 Kumar ,Cotran,Basic Pathology,fourth editionKumar ,Cotran,Basic Pathology,fourth edition
19711971
 Shafer,Hine,Textbook of oral pathology,fourthShafer,Hine,Textbook of oral pathology,fourth
edition 1997edition 1997
 Sheldon Winkler,Essentials of complete dentureSheldon Winkler,Essentials of complete denture
prosthodontics,second, edition 2000prosthodontics,second, edition 2000
 George A.Zarb,Charles LGeorge A.Zarb,Charles L
Bolender,Prosthodontic Treatment forBolender,Prosthodontic Treatment for
Edentulous Patients, twelth edition 2004Edentulous Patients, twelth edition 2004
 Peter E Dawson,Evaluatio Diagnosis andPeter E Dawson,Evaluatio Diagnosis and
Treatment of Occlusal Problems ,secondTreatment of Occlusal Problems ,second
edition1989edition1989
 Fermin A Carranza,Micheal G Newman,ClinicalFermin A Carranza,Micheal G Newman,Clinical
Periodontology eight edition1996Periodontology eight edition1996
www.indiandentalacademy.comwww.indiandentalacademy.com

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Development of muscles of mastication / dental implant courses

  • 1. DEVEOPMENT OF MUSCLESDEVEOPMENT OF MUSCLES OFOF MASTICATIONMASTICATION  The muscular system develops from intra embryonicThe muscular system develops from intra embryonic mesodermmesoderm  Muscle tissues develop from embryonic cells calledMuscle tissues develop from embryonic cells called myoblast.myoblast.  Muscular component ofMuscular component of BranchialBranchial archarch form manyform many striated muscles in the head and neck region.striated muscles in the head and neck region.  Muscles of mastication are derived from first orMuscles of mastication are derived from first or MANDIBULAR ARCH.MANDIBULAR ARCH. www.indiandentalacademy.comwww.indiandentalacademy.com INDIAN DENTAL ACADEMY Leader in continuing Dental Education
  • 2. CONTENTSCONTENTS  INTRODUCTIONINTRODUCTION  DEVELOPMENT OF MUSCLES OF MASTICATIONDEVELOPMENT OF MUSCLES OF MASTICATION  TYPES OF MUSCLESTYPES OF MUSCLES  ANATOMY OF MUSCLESANATOMY OF MUSCLES  GENERAL MECHANISM OF MUSCLE CONTRACTIONGENERAL MECHANISM OF MUSCLE CONTRACTION  MUSCLES OF MASTICATIONMUSCLES OF MASTICATION  PATHOLOGICAL CONDITIONS AFFECTING MUSCLESPATHOLOGICAL CONDITIONS AFFECTING MUSCLES  PROSTHODONTIC CONSIDERATIONSPROSTHODONTIC CONSIDERATIONS  CONCLUSIONCONCLUSION  REFERENCESREFERENCES www.indiandentalacademy.comwww.indiandentalacademy.com
  • 3. MuscleMuscle:: TTISSUE CHARACTERIZED BY AGGREGATION OF CELLSISSUE CHARACTERIZED BY AGGREGATION OF CELLS WHOSE PRIMARY ROLE IS TO PRODUCE CONTRACTION,AND ALLOWINGWHOSE PRIMARY ROLE IS TO PRODUCE CONTRACTION,AND ALLOWING MOVEMENTS OF PARTS AND ORGANS OF THE BODY.MOVEMENTS OF PARTS AND ORGANS OF THE BODY. IT MAY ALSO BE DEFINED AS A BANDIT MAY ALSO BE DEFINED AS A BAND OF CONTRACTILE FIBROUS TISSUE,WHICH PRODUCE MOVEMENTS IN ANOF CONTRACTILE FIBROUS TISSUE,WHICH PRODUCE MOVEMENTS IN AN ANIMAL BODY.ANIMAL BODY. MasticationMastication :: RHYTHMIC OPPOSITION AND SEPARATION OF JAWSRHYTHMIC OPPOSITION AND SEPARATION OF JAWS WITH THE INVOLVEMENT OF TEETH ,LIPS CHEEKS AND TOUNGE FORWITH THE INVOLVEMENT OF TEETH ,LIPS CHEEKS AND TOUNGE FOR CHEWING OF FOOD IN ORDER TO PREPARE IT FOR SWALLOWING ANDCHEWING OF FOOD IN ORDER TO PREPARE IT FOR SWALLOWING AND DIGESTION.DIGESTION. MAIN PURPOSE OF MASTICATION IS TOMAIN PURPOSE OF MASTICATION IS TO REDUCE THE SIZE OF FOOD PARTICLES TO A SIZE THAT IS CONVINIENTREDUCE THE SIZE OF FOOD PARTICLES TO A SIZE THAT IS CONVINIENT FOR SWALLOWING{BOLUS FORMATION} WITH THE HELP OF SALIVA.FOR SWALLOWING{BOLUS FORMATION} WITH THE HELP OF SALIVA. www.indiandentalacademy.comwww.indiandentalacademy.com
  • 4. LATERAL VIEW OF A FOUR WEEK EMBRYO SHOWING MUSCLES DERIVED FROM BRANCHIAL ARCHES www.indiandentalacademy.comwww.indiandentalacademy.com
  • 5. EIGHT WEEK EMBRYO SHOWING DEVELOPMENT OF FACIAL MUSCLES AND TRUNCK MUSCULATUREwww.indiandentalacademy.comwww.indiandentalacademy.com
  • 6. SKETCH OF 20 WEEK FETUS SHOWING MUSCLES DERIVED FROM BRANCHIAL ARCHES www.indiandentalacademy.comwww.indiandentalacademy.com
  • 8. TYPES OF MUSCLESTYPES OF MUSCLES  Muscle cells are mainly of three typesMuscle cells are mainly of three types 1.1. STRIATED MUSCLESTRIATED MUSCLE a. SKELETAL OR VOLUNTARYa. SKELETAL OR VOLUNTARY b. CARDIC MUSCLEb. CARDIC MUSCLE 2.2. NON-STRIATED,SMOOTH ORNON-STRIATED,SMOOTH OR INVOLUNTARYINVOLUNTARY www.indiandentalacademy.comwww.indiandentalacademy.com
  • 9. Longitudinal section of human Skeletal muscle showing Characterstic banding pattern. Transverse section of skeletal muscle Fiber containing myofibrils and muscle Cell nuclei,endomysial sheath lie between The muscle fiber www.indiandentalacademy.comwww.indiandentalacademy.com
  • 10. LONGITUDINAL SECTION OF CARDIAC MUSCLEI TRANSVERSE SECTION OF CARDIAC MUSCLE www.indiandentalacademy.comwww.indiandentalacademy.com
  • 12. Longitudinal section of non striated or smooth muscle www.indiandentalacademy.comwww.indiandentalacademy.com
  • 14. SKELETAL MUSCLESKELETAL MUSCLE  Units of skeletal muscle are theUnits of skeletal muscle are the muscle fibersmuscle fibers,each of which,each of which act as a single cell having hundreds of nuclie(syncytial striatedact as a single cell having hundreds of nuclie(syncytial striated myocytes).myocytes).  Fibers are arranged in bundles of various sizes and patternFibers are arranged in bundles of various sizes and pattern calledcalled fasciculifasciculi..  Connective tissue fills the spaces between muscle fibres withinConnective tissue fills the spaces between muscle fibres within a fasciculus where it is known as thea fasciculus where it is known as the endomysciumendomyscium..  Each fasciculus is also surrounded by a strong connectiveEach fasciculus is also surrounded by a strong connective tissue sheath ortissue sheath or perimysciunperimysciun..  Surrounding the whole muscle liesSurrounding the whole muscle lies epimyscium.epimyscium.  Cell membrane of muscle fibre is known asCell membrane of muscle fibre is known as sarcolemmasarcolemma whilewhile their cytoplasm is calledtheir cytoplasm is called sarcoplasmsarcoplasm..  Sarcoplasm is divided into longitudinal threads orSarcoplasm is divided into longitudinal threads or myofibrilsmyofibrils each of 1micro meter in diam.each of 1micro meter in diam.  Each muscle fiber consists of several hundred to severalEach muscle fiber consists of several hundred to several thousandthousand myofibrilsmyofibrils www.indiandentalacademy.comwww.indiandentalacademy.com
  • 19. THE ULTRASTRUCTURE OF SKELETALTHE ULTRASTRUCTURE OF SKELETAL MUSCLEMUSCLE Electron microscope show myofiril to be composed of myofilaments these are divided Transversely by z band into serially repeating reagions termed sarcomeres about 2.5 Micro-meter long in resting state. www.indiandentalacademy.comwww.indiandentalacademy.com
  • 20. ACTIN AND MYOSIN FILAMENTACTIN AND MYOSIN FILAMENT www.indiandentalacademy.comwww.indiandentalacademy.com
  • 21. GENERAL MECHANISM OF MUSCLEGENERAL MECHANISM OF MUSCLE CONTRACTIONCONTRACTION SLIDING FILAMENT MECHANISM.SLIDING FILAMENT MECHANISM.  Caused by interaction of cross bridges from myosin filamentCaused by interaction of cross bridges from myosin filament with the actin filament.with the actin filament.  Action potential causes sarcoplasmic reticulum to causesAction potential causes sarcoplasmic reticulum to causes release of calcium ion.release of calcium ion.  Calcium ion combines with troponin c of troponinCalcium ion combines with troponin c of troponin tropomyosin complex causing a confirmational change. Andtropomyosin complex causing a confirmational change. And it moves deeper between two actin strands.it moves deeper between two actin strands.  This uncovers the active sites of actin allowing these toThis uncovers the active sites of actin allowing these to attract the myosin head and cause contraction to proceed.attract the myosin head and cause contraction to proceed. www.indiandentalacademy.comwww.indiandentalacademy.com
  • 23. Interaction Between The ‘Activated’ ActinInteraction Between The ‘Activated’ Actin Filament And the Myosin Bridges-The ‘WalkFilament And the Myosin Bridges-The ‘Walk Along Theory’ of contractionAlong Theory’ of contraction  When myosin head attaches to a active site ,it causes head toWhen myosin head attaches to a active site ,it causes head to tilt towards the arm and drag the actin filament along with it,tilt towards the arm and drag the actin filament along with it,  This tilt of the head is calledThis tilt of the head is called Power strokePower stroke..  After tilting head automatically breaks away from the activeAfter tilting head automatically breaks away from the active sitesite  Next it returns to perpendicular position and combines withNext it returns to perpendicular position and combines with new active site farther down along the actin filament.new active site farther down along the actin filament.  Thus the heads of myosin filament bend back back and forthThus the heads of myosin filament bend back back and forth and walk along the actin filament.and walk along the actin filament. www.indiandentalacademy.comwww.indiandentalacademy.com
  • 25. MUSCLE FUNCTIONMUSCLE FUNCTION The motor unit can carry only one action i.e. contraction or shortening,The motor unit can carry only one action i.e. contraction or shortening, the entire muscle, however has three potential function.the entire muscle, however has three potential function.  A)A) ISOTONIC CONTRACTIONISOTONIC CONTRACTION When the muscle shorten and moves a load, the contraction isWhen the muscle shorten and moves a load, the contraction is isotonic. Hence the load remains constant and equal to the muscleisotonic. Hence the load remains constant and equal to the muscle tension throughout the most of the period of contraction. It occurs intension throughout the most of the period of contraction. It occurs in the masseter, when the mandible is elevated forcing the teeththe masseter, when the mandible is elevated forcing the teeth through a bolus of food.through a bolus of food.  B)B) ISOMETRIC CONTRACTIONISOMETRIC CONTRACTION When a muscle does not shorter and length remains same (iso-When a muscle does not shorter and length remains same (iso- same, metry- length), but develops tension, the contraction issame, metry- length), but develops tension, the contraction is isometric. Such type of contraction occurs when muscle attempts toisometric. Such type of contraction occurs when muscle attempts to move a load that is greater than the tension developed in muscles,move a load that is greater than the tension developed in muscles, this occurs in masseter when an object is held between the teeth.this occurs in masseter when an object is held between the teeth. eg. Pipe or pencil.eg. Pipe or pencil.  C)C) CONTRACTION RELAXATIONCONTRACTION RELAXATION When stimulation of the motor unit is discontinued the fibres ofWhen stimulation of the motor unit is discontinued the fibres of motor unit relax and return to their normal length. This is seen inmotor unit relax and return to their normal length. This is seen in masseter when the mouth opens to accept new bolus of food duringmasseter when the mouth opens to accept new bolus of food during mastication.mastication. www.indiandentalacademy.comwww.indiandentalacademy.com
  • 27. Muscle hypertrophy atrophy andMuscle hypertrophy atrophy and hyperplasiahyperplasia  HYPERTROPHYHYPERTROPHY: when total: when total mass of musclemass of muscle enlarges.,oncrease in actin and myosin filament inenlarges.,oncrease in actin and myosin filament in response to maximal force causing enlargement ofresponse to maximal force causing enlargement of muscle fiber.muscle fiber.  HYPERPLASIA:HYPERPLASIA: Under rare condition of extremeUnder rare condition of extreme muscle force generation actual no of muscle fibermuscle force generation actual no of muscle fiber have been observed to increase.have been observed to increase.  ATROPHY:ATROPHY: When total mass of muscle decreases.When total mass of muscle decreases. www.indiandentalacademy.comwww.indiandentalacademy.com
  • 28. MUSCLES OF MASTICATIONMUSCLES OF MASTICATION Mastication forcesMastication forces The aev maximumThe aev maximum sustainable biting force is 756N{170 pounds}.sustainable biting force is 756N{170 pounds}. Molar region:Molar region: Biting force range 400-890NBiting force range 400-890N Premolar region:Premolar region: Biting force range 222-445NBiting force range 222-445N Cuspid regionCuspid region:: Biting force range 133-334NBiting force range 133-334N Incisor regionIncisor region:Biting force range 89-111N:Biting force range 89-111N {20-55 pounds}{20-55 pounds} www.indiandentalacademy.comwww.indiandentalacademy.com
  • 29. PRIMARY MUSCLES OFPRIMARY MUSCLES OF MASTICATIONMASTICATION  MASSETERMASSETER  TEMPORALISTEMPORALIS  MEDIAL AND LATERAL PTERYGOIDMEDIAL AND LATERAL PTERYGOID SECONDARY MUSCLES OF MASTICATIONSECONDARY MUSCLES OF MASTICATION The suprahyoid group of muscles being used asThe suprahyoid group of muscles being used as secondary or supplementary muscles they aresecondary or supplementary muscles they are  DigastricDigastric  MylohyoidMylohyoid  GeniohyoidGeniohyoid www.indiandentalacademy.comwww.indiandentalacademy.com
  • 30. THE MASSETERTHE MASSETER QQuadrilateral and and consist of three layers.uadrilateral and and consist of three layers. ATTACHEMENTSATTACHEMENTS Superficial LayerSuperficial Layer :: Arises by thick aponeurosis.Arises by thick aponeurosis. From zygomatic process of maxilla and anterior 2/3From zygomatic process of maxilla and anterior 2/3 of lower border of zygomatic arch,pass downwardof lower border of zygomatic arch,pass downward and back wards at an angle of 45degree and insertedand back wards at an angle of 45degree and inserted into lower part of lateral surface of ramus ofinto lower part of lateral surface of ramus of mandiblemandible www.indiandentalacademy.comwww.indiandentalacademy.com
  • 31.  MIDDLE LAYERMIDDLE LAYER: Arises from: Arises from anterior 2/3 of the deep surfaceanterior 2/3 of the deep surface and posterior 1/3 of the lowerand posterior 1/3 of the lower border of the zygomaticborder of the zygomatic arch,pass vertically downwardsarch,pass vertically downwards and and inserted into middle partand and inserted into middle part of ramus.of ramus.  DEEP LAYER:DEEP LAYER: Arises from deepArises from deep surface of the zygomatic arch,surface of the zygomatic arch, pass vertically downwards andpass vertically downwards and inserted into the upper part of theinserted into the upper part of the ramus and into the coronoidramus and into the coronoid process.process. www.indiandentalacademy.comwww.indiandentalacademy.com
  • 35. RELATIONS OF MASSETERRELATIONS OF MASSETER SUPERFICIASUPERFICIA  IntegumentIntegument  PlatysmaPlatysma  RisoriusRisorius  Zygomaticus majorZygomaticus major  Parotid glandParotid gland  Parotid ductParotid duct  Branches of facialBranches of facial nervenerve www.indiandentalacademy.comwww.indiandentalacademy.com
  • 36. DEEP SURFACEDEEP SURFACE Overlies the,Overlies the,  Insertion ofInsertion of temporalis and ramustemporalis and ramus of the mandible.of the mandible.  In front buccinatorIn front buccinator and the buccal nerve.and the buccal nerve.  Massetric nerve andMassetric nerve and artery.artery. www.indiandentalacademy.comwww.indiandentalacademy.com
  • 37. ANTERIORANTERIOR MarginMargin projects over theprojects over the buccinator and is crossedbuccinator and is crossed below by the facial vein.below by the facial vein. POSTERIORPOSTERIOR MarginMargin is overlapped by theis overlapped by the parotid gland.parotid gland. www.indiandentalacademy.comwww.indiandentalacademy.com
  • 38. Nerve supplyNerve supply ::  MASSETRICMASSETRIC NERVE, a branch ofNERVE, a branch of anterior division ofanterior division of mandibular nerve (whichmandibular nerve (which is the 3rd part of V cranialis the 3rd part of V cranial nerve- trigeminal nerve).nerve- trigeminal nerve). Blood supplyBlood supply::  Maxillary artery,Maxillary artery, which is a branch ofwhich is a branch of external carotid artery.external carotid artery. www.indiandentalacademy.comwww.indiandentalacademy.com
  • 39. ACTIONS OF MASSETERACTIONS OF MASSETER Actions:Actions: Elevates the mandible to close the mouthElevates the mandible to close the mouth and to occlude the teeth in mastication.and to occlude the teeth in mastication. Its activity in the resting position isIts activity in the resting position is minimal.minimal.  It has a small effect in side-to-sideIt has a small effect in side-to-side movement, protraction and retraction.movement, protraction and retraction. www.indiandentalacademy.comwww.indiandentalacademy.com
  • 41. THE TEMPORALISTHE TEMPORALIS TEMPORAL FASCIAETEMPORAL FASCIAE  Thick aponeurotic sheet that roofs over the temporalThick aponeurotic sheet that roofs over the temporal fossa and covers the temporalis muscle.fossa and covers the temporalis muscle. ATTACHEMENTSATTACHEMENTS  Fan shapedFan shaped  Arises from whole of temporal fossa.(except the partArises from whole of temporal fossa.(except the part formed by zygomatic bone) and deep surface offormed by zygomatic bone) and deep surface of temporal fasciatemporal fascia  Fibers converge and descend into a tendon .Fibers converge and descend into a tendon .  It passes through the gap between the zygomatic archIt passes through the gap between the zygomatic arch and the side of the skulland the side of the skull  Attached to medial surface,apex,anterior and posteriorAttached to medial surface,apex,anterior and posterior border of coronoid process and anterior border of theborder of coronoid process and anterior border of the ramus of the mandible as far as last molar.ramus of the mandible as far as last molar. www.indiandentalacademy.comwww.indiandentalacademy.com
  • 44. RELATIONS OF TEMPORALISRELATIONS OF TEMPORALIS SUPERFICIALSUPERFICIAL  SkinSkin  Auricularis anteriorAuricularis anterior  Temporal fasciaTemporal fascia  Superficial temporal vesselsSuperficial temporal vessels  Auriculotemporal nerveAuriculotemporal nerve  Temporal branch of facial nerveTemporal branch of facial nerve  Galea aponeuroticaGalea aponeurotica  Zygomatic archZygomatic arch  massetermasseter www.indiandentalacademy.comwww.indiandentalacademy.com
  • 45. DEEP SURFACEDEEP SURFACE  Temporal fossaTemporal fossa  Lateral pterygoidLateral pterygoid  Superficial head of medialSuperficial head of medial pterygoidpterygoid  Small part of buccinatorSmall part of buccinator  Maxillary arteryMaxillary artery  Deep temporal nervesDeep temporal nerves  Buccal vessels and nerveBuccal vessels and nerve ANTERIOR border is seperatedANTERIOR border is seperated from the zygomatic bone by afrom the zygomatic bone by a mass of fat.mass of fat. www.indiandentalacademy.comwww.indiandentalacademy.com
  • 46. BLOOD SUPPLYBLOOD SUPPLY  Deep temporal part ofDeep temporal part of maxillary arterymaxillary artery NERVE SUPPLYNERVE SUPPLY  Temporalis isTemporalis is supplied by the deepsupplied by the deep temporal branches oftemporal branches of the anterior trunk ofthe anterior trunk of mandibular nerve.mandibular nerve. www.indiandentalacademy.comwww.indiandentalacademy.com
  • 47. ACTIONS OF TEMPORALISACTIONS OF TEMPORALIS  Elevates the mandible,this movement requiresElevates the mandible,this movement requires both the upward pull of anterior fibers andboth the upward pull of anterior fibers and backward pull of the posterior fibers.backward pull of the posterior fibers.  Posterior fibers draw the mandible backwardsPosterior fibers draw the mandible backwards after it has been protuded.after it has been protuded.  It is also a contrbutor to side to side grindingIt is also a contrbutor to side to side grinding movement.movement. www.indiandentalacademy.comwww.indiandentalacademy.com
  • 48. ELEVATION OF MANDIBLEELEVATION OF MANDIBLE www.indiandentalacademy.comwww.indiandentalacademy.com
  • 49. POSTERIOR FIBER DRAWSPOSTERIOR FIBER DRAWS MANDIBLE BACKWARDSMANDIBLE BACKWARDS www.indiandentalacademy.comwww.indiandentalacademy.com
  • 50. SIDE TO SIDE GRINDINGSIDE TO SIDE GRINDING MOVEMENTMOVEMENT www.indiandentalacademy.comwww.indiandentalacademy.com
  • 51. LATERAL PTERYGOIDLATERAL PTERYGOID ATTACHMENTSATTACHMENTS It is a short thick muscle with two parts or headIt is a short thick muscle with two parts or head  UPPERUPPER head arise from infratemporal surface andhead arise from infratemporal surface and infratemporal crest of greater wing of sphenoid boneinfratemporal crest of greater wing of sphenoid bone  LOWERLOWER head arise from lateral surface of lateralhead arise from lateral surface of lateral pterygoid plate.pterygoid plate.  Its fibers pass backwards and laterally to be inserted intoIts fibers pass backwards and laterally to be inserted into a depression(pterygoid fovea)on the front of the neck ofa depression(pterygoid fovea)on the front of the neck of the mandible and into the articular capsule and disc ofthe mandible and into the articular capsule and disc of the temporomandibular articulation.the temporomandibular articulation. www.indiandentalacademy.comwww.indiandentalacademy.com
  • 55. RELATIONS OF LATERALRELATIONS OF LATERAL PTERYGOIDPTERYGOID SUPERFICIALSUPERFICIAL  Ramus of the mandibleRamus of the mandible  Maxillary arteryMaxillary artery  Tendon of temporalis and the masseter,Tendon of temporalis and the masseter, DEEP SURFACEDEEP SURFACE  Upper part of the madial pterygoidUpper part of the madial pterygoid  Sphenomandibular ligamentSphenomandibular ligament  Middle meningeal arteryMiddle meningeal artery  Mandibular nerveMandibular nerve UPPER BORDERUPPER BORDER  Upper border is in relation with temporal and messetricUpper border is in relation with temporal and messetric branches of the mandibular nervebranches of the mandibular nerve LOWER BORDERLOWER BORDER  In relation with lingual and inferior alveolar nerveIn relation with lingual and inferior alveolar nerve www.indiandentalacademy.comwww.indiandentalacademy.com
  • 56. NERVE SUPPLYNERVE SUPPLY  The lateralThe lateral pterygoid is suppliedpterygoid is supplied by a branch ofby a branch of anterior division of theanterior division of the mandibular nervmandibular nerv www.indiandentalacademy.comwww.indiandentalacademy.com
  • 57. BLOOD SUPPLYBLOOD SUPPLY PterygoidPterygoid branch of 2ndbranch of 2nd part of maxillarypart of maxillary arteryartery www.indiandentalacademy.comwww.indiandentalacademy.com
  • 58. ACTIONS OF LATERALACTIONS OF LATERAL PTERYGOIDPTERYGOID  Assists in opening the mouth with suprahyoidAssists in opening the mouth with suprahyoid muscle.muscle.  Slow elongation while closing the mouth withSlow elongation while closing the mouth with masseter and temporalismasseter and temporalis  Acting with medial pterygoid of same sideActing with medial pterygoid of same side advances the condyle ,while the jaw rotatesadvances the condyle ,while the jaw rotates through the opposite condyle(when the medialthrough the opposite condyle(when the medial and lateral pterygoid of the two sides contractand lateral pterygoid of the two sides contract alternatively to produce side to side movementsalternatively to produce side to side movements of mandible eg chewing).of mandible eg chewing). www.indiandentalacademy.comwww.indiandentalacademy.com
  • 59.  When the medial and lateral pterygoids of twoWhen the medial and lateral pterygoids of two sides act together they protrude the mandible sosides act together they protrude the mandible so that the lower incisors project in front of thethat the lower incisors project in front of the other.other.  Some authorities have ascribed different actionsSome authorities have ascribed different actions to the two parts of pterygoid muscle.to the two parts of pterygoid muscle.  The upper (superior)head being involved inThe upper (superior)head being involved in chewingchewing  The inferior in protrusion,electromyographicThe inferior in protrusion,electromyographic records in rhesus monkey favors this view.records in rhesus monkey favors this view. www.indiandentalacademy.comwww.indiandentalacademy.com
  • 60. The combinded efforts of the Digastrics and LateralThe combinded efforts of the Digastrics and Lateral Pterygoids provide for natural jaw opening.Pterygoids provide for natural jaw opening. www.indiandentalacademy.comwww.indiandentalacademy.com
  • 61. SIDE TO SIDE GRINDINGSIDE TO SIDE GRINDING MOVEMENTMOVEMENT www.indiandentalacademy.comwww.indiandentalacademy.com
  • 62. Medial and lateral pterygoid actMedial and lateral pterygoid act together to protrude the mandibletogether to protrude the mandible www.indiandentalacademy.comwww.indiandentalacademy.com
  • 63. MEDIAL PTERYGOIDMEDIAL PTERYGOID ATTACHEMENTSATTACHEMENTS  It is a thick quadrilateral muscleIt is a thick quadrilateral muscle  Attached to medial surface of lateral pterygoid plate andAttached to medial surface of lateral pterygoid plate and grooved surface of pyramidal process of the palatinegrooved surface of pyramidal process of the palatine bone.bone.  A more superficial slip from the lateral surface ofA more superficial slip from the lateral surface of pyramidal process of the palatine bone and tuberosity ofpyramidal process of the palatine bone and tuberosity of maxillamaxilla  Its fibers pass downwards laterally and backwardsIts fibers pass downwards laterally and backwards  Attached by a strong tendinous lamina ,to the postero-Attached by a strong tendinous lamina ,to the postero- inferior part of the medial surfaces of the ramus and theinferior part of the medial surfaces of the ramus and the angle of the mandibleangle of the mandible  It is attached as high as mandibular foramen and as farIt is attached as high as mandibular foramen and as far forward as the mylohyoid grooveforward as the mylohyoid groovewww.indiandentalacademy.comwww.indiandentalacademy.com
  • 66. RELATIONS OF MEDIALRELATIONS OF MEDIAL PTERYGOIDPTERYGOID SUPERFICIALSUPERFICIAL  Upper part of muscle is separated from theUpper part of muscle is separated from the lateral pterygoid muscle bylateral pterygoid muscle by a) lateral pterygoid platea) lateral pterygoid plate b) lingual nerveb) lingual nerve c) inferior alveolar nervec) inferior alveolar nerve  Inferiorly the muscle is separated from ramus ofInferiorly the muscle is separated from ramus of mandible by same nerves,the maxillary arterymandible by same nerves,the maxillary artery and sphenomandibular ligament.and sphenomandibular ligament. www.indiandentalacademy.comwww.indiandentalacademy.com
  • 67. NERVE SUPPLYNERVE SUPPLY  Branch of theBranch of the main trunk of themain trunk of the mandibular nerve.mandibular nerve. BLOOD SUPPLYBLOOD SUPPLY  Pterygoid branchPterygoid branch of 2nd part ofof 2nd part of maxillary arterymaxillary artery www.indiandentalacademy.comwww.indiandentalacademy.com
  • 68. Actions of medial pterygoidActions of medial pterygoid  Assits in elevating the mandibleAssits in elevating the mandible  Acting with the lateral pterygoid they protrude itActing with the lateral pterygoid they protrude it •Acting with medial pterygoid of sameActing with medial pterygoid of same side advances the condyle ,while the jawside advances the condyle ,while the jaw rotates through the oppositerotates through the opposite condyle(when the medial and lateralcondyle(when the medial and lateral pterygoid of the two sides contractpterygoid of the two sides contract alternatively to produce side to sidealternatively to produce side to side movements of mandible eg chewing)movements of mandible eg chewing) www.indiandentalacademy.comwww.indiandentalacademy.com
  • 69. Secondary muscles taking part inSecondary muscles taking part in the masticationthe mastication The 4 primary muscles of mastication are inThe 4 primary muscles of mastication are in turn supported or supplemented by fewturn supported or supplemented by few secondary muscles known assecondary muscles known as SUPRAHYOID GROUP of muscles theySUPRAHYOID GROUP of muscles they areare DIGASTRICDIGASTRIC MYLOHYOIDMYLOHYOID GENIOHYOIDGENIOHYOID STYLOHYOID is other suprahyoid muscle,STYLOHYOID is other suprahyoid muscle, which does not take part in masticationwhich does not take part in masticationwww.indiandentalacademy.comwww.indiandentalacademy.com
  • 70. DIGASTRICDIGASTRIC •The muscle has secondary role in mastication as a depressor muscle adding to the action of lateral pterygoid muscle when mouth is to be opened agains resistance. Elevation of hyoid bone MYLOHYOID •The secondary role of this muscle is evidnent as a depressor seen in action when mouth is to be opened against resistance. •It elevates the floor of mouth to help in deglutition. www.indiandentalacademy.comwww.indiandentalacademy.com
  • 71. GENIOHYOIDGENIOHYOID •Geniohyoid elevates the hyoid bone and draws it forward, thus acting as a partial antagonist to stylohyoid. •When the hyoid bone is fixed, it depresses the mandible www.indiandentalacademy.comwww.indiandentalacademy.com
  • 72. PATHOLOGICAL CONDITIONSPATHOLOGICAL CONDITIONS AFFECTING MUSCLESAFFECTING MUSCLES CLASSIFICATION OF DISEASES OFCLASSIFICATION OF DISEASES OF MUSCLEMUSCLE II PRIMARY MYOPATHIESPRIMARY MYOPATHIES a)Dystrophiesa)Dystrophies b)Myotoniasb)Myotonias c)Hypotoniasc)Hypotonias d)Myastheniasd)Myasthenias e)Myositise)Myositis f)Metabolic defectsf)Metabolic defects g)Miscellaneous(amyloplasias,contractures,degeng)Miscellaneous(amyloplasias,contractures,degenwww.indiandentalacademy.comwww.indiandentalacademy.com
  • 73. II.II.SECONDARY MYOPATHIESSECONDARY MYOPATHIES a)a)AtrophyAtrophy 1)Denervation1)Denervation 2)Disuse and fixation2)Disuse and fixation 3)Ageing and cachexia3)Ageing and cachexia b) Hypertrophyb) Hypertrophy 1) Developmental1) Developmental 2) Functional2) Functional c) Endocrinec) Endocrine d) Internal environmentd) Internal environment 1)Chemical1)Chemical 2)Vascular2)Vascular e)Infectione)Infection 1.Specific(trichinella,toxoplasma,coxsackie virus,1.Specific(trichinella,toxoplasma,coxsackie virus,tetanustetanus)) 2.General(rikettsial,typhoid,pneumococcal pneumonia)2.General(rikettsial,typhoid,pneumococcal pneumonia) 3.Post infection asthenia.3.Post infection asthenia. www.indiandentalacademy.comwww.indiandentalacademy.com
  • 74. DISEASES OF SKELETAL MUSCLEDISEASES OF SKELETAL MUSCLE  Disorders that produce predominantly myofiberDisorders that produce predominantly myofiber atrophy including neurogenic atrophy andatrophy including neurogenic atrophy and myofiber atrophy.myofiber atrophy.  Disorders of the neuromuscularDisorders of the neuromuscular junction(exemplified byjunction(exemplified by myasthenia gravismyasthenia gravis))  Selected primary myopathies includingSelected primary myopathies including inflammatory myopathies and muscularinflammatory myopathies and muscular dystrophies.dystrophies. www.indiandentalacademy.comwww.indiandentalacademy.com
  • 75. MYASTHENIASMYASTHENIAS a)Myasthenia gravisa)Myasthenia gravis b)familial periodic parslysisb)familial periodic parslysis c)aldosteronismc)aldosteronism Latter two are very rare diseases.Latter two are very rare diseases. MYASTHENIA GRAVISMYASTHENIA GRAVIS  Acquired autoimmune disorder of neuromuscularAcquired autoimmune disorder of neuromuscular transmission charecterized by muscle weaknesstransmission charecterized by muscle weakness ETIOLOGYETIOLOGY  Antibodies to acetylcholine receptor on skeletal muscleAntibodies to acetylcholine receptor on skeletal muscle fiberfiber  Assosiation with systemic lupusAssosiation with systemic lupus erythematosis,rheumatoid artheritis,sjogren syndrome.erythematosis,rheumatoid artheritis,sjogren syndrome. www.indiandentalacademy.comwww.indiandentalacademy.com
  • 76. CLINICAL FEATURESCLINICAL FEATURES  May be present at any age, chiefly inMay be present at any age, chiefly in adults,predilection for womenadults,predilection for women  Rapidly developing weakness in voluntaryRapidly developing weakness in voluntary muscles following even minor activitiesmuscles following even minor activities  Of interest toOf interest to PROSTHODONTISTPROSTHODONTIST is the factis the fact that muscles of mastication and facialthat muscles of mastication and facial expression are involved by this diseaseexpression are involved by this disease frequently before any other muscle group.frequently before any other muscle group. Patient chief complaint may bePatient chief complaint may be difficulty in mastication and deglution, anddifficulty in mastication and deglution, and dropping of the jaw . Speech is often slow anddropping of the jaw . Speech is often slow and slurred. Disturbance in taste sensation in someslurred. Disturbance in taste sensation in some patient.patient. www.indiandentalacademy.comwww.indiandentalacademy.com
  • 77.  Diplopia, ptosis,drooping of the face,lend a veryDiplopia, ptosis,drooping of the face,lend a very sorroful appearance to the patient.sorroful appearance to the patient.  Pt rapidly exausted,lose wt,death frequentlyPt rapidly exausted,lose wt,death frequently occurs from respiratory failure.occurs from respiratory failure.  Clinical course variable,some enter acuteClinical course variable,some enter acute exacerbation of their disease and sccumb butexacerbation of their disease and sccumb but others live for many years,on this basis twoothers live for many years,on this basis two forms are recognized.forms are recognized. a)Steadily progressivea)Steadily progressive b)a remitting relapsing typeb)a remitting relapsing type www.indiandentalacademy.comwww.indiandentalacademy.com
  • 78. TREATMENT AND PROGNOSISTREATMENT AND PROGNOSIS  Drug of choice used in treatment provides suchDrug of choice used in treatment provides such remarkable relief of symptoms in very short time.remarkable relief of symptoms in very short time.  Physostigmine administered intramuscularlyPhysostigmine administered intramuscularly improves the strength of the affected muscle in aimproves the strength of the affected muscle in a matter of minutesmatter of minutes  No cure is known even though the prognosis isNo cure is known even though the prognosis is good in the relapsing type.good in the relapsing type. www.indiandentalacademy.comwww.indiandentalacademy.com
  • 79. TETANUS(LOCK JAW)TETANUS(LOCK JAW)  Tetanus is a disease of the nervous systemTetanus is a disease of the nervous system characterized by intense activity of motor neuroncharacterized by intense activity of motor neuron and resulting in severe muscle spasmand resulting in severe muscle spasm  Caused by exotoxins of gram positive bacillusCaused by exotoxins of gram positive bacillus Ciostridium tetani.Ciostridium tetani. CLINICAL FEATURESCLINICAL FEATURES  Pain and stiffness in the jaws and neckPain and stiffness in the jaws and neck muscles ,with muscle rigidity producing trismusmuscles ,with muscle rigidity producing trismus and dysphagiaand dysphagia  Rigity of facial muscles producing the typicalRigity of facial muscles producing the typical risus sardonicusrisus sardonicus  Sometimes whole body becomes affectedSometimes whole body becomes affected characterized by opisthotonoscharacterized by opisthotonos www.indiandentalacademy.comwww.indiandentalacademy.com
  • 80. TREATMENTTREATMENT  All patients should receive antimicrobial drugsAll patients should receive antimicrobial drugs  Active and passive immunization.Active and passive immunization.  Surgical wound careSurgical wound care  Anticonvulsant if indicatedAnticonvulsant if indicated www.indiandentalacademy.comwww.indiandentalacademy.com
  • 81. PROSTHODONTICPROSTHODONTIC CONSIDERATIONSCONSIDERATIONS MASTICATIORY CYCLEMASTICATIORY CYCLE  The pathways of the mandible in chewing isThe pathways of the mandible in chewing is referred to as the chewing cyclereferred to as the chewing cycle  Masticatory cycle consists of three phasesMasticatory cycle consists of three phases 1) Opening phase(mandible is depressed)1) Opening phase(mandible is depressed) 2) Closing phase(mandible is elevated)2) Closing phase(mandible is elevated) 3) Intercuspal phase(ICP)3) Intercuspal phase(ICP)  The chewing cycle can take many forms and theThe chewing cycle can take many forms and the classicclassic tear droptear drop shape when viewed in frontal orshape when viewed in frontal or saggital plane is oversimplification of realitysaggital plane is oversimplification of reality www.indiandentalacademy.comwww.indiandentalacademy.com
  • 82.  In opening phase teethIn opening phase teeth and condyle move downand condyle move down and forwardand forward  Early closing phase manEarly closing phase man moves laterally to themoves laterally to the selected chewing sideselected chewing side  Chewing side condyleChewing side condyle moves to upwardmoves to upward reareward position well inreareward position well in advance of theadvance of the intercuspal phase(SRP)intercuspal phase(SRP)  During rest of closingDuring rest of closing phase to ICP chewingphase to ICP chewing side condyle show aside condyle show a slight forward(.33mm)slight forward(.33mm) and medialand medial movement(Bennett)movement(Bennett) (.2mm)(.2mm)  Non chewing sideNon chewing side condyle lags somewhatcondyle lags somewhat behind.behind. www.indiandentalacademy.comwww.indiandentalacademy.com
  • 84.  There are about 15 chews in a series from theThere are about 15 chews in a series from the time of food entry until swallowingtime of food entry until swallowing  Aev jaw opening during chewing is between 16-Aev jaw opening during chewing is between 16- 20mm20mm  Aev lateral displacement on chewing is betweenAev lateral displacement on chewing is between 3 and 5mm3 and 5mm  Duration of masticatory cycle varies between .Duration of masticatory cycle varies between . 6and 1 sec6and 1 sec  Men chew faster and have a shorter occlusalMen chew faster and have a shorter occlusal phase than women,it also depends on the typephase than women,it also depends on the type of foodof food www.indiandentalacademy.comwww.indiandentalacademy.com
  • 85. FACTORS THAT REGULATE JAW MOTIONSFACTORS THAT REGULATE JAW MOTIONS  NEUROMUSCULAR SYSTEMNEUROMUSCULAR SYSTEM  GUIDING INFLUNCES OF CONTACTINGGUIDING INFLUNCES OF CONTACTING TEETHTEETH  MANDIBULAR MUSCULATURE WHEN TEETHMANDIBULAR MUSCULATURE WHEN TEETH NOT IN CONTACTNOT IN CONTACT  LIMITING OF MOVEMENT BY CONDYLELIMITING OF MOVEMENT BY CONDYLE The condyles and teeth modify mandibularThe condyles and teeth modify mandibular movements initiated by neuromuscular system.movements initiated by neuromuscular system. www.indiandentalacademy.comwww.indiandentalacademy.com
  • 86. INFLUENCE OF OPPOSING TOOTH CONTACTINFLUENCE OF OPPOSING TOOTH CONTACT IN COMPLETE DENTUREIN COMPLETE DENTURE  The occlusal surface should meet evenly onThe occlusal surface should meet evenly on both sidesboth sides  In this manner mandible is not deflected from itsIn this manner mandible is not deflected from its normal path of closure,nor are the denturesnormal path of closure,nor are the dentures displaced from residual ridgesdisplaced from residual ridges  When mandibular movements are made theWhen mandibular movements are made the inclined planes of the teeth should pass overinclined planes of the teeth should pass over one another snoothlyone another snoothly  It should not disturb the influence of condylarIt should not disturb the influence of condylar guidance posteriorly and incisal guidanceguidance posteriorly and incisal guidance anteriorlyanteriorly www.indiandentalacademy.comwww.indiandentalacademy.com
  • 87. NEUROMUSCULAR REGULATION OFNEUROMUSCULAR REGULATION OF MANDIBULAR MOTIONMANDIBULAR MOTION  Mastication is a programmed event residing in aMastication is a programmed event residing in a “chewing center” located within the brain“chewing center” located within the brain stem(reticular formation of the pons)stem(reticular formation of the pons)  The cyclic nature of mastication is the result ofThe cyclic nature of mastication is the result of the action of this central pattern generatorthe action of this central pattern generator  Concious effort may either induce or terminateConcious effort may either induce or terminate chewing ,but it is not required for thechewing ,but it is not required for the continuation of chewingcontinuation of chewing www.indiandentalacademy.comwww.indiandentalacademy.com
  • 88. REST POSITIONREST POSITION  It is established by muscles and gravityIt is established by muscles and gravity  There are two hypothesis abput postural restThere are two hypothesis abput postural rest positionposition 1)Active mechanism,when muscles are in a1)Active mechanism,when muscles are in a state of minimal contraction to maintain thestate of minimal contraction to maintain the postureposture 2)Passive mechanism, elastic elements of2)Passive mechanism, elastic elements of the jaw musculature and not any muscle activitythe jaw musculature and not any muscle activity balanve the influence of gravitybalanve the influence of gravity  Numerous studies have shown EMG activity atNumerous studies have shown EMG activity at restrest  A range of reduced muscle tension upto anA range of reduced muscle tension upto an interocclusal distance of about 10mm has beeninterocclusal distance of about 10mm has been reportedreported www.indiandentalacademy.comwww.indiandentalacademy.com
  • 90. IMPORTANCE OF OCCLUSALIMPORTANCE OF OCCLUSAL HARMONYHARMONY  When closing muscle pull mandible without interferenceWhen closing muscle pull mandible without interference it is stooped by bone at medial poleit is stooped by bone at medial pole  If tooth inclines interfere lateral pterygoid is forced toIf tooth inclines interfere lateral pterygoid is forced to position the mandible to accommodate to the teethposition the mandible to accommodate to the teeth  There are many variations of timing and degree ofThere are many variations of timing and degree of muscle contraction to position the mandible for maximummuscle contraction to position the mandible for maximum intercuspation of the teeth.intercuspation of the teeth.  Pattern of deviation is reinforced every time contact isPattern of deviation is reinforced every time contact is mademade  Imortant facet of propioceptive memory is that it fades ifImortant facet of propioceptive memory is that it fades if reinforcement of pattern ceases.reinforcement of pattern ceases. www.indiandentalacademy.comwww.indiandentalacademy.com
  • 91.  Elimination of interfering contacts permit anElimination of interfering contacts permit an almost immediate return to normal musclealmost immediate return to normal muscle functionfunction  Willamson Showed using EMG procedures thatWillamson Showed using EMG procedures that posterior tooth intrference caused hyperactivityposterior tooth intrference caused hyperactivity of elevator muscleof elevator muscle  But if the anterior guidance was allowed toBut if the anterior guidance was allowed to disclude all posterior teeth from any contactdisclude all posterior teeth from any contact other than CR elevator muscle stopped activeother than CR elevator muscle stopped active contraction or reduced it.contraction or reduced it. www.indiandentalacademy.comwww.indiandentalacademy.com
  • 92. TOOTH INTERFERENCESTOOTH INTERFERENCES  The reason muscle changes jaw position in theThe reason muscle changes jaw position in the presence of interferences is to protect thepresence of interferences is to protect the interfereing tooth or teeth from absorbing entireinterfereing tooth or teeth from absorbing entire occlusal forceocclusal force  Muscles become patterned to the deviousMuscles become patterned to the devious closure ,such memorized patterns of muscleclosure ,such memorized patterns of muscle activity are calledactivity are called ENGRAMSENGRAMS  Because of engrams it is easy to be fooled byBecause of engrams it is easy to be fooled by freely hinging jaw that appears to be in correctfreely hinging jaw that appears to be in correct CR.CR. www.indiandentalacademy.comwww.indiandentalacademy.com
  • 93. OCCLUSAL PLANEOCCLUSAL PLANE  The curvature of the posterior plane of occlusionThe curvature of the posterior plane of occlusion are divided intoare divided into 1)An anteroposterior curve called the1)An anteroposterior curve called the curve of speecurve of spee.. 2)Mediolateral curve referred to as2)Mediolateral curve referred to as thethe curve of wilsoncurve of wilson Curve of SpeeCurve of Spee  Begins at cusp tip pf lower cuspid and follow theBegins at cusp tip pf lower cuspid and follow the buccal cusp tip of bicuspid and molars, curvebuccal cusp tip of bicuspid and molars, curve line forms an arc through the condyle.line forms an arc through the condyle.  It aligns each tooth for maximum resistance toIt aligns each tooth for maximum resistance to functional loadingfunctional loading www.indiandentalacademy.comwww.indiandentalacademy.com
  • 94.  To prevent increaseTo prevent increase muscle loading of themuscle loading of the teeth and the joints duringteeth and the joints during protrusive movement.protrusive movement.  If there is any toothIf there is any tooth contact posterior tocontact posterior to canine during excursioncanine during excursion the elevator muscles arethe elevator muscles are triggered intotriggered into hypercontractionhypercontraction www.indiandentalacademy.comwww.indiandentalacademy.com
  • 95. CURVE OF WILSONCURVE OF WILSON  Mediolateral curve that contacts the buccal andMediolateral curve that contacts the buccal and lingual cusp tips on each side of archlingual cusp tips on each side of arch  Results from inward inclination of posterior teethResults from inward inclination of posterior teeth  In maxillary arch reverse is there because ofIn maxillary arch reverse is there because of outward inclination of posterior teeth.outward inclination of posterior teeth. There are two reasons for this inclination ofThere are two reasons for this inclination of posterior teethposterior teeth 1) one has to do with resistance to1) one has to do with resistance to loadingloading 2)second has to do with masticatory2)second has to do with masticatory functionfunction www.indiandentalacademy.comwww.indiandentalacademy.com
  • 96.  Axial alignment of allAxial alignment of all posterior teeth is nearlyposterior teeth is nearly parallel with the strongparallel with the strong inward pull of the medialinward pull of the medial pterygoid musclepterygoid muscle  Aligning both upper andAligning both upper and lower posterior teeth withlower posterior teeth with the principal direction ofthe principal direction of muscle contractionmuscle contraction produce the greatestproduce the greatest resistance to masticatoryresistance to masticatory forces, and forms curveforces, and forms curve of wilsonof wilson www.indiandentalacademy.comwww.indiandentalacademy.com
  • 97.  There is another reasonThere is another reason for the curve offor the curve of wilson,tounge andwilson,tounge and buccinator must placebuccinator must place food onto occlusalfood onto occlusal table,there must be easytable,there must be easy access for the food to getaccess for the food to get to the occlusal tableto the occlusal table  The inward inclination ofThe inward inclination of the lower occlusal tablethe lower occlusal table for direct access fromfor direct access from linguallingual www.indiandentalacademy.comwww.indiandentalacademy.com
  • 98.  The outward inclination ofThe outward inclination of the upper occlusal tablethe upper occlusal table provides access from theprovides access from the buccal for the foodbuccal for the food  When the curve of wilsonWhen the curve of wilson is made too flat ease ofis made too flat ease of masticatory function maymasticatory function may be impaired because ofbe impaired because of increased activityincreased activity required to get the foodrequired to get the food onto the occlusal tableonto the occlusal table www.indiandentalacademy.comwww.indiandentalacademy.com
  • 99. BRUXISMBRUXISM Bruxism is the clenching or grinding of the teeth when theBruxism is the clenching or grinding of the teeth when the individual is not chewing or swallowingindividual is not chewing or swallowing  It can occur as a brief rhythmic strong contractions of theIt can occur as a brief rhythmic strong contractions of the jaw muscles during eccentric lateral jaw movements,or injaw muscles during eccentric lateral jaw movements,or in maximum intercuspation,which is called clenching.maximum intercuspation,which is called clenching.  CausesCauses 1) Assosiated with stressful events1) Assosiated with stressful events 2)Non stress related or hereditary2)Non stress related or hereditary  Increased masseter muscle tension is directly related toIncreased masseter muscle tension is directly related to stress situation during the day.stress situation during the day. www.indiandentalacademy.comwww.indiandentalacademy.com
  • 100.  Increased stress levelsIncreased stress levels are strongly correlatedare strongly correlated with increased levels ofwith increased levels of masseter muscle activitymasseter muscle activity at nightat night www.indiandentalacademy.comwww.indiandentalacademy.com
  • 101.  Bruxism can not be casually described asBruxism can not be casually described as "hyperactivity of the lateral pterygoid". "hyperactivity of the lateral pterygoid".                                                               . The definitive component of bruxism is the degree. The definitive component of bruxism is the degree of parafunctional elevation, that is, the clenchingof parafunctional elevation, that is, the clenching component.  An accurated definition of bruxism is: component.  An accurated definition of bruxism is:  Jaw clenching, with or without forcibleJaw clenching, with or without forcible excursive movements, where the intensityexcursive movements, where the intensity of the clenching dictates the severity (orof the clenching dictates the severity (or lack of) grindinglack of) grinding .. www.indiandentalacademy.comwww.indiandentalacademy.com
  • 102. Each of the graphics below displays identical degreess ofEach of the graphics below displays identical degreess of LP "hyperactivityLP "hyperactivity:: •Only the graphic toOnly the graphic to the far left can bethe far left can be considered NOTconsidered NOT be bruxism,be bruxism, although there ISalthough there IS hyperactivity of thehyperactivity of the LPsLPs graphic at thegraphic at the far right is thefar right is the most extrememost extreme form ofform of bruxism).bruxism). www.indiandentalacademy.comwww.indiandentalacademy.com
  • 103.  Bruxism may lead toBruxism may lead to -tooth wear-tooth wear -fracture of the teeth or restoratrion-fracture of the teeth or restoratrion -uncosmetic muscle hypertrophy-uncosmetic muscle hypertrophy  TreatmentTreatment -coronoplasty-coronoplasty -maxillary stabalization appliance-maxillary stabalization appliance www.indiandentalacademy.comwww.indiandentalacademy.com
  • 104. Normal function versusNormal function versus parafunctionparafunction The image to the left is demonstrating normal reciprocal functioning of the Lateral Pterygoids and Masseters/Med.Pteygoids/Temporalis'. The Lateral Pterygoids advance the condyles, thereby opening the mouth (depressing the mandible), with the assistance of the Digastric The oblique orientation of the Masseters and Medial Pterygoids create a sling. The non-working side Medial Pterygoid contacts simultaneously with the opposide side working Masseter. It is this oblique orientation of the Med.Pterygoids and Masseters that create the functional "shift" of the mandible, not an unilateral contraction of a Lateral Pterygoid .www.indiandentalacademy.comwww.indiandentalacademy.com
  • 105.  In the event theIn the event the Temporalis' do not ceaseTemporalis' do not cease their active contractions,their active contractions, scenarios of varyingscenarios of varying degrees of parafunctiondegrees of parafunction result, as the Lateralresult, as the Lateral Pterygoids encounterPterygoids encounter resistance to theirresistance to their attempts at condylarattempts at condylar advancement, therebyadvancement, thereby increasing their intensityincreasing their intensity of contraction and strainof contraction and strain on their origins andon their origins and insertions: the pterygoidinsertions: the pterygoid plates of the sphenoidplates of the sphenoid bone, and the condylarbone, and the condylar neck and disc. neck and disc.  www.indiandentalacademy.comwww.indiandentalacademy.com
  • 106.  The degree of frequency,The degree of frequency, duration and intensity ofduration and intensity of the contractions of athe contractions of a Lateral Pterygoid is aLateral Pterygoid is a function of the resistancefunction of the resistance provided by theprovided by the parafunction ipsilateralparafunction ipsilateral and/or contralateraland/or contralateral Temporalis.  ForTemporalis.  For example, in the animationexample, in the animation to the left, as a Lateralto the left, as a Lateral Pterygoid attempts toPterygoid attempts to translate its condyle, it istranslate its condyle, it is met with resistancemet with resistance provided by theprovided by the contralateral Temporalis,contralateral Temporalis, thereby causing thethereby causing the Lateral Pterygoid to pullLateral Pterygoid to pull its condyle in a medialits condyle in a medial direction toward thedirection toward the contralateral contact.contralateral contact.www.indiandentalacademy.comwww.indiandentalacademy.com
  • 107. The maximum clenching intensity occurs inThe maximum clenching intensity occurs in the musculoskeletally stable positionthe musculoskeletally stable position  The mandibular positionThe mandibular position of the temporalis' mostof the temporalis' most intense contraction is notintense contraction is not when the teeth arewhen the teeth are together, but when theytogether, but when they are a particular distanceare a particular distance apart, and separated byapart, and separated by an object (such as aan object (such as a splint, or food).splint, or food). www.indiandentalacademy.comwww.indiandentalacademy.com
  • 108. CANINE RISE SERVE S TO DIFFUSECANINE RISE SERVE S TO DIFFUSE PARAFUNCTIONPARAFUNCTION  temporalis persists in thetemporalis persists in the elevation of the mandible,elevation of the mandible, the canine teeththe canine teeth contralateral to thecontralateral to the translating condyle aretranslating condyle are often exploited to endureoften exploited to endure the load, thereby allowingthe load, thereby allowing the force to be directed inthe force to be directed in an anterior (and slightlyan anterior (and slightly medial) direction, bracedmedial) direction, braced by the slope of theby the slope of the eminence.  This is calledeminence.  This is called "canine guidance","canine guidance", allowing the posteriorallowing the posterior teeth to separate. teeth to separate.  www.indiandentalacademy.comwww.indiandentalacademy.com
  • 109.  Although the lateralAlthough the lateral engagement of theengagement of the canines can help tocanines can help to diffuse the effects ofdiffuse the effects of parafunction, an end-to-parafunction, an end-to- end canine contact canend canine contact can serve to perpetuate theserve to perpetuate the effects of parafunction. effects of parafunction.  The animationThe animation demonstrates andemonstrates an excursive movement thatexcursive movement that allows for canine-to-allows for canine-to- canine clenching.  Caninecanine clenching.  Canine teeth can alow for nearteeth can alow for near maximal voluntarymaximal voluntary temporalis clenchingtemporalis clenching intensityintensity www.indiandentalacademy.comwww.indiandentalacademy.com
  • 110. Parafunctional chewing cycle: "Outside-inParafunctional chewing cycle: "Outside-in""  Normal opening isNormal opening is straight, unless astraight, unless a chronically-chronically- tensed/fatigued LPtensed/fatigued LP advances its condyleadvances its condyle "faster" that the"faster" that the contralateral LP.contralateral LP.  Excursive parafunctionExcursive parafunction does notdoes not engage theengage the canine during closing (ie,canine during closing (ie, from the outside-in).from the outside-in).  The above example does The above example does not really happen. not really happen.  Interferences areInterferences are enganged by the LP uponenganged by the LP upon opening (at rightopening (at right www.indiandentalacademy.comwww.indiandentalacademy.com
  • 111. Parafunctional chewing cycle: "Inside-out"Parafunctional chewing cycle: "Inside-out"  Deviation upon opening isDeviation upon opening is abnormal and is usuallyabnormal and is usually thethe result of excursiveresult of excursive parafunctional openingparafunctional opening against resistance. against resistance.  Ideally, this activity wouldIdeally, this activity would engage a canine, engage a canine,  but can still fatigue abut can still fatigue a lateral pterygoidlateral pterygoid depending upon thedepending upon the intensity of resistanceintensity of resistance provided by the occludingprovided by the occluding canines.  Occasionally,canines.  Occasionally, canine tip-to-tip clenchingcanine tip-to-tip clenching perpetuates the clinicalperpetuates the clinical presentation of unilateralpresentation of unilateral headache andheadache and contralateral joint strain.contralateral joint strain.www.indiandentalacademy.comwww.indiandentalacademy.com
  • 112. REFERENCESREFERENCES  Kieth L. Moore, The developing human ,fourth editionKieth L. Moore, The developing human ,fourth edition 19921992  Peter.L.Williams,Roger Worwik Grays Anatomy ,thirty sixPeter.L.Williams,Roger Worwik Grays Anatomy ,thirty six edition 1980edition 1980  B.D.Chaurasias, Human anatomy,third edition 2000B.D.Chaurasias, Human anatomy,third edition 2000  Keith L.Moore,Clinically Oriented Anatomy fourth editionKeith L.Moore,Clinically Oriented Anatomy fourth edition 19921992  Anne M.R Agur,Grants atlas of anatomy 10 edition 1991Anne M.R Agur,Grants atlas of anatomy 10 edition 1991  R.M.H Mc Minn,.R.T.Hutchings ,third edition1994R.M.H Mc Minn,.R.T.Hutchings ,third edition1994  Arthur C Guyton,John E Hall,Textbook of MedicalArthur C Guyton,John E Hall,Textbook of Medical Physiology 10 edition 2000Physiology 10 edition 2000  William f ganong,Review of Medical Physiology,eighteenWilliam f ganong,Review of Medical Physiology,eighteen edition 1997edition 1997 www.indiandentalacademy.comwww.indiandentalacademy.com
  • 113.  Kumar ,Cotran,Basic Pathology,fourth editionKumar ,Cotran,Basic Pathology,fourth edition 19711971  Shafer,Hine,Textbook of oral pathology,fourthShafer,Hine,Textbook of oral pathology,fourth edition 1997edition 1997  Sheldon Winkler,Essentials of complete dentureSheldon Winkler,Essentials of complete denture prosthodontics,second, edition 2000prosthodontics,second, edition 2000  George A.Zarb,Charles LGeorge A.Zarb,Charles L Bolender,Prosthodontic Treatment forBolender,Prosthodontic Treatment for Edentulous Patients, twelth edition 2004Edentulous Patients, twelth edition 2004  Peter E Dawson,Evaluatio Diagnosis andPeter E Dawson,Evaluatio Diagnosis and Treatment of Occlusal Problems ,secondTreatment of Occlusal Problems ,second edition1989edition1989  Fermin A Carranza,Micheal G Newman,ClinicalFermin A Carranza,Micheal G Newman,Clinical Periodontology eight edition1996Periodontology eight edition1996 www.indiandentalacademy.comwww.indiandentalacademy.com