Muscles of mastication /orthodontic continuing education

MUSCLES OF
MASTICATIONINDIAN DENTAL ACADEMY
Leader in continuing dental education
www.indiandentalacademy.com

CONTENTS
 INTRODUCTION
 DEVELOPMENT OF MUSCLES OF MASTICATION
 TYPES OF MUSCLES
 ANATOMY OF MUSCLES
 GENERAL MECHANISM OF MUSCLE CONTRACTION
 MUSCLES OF MASTICATION
 PATHOLOGICAL CONDITIONS AFFECTING MUSCLES
 PROSTHODONTIC CONSIDERATIONS
 CONCLUSION
 REFERENCES

“MOTION IS THE CAUSE OF
ALL LIFE”
LEONARDO DA VINCI
INTRODUCTION

 Muscle: TISSUE CHARACTERIZED BY AGGREGATION OF CELLS
WHOSE PRIMARY ROLE IS TO PRODUCE CONTRACTION,AND ALLOWING
MOVEMENTS OF PARTS AND ORGANS OF THE BODY.
IT MAY ALSO BE DEFINED AS A BAND
OF CONTRACTILE FIBROUS TISSUE,WHICH PRODUCE MOVEMENTS IN AN
ANIMAL BODY.
 Mastication : RHYTHMIC OPPOSITION AND SEPARATION OF JAWS
WITH THE INVOLVEMENT OF TEETH ,LIPS CHEEKS AND TOUNGE FOR
CHEWING OF FOOD IN ORDER TO PREPARE IT FOR SWALLOWING AND
DIGESTION.
MAIN PURPOSE OF MASTICATION IS TO
REDUCE THE SIZE OF FOOD PARTICLES TO A SIZE THAT IS CONVINIENT
FOR SWALLOWING{BOLUS FORMATION} WITH THE HELP OF SALIVA.

DEVEOPMENT OF MUSCLES OF
MASTICATION
 The muscular system develops from intra embryonic
mesoderm
 Muscle tissues develop from embryonic cells called
myoblast.
 Muscular component of Branchial arch form many
striated muscles in the head and neck region.
 Muscles of mastication are derived from first or
MANDIBULAR ARCH.

LATERAL VIEW OF A FOUR WEEK EMBRYO SHOWING
MUSCLES DERIVED FROM BRANCHIAL ARCHES

EIGHT WEEK EMBRYO SHOWING DEVELOPMENT
OF FACIAL MUSCLES AND TRUNCK MUSCULATUREwww.indiandentalacademy.com

SKETCH OF 20 WEEK FETUS SHOWING MUSCLES
DERIVED FROM BRANCHIAL ARCHES

TYPES OF MUSCLES
 Muscle cells are mainly of three types
1. STRIATED MUSCLE
a. SKELETAL OR VOLUNTARY
b. CARDIC MUSCLE
2. NON-STRIATED,SMOOTH OR
INVOLUNTARY

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

LONGITUDINAL
SECTION OF CARDIAC
MUSCLEI
TRANSVERSE
SECTION OF CARDIAC
MUSCLE

Longitudinal section of non striated or smooth muscle

SKELETAL MUSCLE
 Units of skeletal muscle are the muscle fibers,each of which
act as a single cell having hundreds of nuclie(syncytial striated
myocytes).
 Fibers are arranged in bundles of various sizes and pattern
called fasciculi.
 Connective tissue fills the spaces between muscle fibres within
a fasciculus where it is known as the endomyscium.
 Each fasciculus is also surrounded by a strong connective
tissue sheath or perimysciun.
 Surrounding the whole muscle lies epimyscium.
 Cell membrane of muscle fibre is known as sarcolemma while
their cytoplasm is called sarcoplasm.
 Sarcoplasm is divided into longitudinal threads or myofibrils
each of 1micro meter in diam.
 Each muscle fiber consists of several hundred to several
thousand myofibrils www.indiandentalacademy.com

THE ULTRASTRUCTURE OF SKELETAL
MUSCLE
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.

ACTIN AND MYOSIN FILAMENT

GENERAL MECHANISM OF MUSCLE
CONTRACTION
SLIDING FILAMENT MECHANISM.
 Caused by interaction of cross bridges from myosin filament
with the actin filament.
 Action potential causes sarcoplasmic reticulum to causes
release of calcium ion.
 Calcium ion combines with troponin c of troponin
tropomyosin complex causing a confirmational change. And
it moves deeper between two actin strands.
 This uncovers the active sites of actin allowing these to
attract the myosin head and cause contraction to proceed.

Interaction Between The ‘Activated’ Actin
Filament And the Myosin Bridges-The ‘Walk
Along Theory’ of contraction
 When myosin head attaches to a active site ,it causes head to
tilt towards the arm and drag the actin filament along with it,
 This tilt of the head is called Power stroke.
 After tilting head automatically breaks away from the active
site
 Next it returns to perpendicular position and combines with
new active site farther down along the actin filament.
 Thus the heads of myosin filament bend back back and forth
and walk along the actin filament.

MUSCLE FUNCTION
The motor unit can carry only one action i.e. contraction or shortening,
the entire muscle, however has three potential function.
 A) ISOTONIC CONTRACTION
When the muscle shorten and moves a load, the contraction is
isotonic. Hence the load remains constant and equal to the muscle
tension throughout the most of the period of contraction. It occurs
in the masseter, when the mandible is elevated forcing the teeth
through a bolus of food.
 B) ISOMETRIC CONTRACTION
When a muscle does not shorter and length remains same (iso-
same, metry- length), but develops tension, the contraction is
isometric. Such type of contraction occurs when muscle attempts to
move a load that is greater than the tension developed in muscles,
this occurs in masseter when an object is held between the teeth.
eg. Pipe or pencil.
 C) CONTRACTION RELAXATION
When stimulation of the motor unit is discontinued the fibres of
motor unit relax and return to their normal length. This is seen in
masseter when the mouth opens to accept new bolus of food during
mastication.

FIBER TYPES

Muscle hypertrophy atrophy and
hyperplasia
 HYPERTROPHY: when total mass of muscle
enlarges.,oncrease in actin and myosin filament in
response to maximal force causing enlargement of
muscle fiber.
 HYPERPLASIA: Under rare condition of extreme
muscle force generation actual no of muscle fiber
have been observed to increase.
 ATROPHY: When total mass of muscle decreases.

MUSCLES OF MASTICATION
Mastication forces The aev maximum
sustainable biting force is 756N{170 pounds}.
 Molar region: Biting force range 400-890N
 Premolar region: Biting force range 222-445N
 Cuspid region: Biting force range 133-334N
 Incisor region:Biting force range 89-111N
{20-55 pounds}

PRIMARY MUSCLES OF MASTICATION
 MASSETER
 TEMPORALIS
 MEDIAL AND LATERAL PTERYGOID
SECONDARY MUSCLES OF MASTICATION
The suprahyoid group of muscles being used as
secondary or supplementary muscles they are
 Digastric
 Mylohyoid
 Geniohyoid

THE MASSETER
 Quadrilateral and and consist of three layers.
ATTACHEMENTS
 Superficial Layer: Arises by thick aponeurosis.
From zygomatic process of maxilla and anterior 2/3
of lower border of zygomatic arch,pass downward
and back wards at an angle of 45degree and inserted
into lower part of lateral surface of ramus of
mandible

 MIDDLE LAYER: Arises from
anterior 2/3 of the deep surface
and posterior 1/3 of the lower
border of the zygomatic arch,pass
vertically downwards and and
inserted into middle part of
ramus.
 DEEP LAYER: Arises from deep
surface of the zygomatic arch,
pass vertically downwards and
inserted into the upper part of the
ramus and into the coronoid
process.

RELATIONS OF MASSETER
SUPERFICIA
 Integument
 Platysma
 Risorius
 Zygomaticus major
 Parotid gland
 Parotid duct
 Branches of facial
nerve

DEEP SURFACE
Overlies the,
 Insertion of
temporalis and ramus
of the mandible.
 In front buccinator
and the buccal nerve.
 Massetric nerve and
artery.

ANTERIOR Margin
projects over the
buccinator and is crossed
below by the facial vein.
POSTERIOR Margin is
overlapped by the parotid
gland.

Nerve supply:
 MASSETRIC NERVE,
a branch of anterior
division of mandibular
nerve (which is the 3rd
part of V cranial nerve-
trigeminal nerve).
Blood supply:
 Maxillary artery,
which is a branch of
external carotid artery.

ACTIONS OF MASSETER
Actions:
 Elevates the mandible to close the mouth
and to occlude the teeth in mastication.
 Its activity in the resting position is
minimal.
 It has a small effect in side-to-side
movement, protraction and retraction.

THE TEMPORALIS
TEMPORAL FASCIAE
 Thick aponeurotic sheet that roofs over the temporal
fossa and covers the temporalis muscle.
ATTACHEMENTS
 Fan shaped
 Arises from whole of temporal fossa.(except the part
formed by zygomatic bone) and deep surface of
temporal fascia
 Fibers converge and descend into a tendon .
 It passes through the gap between the zygomatic arch
and the side of the skull
 Attached to medial surface,apex,anterior and posterior
border of coronoid process and anterior border of the
ramus of the mandible as far as last molar.

RELATIONS OF TEMPORALIS
SUPERFICIAL
 Skin
 Auricularis anterior
 Temporal fascia
 Superficial temporal vessels
 Auriculotemporal nerve
 Temporal branch of facial nerve
 Galea aponeurotica
 Zygomatic arch
 masseter

DEEP SURFACE
 Temporal fossa
 Lateral pterygoid
 Superficial head of medial
pterygoid
 Small part of buccinator
 Maxillary artery
 Deep temporal nerves
 Buccal vessels and nerve
ANTERIOR border is seperated
from the zygomatic bone by a
mass of fat.

BLOOD SUPPLY
 Deep temporal part of
maxillary artery
NERVE SUPPLY
 Temporalis is
supplied by the deep
temporal branches of
the anterior trunk of
mandibular nerve.

ACTIONS OF TEMPORALIS
 Elevates the mandible,this movement requires
both the upward pull of anterior fibers and
backward pull of the posterior fibers.
 Posterior fibers draw the mandible backwards
after it has been protuded.
 It is also a contrbutor to side to side grinding
movement.

ELEVATION OF MANDIBLE

POSTERIOR FIBER DRAWS MANDIBLE
BACKWARDS

SIDE TO SIDE GRINDING MOVEMENT

LATERAL PTERYGOID
ATTACHMENTS
It is a short thick muscle with two parts or head
 UPPER head arise from infratemporal surface and
infratemporal crest of greater wing of sphenoid bone
 LOWER head arise from lateral surface of lateral
pterygoid plate.
 Its fibers pass backwards and laterally to be inserted
into a depression(pterygoid fovea)on the front of the
neck of the mandible and into the articular capsule and
disc of the temporomandibular articulation.

RELATIONS OF LATERAL PTERYGOID
SUPERFICIAL
 Ramus of the mandible
 Maxillary artery
 Tendon of temporalis and the masseter,
DEEP SURFACE
 Upper part of the madial pterygoid
 Sphenomandibular ligament
 Middle meningeal artery
 Mandibular nerve
UPPER BORDER
 Upper border is in relation with temporal and messetric
branches of the mandibular nerve
LOWER BORDER
 In relation with lingual and inferior alveolar nerve

NERVE SUPPLY
 The lateral
pterygoid is supplied
by a branch of
anterior division of
the mandibular nerv

BLOOD SUPPLY
Pterygoid
branch of 2nd
part of maxillary
artery

ACTIONS OF LATERAL PTERYGOID
 Assists in opening the mouth with suprahyoid
muscle.
 Slow elongation while closing the mouth with
masseter and temporalis
 Acting with medial pterygoid of same side
advances the condyle ,while the jaw rotates
through the opposite condyle(when the medial
and lateral pterygoid of the two sides contract
alternatively to produce side to side movements
of mandible eg chewing).

 When the medial and lateral pterygoids of two
sides act together they protrude the mandible so
that the lower incisors project in front of the
other.
 Some authorities have ascribed different actions
to the two parts of pterygoid muscle.
 The upper (superior)head being involved in
chewing
 The inferior in protrusion,electromyographic
records in rhesus monkey favors this view.

The combinded efforts of the Digastrics and Lateral Pterygoids
provide for natural jaw opening.

Medial and lateral pterygoid act together to
protrude the mandible

MEDIAL PTERYGOID
ATTACHEMENTS
 It is a thick quadrilateral muscle
 Attached to medial surface of lateral pterygoid plate and
grooved surface of pyramidal process of the palatine
bone.
 A more superficial slip from the lateral surface of
pyramidal process of the palatine bone and tuberosity of
maxilla
 Its fibers pass downwards laterally and backwards
 Attached by a strong tendinous lamina ,to the postero-
inferior part of the medial surfaces of the ramus and the
angle of the mandible
 It is attached as high as mandibular foramen and as far
forward as the mylohyoid groovewww.indiandentalacademy.com

RELATIONS OF MEDIAL PTERYGOID
SUPERFICIAL
 Upper part of muscle is separated from the
lateral pterygoid muscle by
a) lateral pterygoid plate
b) lingual nerve
c) inferior alveolar nerve
 Inferiorly the muscle is separated from ramus of
mandible by same nerves,the maxillary artery
and sphenomandibular ligament.

NERVE SUPPLY
 Branch of the
main trunk of the
mandibular nerve.
BLOOD SUPPLY
 Pterygoid branch
of 2nd part of
maxillary artery

Actions of medial pterygoid
 Assits in elevating the mandible
 Acting with the lateral pterygoid they protrude it
•Acting with medial pterygoid of same
side advances the condyle ,while the jaw
rotates through the opposite
condyle(when the medial and lateral
pterygoid of the two sides contract
alternatively to produce side to side
movements of mandible eg chewing)

Secondary muscles taking part in the
mastication
The 4 primary muscles of mastication are in
turn supported or supplemented by few
secondary muscles known as
SUPRAHYOID GROUP of muscles they are
 DIGASTRIC
 MYLOHYOID
 GENIOHYOID
 STYLOHYOID is other suprahyoid muscle,
which does not take part in mastication

DIGASTRIC
•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.

GENIOHYOID
•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

PATHOLOGICAL CONDITIONS
AFFECTING MUSCLES
CLASSIFICATION OF DISEASES OF MUSCLE
I PRIMARY MYOPATHIES
a)Dystrophies
b)Myotonias
c)Hypotonias
d)Myasthenias
e)Myositis
f)Metabolic defects
g)Miscellaneous(amyloplasias,contractures,degene
ration) www.indiandentalacademy.com

II.SECONDARY MYOPATHIES
a)Atrophy
1)Denervation
2)Disuse and fixation
3)Ageing and cachexia
b) Hypertrophy
1) Developmental
2) Functional
c) Endocrine
d) Internal environment
1)Chemical
2)Vascular
e)Infection
1.Specific(trichinella,toxoplasma,coxsackie virus,tetanus)
2.General(rikettsial,typhoid,pneumococcal pneumonia)
3.Post infection asthenia.

DISEASES OF SKELETAL MUSCLE
 Disorders that produce predominantly myofiber
atrophy including neurogenic atrophy and
myofiber atrophy.
 Disorders of the neuromuscular
junction(exemplified by myasthenia gravis)
 Selected primary myopathies including
inflammatory myopathies and muscular
dystrophies.

MYASTHENIAS
a)Myasthenia gravis
b)familial periodic parslysis
c)aldosteronism
Latter two are very rare diseases.
MYASTHENIA GRAVIS
 Acquired autoimmune disorder of neuromuscular
transmission charecterized by muscle weakness
ETIOLOGY
 Antibodies to acetylcholine receptor on skeletal muscle
fiber
 Assosiation with systemic lupus
erythematosis,rheumatoid artheritis,sjogren syndrome.

CLINICAL FEATURES
 May be present at any age, chiefly in
adults,predilection for women
 Rapidly developing weakness in voluntary
muscles following even minor activities
 Of interest to PROSTHODONTIST is the fact that
muscles of mastication and facial expression are
involved by this disease frequently before any
other muscle group.
Patient chief complaint may be
difficulty in mastication and deglution, and
dropping of the jaw . Speech is often slow and
slurred. Disturbance in taste sensation in some
patient.

 Diplopia, ptosis,drooping of the face,lend a very
sorroful appearance to the patient.
 Pt rapidly exausted,lose wt,death frequently
occurs from respiratory failure.
 Clinical course variable,some enter acute
exacerbation of their disease and sccumb but
others live for many years,on this basis two
forms are recognized.
a)Steadily progressive
b)a remitting relapsing type

TREATMENT AND PROGNOSIS
 Drug of choice used in treatment provides such
remarkable relief of symptoms in very short
time.
 Physostigmine administered intramuscularly
improves the strength of the affected muscle in
a matter of minutes
 No cure is known even though the prognosis is
good in the relapsing type.

TETANUS(LOCK JAW)
 Tetanus is a disease of the nervous system
characterized by intense activity of motor
neuron and resulting in severe muscle spasm
 Caused by exotoxins of gram positive bacillus
Ciostridium tetani.
CLINICAL FEATURES
 Pain and stiffness in the jaws and neck muscles
,with muscle rigidity producing trismus and
dysphagia
 Rigity of facial muscles producing the typical
risus sardonicus
 Sometimes whole body becomes affected
characterized by opisthotonos

TREATMENT
 All patients should receive antimicrobial drugs
 Active and passive immunization.
 Surgical wound care
 Anticonvulsant if indicated

PROSTHODONTIC CONSIDERATIONS
MASTICATIORY CYCLE
 The pathways of the mandible in chewing is
referred to as the chewing cycle
 Masticatory cycle consists of three phases
1) Opening phase(mandible is depressed)
2) Closing phase(mandible is elevated)
3) Intercuspal phase(ICP)
 The chewing cycle can take many forms and the
classic tear drop shape when viewed in frontal
or saggital plane is oversimplification of reality

 In opening phase teeth
and condyle move down
and forward
 Early closing phase man
moves laterally to the
selected chewing side
 Chewing side condyle
moves to upward
reareward position well in
advance of the
intercuspal phase(SRP)
 During rest of closing
phase to ICP chewing
side condyle show a
slight forward(.33mm)
and medial
movement(Bennett)
(.2mm)
 Non chewing side condyle
lags somewhat behind.www.indiandentalacademy.com

 There are about 15 chews in a series from the
time of food entry until swallowing
 Aev jaw opening during chewing is between 16-
20mm
 Aev lateral displacement on chewing is between
3 and 5mm
 Duration of masticatory cycle varies between
.6and 1 sec
 Men chew faster and have a shorter occlusal
phase than women,it also depends on the type
of food

FACTORS THAT REGULATE JAW MOTIONS
 NEUROMUSCULAR SYSTEM
 GUIDING INFLUNCES OF CONTACTING TEETH
 MANDIBULAR MUSCULATURE WHEN TEETH
NOT IN CONTACT
 LIMITING OF MOVEMENT BY CONDYLE
The condyles and teeth modify mandibular
movements initiated by neuromuscular system.

INFLUENCE OF OPPOSING TOOTH CONTACT IN
COMPLETE DENTURE
 The occlusal surface should meet evenly on both
sides
 In this manner mandible is not deflected from its
normal path of closure,nor are the dentures
displaced from residual ridges
 When mandibular movements are made the
inclined planes of the teeth should pass over
one another snoothly
 It should not disturb the influence of condylar
guidance posteriorly and incisal guidance
anteriorly

NEUROMUSCULAR REGULATION OF MANDIBULAR
MOTION
 Mastication is a programmed event residing in a
“chewing center” located within the brain
stem(reticular formation of the pons)
 The cyclic nature of mastication is the result of
the action of this central pattern generator
 Concious effort may either induce or terminate
chewing ,but it is not required for the
continuation of chewing

REST POSITION
 It is established by muscles and gravity
 There are two hypothesis abput postural rest
position
1)Active mechanism,when muscles are in
a state of minimal contraction to maintain the
posture
2)Passive mechanism, elastic elements of
the jaw musculature and not any muscle activity
balanve the influence of gravity
 Numerous studies have shown EMG activity at
rest
 A range of reduced muscle tension upto an
interocclusal distance of about 10mm has been
reported

IMPORTANCE OF OCCLUSAL
HARMONY
 When closing muscle pull mandible without interference
it is stooped by bone at medial pole
 If tooth inclines interfere lateral pterygoid is forced to
position the mandible to accommodate to the teeth
 There are many variations of timing and degree of
muscle contraction to position the mandible for
maximum intercuspation of the teeth.
 Pattern of deviation is reinforced every time contact is
made
 Imortant facet of propioceptive memory is that it fades if
reinforcement of pattern ceases.

 Elimination of interfering contacts permit an
almost immediate return to normal muscle
function
 Willamson Showed using EMG procedures that
posterior tooth intrference caused hyperactivity
of elevator muscle
 But if the anterior guidance was allowed to
disclude all posterior teeth from any contact
other than CR elevator muscle stopped active
contraction or reduced it.

TOOTH INTERFERENCES
 The reason muscle changes jaw position in the
presence of interferences is to protect the
interfereing tooth or teeth from absorbing entire
occlusal force
 Muscles become patterned to the devious
closure ,such memorized patterns of muscle
activity are called ENGRAMS
 Because of engrams it is easy to be fooled by
freely hinging jaw that appears to be in correct
CR.

OCCLUSAL PLANE
 The curvature of the posterior plane of occlusion
are divided into
1)An anteroposterior curve called
the curve of spee.
2)Mediolateral curve referred to as
the curve of wilson
Curve of Spee
 Begins at cusp tip pf lower cuspid and follow the
buccal cusp tip of bicuspid and molars, curve
line forms an arc through the condyle.
 It aligns each tooth for maximum resistance to
functional loading

 To prevent increase
muscle loading of the
teeth and the joints
during protrusive
movement.
 If there is any tooth
contact posterior to
canine during excursion
the elevator muscles are
triggered into
hypercontraction

CURVE OF WILSON
 Mediolateral curve that contacts the buccal and
lingual cusp tips on each side of arch
 Results from inward inclination of posterior teeth
 In maxillary arch reverse is there because of
outward inclination of posterior teeth.
There are two reasons for this inclination of
posterior teeth
1) one has to do with resistance to
loading
2)second has to do with
masticatory function

 Axial alignment of all
posterior teeth is nearly
parallel with the strong
inward pull of the medial
pterygoid muscle
 Aligning both upper and
lower posterior teeth with
the principal direction of
muscle contraction
produce the greatest
resistance to masticatory
forces, and forms curve
of wilson

 There is another reason
for the curve of
wilson,tounge and
buccinator must place
food onto occlusal
table,there must be easy
access for the food to get
to the occlusal table
 The inward inclination of
the lower occlusal table
for direct access from
lingual

 The outward inclination
of the upper occlusal
table provides access
from the buccal for the
food
 When the curve of wilson
is made too flat ease of
masticatory function may
be impaired because of
increased activity
required to get the food
onto the occlusal table

BRUXISM
Bruxism is the clenching or grinding of the teeth when the
individual is not chewing or swallowing
 It can occur as a brief rhythmic strong contractions of
the jaw muscles during eccentric lateral jaw
movements,or in maximum intercuspation,which is called
clenching.
 Causes
1) Assosiated with stressful events
2)Non stress related or hereditary
 Increased masseter muscle tension is directly related to
stress situation during the day.

 Increased stress levels
are strongly correlated
with increased levels of
masseter muscle activity
at night

 Bruxism can not be casually described as
"hyperactivity of the lateral pterygoid".
. The definitive component of bruxism is the degree
of parafunctional elevation, that is, the clenching
component. An accurated definition of bruxism
is: Jaw clenching, with or without forcible
excursive movements, where the intensity of
the clenching dictates the severity (or lack
of) grinding .

Each of the graphics below displays identical degreess of
LP "hyperactivity:
•Only the graphic to
the far left can be
considered NOT
be bruxism,
although there IS
hyperactivity of the
LPs
graphic at the
far right is the
most extreme
form of
bruxism).

 Bruxism may lead to
-tooth wear
-fracture of the teeth or restoratrion
-uncosmetic muscle hypertrophy
 Treatment
-coronoplasty
-maxillary stabalization appliance

Normal function versus
parafunction
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.com

 In the event the
Temporalis' do not cease
their active contractions,
scenarios of varying
degrees of parafunction
result, as the Lateral
Pterygoids encounter
resistance to their
attempts at condylar
advancement, thereby
increasing their intensity
of contraction and strain
on their origins and
insertions: the pterygoid
plates of the sphenoid
bone, and the condylar
neck and disc.

 The degree of frequency,
duration and intensity of
the contractions of a
Lateral Pterygoid is a
function of the resistance
provided by the
parafunction ipsilateral
and/or contralateral
Temporalis. For example,
in the animation to the
left, as a Lateral
Pterygoid attempts to
translate its condyle, it is
met with resistance
provided by the
contralateral Temporalis,
thereby causing the
Lateral Pterygoid to pull
its condyle in a medial
direction toward the
contralateral contact.

The maximum clenching intensity occurs in
the musculoskeletally stable position
 The mandibular position
of the temporalis' most
intense contraction is not
when the teeth are
together, but when they
are a particular distance
apart, and separated by
an object (such as a
splint, or food).

CANINE RISE SERVE S TO DIFFUSE
PARAFUNCTION
 temporalis persists in the
elevation of the mandible,
the canine teeth
contralateral to the
translating condyle are
often exploited to endure
the load, thereby allowing
the force to be directed in
an anterior (and slightly
medial) direction, braced
by the slope of the
eminence. This is called
"canine guidance",
allowing the posterior
teeth to separate.

 Although the lateral
engagement of the
canines can help to
diffuse the effects of
parafunction, an end-to-
end canine contact can
serve to perpetuate the
effects of
parafunction. The
animation demonstrates
an excursive movement
that allows for canine-to-
canine clenching. Canine
teeth can alow for near
maximal voluntary
temporalis clenching
intensity

Parafunctional chewing cycle: "Outside-in"
 Normal opening is
straight, unless a
chronically-
tensed/fatigued LP
advances its condyle
"faster" that the
contralateral LP.
 Excursive parafunction
does not engage the
canine during closing (ie,
from the outside-in).
The above example does
not really
happen. Interferences
are enganged by the LP
upon opening (at right

Parafunctional chewing cycle: "Inside-out"
 Deviation upon opening is
abnormal and is usually
the
result of excursive
parafunctional opening
against
resistance. Ideally, this
activity would engage a
canine,
but can still fatigue a
lateral pterygoid
depending upon the
intensity of resistance
provided by the occluding
canines. Occasionally,
canine tip-to-tip clenching
perpetuates the clinical
presentation of unilateral
headache and
contralateral joint strain.

CONCLUSION

REFERENCES
 Kieth L. Moore, The developing human ,fourth edition
1992
 Peter.L.Williams,Roger Worwik Grays Anatomy ,thirty six
edition 1980
 B.D.Chaurasias, Human anatomy,third edition 2000
 Keith L.Moore,Clinically Oriented Anatomy fourth edition
1992
 Anne M.R Agur,Grants atlas of anatomy 10 edition 1991
 R.M.H Mc Minn,.R.T.Hutchings ,third edition1994
 Arthur C Guyton,John E Hall,Textbook of Medical
Physiology 10 edition 2000
 William f ganong,Review of Medical Physiology,eighteen
edition 1997

 Kumar ,Cotran,Basic Pathology,fourth edition
1971
 Shafer,Hine,Textbook of oral pathology,fourth
edition 1997
 Sheldon Winkler,Essentials of complete denture
prosthodontics,second, edition 2000
 George A.Zarb,Charles L
Bolender,Prosthodontic Treatment for
Edentulous Patients, twelth edition 2004
 Peter E Dawson,Evaluatio Diagnosis and
Treatment of Occlusal Problems ,second
edition1989
 Fermin A Carranza,Micheal G Newman,Clinical
Periodontology eight edition1996

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