MUSCLES OF MASTICATION

MUSCLES OF
MASTICATION
BY DR. KOMAL GHIYA
MDS PEDODONTICS AND PREVENTIVE DENTISTRY
1

INDEX
• PRIMARY MUSCLES OF MASTICATION :
Masseter
Temporalis
Lateral Pterygoid
Medial Pterygoid
 ACCESSORY MUSCLES OF MASTICATION :
Digastric
Mylohyoid
Geniohyoid
 CLINIAL CONSIDERATIONS :
2

DEVELOPMENT OF MUSCLES OF
MASTICATION
• The muscular system developes from intra-embryonic mesoderm from
embryonic cells called “ myoblast “
Muscles of mastications are derived from first pharyngeal arch i.e
mandibular arch ( first arch )
3

MASSETER
• It is a quadrilateral muscle placed superficial to the ramus of the
mandible.
• It has 3 layers
Human anatomy-B.D.Chaurasia-volume 3 -4th edition
4
Superficial layer
(largest)
Middle layer
Deep layer

ORIGIN
•From anterior 2/3 of lower border of
zygomatic arch & adjoining zygomatic
process of maxilla
Superficial
layer
•From anterior 2/3 of deep surface &
posterior 1/3 of lower border of zygomatic
arch
Middle
layer
•From deep surface of zygomatic arch.
Inferior
layer
5

INSERTION
•Into lower part of lateral surface
of mandible
Superficial
layer
•Into lower part of lateral surface
of mandible
Middle
layer
•Upper part of ramus & coronoid
process of the mandible .
Deep
layer
6

• BLOOD SUPPLY – Masseteric branch of maxillary artery ,
facial artery , superficial temporal artery.
• NERVE SUPPLY – masseteric nerve (branch of anterior division of
mandibular nerve.
7

HOW TO PALPALTE THE MUSCLE
• Ask the patient to clench teeth
and palpate extra-orally .
• The origin of muscle is palpated
bilaterally along the zygomatic
arch & continue to palpate
down the body of the
mandible , where masseter is
attached
Burket’s oral medicine – 11th edition 8

ACTION OF MUSCLE
• Elevates the mandible to close
the mouth to bite.
• While elevating it exerts presure
on the teeth in molar region
• The deep portion of the muscle
has a retracting component
causing a combination of
elevation and retraction
9

APPLIED ANATOMY
• SUBMASSETERIC SPACE
INFECTIONS :
• Sometimes infection around a
mandibular 3rd molar tooth tracks
backwards, lateral to mandibular
ramus & pus localizes deep to
masseter
• Such an abscess lying deep to
thick muscle produce little visible
swelling , accompanied by
profound muscle spasm &
limitation of jaw opening
10

TEMPORALIS
• Fan shaped muscle
• Occupies the temporal fossa
region between superior
temporal line and zygomatic
arch on side of head.
• It is a bipenate type of muscle
11

ORIGIN AND INSERTION
• Origin – from temporal fossa
excluding zygomatic arch and
from temporal fascia
• Fibres – converge and pass deep
to zygomatic arch
• Insertion – margins and deep
surface of coronoid process and
anterior border of ramus of
mandible.
12

TEMPORAL FOSSA AND FASCIA
• Temporal fossa – contains temporalis muscle, auriculotemporal nerve ,
superior temporal artery
• Temporal fascia – thick aponeurotic sheet that roofs the temporal fossa
and covers temporalis muscle
Contains – fat , superior temporal artery , zygomaticotemporal nerve
gray”s anatomy -36th edition 13

Vascular supply – form
deep temporal branches
of second part of
maxillary artery
Nerve supply – deep
temporal branch of
mandibular nerve
14

ACTION OF MUSCLE
• Closes mouth – elevates mandible . This requires upward pull of anterior
fibres and backward pull of posterior fibres because head of condyle
rests n articular eminence when mouth is open.
• Side to side grlnding movement
• Posterior fibres retract protruded mandible
15

HOW TO PALPATE THE MUSCLE
• First the patient is asked to clench teeth
• Fingers are placed over the patients temples to feel the muscle.
Burket’s oral medicine – 11th edition
16

APPLIED ANATOMY
• TEMPORAL TENDONITIS – chronic strain from temporalis muscle pulling
on tendon that attaches to mandible leads to headache in temple
region(at the side of eyes)
Gray”s anatomy – 36th edition
17

LATERAL PTERYGOID MUSCLE
• Short conical muscle
• Has 2 heads – upper and lower
• Unlike the other muscles of mastication , lateral pterygoid is NOT
PENNATE , nor does it have significant no. of golgi tendon organs
associated with its attachments.
18

ORIGIN
• From
infratemporal
surface & crest
greater wing of
sphenoid bone
Upper
head
(small)
• From lateral
surface of lateral
pterygoid plate
Lower
head
(large)
Gray”s anatomy – 36th edition 19

INSERTION
• Fibres run backwards and laterally
and converge for insertion.
INSERTION – pterygoid fovea , on
the anterior surface of neck of
mandible
 Anterior margin of articular disc &
capsule of of temporomandibular
joint (TMJ)
 (INSERTION is posterolateral &
slightly higher level than origin)
20

• VASCULAR SUPPLY – from pterygoid branches of maxillary artery
• NERVOUS SUPPLY – from nerve to lateral pterygoid (branch of anterior
division of mandibular nerve)
21

• Placing the forefinger, or the
little finger , over the buccal
area of the maxillary 3rd molar
region & exerting pressure in a
posterior ,
superior , &
medial direction ,
just behind the maxillary
tuberosity
22

ACTION
• Depress mandible to open mouth with suprahyoid muscles
• Lateral & medial pterygoid protrude mandible
• Left lateral pterygoid & right medial pterygoid turn the chin to left side
as a part of grinding movements (acting with medial pterygoid of same
side it pulls neck of mandible forward with articular disc causing jaw to
rotate around opposite condye as in chewing)
23

Clinical Anatomy-Richard .S.Snell-7th edition
24

APPLIED ANATOMY
• Most commonly involved muscle in MPDS.
• Unilateral failure of lateral pterygoid muscle to contract results in
deviations of mandible towards the affected side on opening
• Bilateral failure results in,
Limited jaw opening
Loss of protrusion
Loss of full lateral deviation
25

MEDIAL PTERYGOID
• It is a quadrilateral muscle
• Has two heads : superficial and deep
26

ORIGIN
• From maxillary tuberosity & pyramidal
process of palatine bone
Superficial
head (small)
• From medial surface of lateral
pterygoid plate & adjoining process of
palatine bone
Deep head
(large)
27

INSERTION
• Fibres run downwards , backwards and
laterally
• Inserted into the posterior
inferior part of the medial
surfaces of the ramus
and angle of the
mandible, as high as
mandibular foramen and
nearly as far forward as
the mylohyoid groove.
28

• VASCULAR SUPPLY – from pterygoid branches of maxillary artery
• NERVOUS SUPPLY – from nerve to medial pterygoid (branch of main
trunk of mandibular nerve)
29

• Gently palpate the muscle on the medial aspect of the jaw.
• Simultaneously from both inside & outside the mouth
30

ACTION
• To elevate the mandible
• To protrude the mandible with lateral pterygoid muscle
31

APPLIED ANATOMY
• Most commonly involved in MPDS
• Trismus following inferior alveolar nerve block is mainly due to
involvement of medial pterygoid muscle
32

DIGASTRIC MUSCLE
33

origin
• ANTERIOR BELLY-
digastric fossa of
mandible
• POSTERIOR BELLY-
mastoid notch of the
temporal bone
INSERTION
• Intermediate tendon (
hyoid bone )
34

•BLOOD SUPPLY :
Anterior belly – submental branch of facial artery
Posterior belly – occipital artery
NERVE SUPPLY :
Anterior belly –mylohyoid nerve , branch of mandibular division (V3) of
trigeminal nerve (CN V)
Posterior belly – branch of facial nerve (CN VII
35

ACTIONS
• Pulls mandible back & down
• Retrusive and opening movements
• Elevation of hyoid bone
36

MYLOHYOID MUSCLE
37

ORIGIN
• It has 3 fibers- posterior,
middle and anterior,
which originates from the
mylohyoid line of the
mandible.
38

INSERTION
• Posterior fibres pass medially and
slightly downwards and are
inserted into the body of the hyoid
bone.
• Anterior and middle fibres from
each side interesect in a medium
fibrous raphe that unites right and
left muscles to form floor of the
mouth
39

• NERVE SUPPLY – mylohyoid nerve (branch of inferior alveolar nerve)
• BLOOD supply – inferior alveolar artery ( branch of maxillary artery)
40

ACTIONS
• depresses the mandible (opening of mouth)
• Aids in swallowing by raising tongue and floor of mouh by elevating the
hyoid bone
41

GENIOHYOID MUSCLE
• Strap shaped muscle
• Origin – genial tubercle of
mandible
• Insertion – anterior surface of
body of hyoid bone
42

• Nerve supply – First cervical nerve, fibers pass through the hypoglossal
nerve.
• Action of muscle –
1. Elevates the hyoid bone
2. Depress the mandible
43

CLINICAL CO-RELATION
• HYPERTROPHY
• ATROPHY
• ANKYLOSIS
• MYASTHENIA GRAVIS
• TETANUS (LOCK JAW)
• BRUXISM
• MPDS
• MYOSITIS OSSIFICANS
• TRISMUS
Oral pathology-Shafer-6th edition 44

MYOSITIS OSSIFICANS
• Disease of unknown etiology affecting interstitial tissue of muscles as
well as tendon,ligament.
• Often masseter muscle is involved leading to fixation of jaw.
• Muscle gradually replaced by connective
tissue
• Then osteoid formation& subsequently
ossification.

Clinical features
• Masster and temporalis most commonly affected
• Leads to spasm of muscles and difficulty in jaw movements.
• Treatment – surgical excision

MPDS (Myofascial pain
dysfunction syndrome)
• Pain disorder in which unilateral pain is referred from trigger points in
myofascial structures to muscles of head and neck.
• Pain is constant and dull

• Symptoms
1. Pain
2. Limitation of motion of jaw
3. Joint noises – clicking
4. Tendernes to palpation of
muscles of mastication
• Diagnosis
1. Palpation
2. Biting tests
3. Radiographs
4. TMJ arthrography
5. CT,MRI
6. Auriculotemporal nerve
block

Treatment
• Analgesics –aspirin(0.3-0.6gm/4 hrly – 2tabs)
• Muscle relaxants – diazepam(2-5mg for 10days)
• Heat application
• Cryotherapy
• Electrogalvanic stimulation
• TENS
• Stretch exercise and biofeeedback
• Intra- articular injections of hydrocortisone
• Oclussal splints

MYASTHANIA GRAVIS
• Acquired autoimmune disorder due to antibodies directed towards
acetylcholine receptor at neuromuscular junction of muscle
• Muscles of mastication and facial expression involved leading to
weakness and fatigabiliy

• Features
1. Difficulty in mastication
2. Dropping of jaw
3. Diplopia , ptosis,sorrowed
appearance of face
4. Exhaustion,loss of weight
• Treatment
1. Physostigmine(anticholinest
ererase)

TRISMUS
•It is a muscular involuntary protective reflex as a
result of localized muscular irritation or
inflammation,which causes foreshortening of
muscles of mastication (esp. temporalis & medial
pterygoid)
• Treatment-
1. Heat therapy
2. Warm saline rinses
3. Analgesics and muscle relaxants
4. Physiotherapy(jaw exercises)

BRUXISM
• Habitual grinding or clenching of teeth either during sleep or as an
unconscious habit during waking hours.
• Effect on teeth , periodontium
• Hypertrophy of masticatory muscles and
trismus
Clinical features
• splints
• Botulinium toxin into masseter to weaken
the muscle
treatment

TETANUS
• Acute infection of nervous system characterized by intense activity of
motor neurons leading to muscle spasms(caused by clostridium tetani
bacteria)
• Trismus,stiffness , pain
Clinical features
• Human tetanus immunoglobulin(antitoxin)-
3000-6000units i.m
• Pennicilin(10-12 million units i. v for 10 days
treatment

References
• Human anatomy-B.D.Chaurasia-volume 3 -4th edition
• Handbook of Local Anaesthesia-Stanley.F.Malamed-5th edition
• Clinical Anatomy-Richard .S.Snell-7th edition
• Oral pathology-Shafer-6th edition
• Cunningham’s manual of practical anatomy-G.J.Romanes – volume 3
• Textbook of clinical neuroanatomy – Vishram Singh
55

• Grays anatomy-36th edition
• Last’s anatomy-10th edition
• Textbook of oral and maxillofacial surgery –Neelima Malik – 2nd edition
• Burket’s oral medicine – 11th edition
56

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