Primary and Accessory Muscles of Mastication

The STOMATOGNATHIC SYSTEM comprises of the teeth and their supporting tissues, the mandible and maxilla, the two temporomandibular joints and the muscular, nerve and vascular systems. The stomatognathic organ functions continuously in mastication, deglutition, speech and respiration and in maintenance of the posture of the head.
The muscles of mastication are the group of muscles that move the mandible during mastication and speech.

1. MUSCLES of
MASTICATION
Dr Akriti
I MDS
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2. CONTENT
★INTRODUCTION
★DEVELOPMENT
★CLASSIFICATION
★PRIMARY MUSCLES
○MASSETER
○TEMPORALIS
○LATERAL PTERYGOID
○MEDIAL PTERYGOID
★ACCESSORY MUSCLES
★MANDIBULAR MOVEMENTS AND ROLE
OF MUSCLES
★MASTICATORY MUSCLE DISORDERS
★REFERENCES
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3. INTRODUCTION
❏The STOMATOGNATHIC SYSTEM comprises of the teeth and their supporting tissues,
the mandible and maxilla, the two temporomandibular joints and the muscular, nerve
and vascular systems. The stomatognathic organ functions continuously in
mastication, deglutition, speech and respiration and in maintenance of the
posture of the head.
❏Mastication is defined as the process of chewing food in preparation for swallowing and
digestion. [GPT 8]
❏The MUSCLES OF MASTICATION are the group of muscles that move the mandible
during mastication and speech.
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5. DEVELOPMENT
The muscular system develops from
intra-embryonic mesoderm from
embryonic cells called myoblast.
Muscles of mastication are derived
from first branchial arch, mandibular
arch.

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6. ❖5th-6th week:
➢Primitive cells form and differentiate
➢Get oriented to site of origin and
insertion
❖7th week:
➢Mandibular arch mass enlarges
➢Cell migrate to areas of formation of
4 major muscles of mastication
➢Cell differentiation occurs before
formation of facial arch
❖10th week:
➢Muscle mass well organized
➢Nerve mass get incorporated
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7. CLASSIFICATION
Functionally classified as:
➔JAW ELEVATORS
◆MASSETER
◆TEMPORALIS
◆MEDIAL PTERYGOID
◆UPPER HEAD OF LAT. PTERYGOID
➔JAW DEPRESSORS
◆LOWER HEAD OF LAT. PTERYGOID
◆ANT. DIGASTRIC
◆MYLOHYOID
◆GENIOHYOID

➔ACCESSORY MUSCLES
◆DIGASTRIC
◆STYLOHYOID
◆MYLOHYOID
◆GENIOHYOID
◆BUCCINATOR
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➔PRIMARY MUSCLES
◆MASSETER
◆TEMPORALIS
◆LATERAL PTERYGOID
◆MEDIAL PTERYGOID

8. MASSETER
Quadrilateral shaped muscle, covers lateral
surface of ramus of mandible, has three layers.
●ORIGIN
1.SUPERFICIAL LAYER (largest): from
anterior 2/3rd of lower border of
zygomatic arch and adjoining process
of maxilla
2.DEEP LAYER: from deep surface of
zygomatic arch
3.MIDDLE LAYER: from lower border of
posterior 1/3rd of zygomatic arch
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9. ●INSERTION
1.SUPERFICIAL LAYER: into lower part of
lateral surface of ramus of mandible
2.DEEP LAYER: into rest of the ramus of
the mandible
3.MIDDLE LAYER: into the central part of
ramus of mandible

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10. ●FIBERS
1.SUPERFICIAL FIBERS pass downwards and
backwards at 45
0
2.DEEP FIBERS pass vertically downwards
3.MIDDLE FIBERS pass vertically downwards
●NERVE and VESSELS
1.MASSETERIC NERVE, a branch of anterior
division of mandibular nerve
2.MASSETERIC ARTERY, a branch of internal
maxillary artery
●ACTIONS
1.ELEVATES mandible to close the mouth to
bite
2.Superficial fibers cause PROTRUSION
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11. TEMPORALIS
Fan shaped muscle, fills the temporal fossa
●ORIGIN
1.Temporal fossa, excluding zygomatic
bone
2.Temporal fascia
●INSERTION
1.Margins and deep surface of coronoid
process
2.Anterior border of ramus of mandible

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ANTERIOR
MIDDLE
POSTERIOR

12. ●FIBERS
1.ANTERIOR FIBERS run vertically
2.MIDDLE FIBERS run obliquely
3.POSTERIOR FIBERS run horizontally
4.All fibers CONVERGE and pass through gap
deep to zygomatic arch
●NERVE and VESSELS
1.Two deep TEMPORAL BRANCHES from
anterior division of mandibular nerve
2.DEEP TEMPORAL BRANCHES of maxillary
artery, MIDDLE TEMPORAL BRANCHES from
superficial temporal artery
●ACTIONS
1.ELEVATES mandible
2.Helps in SIDE TO SIDE GRINDING movement
3.Posterior fibers RETRACT the protruded
mandible
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13. LATERAL PTERYGOID
Short, conical muscle, has two heads.
●ORIGIN
1.UPPER HEAD (smaller): from infratemporal
surface and crest of greater wing of sphenoid
bone
2.LOWER HEAD (larger): from lateral surface of
lateral pterygoid plate.
●INSERTION
1.Pterygoid fovea on the anterior surface of
neck of mandible
2.Anterior margin of articular disc and
capsule of TMJ. Insertion is postero-lateral
and at a slightly higher level than origin

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14. ●FIBERS
1.Fibers run BACKWARDS and LATERALLY
2.Upper and lower head fibers CONVERGE for
insertion
●NERVE and VESSELS
1.LATERAL PTERYGOID NERVE, a branch from
anterior division of mandibular nerve
2.PTERYGOID BRANCHES of maxillary artery,
ASCENDING PALATINE BRANCH of facial artery
●ACTIONS
1.DEPRESSES mandible to open mouth
2.PROTRUDES mandible
3.Right lateral pterygoid turns the chin to left side
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PROTRUSION
DEPRESSION

15. ●RELATIONS OF LATERAL PTERYGOID
1.SUPERFICIAL
a.Masseter
b.Ramus of mandible
c.Tendon of temporalis
d.The maxillary artery
2.DEEP
a.Mandibular nerve
b.Middle meningeal artery
c.Sphenomandibular ligament
d.Deep head of the medial pterygoid
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16. 3.STRUCTURES EMERGING AT THE UPPER BORDER
a.Deep temporal nerves
b.Masseteric nerve
4.STRUCTURES EMERGING AT THE LOWER BORDER
a.Lingual nerve
b.Inferior alveolar nerve
c.The middle meningeal artery passes upwards deep to it
5.STRUCTURE PASSING THROUGH THE GAP BETWEEN THE TWO HEADS
a.The maxillary artery enters the gap
b.The buccal branch of the mandibular nerve comes out through the gap
The pterygoid plexus of veins surrounds the lateral pterygoid.
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18. MEDIAL PTERYGOID
Quadrilateral muscle, has two heads
●ORIGIN
1.SUPERFICIAL HEAD (small slip): from
tuberosity of maxilla and adjoining bone
2.DEEP HEAD (larger): from medial surface of
lateral pterygoid plate and adjoining process
of palatine bone
●INSERTION
1.Roughened area on the medial surface of
angle and adjoining ramus of mandible,
below and behind the mandibular foramen
and mylohyoid groove

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19. ●FIBERS
1.Fibers run downwards, backwards and laterally
2.The two heads embrace part of the lower head of
lateral pterygoid
●NERVE and VESSELS
1.NERVE TO MEDIAL PTERYGOID , branch of the
main trunk of mandibular nerve
2.Maxillary artery through its PTERYGOID
BRANCHES
●ACTIONS
1.ELEVATES mandible
2.Helps PROTRUDE mandible
3.Right medial pterygoid with lateral pterygoid turn
the chin to left side as part of grinding
movements
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20. ●RELATIONS OF MEDIAL PTERYGOID: The superficial and deep heads of medial pterygoid
enclose the lower head of lateral pterygoid muscle.
1.SUPERFICIAL RELATIONS:
a.The upper part of the muscle is separated from the lateral pterygoid muscle by:
i.Lateral pterygoid plate
ii.Lingual nerve
iii.Inferior alveolar nerve
b.Lower down the muscle is separated from the ramus of the mandible by:
i.Lingual nerve
ii.Inferior alveolar nerve
iii.Maxillary artery
iv.Sphenomandibular nerve
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21. 2.DEEP RELATIONS
a.Tensor veli palatini
b.Superior constrictor of
pharynx
c.Styloglossus
d.Stylopharyngeus attached
to the styloid
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22. ACCESSORY MUSCLES OF MASTICATION
1.DIGASTRIC
2.MYLOHYOID
3.STYLOHYOID
4.GENIOHYOID
5.BUCCINATOR
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●DIGASTRIC MUSCLE
○Formed by 2 belly like masses of
muscles joined by an intermediate
tendon
○Has anterior and posterior bellies
○FUNCTIONS:
■Depression of jaw, both sides
contract simultaneously
■Provide antagonism to
elevation of mandible
■Elevation of hyoid during
swallowing

24. ●MYLOHYOID MUSCLE
○Flat, triangular muscle lying deep to the
anterior belly of digastric
○Forms floor of the mouth
○FUNCTIONS:
■Helps in depression of mandible
■Elevates the hyoid bone
■Elevates the floor of mouth to aid
in deglutition
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25. ●STYLOHYOID MUSCLE
○Small muscle that lies along the
upper border of the posterior belly
of digastric muscle
○FUNCTIONS:
■Pulls hyoid bone upwards
and backwards
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26. ●GENIOHYOID MUSCLE
○Short and narrow muscle that lies
above Mylohyoid
○FUNCTIONS:
■Carry hyoid bone and the
tongue forward during
deglutition
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27. ●BUCCINATOR
○Also known an muscle of cheek
○Occupies the gap between mandible
and maxilla forming an important
part of the cheek
○FUNCTIONS:
■Flattens cheek against gums
and teeth
■Prevents accumulation of
food in the vestibule of
mouth
■Brings the food on to the
occlusal table during
mastication
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28. MANDIBULAR MOVEMENTS & ROLE OF MUSCLES
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29. MASTICATORY MUSCLE DISORDERS
★BRUXISM
★TRISMUS
★MPDS
★CONGENITAL HYPOPLASIA/HYPERPLASIA
★MUSCLE HYPOMOBILITY/HYPERMOBILITY
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BRUXISM
GPT-8 defines BRUXISM as parafunctional grinding of teeth or an oral habit consisting of
involuntary rhythmic or spasmodic non-functional gnashing, grinding or clenching of teeth in
other than chewing movements of the mandible which may lead to occlusal trauma.
It can occur as a brief strong rhythmic contractions of the jaw muscles during eccentric
lateral jaw movements or in maximum intercuspation.
Bruxism may lead to:
●Tooth wear
●Fracture of tooth or restoration
●Muscle hypertrophy

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ETIOLOGY:
●Stress and psychological disturbances
●Bite discrepancy and
temporomandibular disorders
●Nutritional disorders
●Hereditary
Increased muscle tension is directly related
to stress activity during the day.

CLINICAL FEATURES:
●Occlusal wear
●Periodontal destruction
●Muscular hypertrophy and
tenderness
●Headache
TREATMENT:
●Coronoplasty
●Occlusal splints

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TRISMUS
TRISMUS refers to the restriction of the range of motion of the jaws.
Commonly referred to as "lockjaw", trismus typically stems from a sustained, tetanic spasm
of the mastication muscles. Initially described in the setting of tetanus, it currently refers to
restricted mouth opening due to any etiology.
Trismus may lead to:
●Mastication issues
●Oral hygiene issues
●Swallowing issues
●Joint immobilization

34. ETIOLOGY:
●Intracapsular
○Arthritis
○Condylar fracture
●Pericapsular
○Irradiation
○Infection and inflammation
○Dislocation
●Muscular
○TMJ dysfunction syndrome
○Tetanus
●Others
○OSMF
○Systemic sclerosis
○Fractures

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TREATMENT:
●Removal of the cause
●Heat therapy
●Warm saline rinses
●NSAIDs
●Passive muscle stretching exercises

35. MPDS
Known as MYOFASCIAL PAIN DYSFUNCTION SYNDROME. Myofascial pain dysfunction
syndrome (MPDS) is a stomatognathic system disturbance, which consists of pain, jaw
movement irregularities, and muscle spasm.
Hyperexcitation of peripheral sensory neurons causes a reaction of induction in the motor
neuron and then spasms of the masticatory muscles follow. Long-term spasm causes
muscular pain and irregular mandibular motion.
MPDS symptoms:
●Deep, aching pain in a muscle.
●Pain that persists or worsens.
●A tender knot in a muscle.
●Difficulty sleeping due to pain.
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36. ETIOLOGY:
●Stress
●Poor habits including gum/hard candy
chewing, bruxism
●Poor dentition

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TREATMENT:
●4 phases of therapy which includes
muscle exercises and drugs involving
NSAIDs and muscle relaxants
●Transcutaneous electric nerve
stimulation
●Bite appliance to aid in muscle
movement

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CONGENITAL HYPO/HYPERPLASIA
The symptoms include enlargement or
decreased size of the affected muscle,
which may show an asymmetric facial
pattern and stiffness in the
temporo-mandibular joint.
This condition occurs very rarely and is
more common in masseter and orbicularis
oris.
It may or may not be associated with
hypomobility/hypermobility of muscles.

38. MUSCLE HYPO/HYPERMOBILITY
This disorder includes extreme or diminished activity of the masticatory muscles.
The etiology involves:
●Decreased/increased threshold potential of neural activity
●Parkinsonism
●Facial paralysis
●Nerve decompression
●Secondary involvement of systemic diseases
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39. REFERENCES
●B D Chaurasia’s Human Anatomy for Dental Students. 3rd Edition
●Cunningham’s Manual of Practical Anatomy - Head, Neck and Brain. 15th Edition
●Burket’s Oral Medicine. 12th Edition
●Textbook of Prosthodontics. V Rangarajan, T V Padmanabhan. 2nd Edition
●Management of Temporomandibular Disorders and Occlusion. J P Okeson. 8th Edition
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