Muscles of masstication s2

MUSCLES OF MASSTICATION
Presented by:
HYSUM MUSHTAQ
1st year PG
“Nothing ismore fundamental to treating
patients than knowing the anatomy”
GOOD MORNING

 Introduction
 Development
 Muscles of mastication (in detail about each)
 Movements of mandible
 Physiology of masticatory muscles
 Mastication – Role of masticatory muscles
 Investigations
 Disorders of muscles of mastication

INTRODUCTION
 Muscle refers to a group of
muscle fibers bound together by
connective tissue.
 The muscles which are required
for mastication are known as the
muscles of mastication.
 These muscles help mainly in
 the movement of the mandible
and not the maxilla as maxilla is
an integral part of the skull and
the mandible being the only
movable bone in the skull.

DEVELOPMENT
 Day 17 – 3 germ layers
 Day 19 – mesodermal plate cleaves – diff of somite plate -
somites
 Day 20-21 – 42-44 pairs of somites
 Myocoele, Sclerotome , Dermatome, Myotome

Rhythmic movement of the jaw is a
series of cyclical movements
 Masticatory system includes
1. Temporomandibular joint
2. Mandible
3. Teeth &
4. Muscles of mastication.

 Participate in all jaw movements involved in mastication,
deglutition and other non masticatory movements
 Voluntary muscles
 Originate from the skull, span the TMJ, and insert into the
mandible. On contraction, they act to move the mandible.

TYPES
• MASSETER
• TEMPORALIS
• MEDIAL PTREYGOID
• LATERALPTERYGOID
PRIMARY
• SUPRAHYOID MUSCLES
• DIGASTRIC
• MYLOHYOID
• GENIOHYIOD
• INFRAHYOID MUSCLES
(Sternohyoid,Omohyoid
,Thyrohyoid muscles)
SECONDARY
Dr.Frank Gaillard et al

Origin
Insertion
Relations
Vascular supply
Innervation
Actions
Clinical importance

MASSETER
 The width of the muscle at its origin ranges from 27 to 39mm
in brachycephalic skulls, its anterior border length 51 –
70mm, and its posterior length 40 – 62mm.
 Its physiologic cross section is 2.75 cm square
 About 29.9% of the total masticatory muscle mass.
1. SUPERFICIALLAYER
2. MIDDLE LAYER
3. DEEPLAYER

ORIGIN –
• Maxillary process of
zygomatic bone
• Ant 2/3rds of inferior
border of zygomatic
arch
Origin – zygomatic arch
and bone
INSERTION –
Angle of the mandible
Lower post half of
lateral surface of
ramus
ORIGINAND INSERTION
Superficial
layer

ORIGINAND INSERTION
Middle
layer
ORIGIN -
• Medial aspect of ant
2/3rds of zygomatic
arch
• Lower border of post
3rd of this arch
ORIGIN--
-medial aspect of and ant
2/3rd of zygomatic arch
INSERTION -
Centralpartoftheramusof
mandible

ORIGINAND INSERTION
Deep
layer
ORIGIN - Deep surface of
zygomatic arch
INSERTION – Upper part
of
• Mandibular ramus
• Coronoid process

RELATIONS
Superficial : Platysma , Risorius ,Zygomaticus
major, Parotid gland, Parotid
duct, Branches of the facial nerve
Deep Surface: Overlies the insertion of
Temporalis &Ramus of the
mandible.

ACTIONS
Elevates the
mandible
• Side to side
movement
• Protraction
• Retraction

Massetric hypertrophy Submassetric space infections

Deep masseter fibers may be fused with
fibers of the temporalis muscle
 A connection with the buccinator muscle was
observed
by Haller (1978)
 Rare anomaly-phocomelia, the muscle is absent.
 Some fibers may circle around the mandibular angle
and join the medial pterygoid muscle – forming a
powerful sling
VARIATIONS

TEMPORALIS
Accounts for 37.5 % of the total masticatory muscle mass with a
crosssectional diameter of 4.1 cm 2
- Mc Donald & Andrews 1953
Zenker 1955 ; Schumacher &
Shinker 1960

ORIGIN
• Whole part of
temporal
fossa
• Deep surface
of temporal
fascia

INSERTION
i) Medial surface,
Apex, Ant & post
borders
Coronoid process
ii) Ant border of
ramus of
mandible upto
the last molar
tooth

Relations
 Superficial – Skin, temporal fascia, superficial temporal
vessels, Auriculotemporal nerve, zygomatic arch , masseter,
 Anterior border – separated from zygomatic bone by a
mass of fat
 Posterior border – Above – temporal fossa
Below – major components of
Infra temporal fossa

ACTIONS
1. Elevates the
mandible
2. Side to side
grinding
movements
3. Posterior fibres –
retract the
protruded
mandible

CLINICAL IMPORTANCE
 When lower dentures are fitted, they should not
extend into the retromolar fossa to prevent trauma
of the mucosa due to the contraction of the
temporalis muscle.
 A plane exists between the temporal fascia which is
attached to the superior surface of zygomatic arch & the
muscle beneath the arch…
 Elevator is introduced into this plane beneath a fractured
zygomatic arch/bone in order to reduce the fracture
 Gillies approach

Variations
 Variations in the thickness and surface areas of temporalis
muscle are relatively common.
 Occasionally the muscle is placed far superiorly and closely
approaches the sagittal suture.
 The most anterior tendon insertion may extend very close to the
third molar
 Henke (1884) applied the term “lesser temporalis” to a bundle
that arises from the articular disc of the TMJ lateral to thelateral
pterygoid muscle and fuses with the posterior border of the
temporalis in the deep layer of the masseter muscle.

ORIGIN AND INSERTION
ORIGIN:
•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
Insertion:It is
attached as
high as
mandibular
foramen and
as far
forward as
the mylohyoid
groove

Relations
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 nerves,the
maxillary artery and
sphenomandibular ligament.
Medial surface – tensor palatine
& superior constrictor
Lateral surface - Ramus

Actions
1.Elevation : (bilateral)
2.Protrusion : (bilateral)
3.Contralateral excursion: (unilateral)

CLINICAL IMPORTANCE
IANB
Intraorally ,to palpate the medial
pterygoid muscle slide the index finger a
little posterior to the insertion site of
inferior alveolar nerve block, to where
the muscle is felt & press laterally.

ORIGIN AND INSERTION
ORIGIN:
•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.

Insertion
Its fibers pass backwards
and laterally 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
SUPERFICIAL
Ramus of the mandible
Maxillary artery
Tendon of temporalis and masseter
DEEP SURFACE
Upper part of the medial pterygoid
Sphenomandibular ligament
Middle meningeal artery
Mandibular nerve
UPPER BORDER
Temporal and massetric branches
of the mandibular nerve
LOWER BORDER
Lingual and inferior alveolar nerve

Nerve supply
i) 1 for each head –
anterior trunk of
mandibular nerve
ii) A) Upper head ,lateral
part of lower head
– buccal nerve
B) Medial part of lower
head – branch from
the anterior trunk

ACTIONS :
Actions by the inferior Head
Protrusion (bilateral):
The inferior lateral pterygoids are the 2 prime protractors of the
mandible.
Depression (bilateral):
Contraction of both the lateral pterygoids not only pull the condyles
forward but also along with the suprahyoid & the infrahyoid muscles
help in the depression of the mandible.
Contralateral Excursion (unilateral):
The insertion of the lateral pterygoids is lateral to its origin & thus
the lateral pterygoid muscle acting singly moves the mandible to
the opposite side.

 The superior lateral pterygoids are inactive during opening.
 They are active during the mandibular elevation or closing
along with Temporalis , Masseter & the Medial pterygoid
muscles.
 The Superior head are particularly active when the teeth ,upon
closure, encounter resistance such as a bolus of food.
 Closure on resistance & the Superior lateral pterygoid play an
active role in this.
Action by Superior Head

Slide the fifth finger along the
lateral side of the maxillary
alveolar ridge to the most
posterior region of the
vestibule
( location for PSA nerve block).
Palpate by pressing in a
superior, medial, & posterior
direction.

 Pain &clicking with mandibular motion
 Tenderness to palpation over TMJ
 Lateral pterygoid draws disc and
mandible anteriorly with opending
 When tight prevents posterior motion
of both.
• Anteriorly displaced mandicle –while
closing
• Posteriorly displaced mandible -while
opening
CLINICAL IMPORTANCE
 TMJ joint dysfunction –
PTERYGOID SIGN

Together Medial and Lateral
Pterygoid muscle
Move the mandible to left side
 Left Lateral Pterygoid
 Right Medial Pterygoid
Move the mandible to right side
 Right Lateral Pterygoid
 Left Medial Pterygoid

Sphenomandibularis-5th
muscle
 Recently discovered.
 Previously thought to be a part of
temporalis.
Origin-
 From infratemporal surface of greater wing
of sphenoid bone.
Insertion-
 Mandible.
Blood supply-
 Maxillary artery, from vessels of medial
pterygoid.
Nerve supply-
 Not yet determined.

ACCESSORY MUSCLES
of mastication

DIGASTRIC
Origin – anterior belly from digastric fossa
of mandible , posterior belly from
mastoid notch of temporal bone.
Insertion – intermediate tendon
Innervation - anterior belly by mylohyoid
nerve , posterior belly by facial nerve.
Action – Depresses the mandible ,
elevates the hyoid bone

 Forms anatomically and
functionally floor of the
oral cavity.
MYLOHYOID
 The right and left muscles are united in the
midline between the mandible and the hyoid bone
by a tendinous strip-the mylohyoid raphae.

ORIGIN
 Mylohyoid line on the inner surface of
the mandible.
 Anterior fibers originate fromlower
border of the mandible.
 Its most posterior fibers take their origin
from the alveolus of the third molar.
INSERTION
 The posterior fibers run steeply
downwards medially and forward n gets
attached to body of the hyoid bone.
 Majority of fibers however join those of
the contralateral muscles in the
mylohyoid raphae.

NERVE & VASCULAR SUPPLY:
 Mylohyoid nerve of the mandibular nerve.
 Submental artery, Facial artery
FUNCTION:
 Posterior fibers run vertically from the mandible to the hyoid; if
mandible is fixed, they lift the hyoid bone, and if the hyoid is in
place they depress the mandible.
 Anterior fibers elevate the floor of the oral cavity there by acts
as elevator of the tongue.

ORIGIN
It arises above the
anterior end of the
mylohyoid line from the
inner surface of
mandible
including inferior
mental spines by a short
and strong tendon.
INSERTION
attachedto the upper half
of the hyoid body.
GENIOHYOID

PHYSIOLOGY OF
MASTICATORY
MUSCLES

Mastication Deglutition Speech

MASTICATION
Human masticatory motor system –
remarkable machine
Chewing, swallowing, speech
 High force activities
 Extremely precise movements (speech)

 Voluntary
 Reflex
 Cyclical
 During closing movement – jaw closing muscles on both
sides are activated at the same time
 Opening – only jaw openers are active
 Chewing stroke – activity of left masseter is less than right
masseter because most of the work is being done by the
muscles on the right hand side
 Highly coordinated activity of masticatory, tongue & cheek
muscles
CONTROL OF MASTICATION

Forces of Mastication
Males –53-65kg
Females – 36-45 kg
Increases with age upto adolescence

Roleofindividualmusclesinchewing
 Major jaw closing muscles – masseter & temporalis
 Direction in which the fibres run – indicates the direction in which
they apply force
 Temporalis – most post fibres- pull posteriorly
- most ant fibres- pull upwards & anteriorly
 Lateral pterygoid – imp role in several phases of chewing cycle
( pulls the mandible forward during jaw opening, controls the rate
at which the condyle should return to its fossa during closing)
 Jaw opening muscles – not normally required to exert much force
during chewing
 In jaw opening – contraction of digastric

INVESTIGATIONS
Experimental analysis of
masticatory system To analyse patterns of
masticatory activity with
abnormal masticatory function
ELECTROMYOGRAPHY
Specialised technique that is used to
measure the activity of individual muscles

ETIOLOGY OF FUNCTIONAL
DISTURBANCESIN THE
MASTICATORY SYSTEM

Eventsinterrupting normal muscle
function
Local factors–
 Restoration in supraocclusion/improperly occluding crown
 Fracture of a tooth
 Secondary to Trauma involving local tissues (post
injection response following L.A, wide opening of
mouth{long dental procedure, yawning}, unaccustomed
use{bruxism, biting on hard object, gum chewing})
Systemic factors-
 Emotional stress
 Acute illness or viral infections
 Constitutional patient factors( immunologic resistance)-
affected by age, gender, diet

Functional
• Speaking
• Chewing
• Swallowing
• Clenching/grinding of
teeth
• Oral habits
Parafunctional/
Nonfunctional
Activities of masticatory
system
Muscle hyperactivity Parafunctional activities +
general increase in level of
muscle tone

SIGNS AND
SYMPTOMS OF
DISODERSOF
MUSCLES
“You can never diagnose something
you have never heard about”

Okeson’s
classification
Masticatory
muscle
disorders
Local myalgia
Myofascial pain
Myositis
Myospasm.
Myofibrotic contraction.
Centrally mediated
myalgia/chronic myositis

PAIN
 Most common complaint
 Central mechanisms
 Slight tenderness – extreme discomfort
 Muscle fatigue, tiredness
 Origin – certain allogenic substances Muscle pain
 Severity of muscle pain ∞ functional activity of muscle
 Cyclic muscle spasm
 Headache

DYSFUNCTION
 Common clinical symptom
 Decrease in range of mandibular movement clinically seen
as inability to open mouth widely
 Acute malocclusion

83
Clinical masticatory muscle pain
model

Protective co-contraction
(Muscle splinting)
 First response of muscles to any event
 CNS response to injury or threat of injury.
 Co - contraction of antagonist muscles (during opening of mouth
increased activity of elevator muscles and vice versa)
 Normal protective or guarding mechanism.
 Not a pathologic condition – prolonged – may lead to muscle
symptoms
84

 Etiology- Any change in sensory input from associated
structures {High restoration/crown ,deep pain input or
emotional stress}
 Clinically - Muscle weakness following an event
 No pain occurs when muscle at rest - Use of muscle increases
pain.
 Limited mouth opening but when slowly opened-full
opening.
 Key factor- immediately follows an event(history)
85

 Altering the restoration, occlusal condition
• SUPPORTIVE TREATMENT
 When cause is tissue injury/ trauma
 Restrict use of mandible
 Soft diet
 NSAIDS
DEFINITIVE TREATMENT
 Directed towards the reason for co-
contraction.

 1st response to prolonged co contraction.
 Co-contraction- CNS induced muscle response
 Soreness- changes in local environment of muscle tissue
 ( release of bradykinin)
 Excessive use- ‘delayed onset muscle soreness’ or ‘postexercise
muscle soreness’
 Clinically – muscle –tender on palpation, increased pain on
function, structural dysfunction, limited mouth opening, acute
muscle weakness
Local muscle soreness
(Non inflammatory myalgia)

 Eliminate ongoing altered sensory input
 Eliminate source of deep pain
 Restrict mandibular use
 Reduce non functional tooth movements
 Decrease emotional stress
SUPPORTIVE TREATMENT
 Mild analgesic –every 4-6hrs for 5-7 days
 Passive muscle stretching, gentle massage

Myospasm (Tonic Contraction
Myalgia)
 Myospam of masticatory muscles –not common.
 Etiology- local muscle conditions (muscle fatigue, changes in
electrolyte balances) ,deep pain input
 Clinically - Structural dysfunction( jaw positional changes
acute malocclusions ), firm muscles on palpation
 Short lived (similar to leg cramps)
 Repeated –DYSTONIA
 Mouth forced open (opening dystonia), or closed(closing
dystonia) or even off to 1 side

Reducing the spasm
Reducing the pain
Passively stretching the involved muscle
Manual massage
Injection – 2% lignocaine without vasoconstrictor
Elimination of the factor
Secondary to fatigue –rest
Physio therapy
 Deep massage& passive stretching
Muscle conditioning exercises
Relaxation techniques

Myofacial pain (Trigger point
Myalgia)
 1st described – Travel & Rinzler-1952
 Arises from hypersensitive bands of muscle tissue – TRIGGER
POINTS
 Felt as taut bands when palpated elicit pain
 Source of constant deep pain central excitatory effects 
referred pain reported as headache pain
 Etiology- trauma,hypovitaminosis, fatigue,viral infections,
emotional stress
 Clinically – trigger points, no local muscle sensitivity, mostly
related to central effects (referred pain)
For treatment to be effective, it must be directed
towards the source of pain

 Diagnosis – trigger points (active/latent)
 Activated by various factors (increased use of muscle,
strain on muscle, emotional stress, upper resp. tract
infections )  headache returns
 Other central excitatory effects – secondary hyperalgesia,
co-contraction, local muscle soreness
Clinical symptoms are associated with the central excitatory
effects created by trigger points and not the trigger points
themselves

 DEFINITIVE TREATMENT
 Eliminate source of deep pain
 Reduce local & systemic factors
 Proper sleep
 Elimination of trigger points (spray & stretch,
pressure & massage, injection & stretch)
 SUPPORTIVE TREATMENT
 Physical therapy
 Manual techniques(soft tissue immobilization,
muscle exercises)
 Muscle relaxants, analgesics

Characteristic sign of MPDS------
LASKIN'S 4 CARDINAL SIGNS
1) Pain in pre-auricular region
2) Tenderness in one or more
muscles of mastication
3) Clicking / popping noise in the
joint
4) Restricted/ deviated mouth
opening
Laskin also emphasized that other than the above positive
signs,,the following signs must be absent
There should be absence of clinical,radiographic or
biochemical evidence of organic changes in TMJ
There should be no tenderness on palpation via external
auditory meatus

Perpetuating factors for Chronic Myalgias
LOCAL
1. Protracted cause
2. Recurrent cause
3. Therapeutic mismanagement
SYSTEMIC
1. Continued emotional stress
2. Sleep disturbances
3. Learned behavior
4. Secondary gain
5. Depression

5) Centrally mediated myalgia
(Chronic myositis)
 Originating from CNS effects felt peripherally in the muscle
tissues
 Symptoms similar to inflammatory condition - MYOSITIS
 Neurogenic inflammation
 Etiology – Prolonged input of muscle pain + local soreness,
central mechanisms
 Clinically - Continuity of muscle pain ,Constant aching
myogenous pain , Pain present during rest and increases with
function, muscles are tender to palpate, structural dysfunction.

 Recognize condition correctly
 Restrict mandibular movement
 Avoid exercise /injections
 Disengage the teeth
 NSAIDS
 Careful physiotherapy
 Moist heat/cold packs
 Gentle stretching

Chronic systemic myalgic
disorders
(Fibromyalgia)
 Global musculoskeletal pain disorder
 Often confused with acute masticatory muscle disorder
 Tenderness - specific tender point sites throughout the
body.
 Etiology – central mechanism

 When other masticatory muscle disorders-
present –therapy
 Perpetuating factors – properly addressed
 NSAIDS
 Sleep
 Depression – managed
 Physical therapy
 Manual techniques(moist heat, gentle massage,
passive stretching, relaxation)
 Mild, well controlled exercise

MUSCULAR DYSTROPHIES
 Rare , inherited muscle diseases
 Muscle fibres are abnormal due to a genetic defect
 Progressively weaker
 Replaced by fat and CT
 Deficiency / malfunction of the muscle protein
(dystrophin / dystropin associated proteins)

Duchenne’s muscular
dystrophy
Most common form of muscular dystrophy
in children
Young boys
Muscles of pelvis & limbs – 1st affected
Masticatory system – involved later
Weakness in masticatory & facialmuscles
Abnormal patterns of force production
Remodelling of facial bones , malocclusions

BRUXISM
 Parafunctional activity
 Clenching/grinding of teeth
 1 of the structures involved- Muscles of mastication
 Fatigue to muscles of mastication
 Not giving them time to relax
 Tender

Treatment usually includes medication,
trigger point injection and physical therapy.
Drugs usually used are :-
• Aspirin : 300 to 600 mg /4 hourly
(escosprin)
• Piroxicam: 10 to 20 mg /tid (pirox)
• Ibuprofen :200 to 600 mg tid(combiflam)
• Pentazocine:50mg bd/tid(Talwin)
• Valim:5 to 10 mg bd(Valim5)
• Methocarbamol :500mg bd(Neuromol-MR)
• Amitriptyline :10-25mg bd/od(Amitrip 25)
TREATMENT AND DRUGS

Trismus/Lock jaw
 Trismus-defined as a prolonged tetanic spasm of the jaw
 muscles by which the normal opening of mouth is
restricted
 (locked jaw) Avg interincisal opening-13.7mm (5 to
23mm)
 Causes- inflammation of muscles of mastication due to needle
prick to medial pterygoid .
 Management- Analgesics, muscle relaxants,
antibiotics,physiotherapy

Trismus/Lock jaw
Management-
Analgesics –NSAID’s e.g. ; Ibuprofrn (400-800mgTDS),
Ketorolac (10-20mgTDS), Piroxicam(20mgBD)
Muscle relaxants– e.g.;chlorzoxazone (250mg TDS)
Methocarbamol( 0.5mg TDS)
Antibiotics –e.g; penicillins(500mgTDS)
Cephalosporins like cefixime ,cefadroxil (200-400mgBD) b
physiotherapy

 Gray’s Anatomy – the anatomical basis of clinical practice, 40th edition,
Churchill and Livingstone
 B.D. Chaurasia’s, Human anatomy, vol 3 - 4th edition - CBS publishers –
2004
 K.D. Tripathi Essentials of Medical Pharmacology.
REFERENCES

Muscles of masstication s2

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