Muscles of mastication /orthodontic courses by Indian dental academy

MUSCLES
OF
MASTICATION
INDIAN DENTAL ACADEMY
Leader in continuing Dental Education
www.indiandentalacademy.com

CONTENTS
Introduction
Development.
Muscles of mastication
Nerve supply
Blood supply
Non masticatory muscles
Prosthodontic considerations of
muscles of mastication
Conclusionwww.indiandentalacademy.com

INTRODUCTION
The muscles of mastication move the
mandible during mastication,speech and
other functional and para functional
activities of the mandible.
These are derived from one muscle mass
and are arranged in that order from
superficial to deep plane.

DEVELOPMENTDEVELOPMENT
Muscles of mastication are formed
from the mesoderm of first
pharyngeal arch.
The mesoderm of arch contains
Skeletal element(mandible)
Striated muscle-supplied by the
nerve of the arch.
Arterial arch.www.indiandentalacademy.com

Muscles ofMuscles of
MasticationMastication
MasseterMasseter
TemporalisTemporalis
Lateral pterygoidLateral pterygoid
Medial pterygoidMedial pterygoidwww.indiandentalacademy.com

MASSETERMASSETER
 Quadrilateral muscle
 Situated between face and parotid
region
 Consists of three layers of fibres
 Superficial fibres
 Middle fibres
 Deep fibres.

MASSETE
R

Origin
Superficial fibres
Anterior 2/3 of lower border of
zygomatic arch and adjoining
zygomatic process of maxilla
Fibres runs downwards and
slightly backwards at an angle
of 45 degree.www.indiandentalacademy.com

Middle fibres
Deep surface of anterior 2/3 and lower
border of posterior 1/3 of zygomatic
arch.
Fibres pass vertically downwards.
Deep fibres
Deep surface of zygomatic arch
Fibres run predominantly in vertical
direction..

INSERTION
Superficial fibres
Lower and posterior part of outer surface of
ramus of mandible
Middle fibres
Middle of the mandibular ramus
Deep fibres
Upper and anterior part of lateral surface of
ramus including a part of coronoid process.

 Middle and deep fibres together constitute the
deep part.
 Deep masseter muscle is also called as-
zygomaticomandibular muscle.
ACTIONSACTIONS
 Strong elevator of mandible
 Superficial fibres helps in protraction.
 Deep fibres in retraction of mandible.
 Electrical activity with mandible at rest is
minimal. www.indiandentalacademy.com

TEMPORALI STEMPORALI S
•It is a fan shaped muscle
ORIGIN
• floor of temporal fossa below inferior
temporal line and from overlying fascia.
•It can be divided into three distinct areas
according to fibre direction and ultimate
function

Anterior Fibres
•Directed almost vertical
Middle Fibres
•Run obliquely across the lateral aspect of
skull (slightly forward as they pass downwards).
Posterior Fibres
•Aligned almost horizontally coming forward
above the ear to join other temporal fibres as
they pass under zygomatic arch.

The fibres converge below to form a
tendon which passes deep to
zygomatic arch
Insertion
• into the coronoid process involving
tip, medial surface and anterior
border of the ramus of the mandible.

Action
 Elevates the mandible
 Anterior fibres: mandible is raised
vertically.
 Middle fibres - elevates the mandible.
 Posterior fibres:retrudes the mandible

 If only one portion contracts the
mandible is moved according to the
direction of those fibres that are activated.
 It is significant positioning muscle of
mandible.
 Actions from both the sides: side to
side movement.
 It is more sensitive to occlusal
interferences than any other masticatory
muscle. www.indiandentalacademy.com

LATERAL PTERYGOID
It is short and thick muscle.
Arises from two heads:
Upper
Lower
Upper head: from infratemporal surface
and infratemporal crest of greater wing of
sphenoid
Lower head: lateral surface of lateral
pterygoid plate

LATERAL
PTERYGOID

LATERAL PTERYGOID

Both heads proceed backward and
laterally.
Converge to form a tendon.
Insertion: lower head depression in front
of neck (pterygoid fovea).
Upper head partly to pterygoid fovea and
partly to capsule and articular disc of TMJ.

Action:
 Both the heads function differently.
 When the lower head of right and left
muscles contract simultaneously the condyles
are pulled down the articular eminence and
mandible is protruded.
 Unilateral contraction causes lateral
movement of mandible to opposite side.

Upper head
It is smaller than the lower head
It is inactive in opening.
Active only in conjunction with elevator
muscles.
Active when closure is against resistance
such as chewing/clenching of teeth.
It is also referred as sphenomeniscussphenomeniscus
muscle.

MEDI AL PTERYGOI D
Quadrilateral muscle & has a superficial and
a deep head.
Origin: Superficial head :
 tuberosity of maxillae
 pyramidal process of palatine bones
Deep head:
 media surface of lateral pterygoid plate.
The fibres passes downwards, backwards
and laterally. www.indiandentalacademy.com

MEDIAL PTERYGOID

INSERTION:
 medial surface of ramus and angle of
mandible below and behind the mandibular
foramen and Mylohyoid groove.
ACTIONS:
elevation of the mandible.
In combination with lateral pterygoid bilateral
and simultaneous contraction helps protrusion.
Alternate contraction produces side to side
movement of mandible.

Since Masseter Temporalis and Medial
Pterygoid Elevates the Mandible and
Exert Antigravity Action They Produce
Rough Markings or Projections on
Ramus of the Mandible.

NERVE SUPPLY:
all muscles of mastication are supplied by the
branches of mandibular nerve.
Nerve to medial pterygoid
It arises from the main trunk of mandibular
nerve.
It is a small branch which supplies the
muscle from the deep surface.

Nerve to masseter muscle:
It arises from the anterior division of the
mandibular nerve.
It passes laterally above the lateral
pterygoid behind the tendon of Temporalis
and in front of TMJ.
The nerve emerges through the sigmoid
notch wit Massetric muscle and supplies
muscle from deep surfaces.

Nerve to Temporalis:
Deep temporal nerves
Usually two in number.
Ascend deep to the upper border of lateral
pterygoid and enter the deep surface of
Temporalis.
Nerve to lateral pterygoid:
It enters the deep surface of muscle.

BLOOD SUPPLY
Second part of Maxillary artery which is
terminal branch of external carotid artery.
Deep temporal – usually two in number
ascend between the bone and Temporalis.
Pterygoid branches: lateral and medial
pterygoid muscles.
Massetric artery: passes laterally through
the mandibular notch and supplies masseter
from deep surfaces.

Non masticatory muscles
Infra hyoid muscles
Supra hyoid muscles
Superficial lateral cervicalwww.indiandentalacademy.com

INFRAHYOID MUSCLESINFRAHYOID MUSCLES
STERNOHYOID
OMOHYOID
STERNOTHYROID
THYROHYOID

STERNOHYOIDSTERNOHYOID
Thin narrow strap like muscle.
Origin-
Posterior aspect of capsule of
sternoclavicular joint and from adjoining parts
of manubrium sterni and clavicle.
Insertion - lower border of body of hyoid bone.
Nerve supply - ansa cervicalis
Action:
 Hyoid depression after elevation in
deglutition, speech and mastication.www.indiandentalacademy.com

OMOHYOIDOMOHYOID
Consists of inferior and superior bellies
united by an intermediate tendon.
Inferior belly - flat and narrow
Arises from the upper border of
scapulae and supra scapular ligament.
It passes forwards and upwards
beneath the sternomastoid where it
ends in the intermediate tendon.

From the latter, the superior belly proceeds
upward lateral to the Sternohyoid muscle
and inserted to the lower border of body of
hyoid bone.
Action
 hyoid depression in prolonged inspiration.

STERNOTHYROIDSTERNOTHYROID
Shorter and wider than Sternohyoid.
Deep and medial to Sternohyoid.
Origin - posterior surface of manubrium
The muscles of both sides diverge above
Overlap the lateral lobe of thyroid gland
Inserted into oblique line of thyroid cartilage
Action-
 depression of elevated larynx after
swallowing or in vocal movements.www.indiandentalacademy.com

THYROHYOIDTHYROHYOID
Small quadrilateral muscle, appears as
upward continuation of sternothyroid.
Origin- oblique line of thyroid cartilage
Passes upward and inserted to lower border
of greater cornu and adjacent part of hyoid
bone.
Action- hyoid depression or elevation of
larynx.

SUPRAHYOID MUSCLESSUPRAHYOID MUSCLES
DIGASTRIC MUSCLE
STYLOHYOID
MYLOHYOID
GENIOHYOID

Digastric MuscleDigastric Muscle
• Consists of posterior and anterior belly united
by an intermediate tendon.
• The posterior belly is longer than the anterior
belly.
POSTERIOR BELLY-
Origin
• Mastoid notch of temporal bone.
• Passes downward and forward and is
inserted into intermediate tendon.www.indiandentalacademy.com

ANTERIOR BELLY:
Origin
• Digastric fossa on lower border of mandible
close to symphysis menti
• It passes downward and backward resting on
mylohyoid and is inserted into intermediate
tendon.
• Intermediate tendon is connected to the junction
of body and greater cornu of hyoid bone by
means of
• Inverted U shaped fascial sling of deep
cervical fascia. www.indiandentalacademy.com

Nerve supply-
Posterior belly- facial nerve
anterior belly- mylohyoid branch inferior
alveolar nerve.
Actions –
•Depresses the mandible.
• Electromyographically it is secondary to
lateral pterygoid in maximal mandibular
depression

• Assists lateral pterygoid to rotate the
mandible at Temporomandibular Joint
• Posterior belly is active in swallowing and
chewing. Both bellies of digastric pull hyoid
bone upward and help in deglutition.
• When right and left digastric muscles
contract , mandible is depressed & pulled
backward and the teeth are brought out of
contact

STYLOHYOIDSTYLOHYOID
Slender muscle, accompanies upper border
of posterior belly of diagastric
ORIGIN
Posterior surface of styloid process of
temporal bone midway between its tip and
base
INSERTION
Hyoid Bone, at junction between body &
greater cornu

NERVE SUPPLY
FACIAL NERVE
ACTIONS
Draws hyoid bone upward and backward
Elongates floor of the mouth

MYLOHYOIDMYLOHYOID
Flat & triangular
Superior to anterior belly of diagastric
With its fellow, forms muscular floor of
oral cavity
ORIGIN
Mylohyoid line on inner surface of
mandible
Fibres slopes downwards and medially

INSERTION
 Posterior ¼ th into body of Hyoid bone
 Anterior ¾ interdigitate in median fibrous
Raphe that extends from Symphysis Menti to
Hyoid Bone
NERVE SUPPLY
 Mylohyoid branch of Inferior Alveolar nerve
ACTIONS
 Elevation of Floor of the Mouth in
deglutition
 Assists in depression of mandible
 Elevates the hyoid bone

GENIOHYOIDGENIOHYOID
Ribbon shaped, lies deep to medial part of
Mylohyoid
ORIGIN
Inferior Genial Tubercle of symphysis
menti
Passes downward & backward
INSERTION
Body of the Hyoid Bone

NERVE SUPPLY
Fibres of C1 conveyed by Hpoglossal nerve
ACTIONS
Depresses the Mandible
Moves Hyoid bone upward & forward
Shortens floor of The Mouth

SUPERFICIAL CERVICALSUPERFICIAL CERVICAL
MUSCLESMUSCLES
Platysma
Sternocleido mastoid
Trapezius

PLATYSMAPLATYSMA
Broad sheet like
ORIGIN
Upper part of Pectoralis Major
Deltoid fasciae
Fibres run upwards & medially across the
clavicle to the side of neck
INSERTION
Anterior fibres interlace across midline
inferoposterior to Symphysis Menti

Intermediate fibres
attached to Lower Border of mandibular body or
passes upwards & medially deep to Depressor
Anguli oris to their attachments in the lateral half
of lower lip(pars labialis)
Posterior fibres
Crosses the midline and anterolateral part of
Masseter blending with the skin and subcutaneous
tissue in the lower face

NERVE SUPP;LY
 cervical branch of Facial nerve
ACTIONS
Anterior thickest part assists in mandibular
depressors
Pulls angle of mouth downward and
backward

STERNOCLEIDOMASTOIDSTERNOCLEIDOMASTOID
Descends obliquely across the neck
Thick and narrow centrally
Broad and thin at each end
ORIGIN
Sternal head – superolateral part of front of
Manubrium Sterni
Clavicular head – medial 1/3 of superior surface
of clavicle
The heads blend in middle of the neck

INSERTION
 Sternal head – lateral surface of Mastoid process from its
tip to its superior border
 Clavicular head – lateral half of superior Nuchal lines of
Occipital bone
NERVE SUPPLY
 Motor supply – spinal accessory nerve
 Sensory supply – branches from ventral rami of C2 & C3
ACTIONS
 When both muscles contract they draw the head forward

TRAPEZIUSTRAPEZIUS
Flat and triangular
Extends over dorsum of neck and upper
thorax
Medially attached to medial 3rd
superior
Nuchal Lines
Superior fibres descend , Inferior ascend,
intermediate fibres approach the horizontal
All converge laterally to the shoulder

INSETION
SUPERIOR FIBRES - posterior border of
lateral 3rd
of clavicle
Middle fibres – to crest of scapular spine
Inferior fibres – medial end of scapular spine
NERVE SUPPLY
Spinal part of acessory nerve
Ventral rami of 3rd
& 4th
cervical spinal nerves
ACTION
Steadies the bone, controlling it during
movement of arm

ProsthodonticProsthodontic
ConsiderationsConsiderations

MASSETER
Only MUSCLE that influences the denture
flanges ,
MASSETRIC NOTCH in distobuccal area of
denture accommodates the mesial border of
masseter,it influences the denture base during
both opening and closing movements of
mandible
Overextension will result in tissue soreness and
displace the mandibular denture .

TEMPORALIS
 The function of middle and posterior fibres
is to elevate and retrude the mandible
respectively
 It is used as a test to determine whether the
patient is closing in centric relation, which is
confirmed with the bulging felt at the
temporal region.m

Helps in lateral and protrusive movements of the
mandible to make extrinsic interocclusal records
or pantographic tracings used to adjust the
horizontal condylar guidance
Superior head acts to fix or stabilize condyle &
disk during elevation of mandible
Uncordinated contraction of two heads produces
unsynchronised movements between condyle and
disc with a resultant click sound in affected joint.
LATERAL PTERYGOID

M YLOHYOID
Influences border of mandibular denture
It elevates floor of mouth during swallowing
If the flanges extends below and under
mylohyoid line, it impinges upon the muscle
leading to displacement of the denture
In extensively resorbed ridges the muscle can
be surgically detached from its attachment &
reattached more inferiorly without impairment
of function

GENIOHYOID
Presents no problem on complete denture
construction until there is extensive loss of
residual ridge

INFRAHYOID MUSCLES
these muscles have no particular significance
in complete denture prosthodontics other
than fixing the hyoid bone
This fixed position of the hyoid bone helps
the action of Suprahyoid muscles on the
mandible

 Muscle activity decreases with lessening
number of posterior teeth and drops dramatically
when only incisors are in contact
 Prior to restorative treatment part of occlusal
examination should evaluate state of TMJ and
masticatory muscles
 Pain resulting from palpating masticatory
muscles may be related to a joint disorder

PALPATION OF MUSCLESPALPATION OF MUSCLES
MASSETER
 Extra orally at origin and insertion(lateral to
maxillary 2nd
& 3rd
Molars)
TEMPORALI S
 Intra orally along the upper aspect of ascending
ramus
LATERAL PTERYGOI D
 Cannot be palpated
 A soft tissue in distal aspect of maxillary buccal
vestibule beyond 3rd
molar and alveolar
ridge(Ash & Ramfjord)

MEDI AL PTERYGOI D
 palpation at the insertion of muscle is at
medial of angle of mandible
 can be done intraorally also with two fingers
placed externally
 Muscle should be palpated bilaterally and
simultaneously (to compare left and right side)

Para functional habits like bruxism or clenching
leads to hypertrophy of muscles of mastication
 If an hypertrophied elevator muscle is identified
during extra oral examination with multiple
Intraoral facets loading on teeth will be quite
high(consider implant system)
Asymmetric muscle activity can be diagnosed by
opening and closing movements

Uncoordinated muscle activity and associated muscle
spasm can luxate or dislocate the mandible and sustain
this position due to spasm of Masseter ,Temporal and
Medial Pterygoid.
Inability of patient to move mandible to right place at
right time will reveal problems in making jaw relation
records
Sex ,state of dentition , physical status & age ,influence
muscle strength and thus masticatory efficiency
Pain in muscles is indicative of TMJ disorders and must
either be treated or compensated in construction of new
prosthesis.(recovering lost occlusal vertical dimension)

Conditioning of Patients Musculature
If the patient responds with difficulty to
instructions for relaxation and coordinated
mandibular movements, mandibular exercises
can permit relaxation of muscles of mastication
and strengthen their coordination which is
beneficial in stages of registration of jaw
relations

 There will be REFERRED PAIN from various
masticatory muscle disorders such as
1. Myofacial pain (trigger points in muscles, tender
to palpate)
2. Myositis (overuse,injury,infection)
3. Myospasm (contraction of muscle-painful-increase
EMG at rest
4. Contracture (resistance of muscle to stretch-
hypomobility).

5. Myalgias (pain in muscles/ TMJ due to increase
activity which is due to increase occlusal impulses)
6. Temporal arteritis
 Symptoms resemble TMJ disorders
 Temporal artery is tender and swollen
 Pain radiated to temporal and masseter muscle.
Referred pain from-
 Lateral pterygoid- to the TMJ
 Medial pterygoid- to maxillary teeth,gonial
angle,ascending ramus.
 Temporalis-TMJ ,orbital regions

Treatment
Elimination of etiologic factors
symptomatic relief
Diet restriction
 NSAID
LA in trigger spots
Occlusal splints,later occlusal therapy

Postural head and body posture
It is maintained by balance between muscular
tone(elevator muscles) and effect of gravitational
forces
Head is flexed-mandible moves upwards and
forward,interocclusal distance is decreased.
Head is extended-mandible moves downwards
and backwards with increase in interocclusal
distance.
Thus patient should be sitting/standing in upright
position and looking straight ahead.

CONCLUSIONCONCLUSION
Movements of head and neck is a result of
finely coordinated efforts of many muscles
which play major roles in stabilizing the
skull and enabling controlled movements of
the mandible .
Muscles of mastication represent only a part
of this complex system.

Ref erencesRef erences
 William’s :Grays anatomy
 Chaurasia :human anatomy vol3.head and neck ,2nd
edition 1992,varghese
 Grants;method of anatomy
 Zarb&Bolender:Boucher’s ;Prosthodontic treatment or
edentulous patients,9th
edition,CBS
 Heartwell :syllabus of complete dentures,1992,4th
edition,Varghese
 Jeffery P.Okeson:Management of TMJdisorders and
occlusion,4th
edition,1998Mosby
 Ramfjord/Ash:Occlusion,3rd
edition,WBSaunders

Rosenstiel . Land. Fujimoto.Contemporary
Fixed prosthodontics, 3rd
edition
Tylman .Theory and practice of Fixed
prosthodontics, 8th
edition
Carl E Misch. Implant dentistry, 2nd
edition
Sheldon winkler. Essentials of complete
denture prosthodontics, 2nd
edition

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