Muscles of mastication /certified fixed orthodontic courses by Indian dental academy

Department of
orthodontics
Good morning to all
INDIAN DENTAL ACADEMY
Leader in continuing dental education
www.indiandentalacademy.com

MUSCLES OF MASTICATION
A. Introduction.
B. Embryological Development.
C. Anatomy of Muscles.
D. Actions or Physiology.
E. Clinical Evaluation.
f. Significance in relation to
orthodontics.
g. Effect of functional appliance.

INTRODUCTION
Masticatory functions like speaking, yawning and swallowing
involve reflex contraction and relaxation of the muscles of
mastication.
It is Impossible to determine clinically if a particular muscle is
participating in a particular movement solely from its origin and
insertion.

 The Masticatory muscles concerned
with the mandibular movements are
following :-
1. Major Masticatory muscles
2. Ancillary Masticatory muscles
1. Major Masticatory muscles :-
(a) Masseter muscle
(b) Temporails muscle
(c) Lateral pterygoid muscle
(d) Medial pterygoid muscle
2. Ancillory Masticatory Muscles :
(a) Digestric Muscle
(b) Mylohyoid Muscle
(c) Geniohyoid Muscle

Embryological Development of
masticatory muscle.
Muscles of mastication develops from the mesoderm of the first
brachial arch that is also called mandibular arch.
Formation of pharyngeal arches

- All the muscles of mastications are the straighted
muscles. They derived from first branchial arch except
the posterior belly of digestric muscle which is derived
from the second branchial arch and supplied by the
branches of facial nerve.
- These muscles in later body development may or may
not retain it's attachments to the skeletal element
derived from the arch. It may subdivide to form number
of distinct muscle which may migrate away from the
pharyngeal region. When they do so how ever they carry
these nerve with them and the were embryolgical origin
can thus determine from their nerve supply.

ANATOMY OF MUSCLES OF
MASTICATION
1. Massater Muscle
• Massater muscle is a quadrilateral muscle
• It consists of three layers
(a) Superficial layer
(b) Medial layer
(c) Deep Layer

Origin :
(a) Superficial layer
• It is largest layer.
• It arises by a thick aponeurosis from the maxillary
process of zygomatic bone and from the anterior two
third of the inferior border of zygomatic arch.
(b) Medial Layer
• It arises from the medial aspect of the anterior two
thirds of the zygomatic arch and from the lower border
of the posterior third of the zygomatic arch.

(c) Deep layer
• It arises from deep surface of the zygomatic arch.
Insertion :
• Fibres of the superficial layer pass downwards and
backwards to insert into the angle and lateral surface of
the mandibular ramus.
• Fibres of the middle layer Insert into the central part
of the mandiblular ramus
• Fibres of the deep layer insert into upper part of the
mandibular ramus and into it's coronoid process.

Relations :
(a) Superficial relations
- Skin, Platysma Risorious, Zygomaticus Major and Parotid Gland.
- Muscle is crossed by the parotid duct, branches of facial nerve
and transverse facial vessels.
(B) Deep relations
- Temporails and mandibular ramus.
- A mass of fat separates it in front of the buccinator and the buccal
nerve.
- Masseteric nerve and artery reach the deep surface of the muscle.

Nerve Supply :
Supplied by the branches of the anterior trunk of the
mandibular nerve.
Actions :
i. Elevate the mandible to occludes the teeth in
mastication.
ii. Masseter has small effect in side to side movements,
protraction and retraction.

(b) Temporails muscle
Temporails muscle is covered by temporal fascia.
Origin :
temporalis muscle arises from the whole of the temporal fossa and
from the deep part of the temporal fascia.

Insertion-
It's fibers converge and descend into a tendon which
passes through the gap between zygomatic arch and
side of skull and attaches to the medial surface, apex,
anterior and posterior borders of the coronoid process
and the anterior border of ramus of the mandible.
· Anterior Fibers of this muscle are oriented
vertically, the most posterior fibers horizontally and
intervening fibers obliquely in a manner of fan.

RELATIONS :
Superficial :
Skin, temporal fascia, superficial temporal vessels,
auriculotemporal nerve, zygomatico temporal nerve
zygomatic arch and Massater muscle.
Deep Relation :
Temporal fossa lateral pterygoid, superficial head of the
medial pterygoid and maxillary artery.
Nerve Supply :
Deep temporal branches of the anterior trunk of the
mandibular nerve.

ACTIONS :
i. Temporalis elevates the mandible to close mouth
and approximate the teeth, this movement requires the
both the upward pull of the anterior fibres and
backward pull of the posterior fibres.
ii. It also contributes in the side by side grinding
movements.


(c) Lateral pterygoid muscle

It is a short, thick muscle with two heads -
a) Upper head
b) Lower head

Origin :
a) Upper head arises from infratemporal surface and
intratemporal crest of the greater wing of the sphenoid
bone.
b) Lower head arises from the lateral surface of the
lateral pterygoid plate.

Insertion :
It's fibres pass backward and laterally to be instered into a
depression on the front of the neck of the mandible and into
the articular disc and capsule of T.M.J.
RELATIONS:
Superficial :
Ramus of manidble, maxillary artery. The tendon of
temporalis.

Deep :
Upper part of the medial pterygoid, sphenomandibular
ligament, middle meningeal artery and mandibular nerve.
Upper border :
It is related to the temporal and Masseteric branch of
mandibular nerve.
Lower border : It is related to the lingual and inferior alveolar
nerve.
- The buccal nerve and maxillary artery pass between two
heads.
Nerve Supply : Branches from the anterior division of mandibular
nerve.
Actions : Protraction of mandible.

(d) Medial pterygoid muscle :
- It's a quadrilateral muscle. It has a small
superficial head and a large deep head which forms
of the major part of the muscle.
Origin :
a) Superficial head : It arises from the
tuberocity of the maxilla and adjoining bone.

b) Deep head from the medial surface of the lateral
pterygoid plate and adjoining part of the palatine
bone.

Insertion :
The fibres sun downwards backwards and laterally to
be inserted into the roughened area on the medial surface of the
angle and the adjoining part of the ramus of the mandible, below
and behind the mylohyoid groove.
Nerve Supply :
Nerve which is a branch of the main trunk of the
mandibular nerve.

Actions :
·        Elevates the mandible.
·        Helps to protrude the mandible.
·        Helps in producing side to side movement of mandible along
with the lateral pterygoid muscle.
(D) Actions or Physiology :
Mandibular movements during normal function and during Para
function involve complex neuromuscular patterns originating in part
is a pattern generator in the brain stem and modified by influences
from higher centers namely :-
·        cerebral cortex
·        basal ganglia
· peripheral influences (e.g. peridontium, muscles etc.)

MANDIBULAR OPENING :
The digastric mylohyoid and Geniohyoid muscles are
active during the jaw opening either slowly or maximally
against resistance.
No activity occurs in the Temporalis and masseter
muscles when the mouth ins opened slowly and the jaw
opened maximally.
When the jaw is opened against resistance the
Temporalis muscle remains silent. During opening
movements, the lateral pterigoid muscles show initial and
sustained activity.
In forced depression the digastic muscle is activated
along with the lateral pterygoid muscle.

Mandibular Closing :
Mandible is elevated slowly without contact of
the teeth or resistance, it is brought about by the
contraction of the masseter and medial pterygoid muscle.
Mandible is elevated against resistance, it is
brought about by the contraction of the temporalis,
masseter and medial pterygoid muscles.

RETRUSION :
· Voluntary mandibular retrusion with the
mouth closed is brought about by contraction of the
posterior fibers of the Temporalis muscle and by the
suprahyoid and infrahyoid muscles.
· Retraction of the mandible from protrusion and
without occlusal contact is effected by the
contraction of the posterior and middle fibers of the
Temporalis muscles.

PROTUSION :
Lateral movement of the mandible to the right side
without occlusal contact is achieved by ipsilateral contraction of
primarily the posterior fibers of the Temporalis muscle.
Movement to the left side without occlusal contact is
brought about by the contralateral contraction of the medial
pterygoid and masseter muscles.
Movement to the right side with occlusal contact is
achieved by ipsilateral contraction of the Temporalis muscle.
Movement to the left with occlusal contact is brought
about by contralateral contraction of the medial pterygoid and
masseter muscles.

CCHEWING :
Chewing is highly complex and oral motor behaviour usually
seen in the frontal plane in simple form.
· The vertical dimensions of chewing cycle are between 16
and 20 mm and between 3 and 5 mm for lateral movements.
Duration of the cycle varies between 0.6 to 1 second depending
on the type of food and among individual.
· The speed of masticatory movement varies within each
cycle, according to types of food, and among individuals. Speed,
duration and form of the chewing cycle varies with the type of
occlusion, kind of food and presence of dysfunction.

(E) CLINCIAL EVALUATION :
·        Muscles of mastication are evaluated extra orally and
intra orally by palpation.
·        As a guide to extra oral digital palpation of the muscles,
two pounds of pressure is the normal recommendation.
·        For intraoral palpation one pound or less is normally
recommended.
·        Digital palpation should be simultaneously bilateral, in
order for the patient to be able to make a comparison, especially if
the pain symptoms are unilateral.
·        The muscles are examined with bilateral palpation for
comparison, for pain, rigidity and size.

Palpation of Masseter muscle :
· The superficial masseter is palpated at three sites -
1. the origin along the inferior border of the zygomatic arch.
2. the insertion along the lateral aspect of the ramus,

3. the body of the muscle.
· It is best examined using a bi-digital
approach of one index finger extra orally (over the
body of the masseter muscle) and the other index
finger intra-orally, adjacent of the extra oral finger.
· The deep masseter is palpated extraorally at the
angles of the mandible, about one inch below the
condyle.

Palpation of the temporalis Muscle:
        The temporalis muscle is palpated at three sites as it
is a fan-shaped muscle.
o      the anterior temporalis muscle is palpated posterior to the
orbit in an area that is slightly depressed.
o      the mid or deep temporalis is palpated directly above the
zygomatic arch on a vertical line with the TMJ.
o      The posterior temporalis is palpated directly over the tops
of the ears.

Palpation of the medial pterygoid muscle :
· The insertion area of the medial pterygoid muscle at the
inferior inner surface of the body of the mandible can be
approximately palpated with two fingers pressing upward and
laterally against the inner bony mandible.

Palpation of the lateral pterygoid muscle
:
The little finger is inserted facial to the
maxillary teeth and around distal to the
ptergoymaxillary, or hamular notch to palpate
the lateral pterygoid muscle.

f. Significance in relation to orthodontics
The facial muscles can affect jaw growth in two ways:
a. The formation of bone at the point of muscle attachments
depends on the activity of muscle.
b. The musculature is an important part of the total soft tissue
Matrix whose growth normally caries the jaws downwards and
Forwards.
•If Loss of part of musculature occur in utero due to any birth
Injury it results in underdevelopment of that part of face .
•In cerebral palsy – decreased muscle tonicity which leads to
increase in ant. Facial height ,distortion of facial proportion
and mandibular height ,excessive eruption of post teeth and
ant open bite.

G. Effect of myofuntional appliance
It improve the muscle tonicity.
If there is disturbance in the equilibrium of the muscular forces
That may lead to malocclution.only masticatory muscle is not
Involved in maintaining the equilibrium .Respiratoy,Swallowing
Yawning ,other physiological processes musculature also contribute
in maintaining equilibrium. if there is any disturbance that may lead
To malocclution.That may be corrected by myofuntional appliance.

Books Referred
1
2.
Inderbir singh (human embryology)
Grays-text book of anatomy.
Wheelers --dental anatomy3.
4. Proffit— contamporary orthodontics
5. Graber and neumann –removable orthodontic appliances
6. Graber --orthodontics 3rd
edition.
7. S.R.Prabhu –text book of oral medicine.
8. Shillingburg et al –fundamental of fixed prosthodontics.

THANK YOU
BY- DR. NITIN GOYAL
Under guidance of DR.SANDESH PAI
(HOD)

Thank you
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Muscles of mastication /certified fixed orthodontic courses by Indian dental academy

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