Download - Muscles of mastication
MUSCLES OF MASTICATION
• DR.ASiF IQBAL
• 2nd Year P.G
CONTENTS• INTRODUCTION
• DEFINITIONS
• MUSCLES OF MASTICATION
• CLINICAL CONSIDERATIONS OF MUSCLES
• REFERENCES
MASTICATION :
• Rhythmic opposition and separation of jaws with the
involvement of teeth ,lips ,cheeks and tongue for
chewing of food in order to prepare it for swallowing
and digestion.
• Main purpose of mastication is to reduce the size of
food particles to a size that is convenient for
swallowing (bolus formation) with the help of saliva.
MUSCLE OF MASTICATION• 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.
• There are many muscles which help in the
process of mastication but the main muscles
which take part in the process are
PRIMARY MUSCLES OF MASTICATION
• Masseter
• Temporalis
• Lateral pterygoid
• Medial pterygoid
SECONDARY MUSCLES OF MASTICATION
• Suprahyoid
• Digastric
• Stylohyoid
• Mylohyoid
• Geniohyoid
• Infrahyoid muscles
• Sternohyoid
• Thyrohyoid
• Omohyoid
THESE MUSCLES ATTACHED TO MANDIBLE ARE PRIMARILY RESPONSIBLE FOR :
• ELEVATING
• DEPRESSING
• LATERAL MOVEMENT
• RETRUDING
• They are funtionally classified as:
Jaw elevator
1. Masseter
2. Medial pterigoid
3. Temporalis
Jaw depresser
1. Lateral pterigoid
2. Digastric
3. Geniohyoid
4. Mylohyoid
LATERAL VIEW OF A FOUR WEEK EMBRYO SHOWING
MUSCLES DERIVED FROM BRANCHIAL ARCHES
COMMEN CHARATERSTIC OF ALL MUSCLE OF MASTICATION
All are inserted to the mandible.
All are innervated by the mandibular division of the trigeminal nerve.
All are concerned for biting and chewing.
FUNCTIONS
To move the mandible.
To secure then stabilize the mandibular positions.
To determine the direction of mandibularmovements .
Masseter• The masseter is a thick, somewhat
quadrilateral muscle, consisting of two parts, superficial and deep. The fibers of the two portions are continuous at their insertion. The masseter muscle is sometimes the target of plastic jaw reduction surgery.
• MIDDLE LAYER
• Origin -anterior 2/3 of the deep
surface and posterior 1/3 of the
lower border of the zygomatic arch,
• Insertion - middle part of ramus.
• DEEP LAYER:
• Origin -deep surface of the
zygomatic arch,
• Insertion - upper part of the
ramus and into the coronoid
process.
Origin : zygomatic arch and maxilla
Insertion : coronoid process, ramus of mandible
Artery Supply :masseteric artery
Nerve supply : mandibular nerve (V3)
Actions : elevation (as in closing of the mouth) and protraction of mandible
ACTIONS OF MASSETER
Actions:
• Elevates the mandible to close
the mouth and to occlude the
teeth in mastication.
• Its activity in the resting
position is minimal.
• It has a small effect in side-to-
side movement, protraction and
retraction.
Palpation• The patient is asked to clench their teeth and,
using both hands, the practitioner palpates the masseter muscles on both sides extraorally, making sure that the patient continues to clenchduring the procedure.
• Palpate the origin of the masseterbilaterally along the zygomatic arch and continue to palpate down the body of the mandible where the masseter is attached
Palpate multiple areas
of massetermuscle
Clinical Importance of Masseter Muscle of
Mastication:• Masseter muscle can be palpated both intraorally and
extraorally
• The masseter muscle is sometimes the target of plastic jaw reduction surgery.
• The muscle that commonly undergoes Hypertrophy in Bruxismis Masseter
• Because of the Multipennate arrangement of fibers masseter is a very powerful muscle
TEMPORALIS
Temporalis The temporal muscle, also known as the temporalis, is one
of the muscles of mastication. It covers much of the temporal bone.
Structure : It arises from the temporal fossa and the deep part of
temporal fascia. It passes medial to the zygomatic arch and inserts onto the coronoid process of the mandible.
The temporal muscle is covered by the temporal fascia, also known as the temporal aponeurosis.
The muscle is accessible on the temples, and can be seen and felt contracting while the jaw is clenching and unclenching.
Origin and Insertion: From the Parietal bone of the skull and is inserted on the coronoid process of the mandible.
Arterial supply: The Deep Temporal artery supplies the large muscle.
Nerve Supply: Trigeminal nerve( this nerve has been associated with being the cause of Headache and migrane.
Embryology :The temporalis is derived from the first pharyngeal arch in development.
Functions:
• Elevation of the mandible
• Retraction of the mandible.
• Crushing of food between the molars.
• Posterior fibers draw the mandible backwardsafter it has been protruded.
• It is also a contributor to side to side grinding movement.
ACTIONS OF TEMPORALIS
• Elevates the mandible, this
movement requires both the upward
pull of anterior fibers and backward
pull of the posterior fibers.
• Posterior fibers draw the mandible
backwards after it has been
protruded.
• It is also a contributory to side to
side grinding movement.
SIDE TO SIDE GRINDING MOVEMENT
Palpation
Palpation• To locate the muscle ,have the patient clench.
• Apply two pounds of pressure
Clinical Importance of Temporalis Muscle:
• Sudden contraction of temporalis muscle will result in coronoid fracture, which is rare.
LATERAL PTERYGOID
LATERAL PTERYGOIDATTACHMENTS
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.
• Its fibers pass backwards and laterally
to be 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.
BLOOD SUPPLY
Pterygoid branch of
2nd part of maxillary
artery
NERVE SUPPLY
Nerve to lateral
pterigoid branch
anterior division of
trigiminal nerve
ACTIONS OF LATERAL PTERYGOID
• Assists in opening the mouth with suprahyoid muscles.
• Right lateral pterygoid and right medial pterygoid turns the
chin to left side as a part of grinding movement.
• When the medial and lateral pterygoids of two sides act
together they protrude the mandible so that the lower incisors
project in front of the other.
• The upper (superior) head being involved in chewing
The combinded efforts of the Digastrics and Lateral Pterygoidsprovide for natural jaw opening.
SIDE TO SIDE GRINDING MOVEMENT
Medial and lateral pterygoid act together to protrude the
mandible
Palpation of Lateral pterygoid
Medial Pterygoidmuscle
Medial Pterygoidmuscle:
• It is a thick muscle of mastication.
Origin and Insertion :
• It Arises lateral pterygoid plate, and from the maxillary tuberosity.
• Insertion is seen on the Medial angle of the Mandible
NERVE SUPPLY
• Branch of the main
trunk of the
mandibular nerve.
BLOOD SUPPLY
• Pterygoid branch of
2nd part of maxillary
artery
• Functions:
• Elevates the mandible.
• Closes the jaw.
• Helps in side to side movement.
Palpation of medial pterigoid
Palpation of medial pterygoid
• gently palpate them on the medial aspect of the jaw,
• simultaneously from both inside and outside the mouth
Clinical Importance of Medial Pterygoid Muscle:
• Medial Pterygoid muscle can be palpated only intraorally
• Most commonly involved in MPDS
• Trismus following inferior alveolar nerve block is mostly due to involvement of medial pterygoidmuscle
The 4 primary muscles of mastication are in turn supported
or supplemented by few secondary muscles known as
SUPRAHYOID GROUP of muscles they are
• DIGASTRIC
• MYLOHYOID
• GENIOHYOID
DIAGASTRIC MUSCLE
• Two bellies united by tendon
• The muscle has secondary role in mastication as a
depressor muscle adding to the action of lateral
pterygoid muscle when mouth is to be opened against
resistance.
MYLOHYOID MUSLE• Flat triangular
• The secondary role of this muscle is evident as a
depressor seen in action when mouth is to be opened
against resistance.
• It elevates the floor of mouth to help in deglutition.
GENIOHYOID
• Short and narrow musle lies above
mylohyoid
• When the hyoid bone is fixed, it
depresses the mandible
GENIOHYOID MUSCLE
IMPORTANT FACTS ABOUT MASTICATION
• There are about 15 chews in a series from the time of food
entry until swallowing
• Average jaw opening during chewing is between 16-20mm
• Average lateral displacement on chewing is between 3 and
5mm
• Men chew faster and have a shorter occlusal phase than
women, it also depends on the type of food
• CLINICAL
CONSIDERATIONS
TETANUS(LOCK JAW)
• Caused by exotoxins of gram positive bacillus Clostridium
tetani.
• Disease of the nervous system characterized by intense
activity of motor neuron and resulting in severe muscle
spasm
CLINICAL FEATURES
• Pain and stiffness in the jaws and neck muscles ,with
muscle rigidity producing trismus and dysphagia
TREATMENT
• All patients should receive antimicrobial drugs
• Active and passive immunization.
• Surgical wound care
• Anticonvulsant if indicated
BRUXISMBruxism : Jaw clenching, with or without forcible excursive movements,
where the intensity of the clenching dictates the severity (or lack of)
grinding .
Clenching- It can occur as a brief rhythmic strong contractions of the jaw
muscles during eccentric lateral jaw movements, or in maximum
intercuspation,
Causes
1) Associated with stressful events
2)Non stress related or hereditary
• Bruxism may lead to
-tooth wear
-fracture of the teeth or restoratrion
-uncosmetic muscle hypertrophy
• Treatment
-coronoplasty
-maxillary stabalization appliance
MYOFACIAL PAIN DYSFUNCTION SYNDROME
• Pain
• Muscle tenderness
• Clicking in the joint
• Limitation in the mouth opening
TREATMENT
• Physiotherapy and Myotherapeutic exercises
• Transcutaneous Electronic Nerve Stimulation
• Muscle relaxants
• surgery
REFERENCES
• B.D.Chaurasias, Human anatomy• Shafer,Hine,Textbook of oral
pathology
• Human anatomy A K Dutta
• Grays Anatomy
• Journal Refernces
THANK YOU