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