muscles of mastication saurav 2

7/28/2019 Muscles of Mastication Saurav 2

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MUSCLES OF MASTICATION

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Presented by - Dr. Saurav Chaturvedi

PG 1st Year, Dept. of Orthodontics

PCDS & RC, Bhopal

Ortho.fourthmolar.com
http://www.fourthmolar.com/


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Contents

Introduction

Development

Primary muscles

Accessory muscles

Physical examination of muscles Muscles & Malocclusion

Chewing

Muscle disorders

Literature Reviews Conclusion

References

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INTRODUCTION

Masticationis defined as the process of chewing food in

preparation for swallowing and digestion. Four pairs of

muscles in the mandible make chewing movements possible.

These muscles along with accessory ones together are termed

as MUSCLES OF MASTICATION.

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These muscles can be divided into:

Basic muscles:-Lateral pterygoid

-Medial pterygoid

-Temporalis

-Masseter

Accessory muscles:

-Buccinator

-Digastric muscle (anterior belly)-Mylohyoid

-Geniohyoid

-Orbicularis oris

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DEVELOPMENT

The basic muscles of mastication develop from themesenchyme of the first branchial arch.

So they receive all their innervations from the mandibular

branch of the trigeminal nerve, all from the anterior divisionexcept the medial pterygoid which gets its nerve supply from

the main trunk.

Also they originate from the same origin from temporal andinfra-temporal fossa of the skull and are inserted in the

mandible.

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MOVEMENTS OF MANDIBLE

Movements that the mandible can undergo are:

1. Depression: as in opening the mouth.

2. Elevation: as in closing the mouth.

3. Protraction: horizontal movement of the mandible anteriorly.

4. Retraction: horizontal movement of the mandible posteriorly.

5. Rotation: the anterior tip of the mandible is slewed from side toside.

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These movements of mandible are performed by various

muscles involved in it. So, functionally, the muscles of

mastication are classified as:

Jaw elevators:

Masseter

Temporalis

Medial pterygoid

Upper head of lateral pterygoid

Jaw depressors:

Lower head of lateral pterygoid

Anterior digastric

Geniohyoid

Mylohyoid8


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TEMPORALIS

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TEMPORALIS

It is the largest among all the masticatory muscles andis a fan shape muscle.

Origin; from the inferior temporal line , floor of thetemporal fossa and from the overlaying temporalfascia.

Insertion; anterior and medial tip of the coroniodprocess.

It has been divided into 2 heads: Deep head (anterior, middle and posterior fibers)

Superficial head (much smaller)

10Human anatomy by B.D. Chaurasia, 3rd ed.


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Action:

Elevation (anteriorfibers)

Retraction (posteriorfibers)

Nerve supply:

Anterior division of

the mandibular nerve

(by 2 deep temporalnerves)

14Human anatomy by B.D. Chaurasia, 3rd ed.


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Its action is done by;

The anterior fibers during function actvertically and elevate the mandible.

The posterior fibers diverge and becomehorizontal and retract the mandible.

Blood supply; from the maxillary artery (oneof 2 termination of external carotid artery).

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Human anatomy by B.D. Chaurasia, 3rd ed.


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MASSETER

It consist of 2 overlapping heads:

The origin of the whole muscle is mainly from

the zygomatic process, in which:

-The superficial head arises from the lower border

of the zygomatic arch.-The deep head arises from the inner surface ofthe zygomatic arch.

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SUPERFICIAL HEAD

DEEP HEAD

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Insertion of both the heads is into the outersurface of the ramus of the mandible.

The superficial head passes downwards andbackwards to insert into the lower half of the

lateral surface of the ramus.

While in the deep head, the fibers are more

vertically oriented and inserted into the upperhalf of the lateral surface of the ramus.

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Essentials of oral anatomy, histology and embryology, by Avery and Chiego, 3rd ed.


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Action of masseter is mainly to elevate themandible (antigravity action) and also helps in

protrusive movement.

It is the main muscle involved in the elevation

of the mandible

Nerve supply: by the mandibular branch ofthe trigeminal nerve, from the anteriordivision(massetric nerve).

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Essentials of oral anatomy, histology and embryology, by Avery and Chiego, 3rd ed.


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Blood supply is from the maxillary arterywhich is a terminal branch from externalcarotid artery.

One of the interesting properties of thismuscle is that, internally, the muscle has many

tendinous septa that greatly increase the areafor muscle attachment and so increase itspower.

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Masseteric Hypertrophy

Masseteric Hypertrophy was first described by Legg in 1880.

A hypertrophied muscle will alter facial symmetry, generating

discomfort and negative cosmetic impact in many patients.

It may also produce functional alterations like bruxism,

mandibular prognathism and trismus.

It can be treated by using Botulinum toxin, RF

Electrocoagulation and surgical methods.

Botulinum toxin can reduce upto one third where as surgical

methods can reduce upto two third of the muscle mass.

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An orthodontic perspective. J Ind Orth Soc 2012;46(4):233-237


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MEDIAL PTERYGOID

It is also called as the Pterygoideus internus (Internalpterygoid muscle).

It consist of 2 heads which differ in origin:

Origin:

The deep head originates from the medial surface of

lateral pterygoid plate of the sphenoid bone.

While the superficial head originates from the maxillarytuberosity.

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SUPERFICIAL HEAD

DEEP HEAD

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The muscle inserts into the inner surface ofthe angle of the mandible.

Nerve supply of the muscle comes from themain trunk of the mandibular nerve.

Blood supply is chiefly from the maxillaryartery.

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Action:

1. Elevate the mandible .2. Protrusion of the mandible (lateral & medial

pterygoid on one side protrude the

mandible to the opposite side).3. Side to side movement (these lateral

movements are achieved by lateral & medial

pterygoid on both sides acting together toproduce side to side movements).

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LATERAL PTERYGOID

Also called as the Pterygoideus externus(External pterygoid muscle).

It is a short conical muscle, having 2 heads:upper and lower.

Upper head: Origin: infra-temporal surface & crest of the greater

wing of sphenoid

29JCO -VOLUME 19 : NUMBER 08 : PAGES (584-587) 1985


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Insertion: enters the TMJ & inserted into:

a) Pterygoid fovea of the neck of the mandible

b) Articular disc

c) Capsule of TMJ (anterior aspect)

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Lower head: Origin: Lateral surface of the lateral pterygoid plate

Insertion: its insertion is same as that of the upper head, it

enters the TMJ & gets inserted into:a) Pterygoid fovea of the neck of the mandible

b) Articular disc

c) Capsule of TMJ (anterior aspect)

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The insertion of the lateral pterygoid in the articular disc

occurs in the medial aspect of the anterior border of the disc

and thus it plays a role in the T.M.J. diseases especially

internal derangement.

Some of the T.M.J. diseases have been due to an attributed

variation of the function and attachment of the superior head

as an etiological factor in T.M.J. diseases.

Nerve supply is from the anterior division of the mandibular

branch of trigeminal nerve(nerve to lateral pterygoid).

Blood supply of lateral pterygoid muscle is from maxillary

artery .

33JCO -VOLUME 19 : NUMBER 08 : PAGES (584-587) 1985


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Actions of lateral pterygoid:

1. Depression of the mandible .

2. Side to side movement (lateral movement) .

3. Protrusion of the mandible.

If the Pterygoid muscles of one side act, the

other side of the mandible is drawn forwardwhile the same condyle remainscomparatively fixed.

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ACCESSORY MUSCLES OF MASTICATION

1. BUCCINATOR:

It is an accessory muscle of mastication, occupying

the gap between mandible and maxilla formingimportant part of the cheek.

Its origin is from buccal plate of bone of the socketsof the upper and lower three molars andpterygomandibular ligament.

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BUCCINATOR

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Course and insertionUpper fibers gets inserted into upper lip,Lower fibers gets inserted into lower lip,Middle fibers decussate at the angle of the mouth,

the upper fibers pass to lower lip while the lowerfibers pass to the upper lip .

Nerve supply is from buccal branch of facialnerve.

Blood supply is from facial artery.

The main action of buccinator is to prevent theaccumulation of food in the vestibule of mouth.

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2. ANTERIOR BELLY OF DIGASTRIC:

Origin; it arises from the digastric fossa on the lower border ofmandible on both sides of symphysis menti.

Insertion; into the intermediate tendon which is connected to

the hyoid bone by a fibrous loop.

Nerve supply; is through anterior division of mandibular

branch of trigeminal nerve.

Action; its main action is to depress the mandible .

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ANTERIOR BELLY AND ITS ACTION

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3. MYLOHYOID MUSCLE:

It form the floor of the mouth.

Origin is from mylohyoid line on the internal aspect

of mandible.

Insertion; The fibers slops downwards and forwards

to inter-digitate with the fibers of the other side to

form the median raphe.

This median raphe insert in the chin from above and

the hyoid bone from below.

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Action; Elevates hyoid bone,

supports and raises floor of mouth

which aids in early stage of

swallowing, depress the mandible.

Nerve supply; by nerve to

mylohyoid: which is a branch of

Inferior alveolar branch of

mandibular nerve, which

originates before it enters inferior

alveolar canal.

Blood supply; by Facial artery and

Lingual artery.

This muscle provides a separation

between the submandibular and

sublingual salivary glands.

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MYLOHYOID MUSCLE


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4. GENIOHYOID:

Origin; from inferior genial tubercle (in the midline of inner

surface of mandible).

Insertion; is into the hyoid bone.

Action; depresses the mandible.

Blood supply; is through lingual artery.

Nerve supply; is by hypoglossal nerve.

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GENIOHYOID

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5. ORBICULARIS ORIS:

It has two parts: intrinsic and extrinsic part.

Intrinsic part is a very thin sheet and originates fromsuperior and inferior incisivus. It inserts into the angleof mouth.

The extrinsic part is actually formed by elevator anddepressor muscles of the lips and their angles, andinserts into the angle of the mouth.

The orbicularis oris functions to close and shut themouth and formes the most versatile types ofgrimaces.

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ORBICULARIS ORIS

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Physical Examination Of Muscles Of Mastication

1. EXAMINATION OF MASSETER: The patient is asked to clench their teeth and,

using both hands, the practitioner palpates themasseter muscles on both sides, making sure that

the patient continues to clench during theprocedure.

Palpate the origin of the masseter along thezygomatic arch and continue to palpate down thebody of the mandible where the masseter isattached.

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The masseter is most often tender along the central fibers

of at its insertion.

Masseter hypertonicity is found in patients who have

premature contacts on the nonworking side.

Parafunctions such as bruxism and clenching also give riseto masseter pain that is frequently associated with pain in

the temporalis muscle.

2. TEMPORALIS: The temporalis is palpated in much the same manner

to detect lateral interferences.

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3. LATERAL PTERYGOID:

In patients with nonworking side interferences, thelateral pterygoid muscle on the opposite of theinterference is sometimes painful.

In addition, this muscle will be painful wheneverthere is a centric slide with an anterior componentand the patient is bruxing or clenching in thisanterior position.

The lateral pterygoid, despite its commonality indisplaying a spasm, cannot be palpated intraorally.

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JCO -VOLUME 19 : NUMBER 08 : PAGES (584-587) 1985


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4. MEDIAL PTERYGOID:

The medial pterygoid muscle is not usually

involved in gnathic dysfunctions but whenthey are hypertonic, the patient is usually

conscious of a feeling of fullness in the throat

and an occasionally pain on swallowing.

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Muscles and Malocclusion


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Muscles and Malocclusion

Article published by T.M.Graber. in 1963 June

in AJODO.

This study attempts to balance orthodontic

therapy and musculature philosophically

Orthodontist can balance them physically withappliances.

It deals with the role of muscles in the

etiology and correction of malocclusion.

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Graber TM., T (1963). "The "Three m's": Muscles, Malformation and Malocclusion".Am. Jour.

Orthod.49 (6): 418450.


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Muscles function is normal.

The teeth are in state of balance with

environmental force.

The open bite problem may arise because of

thumb and finger sucking, that gives anexcellent example of applied muscles

physiology.

With changes in tongue ,cheek, and lip musclefunction, the net effect is narrowing of the

maxillary arch and over eruption of post teeth.

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CLASS I MALOCCLUSION

CLASS II DIV I MALOCCLUSION


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CLASS II, DIV I MALOCCLUSION

Abnormal muscle activity.

A change in muscle function is a requisite expansion

is a treatment objective.

In hereditary type of class II malocclusion the teeth

merely reflect the abnormal antero-posterior jawrelationship, and the excessive over jet is

consequence.

If structural mal-relationship exists, the muscle

function adapt to this pattern as best it can in line

with the requirement of mastication, deglutition and

speech.

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The lip may become hypertrophic as a result.

The lower incisors buckle as the mandibular segment isflattened by continuously abnormal mentalis muscleactivity.

The curve of spee increases, buccinator muscle activity.

Openbite also occurs in this abnormal muscle activity cancause the pseudo class II div I.

t/t for this should creation of normal basal bone

relationship that permit muscle function properly andexpansion with appliance.

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CLASS II DIV 2 MALOCCLUSION


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CLASS II, DIV 2 MALOCCLUSION

The role of musculature is more difficult to establish.

Activity of the cheek and lip muscles is usually

normal but curve of spee is excessive that interferes

with the eruption of post teeth.

Because of this TMJ problems arise like clicking, andpain.

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CLASS III MALOCCLUSION

In this we deal with dominant bone dysplasia, with

adaptive muscle function and tooth irregularitiesreflecting a severe basal dysplasia.

It has got strong hereditary pattern the upper lip is

short and lower lip is hypertrophic.

During deglutition cycle there is greater mobility of

the hyoid bone as the suprahyoid and infrahyoid

muscles demonstrate activity.

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CHEWING


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Two separate acts are recognized in the chewing process.

First is a combination of prehension and incision in which the foodis secured by the lips and bitten by the front teeth.

The second is mastication, the major activity during which the foodis mashed between the back teeth.

The total chewing cycle occurs through three phases:

1. The opening stroke during which the mandible is lowered.

2. The beginning closing stroke during which the mandible is rapidly

raised until the entrapped food is felt and

3. The power stroke in which the food is compressed, punctured,crushed and sheared.

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CHEWING MOVEMENTS AND MECHANICS

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The chewing process generally acts as a 2nd order lever system

resulting in compression at TMJ.

The turning moment generated along mandibular body andramus creates a sheer at TMJ.

In 2nd order lever system resistance is present between lever

and fulcrum.

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Chewing in humans is actually asymmetrical and

unilateral.

At the working side: It possesses the greatest adductor force, but articular

emminence is less substantially loaded.

At the balancing side: It possesses the less adductor force and the articular

emminence is substantially loaded.

At the initial action, contraction of inferior head oflateral pterygoid muscle occurs to initiate mandibular

deviation to working side.

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Masticatory Muscle Disorders

Some of the common masticatory muscle disorders

involve:

Congenital hyperplasia/ hypoplasia Hypermobility/ hypomobility of the muscle

Muscle pains

MPDS Myositis ossificans etc.

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CONGENITAL HYPOPLASIA/ HYPERPLASIA

It occurs very rarely, and is more common inmasseter and orbicularis oris.

Its oral symptoms include enlargement ordecreased size of the affected muscle, which mayshow an asymmetric facial pattern and stiffnessin the temporo-mandibular joint.

It may or may not be associated withhypermobility/ hypomobility of the muscles.

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MUSCLE HYPERMOBILITY/ HYPOMOBILITY

This disorder involves extreme or diminishedactivity of the masticatory muscles.

Its etiology includes various factors such as:

Decreased/ increased threshold potential ofneural activity.

Parkinsonism

Facial paralysis

Nerve decompression

Secondary involvement of systemic diseases.

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Muscle Pains

It usually occurs as a result of reflex protective mechanismand myofacial triggers.

It is usually felt as a non-pulsatile variable aching sensation,with a boring quality. It may also present with tightness,weakness, swelling or tenderness.

It includes 3 types:

1. local muscle soreness:

it is a primary hyperalgesia with lowered pain thresholddue to local factors such as stress, injury, infection etc.

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This may be due to:


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This may be due to:

1. distortion of blood vessels within the muscle or

2. forceful or sustained contraction repeatedly.

2. Muscle splinting pain:

it is defined as rigidity of the muscle occuring as ameans of avoiding pain caused by movement of the

part.

it is a reflex protective mechanism.

Splinting of masticatory muscle may occur as a protectivemechanism in conditions such as toothache,overstressed teeth, effect of local anaesthetics, traumaetc.

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3. Non-spastic myofacial pains:

There is no spasm and pain is the only complaint and

this is generally referred to structures outside the

muscle proper.

it may be due to atrophied muscle mass because of

inactivity, illness or nutritional deficiency.

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Zones of referred pain

The masseter muscle pain refers to the ear, TMJ andthe mandibular teeth.

The temporalis refers to the temple, orbit and maxillaryteeth.

The medial pterygoid refers to the infra-auricular andpost-mandibular area.

The lateral pterygoid always refers its pain to the TMJ.

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Myofacial Pain Dysfunction Syndrome (Mpds)


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Myofacial Pain Dysfunction Syndrome (Mpds)

Muscular Disorders (Myofascial Pain Disorders) are the

most common cause of TMJ pain associated withmasticatory muscles.

Common etiologies include:

1. Many patient with high stress level

2. Poor habits including gum chewing, bruxism, hardcandy chewing

3. Poor dentition

Its treatment includes 4 phases of therapy which includes

muscle exercises and drugs involving NSAIDs and musclerelaxants.

A bite appliance is also worn by the patient in the furtherstages to splint the muscle movement.

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Myositis Ossificans

It is a condition wherein fibrous tissue and heterotropic boneforms within the interstitial tissue of muscle, as well as in

associated tendons or ligaments.

It is of two types: localized and generalized.

Localized myositis ossificans:

It is caused by trauma or heavy muscular strains or by metaplasia

of pluripotential intermuscular cnnective tissue.

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The affected site remains swollen and tender, and

the overlying skin may be red and inflamed.

There may present a difficulty in the opening of the

mouth.

management is done by giving sufficient rest to the

muscle and excision of the involved muscle after the

process has stopped.

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Generalized myositis ossificans:

In this, formation of bone in tendons and fascia

occurs along with subsequent replacement of musclemass by the bony tissue.

The masseter muscle is the most frequently involved.

It usually occurs in children less than 6 years of age.

It shows an evidence of dense osseous structures in

the greater part or whole of the muscle.

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There is a gradual increase in stiffness and limitation

in the motion of masticatory muscles. Ultimately, the

entire muscle may get transformed into bone

resulting in no movement.

Management: there is no specific treatment. The

muscles involved are to be excised.

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Literature Reviews


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Nakamura, Zerado and Yoshida concluded that the masseter

muscles activity level was significantly lower in the

malocclusion group than in normal mice. It is, therefore,

suggested that malocclusion interferes with optimizing the

chewing pattern and establishing appropriate masticatory

function.

It is also suggested that masseter muscle activity decreases

following a reduction in masticatory stimulation of the

periodontal ligament. Persistence of this condition might

inhibit the growth and development of masticatory muscles

and their function.

Angle Orthod. 2013;83:749757

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Literature Reviews


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Rowlerson, Raoul & Daniel concluded that there were

significant differences in percentage of occupancy of fiber

types in masseter muscle in bite groups with different vertical

dimensions.

Type I fiber occupancy increased in open bites, and

conversely, type II fiber occupancy increased in deep-bites.

The association between sagittal jaw relationships and mean

fiber area was less strong, but, in the Class III group, the

average fiber area was significantly different between the

openbite, normal bite, and deepbite subjects.

In the Class III subjects, type I and I/II hybrid fiber areas were

greatly increased in subjects with deepbite.

Am J Orthod Dentofacial Orthop 2005;127:3746

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Literature Reviews


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Keisuke, Yasuo and Kazuo employed electrophysiologic

techniques (electromyogram) and found that masseter muscle

activity decreases during the orthodontic treatment and this

must be due to discomfort or pain and the alterations in the

occlusal condition produced by the tooth movement or the

ortho appliance itself.

The Angle Orthodontist Vol 66 no3 1996, 223-228

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Sood, Kharbanda & Duggal found that there was a significant

decrease in the muscle activity (ant. temporalis and masseter)

one month after rigid fixed functional appliance insertionduring swallowing of saliva and maximal voluntary clenching.

Decreased EMG activity of these muscles supported this

finding.Virtual Journal of Orthodontics[serial online] 2011 September, 9 (2)

Literature Reviews


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Easton & David found that there was an increase in action of

lateral Pterigoid and Masseter muscles along with the slight

increase in mandible in rats after treatment with a protrusive

appliance

AM J ORTHOD DENTOFAC ORTHOP 1990;97:149-58

Carene & Steenberghe proposed that during the first phase of

functional treatment ,reflexes in jaw muscles are transiently

brought into imbalance. This phase of imbalance could act as

a trigger for the mandible to attain a new functional position

that subsequently leads to morphologic changes.

AM J ORTHOD DENTOFAC ORTHOP 90: 41 O-41 9, 1986.

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CONCLUSION


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The masticatory muscles include a vital part of the orofacial

structure and are important both functionally andstructurally.

The effect of muscle forces is three-dimensional althoughmost orthodontists have considered it only one vector thatis expansion.

A change in muscle function can initiate morphologicvariation in normal configuration of the teeth andsupporting bone, or it can enhance already existingmalocclusion.

It is imperative that the orthodontist appraise muscle

activity and that he conduct his ortho therapy in such amanner that the finished result reflect balance b/wstructural changes obtain and the functional forces actingon the teeth an investing tissues at that time.

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REFERENCES


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REFERENCES

Oral diagnosis: the clinicians guide- by Birnbaum,Dunne, 2nd ed.

Human anatomy by B.D. Chaurasia, 3rd ed.

Human anatomy by dental students by M.K.Anand,1st ed.

Clinical anatomy and physiology for medicalstudents, by Snell.

Essentials of oral anatomy, histology and embryology,by Avery and Chiego, 3rd ed.

Jco -volume 19 : number 08 : pages (584-587) 1985

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REFERENCES


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REFERENCES

Textbook of oral pathology by Shafers, 4th ed. Textbook of oral medicine, by Avindrao ghom, 1st ed.

Oral anatomy and physiology, bu DuBuller

Burkets oral medicine: diagnosis and treatment, 10th ed.

The Angle Orthodontist Vol 66 no3 1996, 223-228

Virtual Journal of Orthodontics[serial online] 2011September, 9 (2)

Am j orthod dentofac orthop 1990;97:149-58

Am j orthod dentofac orthop 90: 41 o-41 9, 1986.

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