Muscles of Mastication

12th JULY 2011 09:30 HrsDEPT OF ORAL MEDICINE, DIAGNOSIS &

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PRESENTED BY: Dr LALIT SINGH NEGIPG STUDENT

GUIDED BY : Dr NAGESH BINJOODr PUNEET BHARGAVADr CHANDNI SHEKHAWATDr ROOPIKA HANDA

CONTENTSINTRODUCTIONTMJ MOVEMENTSCHIEF MUSCLES OF MASTICATIONACCESSORY MUSCLES OF MASTICATIONCLINICAL EXAMINATIONMEDICAL & SURGICAL CONSIDERATIONSCLINICAL APPLIED CONCLUSIONBIBLIOGRAPHY


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MUSCLES


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DEFINITION :Muscle (from Latin musculus, diminutive of mus "mouse") is a contractile tissue of animals and is derived from the mesodermal layer of embryonic germ cells. Muscle cells contain contractile filaments that move past each other and change the size of the cell. They are classified as skeletal, cardiac, or smooth muscles. Their function is to produce force and cause motion. Muscles can cause either locomotion of the organism itself or movement of internal organs.

MUSCLES OF MASTICATION


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During mastication ie chewing of food, four muscles of mastication are responsible for adduction and lateral movements of the mandible which is the only moving jaw.

The four muscles of mastication are :The MasseterThe Temporalis The Lateral PterygoidThe Medial Pterygoid Each of these primary muscles of mastication is

paired, with each side of the mandible possessing one of the four.

Introduction to the TMJ Introduction to the TMJ movementsmovements


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MOVEMENTS MOVEMENTS


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1. Depression of mandible

(mouth opening)

3 muscle groups 1- lateral pterygoid

2- Suprahyoid. 3- Infrahyoid.

* Main mover is Gravity

2. Elevation of mandible

(mouth closing)

3 muscles 1- Masseter. 2- Medial pterygoid.

3- Anterior half of temporalis muscle.


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3. Protrusion of mandible(forwards)3 muscles 1- Lateral pterygoid. 2- Masseter.

3- Medial pterygoid.

main one is Lateral pterygoid.

4. Retrusion/Retraction of mandible

(backwards)by 1- Posterior half of temporalis

2- Deep part of masseter

5. Lat. Movement to the sides:by 1- Lateral and Medial pterygoid of the opposite side

2- Temporalis of the same side.


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CHIEF MUSCLES OF MASTICATION

• Masseter muscle• Temporalis muscle• Medial pterygoid muscle• Lateral pterygoid muscle


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THE MASSETERTHE MASSETER

Thick, somewhat quadrilateral muscle

It has two heads: superficial and deep


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Deep part

Superficial part

TheThe superficial partsuperficial part of of MasseterMasseter

•The largest of the two heads

•Origin: It arises by a thick, tendinous aponeurosis from the zygomatic process of the maxilla, and from the anterior two-thirds of the lower border of the zygomatic arch.

•Insertion: Its fibers pass downward and backward, to be inserted into the angle and lower half of the lateral surface of the ramus of the mandible.


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TheThe deep part of Masseter deep part of Masseter musclemuscle

• Much smaller, but more muscular in texture

Origin: arises from posterior third of the lower border and whole of the medial surface of the zygomatic arch.

Insertion: its fibers pass downward and forward,

to be inserted into the upper half of the ramus

• The deep portion of the muscle is relatedAnt.: the superficial portion

Post.: the parotid gland.

*The fibers of the two portions are continuous at their insertion. 12th JULY 2011 09:30 Hrs

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elevates and protrudes the mandible thus closing the mouth;

deep fibers retrudes it. Swings the chin from one side to

another producing a grinding movement


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ACTIONS OF MASSETER

Innervation:

Mandibular division of trigeminal nerve through masseteric nerve which passes through the mandibular notch to enter its deep surface.


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Blood supply:

masseteric artery from the 2nd part of

maxillary artery


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THE TEMPORALIS MUSCLETHE TEMPORALIS MUSCLEis a broad, radiating muscle,

situated at the side of the head.

ORIGIN: It arises from the whole of the temporal fossa and the deep surface of temporal fascia

INSERTION : Its fibers converge as they descend, and end in a tendon, which passes deep to the zygomatic arch and is inserted into the medial surface, apex, and anterior border of the coronoid process, and the ant. Border of mandibular ramus 12th JULY 2011 09:30 Hrs


Action: its anterior and middle fibers elevate the mandible thus closing the mouth; its posterior fibers retrudes it.


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Innervation:

Deep temporal branches of mandibular nerve.


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Blood supply:

Deep temporal

branches of maxillary artery.


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THE LATERAL PTERYGOID MUSCLETHE LATERAL PTERYGOID MUSCLE

Has two heads: superior and inferior

Origin : the superior head arises from greater wing of sphenoid bone while the inferior head arises from the lateral surface of the lateral pterygoid plate

Insertion: fibers pass backward to be inserted into the neck of mandible and articular disc of TMJ. 12th JULY 2011 09:30 Hrs


Innervation: Ant. division of mandibular nerve through lateral pterygoid nerve


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Blood supply: maxillary artery

through the pterygoid branch.

From the 2nd part


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Action: acting together they protrude and depress the mandible;

acting alone and alternatively they produce side to side movements of the mandible.


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(rotates the mandible to

the opposite side)

THE MEDIAL PTERYGOID THE MEDIAL PTERYGOID MUSCLEMUSCLE

It has two heads: superficial and deep

Origin: the superficial head arises from the maxillary tuberosity. The deep head arises from medial surface of the lateral pterygoid plate

Insertion: fibers run downward, backward and laterally and are inserted into the medial surface of the angle of the mandible


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Innervation: main trunk of mandibular nerve through nerve to medial pterygoid

it also innervates Tensor veli palatini & Tensor tympani.


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Blood supply: Maxillary artery through the medial pterygoid artery

From the 2nd part


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Action: assets in elevating

and protrusion of the mandible

acts together with lat. Pterygoid of the same side in rotating the mandible


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ACCESSORY MUSCLES OF MASTICATION


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Accessory muscles of mastication are those muscles which assist the main muscles of mastication to move the mandible during mastication and speech.These are mylohyoid, geniohyoid and diagastric muscles.

THE DIAGASTRIC MUSCLEThis muscle is so called because it has two

bellies. The bellies are united by an intermediate tendon.

ORIGIN:Anterior belly originates from the digastric fossa of the

mandible.Posterior belly originates from the mastoid notch of the

temporal bone. INSERTION:

The anterior belly runs downwards and backwards, and the posterior belly run downwards and forwards to meet at an intermediate tendon. The tendon is held by a fibrous pulley attached to the hyoid bone.


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NERVE SUPPLY:Anterior belly is supplied by the

mylohyoid nervePosterior belly is supplied by the

facial nerve.

ACTIONS:Helps to depress the mandible when

the mouth is opened widely or against resistance. This action is secondary to that of the lateral pterygoid.

Elevates the hyoid bone12th JULY 2011 09:30 Hrs


THE MYLOHYOID MUSCLE


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This is a flat, triangular muscle lying deep to the anterior belly of digastric. The right and left mylohyoid muscles together form the floor of the mouth.ORIGIN:

It originates from the mylohyoid line of the mandible.INSERTION:

The fibers run medially and slightly downwards. The posterior fibers are inserted into the body of

the hyoid bone. The middle fibers are inserted into median raphae.

NERVE SUPPLY:It is supplied by mylohyoid nerve

ACTIONS:Elevates the floor of the mouth during

the first stage of deglutitionHelps in depression of the mandible

and in elevation of the hyoid bone.


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THE GENIOHYOID MUSCLE

A short and narrow muscle which lies above the medial part of the mylohyoid.

ORIGIN:

From the inferior mental spine (genial tubercle) of the mandible.

INSERTION:

The fibers run backwards and downwards to be inserted into the anterior surface of the body of the hyoid bone.

NERVE SUPPLY:

1st cervical nerve. The fibers pass through the hypoglossal nerve.

ACTIONS:

Elevates the hyoid bone.

May depress the mandible when the hyoid bone is fixed


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CLINICAL EXAMINATION

The temporalis muscles should be examined first and this is accomplished via bilateral finger pressure applied to the muscle along the anterior, middle, and posterior portions


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The masseter is divided into superficial and deep portions that should be individually palpated


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Intra-orally, the temporalis insertion, masseter origin, lateral and medial pterygoids are evaluated bilaterally. In order to palpate the temporalis insertion, the patient opens the mouth and a finger is placed on the anterior border of the ramus of the mandible (just lateral and distal to the third molar area). The finger is then moved superiorly until the most superior portion of the anterior border of the ramus is palpated. This is the coronoid process where the temporalis muscle insertion exists.

Immediately after palpating the temporalis insertion with the finger in the same location, the patient is asked to move the mandible to the ipsilateral side. After the patient moves the mandible laterally, the finger is moved just lateral and superior-distally, and the lateral pterygoid muscle can be palpated


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In addition, the masseter origin can be palpated by next moving the finger from the lateral pterygoid position in an anterior and superior direction. The masseter originates as a thick tendon from the zygomatic process of the maxilla and from the inferior border of the zygomatic arch.

The medial pterygoid muscle is palpated by having the patient open the mouth, and the examiner places finger pressure in the posterior, floor of the mouth (lateral to the tongue and medial to the mandibular posterior teeth).

Intra-oral palpation of the lateral and medial pterygoid muscles is difficult due to limited access. Tenderness elicited with these two specific muscle groups should be interpreted with caution, as an unacceptable rate of false positives can occur.


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MEDICAL & SURGICAL CONSIDERATIONS

The muscles of mastication have important clinical implications as they have important anatomical entities around them like the arteries, nerves & salivary glands.

The disorders affecting the muscles of mastication can have manifestations/symptoms on these surrounding structures and vice versa.

Likewise the medical and surgical treatment of the muscles of mastication can have an impact on these relations & vice versa.

The parotid duct runs anteriorly across the masseter, & hooks medially over the anterior border and can be felt by rolling it against the muscle with the jaw clenched.


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The palpation of Stenson’s duct is important clinically as in to diagnose sialolithiasis in this duct.

The muscles of mastication play an important role in the fracture displacement as they have strong tendinous attachments.

Osteaoarthritis has an early manifestation in the form of spasms of muscles of mastication, resulting in stiffness and locking of the jaw.

Due to a long standing case of TMJ ankylosis there is atrophy or fibrosis of these muscles.

In dystrophic myotonia there is masseteric atrophy which produces a narrowing of the lower half of the face.


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CLINICAL AND APPLIED ANATOMY

MYOFACIAL PAIN DYSFUNCTION SYODROME:A functional disorder involving painful self perpetuating spasm of masticatory muscles.Begins with stress which causes clenching and grinding of teeth, which in turn can lead to muscle fatigue and finally spasm. Results in a self perpetuating cycle of stress-pain-stress is created. Muscles most often involved are lateral pterygoids and masseter muscles.

SYMPTOMS:Unilateral dull pain in the ear or preauricular

region ;commonly worse on awakening.Tenderness of one or more of the muscles of masticationLimitation or deviation of the mandible during opening


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TREATMENT:To relieve the symptoms of this syndrome, it is necessary to break the stress-pain-stress cycle and to treat the emotional and physical components of the disease.Other treatment modalities include:

Spray and stretch: fluoromethane refrigerant spray can be applied to the skin overlying the involved muscles. This anesthetizes the area and allows the patient to slowly stretch the muscles in spasm.

Injecting local anesthetic solution without epinephrine in the involved muscle. Helpful in breaking the spasm and disrupting the stress-pain-stress cycle.


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FACIAL PARALYSIS: Facial paralysis is a disfiguring condition since it leads to not only the inactivity of one side of the face during the active movements of smiling, frowning, but also causes obliteration of the facial furrows that are very important in facial expression.The muscles paralysis manifests itself by the drooping of the corner of the mouth, from which the saliva may run, the watering of the eye, and inability to close the eye which may lead to infection.The patient has typical mask like appearance.

TREATMENT:

Masseter muscle is best used to give motion to lower half of the face. Transplantation of temporalis muscle, aided by a tendon or facial slip is best suited to lend support and dynamic action to the eyelids


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CONCLUSIONIt is of utmost importance to have a thorough

knowledge of the anatomy, actions and clinical relevance of the muscles of mastication and its importance in diagnosis and take maximum advantage of it in surgical management in various conditions of orofacial region.

The muscles of mastication play a vital role in chewing food and speaking hence any anomaly or dis-ease of these can have serious implications on the nutritional status and psycho social development of an individual.

Every clinician must invariably examine them for any signs of tenderness, associated swellings, ulcers or growths so as to diagnose the disorders pertaining to them or the related structures.


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BIBLIOGRAPHYGRAYS ANATOMY: 38TH EDITIONCUNNIGHAM’S MANUAL OF PRACTICAL

ANATOMY VOL. 3 HEAD & NECKANATOMY REGIONAL AND APPLIED:

R.J.LASTHUMAN ANATOMY, REGIONAL AND

APPLIED: B.D.CHAURASIA (VOL-3 HEAD AND NECK)

BURKET’S ORAL MEDICINE: GREENBERG & GLICK ( 10TH EDITION)


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Muscles of Mastication

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