MUSCLES OF MASTICATION

PRESENTED BY

DR MANJIMA KHANDELWAL

PRECEPTOR

DR VISHWAS BHATIA

• Human Beings have got 639 muscles , composed of 6 billion muscle fibers.

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• Each fiber has 1000 fibrils, which means that there are 6000 fibrils that work at one time or another.

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• Muscle is a contractile tissue and is primarily designed for movements.

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• The word muscle is derived from the latin word musculus which means mouse. Certain muscles resemble a mouse with their tendon representing the mouse tail.

• All muscles of the body are developed from mesoderm, except
• Arrector Pilorum
• Muscles of iris
• Myo-epithelial cells of salivary, sweat and lacrimal glands

Derived from ectoderm

CLASSIFICATION of muscles in general

All masticatory muscles are skeletal muscles.

SKELETAL MUSCLES

• Skeletal muscles are supplied by spinal and cranial nerves and are usually under voluntary control.
• Muscles of pharynx and diaphragm are striated but not entirely under voluntary control.

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• Parts of striated muscles: Each muscle presents with the following two parts:
• 1. Fleshy part: It is the contractile, highly vascular part and has a

higher metabolic rate.

• 2. Fibrous part: May be tendinous or aponeurotic, is non elastic, less

vascular and resistant to friction.

• Attachment of Skeletal Muscles:
• The skeletal muscles are attached to the bones and originate from one site and attached to the another site on a different bone usually crossing the corresponding joint.
• Origin of a muscle: The end of a muscle which is fixed during contraction is

known as origin of the muscle.

• Insertion of the muscle: Movable end of a muscle is known as insertion of muscle. In limbs the distal end generally corresponds to insertions. The attachment of skeletal muscles is via tendons, aponeurosis and fasciae.

These are varieties of regular connective tissue which contain dense arrangement of collagen fibers and are continuous with the muscle fibers near the site of attachment. They help attach the muscle to the periosteum of the corresponding bone. They provide strength to attachment, are responsible for change in direction of pull of muscle and help resist forces of stress.

Composition of skeletal muscles

Water- 75%

Solids-25%

20%- proteins

5%- organics other than proteins + inorganic substances

• Classification of skeletal muscles according to Direction of Muscle Fibers:

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• Parallel muscles: Muscle fibers are parallel to the line of pull. The fibers are

long, but their numbers are relatively few.

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Example:

a. Strap muscles: Rectus Abdominus, Sternohyoid.

b. Quadrate muscle: Quadratus Lumborum.

c. Fusiform muscle: Biceps Brachii, Digastric.

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• Functional characteristics: These muscles provide more range of movement but total force of contraction is less.

• Pennate muscles or oblique muscles: Fleshy part of fibers are arranged obliquely to the line of pull. The fibers are short and a greater number of them can be accommodated.
• They are of the following types:

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a. Unipennate muscle: All fleshy fibers slope into

one side of the tendon which is

formed along one margin of the

muscle.

Example: Flexor pollicis longus,

Extensor digitorum.

b. Bipennate muscle: Tendon is formed in the central

axis of the muscle and the muscle

fibres slope from the two sides into

the central tendon, like a feather.

Example: Dorsal interossei of foot and hand.

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• c. Multipennate muscle: A series of bipennate fibers lie side by side in one plane.

Example: Acrominal fibers of deltoid

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• d. Circumpennate muscles: Muscle is cylindrical with a central tendon. Oblique muscle fibers converge into the central tendon from all sides.

Example: Tibialis anterior.

Functional characteristics: It provides for a wide range of movements.

Functional characteristics: Total force of contraction is increased though the range of movement is less.

• Spiral muscle: This type of muscle has a twisted arrangement close to its insertion.

Example: Pectoralis major, Supinator.

• Functional characteristics: Spiral course imparts rotational movement.

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• Cruciate muscle: Muscle fibers are arranged from the superficial to deep planes in a crisscross X-shaped pattern.

Example: Masseter, Sternocleidomastoid.

• Functional characteristic: This arrangement increases the range of movement.

SMOOTH MUSCLES

CARDIAC MUSCLES

MASTICATION

MASTICATION

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The process of chewing food for swallowing and digestion.

-GPT-9

MASTICATING CYCLE

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The pattern of mandibular movements formed during the chewing of the food.

-GPT-9

CHEWING

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CYCLE

MUSCLES OF MASTICATION

EMBROLOGY AND DEVELOPMENT of masticatory muscles

Muscles of mastication develop from the mesoderm of the First pharyngeal arch i.e. mandibular arch and is supplied by the mandibular nerve

Main Muscles of Mastication

• They present with the following features:
• 1. The muscles except masseter are located in the infratemporal region.
• 2. They are inserted in the ramus of mandible.
• 3. All four muscles are innervated by branches of the anterior division and

trunk of mandibular nerve which is the branch of trigeminal nerve.

• 4. Their vascular supply is derived from branches of maxillary vessels.
• 5. All act on the temporomandibular joint

Accessory Muscles of Mastication

MASSETER muscle

• Quadrilateral in shape.

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• Covers the lateral surface of the

ramus of mandible.

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• Partly tendinous, partly fleshy.

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• 3 Parts:

- Deep Surface

- Middle Surface

- Superficial Surface

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Origin:

• Superficial Layer:
• Anterior 2/3 of the lower border of the zygomatic arch, zygomatic process of maxilla.

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• Middle Layer:
• Anterior 2/3 of the deep surface and posterior 1/3 of the lower border of the zygomatic arch.

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• Deep Layer:
• Deep surface of zygomatic arch.

Insertion:

Lateral surface of ramus of mandible.

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(superficial- lower part

middle- middle part

deep- upper part of ramus)

Relations:

1. Superficial: Skin, platysma, parotid gland, branches of facial nerve and transverse facial branches of superficial temporal vessels.
2. Deep: Ramus of mandible, temporalis muscle.
3. Anterior: Buccal pad of fat, buccal branch of mandibular nerve, buccinator muscle.
4. Posterior: It is overlapped by parotid gland.

Action:

1. Elevation of mandible to approximate the teeth.
2. Retraction of mandible.
3. Superficial fibers help in protrusion of mandible.

Nerve Supply:

Masseteric branch of anterior division of mandibular nerve

Clinical Implication:

• ON DENTURE BORDER:
• An active masseter muscle will create concavity in the outline of the

distobuccal border

• A less active masseter may result in convex border

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• In this area the buccal flange must converge medially to avoid displacement due to contraction of the masseter muscle, because the muscle fibers in that area are vertical and oblique

Masseteric Notch:

Instruct the patient to open mouth wide and then close against the resting force of your finger

Opening wide activates the muscles of pterygomandibular raphe by stretching, which thereby defines the most distal extension

Instructing the patient to close against the finger on tray handle causes masseter muscle to contract & push against the medially situated buccinator muscle.

TEMPORALIS muscle

• Largest and most powerful muscle of mastication.
• Fan shaped muscle.
• Fills temporal fossa.
• Anterior fibers are vertical while posterior fibers are almost horizontal with intermediate fibers of variable degrees of obliquity for different actions this muscle can perform.
• Often visible when chewing.

Origin:

1. Floor of temporal fossa up to inferior temporal line.
2. Under surface of temporal fascia.

The fibers converge to form a tendon which passes down from temporal fossa, medial to anterior part of zygomatic arch and inserts on:

1. Tip, anterior and posterior borders and medial surface of coronoid process of mandible.
2. Anterior border of ramus of mandible.

Insertion:

Relations:

• 1. Superficial: Skin, temporal fascia, superficial temporal vessels, auriculotemporal nerve, temporal branches of facial nerve, zygomatic arch and masseter muscle.
• 2. Posterior: Contents of infratemporal fossa in lower part.
• 3. Anterior: The tendon is separated from zygomatic bone by pad of fat.

Action:

1. Anterior and middle fibers elevate mandible to occlude the teeth.
2. Posterior fibers retract the mandible after protrusion.

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2 deep temporal branches of mandibular nerve.

Nerve Supply:

MEDIAL PTERYGOID MUSCLE

• It is a thick quadrilateral muscle.

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• It has a small superficial and a large deep head.

• 1. Superficial head: Maxillary tuberosity on infratemporal surface of maxilla and adjoining surface of pyramidal process of palatine bone.
• 2. Deep head: It is larger and arises from medial surface of lateral pterygoid plate of sphenoid bone.

The fibers form a tendinous lamina and insertion:

1. Medial surface of ramus of mandible postero-inferior to the mylohyoid groove.
2. Inner aspect of angle of mandible.

Origin:

Insertion:

Relations:

• Lateral: It is separated from ramus of mandible by lateral pterygoid muscle, spheno-mandibular ligament, maxillary artery, inferior alveolar vessels and nerve, lingual nerve, part of parotid gland.
• Medial: Tensor veli palatini, styloglossus, stylopharyngeus and superior constrictor muscles.

Action:

1. Assist in elevation of mandible.

2. Along with lateral pterygoid muscle it causes protrusion of mandible.

3. Helps in side to side movements of the jaw and grinding of food between teeth of same side.

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Nerve Supply:

Nerve to medial pterygoid

(branch of main trunk of Mandibular Nerve)

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Clinical Implication:

Most commonly involved in MYOFACIAL PAIN DYSFUNCTION SYNDROME.

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Trismus following inferior alveolar nerve block is mainly due to involvement of medial pterygoid muscle.

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LATERAL PTERYGOID

• It is the key muscle of the infratemporal fossa.

• Origin:
• It is a short thick muscle which arises from two heads:
• 1. Upper head: Lower part of infratemporal surface of the greater wing of sphenoid and adjoining infratemporal crest.
• 2. Lower head: It is larger and arises from lateral surface of lateral pterygoid plate of sphenoid bone.

Insertion:

• Both heads converge as a single tendon to insert on:
• 1. Pterygoid fovea in the anterior surface of neck of mandible.
• 2. Adjoining articular disc and capsule of temporomandibular joint.

Relations:

Superficial: Ramus of mandible, masseter, superficial head of medial pterygoid and tendon of temporalis muscles.

Deep: Deep head of medial pterygoid muscle, spheno-mandibular ligament, maxillary and middle meningeal arteries, mandibular nerve.

Superior border: Temporal and masseteric branches of mandibular nerve.

Inferior border: Lingual and inferior alveolar nerves.

Structures present between two heads: Buccal nerve and maxillary artery.

Action:�1. Assists in depression of mandible to open jaw. �2. Protrusion of mandible along with medial pterygoid. �3. Helps in side to side movements of the jaw and grinding of food between teeth of same side.�

• Nerve Supply:
• Branch of anterior division of mandibular nerve

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Clinical Significance:

• Most commonly involved in MPDS.
• Unilateral failure of lateral pterygoid muscle to contract results in deviation of the mandible toward the affected side on opening

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• Bilateral failure results in limited opening, loss of protrusion and loss of full lateral deviation.

Accessory muscles of mastication

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DIGASTrIC MUSCLE

Digastric muscle divides suprahyoid part of neck into digastric and submental triangles.

It has two bellies joined by a central tendon.

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Insertion

Facial Sling

Nerve Supply:�Anterior belly by inferior alveolar nerve �Posterior belly by a facial nerve

Action:

Depresses the mandible

Elevates the hyoid bone

Mylohyoid muscle

Also called Diaphragma oris.

Overlies extrinsic muscles of tongue

Origin: Mylohyoid line of mandible

Insertion: Hyoid bone, median raphe.

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Innervation: Mylohyoid nerve

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Action: Elevates the floor of the mouth, depression of mandible

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Geniohyoid MUSCLE

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Innervation: First cervical (C1) nerve along with hypoglossal nerve.�����������������Action: Elevates the hyoid bone, depress the mandible when hyoid is fixed.�

Stylohyoid muscle

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�Nerve supply: Facial nerve

BUCCINATOR MUSCLE

• Helps to prevent accumulation of food in the vestibules during mastication.
• 3 fibres: Upper

Middle

Lower

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Origin: Upper: Outer surface of the alveolar process of the maxilla, opposing molars.

Middle: Pterygomandibular raphe

Lower: Outer surface of the alveolar process of the mandible, opposing molars.

• Action: Flattens the cheeks against gums and teeth

Prevent accumulation of food in the mouth.

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• Nerve Supply: Facial Nerve

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Insertion: Upper: Skin and submucosa of upper lip

Middle: Decussate and pass into upper and lower lip

Lower: Skin and submucosa of lower lip

MANDIBULAR MOVEMENTS

ELEVATION

PROTRACTION

MYLOHYOID, STYLOHYOID, INFRAHYOID

DEPRESSION

RETRACTION

Palpation of masticatory muscles

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Temporalis

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Lateral Pterygoid

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Medial Pterygoid

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Masseter

Masticatory Muscle Disorders

• Some commonly involved masticatory muscle disorders are:
• - Trismus
• - Bruxism
• - Tetanus
• - MPDS
• - Muscle Pain
• - Hyper/ Hypomobility of Muscles

Masticatory Muscle

Disorders

CONCLUSION

• Mastication is oral motor behavior reflecting central nervous system commands, and many peripheral sensory inputs to modulate the rhythmic jaw movements.

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• Since tooth guidance has an enormous influence on muscle activity during chewing and swallowing, it is advisable to make restorations and replacements as much compatible as possible, with the functional movement patterns of the patient, rather than expect the patterns of the mastication to adapt to the new made replacements.

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REFERENCES

- B .D Chaurasia’s. Human Anatomy . Head , neck and Brain

- Zarb; Bolender; Prosthodontic Treatment for Edentulous Patients; 12^TH Ed

• Winkler; Essentials of complete denture Prosthodontics, 2^nd Ed
• Okeson; Management of temporomandibular disorders and occlusion; 5^th Ed

THANK YOU