MUSCLES OF MASTICATIONMasseter

Temporalis

Lateral Pterygoid

Medial Pterygoid

MASTICATORY SYSTEM

The masticatory system is a functional unit composedof the teeth; their supporting structures, the jaws;the temporomandibular joints; the muscles involved directlyor indirectly in mastication (including the musclesof the lips and tongue); and the vascular and nervoussystems supplying these tissues. Functional and structuraldisturbances in any one of the components of themasticatory system may be reflected by functional orstructural disorders in one or more of its other components

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MASTICATORY FUNCTIONS

Mastication is the action of breaking down of food,preparatory to deglutition. This breaking-down action ishighly organized complex of neuromuscular and digestive activities that, in normal individuals, integrate thevarious components of the masticatory system, such asthe teeth and their investing structures, the muscles, thetemporomandibular joints, the lips, the cheeks, the palate,the tongue, and the salivary secretions.

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MASTICATION- ORAL BEHAVIOUR

Mastication is oral motor behavior reflecting centralnervous system commands, and many peripheral sensoryinputs to modulate the rhythmic jaw movements.The action of masticatory muscles during chewingvaries between subjects in amplitude, onset timing, andduration of the chewing cycle. However, it is possible torecognize similarity between muscle actions. These widevariations (within and between individuals) can be explainedby differences related to individual occlusal contactfeatures and specific musculoskeletal morphology.Since tooth guidance has an enormous influence onmuscle activity during chewing and swallowing, it is advisableto make restorations compatible with the functionalmovement patterns of the patient rather than expectthe patterns of the mastication to adapt to the newmade restorations

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CHEWING CYCLE

The masticatory sequence is the whole set of movementsfrom ingestion to swallowing. It is made up of masticatorycycles that change in form as the food is gathered, moved backward to the molar teeth, then brokendown and prepared for swallowing.chewing.flv

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tooth bolus

jaw opening

stretch of elevator musclesjaw closing

re-opening of jaw via stimulation of periodontal and soft tissue receptors

NEUROLOGICAL CONTROLTo create precise mandibular movements, inputs fromvarious sensory receptors must be received by the centralnervous system through afferent nerve fibers. Thebrain assimilates and organizes these inputs and elicitsappropriate motor activities through the efferent nervefibers. These motor activities involve the contraction ofsome muscle groups and the inhibition of others. Chewingis a subconscious activity, yet can be brought toconscious control at any time 4

MUSCLES OF MASTICATION

muscles of mastication.flv

The muscles of mastication help in mastication. All supplied by the mandibular division of the Trigeminal nerve.Additional muscles of mastication supplied by trigeminal nerveAnterior belly of digastricMylohyoidTensor tympani (attaches to the malleus - 1st arch bone - part of the reptilian jaw joint)Tensor palati

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PAROTIDEOMASSETERIC FASCIA

Also referred to as the ‘Masseteric Fascia’. A strong layer of fascia derived from the

deep cervical fascia. Above it, the lower border of zygomatic arch

is attached. Behind, it invests the parotid gland.

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MASSETER

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Arises by thick, tendinous aponeurosis from zygomatic process of maxilla and 2/3 of lower border of zygoma.

Fibres pass downwards and backwards.

Inserted into the angle and lower half of lateral surface of ramus of mandible.

Arises from posterior 2/3 of lower border and whole of medial surface of zygomatic arch.

Fibres pass downwards and forwards.

Inserted into the upper half of ramus and lateral surface of coronoid process of mandible.

Superficial Layer Deep Layer

Deep layer is partly concealed in front by superficial layer and behind by parotid gland.

A thick, quadrilateral muscle and it consists of two portions:

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TEMPORAL FASCIA

Covers the temporalis muscle. It is a strong, fibrous investment covered

laterally by auricularis anterior and superiorly by galea aponeurotica and by part of orbicularis oculi.

It consist of two layers:-one of which is inserted into the lateral and other into medial border of the arch.

Between these two layers- a small quantity of fat, orbital branch of superficial temporal artery and a filament from zygomatic branch of zygomatic nerve are present. 9

TEMPORALIS

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Arises from whole of the temporal fossa and from deep surface of temporal fascia.

Fibres converge as they descend and end in a tendon which passes which passes deep to the zygomatic arch.

Inserted into the medial surface, apex and anterior border of coronoid process and anterior border of ramus of mandible nearly as far forward as last molar teeth.

Broad, radiating muscle situated at the side of the head.

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LATERAL PTERYGOID

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Arises from lower part of lateral surface of greater wing of sphenoid and from infratemporal crest.

It is active during various jaw closing movements only.

Arises from lateral surface of lateral pterygoid plate.

It is active during jaw opening movements and protrusion only.

Upper Head Lower Head

Short, thick muscle, conical in form.Extends horizontally between infratemporalfossa and condyle of mandible.Arises by two heads:- upper and lower

Fibres pass horizontally backwards and laterally.Inserted into a depression in front of neck of condyle of mandible, and into front margin of articular disc of temporomandibular articulation.

Suited for Protraction, Depression and Contralateral Abduction.

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MEDIAL PTERYGOID

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Arises from medial surface of lateral pterygoid plate and grooved surface of pyramidal process of palatine bone.

Fibres pass downward, lateral and backwards.

Inserted by strong tendinous lamina, into the lower and back part of medial surface of ramus and angle of mandible, as high as the mandibular foramen.

Thick, quadrilateral muscle.Principle functions are elevation and lateral positioning of mandible.

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ADDITIONAL MUSCLES WHICH ARE SUPPLIED BY TRIGEMINAL NERVEDigastric

Geniohyoid

Tensor tympani

Tensor veli palitini 16

DIGASTRIC

Attachment is at or near lower border of mandible and near midline.

Anterior digastric muscle covered by platysma muscle, beneath lie the mylohyoid and geniohyoid muscle.

Mylohyoid branch of mandibular division of fifth nerve innervates anterior digastric.

Digastric branch of facial nerve innervates posterior digastric muscle.

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GENIOHYOID

Lies superior to mylohyoid muscle and adjacent to the midline.

Arises from mental spine on posterior aspect of symphysis menti of mandible.

Inserts on anterior surface of hyoid bone. Innervation is from C1 to C2 and hypoglossal

nerve.

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The tensor tympani, the larger of the two muscles of the tympanic cavity, is contained in the bony canal above the osseous portion of the auditory tube. Its role is to dampen sounds, such as those produced from chewing.

When tensed, the action of the muscle is to pull the malleus medially, tensing the tympanic membrane, damping vibration in the ear ossicles and thereby reducing the amplitude of sounds.

It arises from the cartilaginous portion of the auditory tube and the adjoining part of the great wing of the sphenoid, as well as from the osseous canal in which it is contained.

Inserted into the handle (manubrium) of the malleus, near its root.

Passing backward through the canal, it ends in a slender tendon which enters the tympanic cavity, makes a sharp bend around the extremity of the septum, known as the processus cochleariformis

TENSOR TYMPANI

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TENSOR VELI PALITINI

The tensor veli palatini (tensor palati) is a broad, thin, ribbon-like muscle in the head that tenses the soft palate.

It arises by a flat lamella from the scaphoid fossa at the base of the medial pterygoid plate, from the spina angularis of the sphenoid and from the lateral wall of the cartilage of the auditory tube.

The tendon then passes medially and is inserted into the palatine aponeurosis and into the surface behind the transverse ridge on the horizontal part of the palatine bone.The tensor veli palatini is innervated by the medial pterygoid nerve, a branch of mandibular nerve, the third branch of the trigeminal nerve (CN V).

The tensor veli palatini tenses the soft palate and by doing so, assists the levator veli palatini in elevating the palate to occlude and prevent entry of food into the nasopharynx during swallowing.

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MASTICATORY MOVEMENTS

Masticatory Movement.flv

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IMPORTANCE TO DENTISTSThe knowledge of this system is important in removable prosthodontics. Information based on this system was used in the design andsetting of articulators, and in the design of the denturesand denture teeth themselves. Today the importance ofjaw movements has become apparent in fixed prosthodontics,periodontics, orthodontics, and in the diagnosis andtreatment of pain disorders of the masticatory system.The most important reason why dentists maintain andreplace missing teeth should be to provide patients withgood masticatory abilities. Therefore, it is important that dentists know how mastication normally occurs.

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CLINICAL SIGNIFICANCE Horner's syndrome can be produced by lesions of the

nasociliary nerve as it runs with the ophthalmic division. Lesions of the ganglion: herpes zoster infection, primary and

metastatic tumors. Trigeminal root lesions: adjacent tumors and vascular

malformations, especially acoustic neurinoma and cholesteatomas. These lesions are prone to produce facial pain that is often misdiagnosed as tic douloureux or tooth pain.

Clinically there is atrophy and flaccid paralysis of the muscles of mastication.

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