muscles of mastication
Post on 17-Aug-2015
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Introduction
• Mastication is the process of chewing food in preparation for deglutition (swallowing)and digestion
• All muscles of mastication originate on the skull and insert on the mandible
• All muscles of mastication are innervated by the mandibular division of the trigeminal nerve
• All muscles of mastication are derivatives of the 1st pharyngeal arch
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Muscles of Mastication
• Chief muscles of mastication
– Temporalis
– Masseter
– Medial Pterygoid
– Lateral Pterygoid
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Masseter• Most superficial, bulky, and
powerful of the muscles of mastication.
• It is four sided in shape and average volume is over twice that of the medial pterygoid.
• Origin: it originates from 3 head i.e– Superficial head - Zygomatic bone
(maxillary process) and zygomaticarch (lateral aspect of anterior ⅔)
– Middle head - Zygomatic arch (medial aspect of anterior ⅔)
– Deep head: Zygomatic arch (deep surface of posterior ⅓)
• Insertion: the three layer merges as fibers passes downward and backward to insert on the lateral aspect of angle of Ramuswww.facebook.com/notesdental
Masseter
• Nerve Supply: Masseteric n. (anterior division of CN V 3)
• Action: Elevates mandible; also assists in protraction, retraction, and side-to-side motion
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Temporalis• Fan-shaped - arises from
the entire temporal fossa• Origin
– Superficial head: Temporal fascia
– Deep head: Temporal fossa(inferior temporal line)
• Insertion : Coronoidprocess of mandible - the medial surface of the anterior border of the ramus and temporal crest of the mandible via one common tendon
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Temporalis• Nerve Supply: Deep temporal
nerve (anterior division of Mandibular nerve of trigeminal nerve)
• Vasculature: Superficial and deep temporal artery of maxillary artery and
• Actions– Vertical (anterior) fibers:
Elevate mandible, – Horizontal (posterior) fibers:
Retract (retrude) mandible– Unilateral: Lateral movement
of mandible (chewing)
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MEDIAL PTERYGOID MUSCLE• Located on the medial surface
of the ramus.• Pterygoid sling: masseter
located on the lateral surface and medial pterygoidattached on the medial side of the angle of the mandible serves as a sling
• Origin: – Superficial (external) head:
maxillary tuberosity and palatine bone (pyramidal process)
– Deep (internal) head: Medial surface of lateral pterygoidplate and pterygoid fossa
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MEDIAL PTERYGOID MUSCLE
• Insertion : medial surface of the mandible in a triangular region at the angle and on the adjacent portions of the ramus just above the angle
• Nerve supply: Nerve to medial pterygoidarises from the main branch of mandibularnerve before it divides into anterior and posterior divisions
• Blood Supply: it gets supply from maxillary artery
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MEDIAL PTERYGOID MUSCLE• Action
– elevates the mandible (closes jaw) like the masseter and the anterior (and middle) fibers of the temporalismuscles.
– Although not as large or powerful, it works together with the masseter muscle in helping to apply the power or great force upon closingthe teeth together.
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LATERAL PTERYGOID MUSCLE• Unlike the other three
pairs of muscles where most fibers are oriented primarily vertically -its fibers aligned mostly horizontally
• Short, thick, somewhat conical muscle located deep in the infratemporalfossa
• Prime mover of the mandible except closing of jaw
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LATERAL PTERYGOID MUSCLE• Origin
– arises from two heads– Smaller superior head - attached to the infratemporal
surface of the greater wing of the sphenoid bone– larger inferior head - attached to the adjacent lateral
surface of the lateral pterygoid plate on the sphenoid bone
• Insertion• Two heads joins together before inserting • Inferior head inserts on the front of the neck of the condyloid
process called the pterygoid fovea• Superior head into the anterior margin of the articular disc of
TMJ
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LATERAL PTERYGOID MUSCLE• Nerve supply: nerve to lateral pterygoid from anterior
division of mandibular nerve
• Vasculature: pterygoid branches of maxillary artery
• Action– Protrusion of mandible
• No other muscle or groups of muscles are capable of doing this
• Others can only assist in this action as stabilizers or by controlling the degree of jaw opening during the protrusion
– Depression of mandible• pulling the articular discs and the condyles forward and down onto
the articular eminences
• moves the mandible inferiorly and helps rotate it, thereby opening the mouth
• assisted somewhat in this task by suprahyoid and infrahyoid muscleswww.facebook.com/notesdental
LATERAL PTERYGOID MUSCLE• Lateral excursion
– When only one lateral pterygoidcontracts,
– it pulls the condyle on that side toward the midline and anteriorly
– This moves the body of the mandible toward the opposite side
• Left lateral excursion : contraction of the right lateral pterygoid muscle draws the right condyle medially (to the left) and forward, causing the mandible to move toward the left side
• Right lateral excursion: contraction of the left lateral pterygoid muscle causes the mandible to move to the right side
• No other muscle is capable of moving the mandible sideways, although synergistic
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OTHER MUSCLES AFFECTINGMANDIBULAR MOVEMENT
• Suprahyoid : stylohyoid, digastric, mylohyoid, geniohyoid
• Infrahyoid: omohyoid, sternohyoid, sternothyroid, and thyrohyoid
• Neck muscle: sternocleidomastoid muscle
• Other factors affecting movement of mandible– Ligaments of TMJ
– Fascia
– Facial muscles : orbicularis oris, buccinator, upper oral group, lower oral group
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