Muscles of mastication

Muscles of Mastication

Dr. Deepak K Gupta

www.facebook.com/notesdental

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



• Chief muscles of mastication

– Temporalis

– Masseter

– Medial Pterygoid

– Lateral Pterygoid


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


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


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)


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


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


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.


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


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


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


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


References

• Woelfel's Dental Anatomy 8th edition

• Netter’s Head and Neck Anatomy for Dentistry, 2nd Edition Neil S norton

• B.D. Chaurasia Head and Neck


Muscles of mastication

Health & Medicine

Transcript of Muscles of mastication