TEACHING HUNT CONTESTANT NO 22 MUSCLES OF MASTICATION Dr. ABHIJITH KALLU

everyone this is dr abhijit pursuing mds in the department of conservative dentistry and endodontics i am going to discuss about muzzles of mastication these are a group of muscles that help in movement of mandible during chewing and speech all these muscles originate on skull and insert onto mandible they also play a role in the configuration of face here is a mnemonic to remember the muscles of mastication take time to chew food the lettuce in the word time represents muscles of mastication t for temporalis eye for internal terrigord emperor masseter if a external terry god internal pterygoid is also known as medial terracoid whereas external telecoil also known as lateral pterygoid these muscles have certain characteristic features all these muscles develop from mesoderm of first pharyngeal arch that is mandibular arch hence they are supplied by the nerve of that arch these muscles are located in and around infra temporal fossa and are inserted into the ramus of the mandible these are concerned with the movements of mandible at tmj let us see in detail the origin insertion and action of each muscle masseter this is a thick quadrilateral muscle the muscle fibers are arranged in multi-pin net it is regarded as the strongest muzzle of the body it includes three layers superficial layer middle layer and deep layer let us see in detail the origin and insertion of each layer blue denotes the superficial layer which arises from the zygomatic arch and adjoining zygomatic process of maxilla and inserts onto the ramus of the mandible whereas the middle layer arises from the posterior one-third of zygomatic arc and inserts into the central portion of the ramus of the mandible and the deep layer arises from the deep surface of the zygomatic arch and inserts onto the upper part of ramus and coronoid process one important thing about masseter is this is the most commonly affected muscle in bruxism temporalis this is a fan shaped muscle it this muscle fills up the temporal fossa the muscle fibers are arranged in different directions anterior fibers run vertically downwards middle fibers run obliquely and the posterior fibers run horizontally all these fibers originate from inferior temporal line and converge to form a tendon that passes beneath the zygomatic arch and attaches to coronoid process of mandible before discussing about pterygoids let me familiarize you with one special bone that is spinoid it is also known as bad bone the spinoid bone has two pterygoid plates medial and lateral both the pterygoid muscles arise from lateral pterygoid plate guys remember both the pterygoid muscles arise from lateral teleguard plate lateral terrigord this is a short conical muscle consisting of small upper head and a large lower head this is regarded as the key muscle of the infra temporal region it is also known as external pterygoid muscle the upper head arises from the infra-temporal surface and crests of greater wing of spinoid and inserts onto the articular disc and capsule of the tmj whereas the lower head arises from the lateral surface of lateral pterygoid plate and inserts onto the perigold phobia present on the neck of the mandible one important thing about this muzzle is this is the most commonly affected muscle in myofascial pain dysfunction syndrome medial paracord this is also quadrilateral in shape consisting of superficial head and deep head the superficial head arises from the maxillary tuberosity and palatine bone whereas the deep head arises from the medial surface of lateral pterygoid plate both these heads insert into the medial surface of angle and ramus of the mandible close to the mandibular foramen and myelohyde grow this slide shows the actions of muscles of mastication protrusion is a forward moment of mandible retraction is the backward moment of the mandible elevation is upward moment of mandible depression is downward moment of the mandible among every muscle group there will be one or muscle which differs from others with respect to muscles of mastication lateral pterygoid is considered as odd because it causes depression of mandible that is opening of the jaw whereas the other three muscles cause elevation of mandible that is closing of the jaw here is a mnemonic to remember the action of lateral pterygoid muscle when you pronounce the word lateral there is opening of jaw which indicates that lateral pterygoid is associated with depression of mandible apart from the lateral pterygoid there are certain accessory muscles which cause depression of mandible these include myelohyde geniohyoid and digastric both the medial pterygoid and lateral pterygoid cause side to side grinding moments help in the protrusion of the mandible when medial and lateral terragoids of one side act together the corresponding side of the mandible is rotated forwards and to the opposite side the superficial fibers of masseter also cause protrusion of mandible whereas the posterior fibers of temporalis help in the retraction of the mandible coming to vascular and nerve supply since these muscles are derived from first pharyngeal arch these are supplied by the nerve of the torch that is mandible are now the masseter temporalis and lateral terracode derive their supply from the anterior division of mandible arnold whereas the medial pterygoid derives its supply from the main trunk with respect to blood supply all these muscles derive their arterial supply from the second part of maxillary artery which is a branch of external carotid artery this is a short discussion about muscles of mastication which includes all the important points and thank you for listening