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  • 1. Muscles of Mastication INDIAN DENTAL ACADEMY Leader in continuing dental education www.indiandentalacademy.com www.indiandentalacademy.co m
  • 2. Introduction The muscles of mastication are involved in the masticatory and non masticatory movements of the mandible . www.indiandentalacademy.co m
  • 3. www.indiandentalacademy.co m
  • 4.  The masseterand temporalis are superficially located, just deep to the subcutaneous tissue, and can be easily palpated.  The medial and lateral pterygoid, however, lie more deeply and are placed in the infratemporal fossa. www.indiandentalacademy.co m
  • 5. MASSETER • Quadrilateral muscle • Covers lateral surface of mandible coronoid process of the mandible. • Consists of 2 portions Origin Superficial portion(larger) - Lowerborderof ant. 2/3 of Zygomatic arch - Thick tendinous aponeurosis from the zygomatic process of the maxilla www.indiandentalacademy.co m
  • 6. Deep portion(smaller) - Posterior 1/3of the lowerborder - Whole of the medial surface of the zygomatic arch Insertion Superficial fibres – fibers pass downward and backward to insert into angle and lowerhalf of the lateral surface of thewww.indiandentalacademy.co m
  • 7. Deep fibres. - Fibers pass downward and forward, to be insertedinto the upper half of the ramus and the lateral surface of the coronoid process of the mandible. www.indiandentalacademy.co m
  • 8. • The deep portion of the muscle is partly concealed, in front, by the superficial portion • Behind , it is covered by the parotid gland. • The fibers of the two portions are continuous at theirinsertion. • A portion of the parotid gland, the parotid duct, transverse facial artery and branches of the facial nerve lie superficially to the muscle. Nerve supply : Mandibularnerve via masseteric nerve that enters its deep surface. Arterial supply: Masseteric branch of the maxillary artery.www.indiandentalacademy.co m
  • 9. Action : - Themasseter elevates the mandibleduring thecentric occlusion. - Moves the mandibleto the sidein lateral excursions, - Retrudes the mandiblewhen in protrusion. (deep fibres) www.indiandentalacademy.co m
  • 10. Function of Masseter Next Slide****Previous Slide****Slide avigatior Home www.indiandentalacademy.co m
  • 11. TemporalisTemporalis A fan-shaped muscle covered by a fascia sheet. The large fan-like portion attaches to the side of the skull and the smallertapering portion attaches to the coronoid process of the mandible. It is a powerful masticatory muscle that can easily be seen and felt during closure of the mandible. www.indiandentalacademy.co m
  • 12. www.indiandentalacademy.co m
  • 13. Origin : - Floorof temporal fossa. - deep surface of temporal fascia. Insertion fibers converge as they descend, and end in a tendon, which passes deep to the zygomatic arch and is inserted into the. - Medial surface, apex, anteriorand posterior borderof coronoid process. - anteriorborderof the ramus of the mandible nearly as farforward as the last molartooth. superficial tendon - anteriorborderof coronoid. process. deep tendon - internal oblique line.www.indiandentalacademy.co m
  • 14. www.indiandentalacademy.co m
  • 15. Arterial supply : anteriorand posteriordeep temporal arteries. Nerve supply : anteriorand posteriordeep temporal nerves from the mandibulardivision of the trigeminal nerve (V) Action : - Elevation (bilateral) - Retrusion (bilateral) activated during end to end and centric occlusal biting positions, and pulls the mandible back in retrusive. - Ipsilateral excursion (unilateral) - Resting tonus (bilateral) maintains the rest position of the mandible when the person is upright www.indiandentalacademy.co m
  • 16.  Due to the fan-shaped arrangement of the fibers of temporalis, the pull of the muscle is a continuous arc from the essentially vertical pull of the anterior fibers (which elevate the mandible) to the posteriorportion which pulls almost horizontally and thereby retracts the mandible.  This is necessary in closing the mouth since in the open position the head of the mandible has moved anteriorly against the articulartubercle.  Note that the posteriorfibers of temporalis are the only retractors of the mandible. www.indiandentalacademy.co m
  • 17. www.indiandentalacademy.co m
  • 18. Temporal fascia  Thick aponeurotic sheet that roofsover temporal fossaand coversthe temporalismuscle.  Superiorly attached to superior temporal line  Inferiorly attached to upper border of zygomatic arch  Deep surfacegives origin to afew fibresof temporalis. www.indiandentalacademy.co m
  • 19. Lateral pterygoid  It is a short, thick muscle, somewhat conical in form, which extends almost horizontally between the infratemporal fossa and the condyle of the mandible and has two heads superiorand inferior.  Only muscle of the fourmuscles of mastication to occupy a horizontal position. www.indiandentalacademy.co m
  • 20. Origin : both heads arise from sphenoid bone. • Upperhead (small) – infratemporal surface and infratemporal crest of greaterwing of sphe noid bone • Lowerhead - lateral surface of lateral pterygoid plate www.indiandentalacademy.co m
  • 21. Insertion : - Anteromedial surface of articula rcapsule - Anteriorborderof articulardisc - Anteriorsurface of mandibularneck i.e. Pterygoid fovea. www.indiandentalacademy.co m
  • 22. Nerve supply nerve to lateral pterygoid Arterial supply Pterygoid branch of the maxillary artery. Action : The purpose of the lateral pterygoids is to work togetherto pull the mandible forward ("advance" it), and to translate the condyles (open the mouth). www.indiandentalacademy.co m
  • 23. • Protrusion (bilateral) Thelateral pterygoidsacting together aretheprime protractersof themandible, moving it into a protrusiveposition. www.indiandentalacademy.co m
  • 24. • Depression (bilateral) Contractions of both lateral pterygoids along with the suprahyoid and infrahyoid muscles, help depress oropen the mandible. • Contralateral Excursion (unilateral) The lateral pterygoid can act singly to move the mandible in lateral excursions. www.indiandentalacademy.co m
  • 25. Medial Pterygoid  Thick, quadrilateral muscle.  This muscle mirrors the masseterin position and action,togetherwith the masseterit forms a "sling"around the ramus.  It is rhomboidal in shape and located deep to the ramus of the mandible and runs almost in the same direction.  Has small superficial head and large deep head. www.indiandentalacademy.co m
  • 26. Origin : Superficial head - Maxillary tuberosity - Lateral surface of pyramidal process of palatine bone Deep head - Pterygoid fossa - Medial surface of lateral pterygoid pl ate www.indiandentalacademy.co m
  • 27.  Insertion : fibers pass downward, lateral and backward, and are inserted, by a strong tendinous lamina, into  the lowerand back part of the medial surface of the ramus  angle of the mandible, as high as(inferiorto) the mandibularforamen.www.indiandentalacademy.co m
  • 28.  Arterial supply : pterygoid branch of the maxillary  Nerve supply : nerve to medial pterygoid  Action : The medial pterygoid elevates and orientates the mandible laterally during chewing in conjunction with the masseter. Elevation (bilateral) The medial pterygoid acts with the masseterto elevate. www.indiandentalacademy.co m
  • 29. • Protrusion (bilateral) The insertion of the muscle is posterior to its origin so the right and left muscles aid in protrusion. • Contralateral Excursion (unilateral) The insertion of this muscle is also lateral to its origin, so the muscle fibers www.indiandentalacademy.co m
  • 30. Sphenomandibularis  Origin - Sphenoid bone, behind orbit  Insertion - temporal crest (internal obliqueline) of the mandible  Most efficient asnon- working sideelevator of mandible  Had previously been thought to be"medial belly of temporalis" www.indiandentalacademy.co m
  • 31. Zygomandibularis Origin: Posterior region of theorbital part of the zygomatic boneand thesphenoid bone Insertion : Anterior mandibular ramus Function: Believed to aid in elevating themandible www.indiandentalacademy.co m
  • 32. Non masticatory muscles  Depressorsof themandible  Platysma  Suprahyoid muscles  Infrahyoid muscles www.indiandentalacademy.co m
  • 33. Suprahyoid muscles - This group of muscles is located superiorto the hyoid bone and connects to this bone and the skull. - Includes the mylohyoid, geniohyoid, stylohyoid and digastric muscles. Infrahyoid muscles - These muscles are often referred to as strap muscles due to theirribbon-like appearance. - They are located inferiorto the hyoid bone. - These muscles anchorthe hyoid bone and depress the hyoid and larynx during swallowing and speaking.www.indiandentalacademy.co m
  • 34. SUPRAHYOID MUSCLES Muscle Origin Insertion Action DIGASTRIC ANTERIOR digastric fossa of mandible Intermediate tendon at hyoid depresses the mandible and raises the hyoid bone, steadies the hyoid bone during swallowing and speaking. POSTERIOR DIAGASTRIC mastoid notch of temporal bone. Intermediate tendon at hyoid STYLOHYOID Styloid process Hyoid elevates and retracts the hyoid bone, elongating the floorof thewww.indiandentalacademy.co m
  • 35. GENIOHYOID LOWER GENIAL TUBERCLE HYOID Raises hyoid and larynx; fixes hyoid. MYLOHYOID Mylohyoid line of mandible Raphe and body of hyoid bone. Elevates the hyoid bone, floor of the mouth and the tongue during swallowing and speaking  www.indiandentalacademy.co m
  • 36. INFRAHYOID MUSCLES Omohyoid superior borderof scapula inferior borderof hyoid bone. depresses, retracts and steadies the hyoid during swallowing and speaking STERNO-HYOID Manubrium sterni Body of hyoid steady the hyoid during movements of the tongue, larynx and pharynx www.indiandentalacademy.co m
  • 37.  STERNO –THYROID Origin - Sternum Insertion - Side of thyroid cartilage Action - depresses the hyoid bone and larynx afterit has been elevated by muscles during swallowing and vocal movements.  THYROHYOID Origin - oblique line of thyroid cartilage. Insertion - Cornu and body of hyoid Action - responsible forpreventing food from entering the larynx during swallowing (it pulls the larynx and hyoid bone together).. www.indiandentalacademy.co m
  • 38. Platysma  Subcutaneous sheet of striated muscle, located in the superficial fascia.  Origin-fascia and skin overthe pectoralis majorand deltoid muscles.  Insertion - inferiorborderof the mandible and skin of the lowerface  Actions – - tenses the skin of the neck. -It draws the corners of the mouth inferiorly and assists in depressing the mandible. -one of the muscles of facial expression that we use to express sadness, horror, or frightwww.indiandentalacademy.co m
  • 39. Mandibular Division Of Trigeminal Nerve (Cn-v).  All the muscles of mastication are supplied by branches of the mandibularportion of the trigeminal.  This nerve carries the motorroot of CN-V. Afterpassing through the foramen ovale, its short trunk branches immediately into sensory and motornerves.  The Sensory Nerves include: -InferiorAlveolar -Lingual, www.indiandentalacademy.co m
  • 40. - Auriculotemporal - Buccal  The motornerves include - Anteriorand posteriordeep temporal - Nerve to the medial pterygoid muscle - Masseteric - Nerve to the lateral pterygoid muscle www.indiandentalacademy.co m
  • 41. Maxillary artery www.indiandentalacademy.co m
  • 42. Pterygoid venous plexus This large venous plexus lies partly between the lateral pterygoid and temporalis muscles and the two pterygoid muscles.www.indiandentalacademy.co m
  • 43. Development  The muscles of mastication arise from the mesoderm of the mandibulararch. The mandibulardivision of the trigeminal nerve enters this premuscle mass before it splits into the Temporal, Masseterand Pterygoideus. www.indiandentalacademy.co m
  • 44. Review of actions of the muscles of mastication  DEPRESSION OF MANDIBLE Gliding and hinge movements. Lateral pterygoid aided by Suprahyoid and Platysma.  ELEVATION OF MANDIBLE Masseter, medial pterygoids and anterior fibers of temporalis.  PROTRUSION OF MANDIBLE: Lateral and medial pterygoids on both sides. www.indiandentalacademy.co m
  • 45. RETRUSION OF MANDIBLE: Post (horiz.) fibers of temporalis. LATERAL MOVEMENT: Medial and lat pterygoids on one side only www.indiandentalacademy.co m
  • 46. Clinical considerations  The muscles of mastication are involved in the masticatory movements of the mandible and also the non masticatory .  In complete denture prosthodontics the non masticatory movements and contacting of teeth during these movements are of more concern.  As a group they are very powerful.  Only the MASSETERinfluences the contourof the distobuccal cornerof the buccal flange.  The magnitude of its force is felt in the molar www.indiandentalacademy.co m
  • 47.  The denture should be contoured to accommodate the contraction of the masseteras it force the buccinator onto the retromolarpad,otherwise it will lead to anteriordisplacement of the denture.  The temporal muscle does not participate in biting force when mandible is in protrusion and can be used as a test to determine if patient is closing in centric relation.  The muscles that protrude the mandible and move it side to side are strongerthan the retractors.  The precise control and coordination existing between the muscles enables them to apply powerful force to piece of food and yet bring teeth into occlusion without jarring,by the neuromuscular www.indiandentalacademy.co m
  • 48.  Premature contact of the teeth causes discomfort and damage to the underlying muscles and hence dentures should not be fitted with increased vertical dimension,and is a common cause of denture failure.  When vertical dimension is reduced,the muscles lose theirpower,as they develop maximum powerwithin a short range of vertical dimension.  In protrusion when posteriorteeth are present the forward pull of the muscle fibres of the pterygoids are balanced but the gradual relaxation of the posteriorfibres of the temporalis and masseterand anteriorteeth and vice versa.www.indiandentalacademy.co m
  • 49.  When posteriorteeth are lost,mastication is performed on anteriorteeth,orlong period of edentulism abnormal habits of chewing are developed with loss of the delicate balance between the groups of muscles and the protrusive muscles become dominant,and leads to difficulty in recording anteroposteriorocclusal relationship.  When the masticatory muscles try to bring the teeth into occlusion and there are interfering inclines within the closing and opening paths of mandibular movement, the muscles of mastication may become furtherirritated resulting in muscle tenderness and muscle pain. Muscles that are irritated can affect the "quality" of mandibularmovement, function andwww.indiandentalacademy.co m
  • 50.  The freeway space is the space between the occlusal surfaces of the teeth when the mandible is at rest and the muscles in a state of minimum contraction.  When recording jaw relations the centric relation is recorded with aid of posterior fibres of temporalis.  The function of the muscles is not only the mastication but also the mandibular movements which is of importance to the prosthodontist.  The mandible attached to the TMJis capable of various movements aided by thewww.indiandentalacademy.co m
  • 51. -opening mvt -closing mvt -shearing mvt -lateral and chewing mvts.  Bruxism-the grinding of teeth for nonfunctional purposes in response to an increased tonus of the muscles of mastication. It usually happens during sleep  Clenching- forceful clamping of jaws in static relationship  Trismus – Arthritis of the TMJcould affect the tone of the lateral pterygoid muscle, the patient cannot open the mouth. www.indiandentalacademy.co m
  • 52. Summary  Themasticatory system isextremely complex,primarily madeof bonesmuscles ligamentsand teeth.  Precisemovement of themandibleby the musculatureisrequired to movetheteeth efficiently acrosseach other during function.  Theknowledgeof theanatomy ,physiology and mechanicsof thismovement arebasic to understanding thismovement. www.indiandentalacademy.co m
  • 53. references  William’s :Grays anatomy  Chaurasia :human anatomy vol3.head and neck ,2nd edition 1992,varghese  Grants;method of anatomy  Zarb&Bolender:Boucher’s ;prosthodontic treatment or edentulous patients,9th edition,CBS  Heartwell :syllabus of complete dentures,1992,4th edition,Varghese  Jeffery P.Okeson:Management of TMJdisorders and occlusion,4th edition,1998Mosby  Ramfjord/Ash:Occlusion,3rd edition,WBSaunders  www.drjimboyd.com  Federal services board review 2000 website www.indiandentalacademy.co m
  • 54. Anatomy.uams.edu www.med.mich.edu Geocities.com/medinotes Pubmed :Dunn GF,Anatomical observation of a craniomandibularmuscle originating from the skull base: the sphenomandibularis.Cranio. 1996 Apr;14(2):97-103; discussion 104-5. http://www.drjimboyd.com/book/spheno.ht m. www.indiandentalacademy.co m
  • 55. Thank you For more details please visit www.indiandentalacademy.com www.indiandentalacademy.co m